## 1. Project Overview & Quickstart (drduh/macOS-Security-and-Privacy-Guide) This guide is a collection of techniques for improving the security and privacy of macOS on [Apple silicon](https://support.apple.com/116943) Macs. It targets experienced users who want security practices commonly used by organizations, but is also suitable for novice users with an interest in privacy and security. For organization-managed Macs, see the [macOS Security Compliance Project](https://github.com/usnistgov/macos_security), maintained by the [U.S. National Institute of Standards and Technology](https://en.wikipedia.org/wiki/National_Institute_of_Standards_and_Technology). This guide is provided "as is" - without warranties of any kind. You are solely responsible for any consequences of following it. - [Basics](#basics) - [Threat modeling](#threat-modeling) - [Assets](#assets) - [Adversaries](#adversaries) - [Capabilities](#capabilities) - [Mitigations](#mitigations) - [Example model](#example-model) - [Hardware](#hardware) - [Installing macOS](#installing-macos) - [System activation](#system-activation) - [Apple Account](#apple-account) - [App Store](#app-store) - [Virtualization](#virtualization) - [Apple containers](#apple-containers) - [First boot](#first-boot) - [Admin and user accounts](#admin-and-user-accounts) - [Caveats](#caveats) - [Setup](#setup) - [Firmware](#firmware) - [FileVault](#filevault) - [Lockdown Mode](#lockdown-mode) - [Firewall](#firewall) - [Application layer firewall](#application-layer-firewall) - [Stealth mode](#stealth-mode) - [Signed apps](#signed-apps) - [Reload firewall](#reload-firewall) - [Get state](#get-state) - [AirDrop](#airdrop) - [Third-party firewalls](#third-party-firewalls) - [Packet filter](#packet-filter) - [Example pf config](#example-pf-config) - [Firewall commands](#firewall-commands) - [Block networks](#block-networks) - [Services](#services) - [Siri Suggestions and Spotlight](#siri-suggestions-and-spotlight) - [Homebrew](#homebrew) - [DNS](#dns) - [DNS profiles](#dns-profiles) - [Hosts file](#hosts-file) - [DNSCrypt](#dnscrypt) - [Dnsmasq](#dnsmasq) - [Certificate authorities](#certificate-authorities) - [Privoxy](#privoxy) - [Browser](#browser) - [Firefox](#firefox) - [Chrome](#chrome) - [Safari](#safari) - [Web browser privacy](#web-browser-privacy) - [Tor](#tor) - [VPN](#vpn) - [PGP/GPG](#pgpgpg) - [Email](#email) - [Thunderbird](#thunderbird) - [Messengers](#messengers) - [XMPP](#xmpp) - [Signal](#signal) - [iMessage](#imessage) - [Viruses and malware](#viruses-and-malware) - [Downloading Software](#downloading-software) - [App Sandbox](#app-sandbox) - [Hardened Runtime](#hardened-runtime) - [Antivirus](#antivirus) - [Gatekeeper](#gatekeeper) - [System Integrity Protection](#system-integrity-protection) - [Metadata and artifacts](#metadata-and-artifacts) - [Authentication](#authentication) - [Backup](#backup) - [Wi-Fi](#wi-fi) - [SSH](#ssh) - [Physical access](#physical-access) - [Monitoring](#monitoring) - [Logs](#logs) - [DTrace](#dtrace) - [Processes](#processes) - [Network](#network) - [Miscellaneous](#miscellaneous) - [Related software](#related-software) - [Additional resources](#additional-resources) --- # Basics Apply general security best practices: - Create a [threat model](#threat-modeling) - Is your adversary a local eavesdropper, a criminal using common malware, or a well-funded and highly capable organization? - Define the threats or groups you are defending against and what they can realistically do. - Keep the system and software up to date - Regularly install available updates for the operating system and all applications. - Updates are installed in [System Settings](https://support.apple.com/guide/mac-help/keep-your-mac-up-to-date-mchlpx1065) or with the [`softwareupdate`](https://ss64.com/mac/softwareupdate.html) command-line utility. Neither requires an Apple Account. - Subscribe to the [Apple security-announce](https://lists.apple.com/archives/list/security-announce@lists.apple.com/) mailing list or check [Apple security releases](https://support.apple.com/100100). - Encrypt sensitive data - Enable [FileVault](https://support.apple.com/guide/mac-help/protect-data-on-your-mac-with-filevault-mh11785) to encrypt internal storage. - Use a [password manager](https://support.apple.com/105115) for account credentials and consider encrypting especially sensitive files separately. - Ensure data availability - Create [regular backups](https://support.apple.com/104984) of critical data and be ready to [restore from a backup](https://support.apple.com/102551) in case of compromise. - [Encrypt backups](https://support.apple.com/guide/mac-help/keep-your-time-machine-backup-disk-secure-mh21241) before copying them to external media or third-party cloud storage. Alternatively, use a backup service that provides [end-to-end encryption](https://support.apple.com/guide/security/advanced-data-protection-for-icloud-sec973254c5f). - Verify backups by accessing them on a regular, scheduled basis. - Click carefully - Ultimately, the security of a system depends on the capabilities and habits of its administrator. - Take care when installing new software: install it only from sources the developer identifies as official, such as their website or GitHub repository. # Threat modeling The most important step to meaningfully improve security and privacy is to create a [threat model](https://owasp.org/www-community/Threat_Modeling): a general description of what you want to protect, who might try to access it, how they could do so, and which controls are worth usability trade-offs. This creates an understanding of potential adversaries and their motivations, which leads to stronger defenses. ## Assets Assets may include a phone, laptop, credentials, and personal information, such as browsing history. List them in order of importance, starting with those most worth protecting. ## Adversaries Define whom you are defending against. Start by defining the motivation each adversary might have to attack important assets. [Financial gain](https://www.verizon.com/business/resources/reports/dbir/) is a big motivator for many attackers, for example. ## Capabilities For each adversary, list what they can and cannot do, ranking them from least to most capable. For example, a casual thief operates opportunistically: they will likely be defeated by basic controls, such as screen lock and encrypted storage with strong passwords. A more sophisticated and determined adversary may require fully powering off a device when not in use to clear credentials from memory and stronger authentication mechanisms. ## Mitigations Choose the best mitigation for each threat. For example, avoid writing passwords on paper if a roommate might find them, or encrypt storage to protect its data if it is stolen. Security should be balanced with usability: every mitigation should counter some adversarial capability to justify any inconvenience. Stop adding defenses when the remaining risks are acceptable for a situation. Revisit the model when devices, data, travel, work, or adversaries change. ## Example model The following table is an example of a simple threat model: Adversary | Motivation | Capabilities | Mitigation :-: | :-: | :-: | :-: Roommate | See private chats or browsing history | Close proximity; can see screen or observe credentials | Use biometric (fingerprint or face) authentication, use privacy screen, keep phone locked when not using it Thief | Unlock phone and steal personal info and drain bank accounts, sell phone for money | Observe password being entered, steal logged-in device left unattended | Maintain physical custody of device at all times, lock devices when not in use, avoid typing password in public view, use Find My or similar services to track or remotely disable stolen devices Criminal | Financial gain | Social engineering (tricking a user into revealing information or taking unsafe actions), readily-available malware, password reuse, exploiting vulnerabilities | Sandbox software, enable OS security features, maintain software updates automatically Corporation | Marketing based on user data | Telemetry and behavioral data collection | Block network connections, reset device-specific identifiers, avoid adding payment data Nation State/APT | Targeted surveillance | Passive surveillance of internet infrastructure, advanced encryption analysis | Use open-source software, strong diceware credentials, hardware with secure element, shut down devices when not in use, tripwire/honeypot/[canary tokens](https://canarytokens.org/) alerts Read more about [threat modeling](https://www.netmeister.org/blog/threat-model-101.html). # Hardware [Apple silicon hardware](https://support.apple.com/guide/security/hardware-security-overview-secf020d1074/1/web/1) provide hardware-backed security features, including Secure Enclave-based key protection and stronger boot security options. They are generally the preferred platform for the protections discussed in this guide. Some Intel-based Macs, especially models with vulnerable [T2-era hardware](https://en.wikipedia.org/wiki/Apple_T2), are affected by hardware vulnerabilities that cannot be fully fixed by a macOS update. Avoid non-Apple hardware running macOS and systems that do not support the latest macOS release, as Apple does not [patch all vulnerabilities](https://support.apple.com/guide/deployment/about-software-updates-depc4c80847a) in legacy versions. Apple accessories generally receive firmware updates through macOS and support current [Bluetooth security features](https://support.apple.com/guide/security/bluetooth-security-sec82597d97e/web). For example, [Bluetooth Low Energy](https://en.wikipedia.org/wiki/Bluetooth_Low_Energy) (BLE) Privacy uses rotating device addresses to reduce tracking; third-party accessories may not support this feature. # Installing macOS There are several ways to [install macOS](https://support.apple.com/102662). Install the latest supported version of macOS; newer versions of macOS include security fixes and other improvements not available in previous releases. ## System activation During installation, Apple silicon Macs contact Apple activation service to confirm that the device is not reported [lost or stolen](https://support.apple.com/102541). Read about [how this process works](https://support.apple.com/guide/security/localpolicy-signing-key-creation-management-sec1f90fbad1). ## Apple Account An [Apple Account](https://www.apple.com/legal/privacy/data/en/apple-id/) is optional for basic macOS use but required for the App Store and many Apple services. Review [data privacy settings](https://support.apple.com/102651) before enabling features. Enable [end-to-end encryption](https://support.apple.com/guide/security/advanced-data-protection-for-icloud-sec973254c5f/web) for iCloud and review [Apple Account data](https://support.apple.com/102283). ## App Store The [App Store](https://en.wikipedia.org/wiki/Mac_app_store) is a software distribution platform where applications are [reviewed](https://developer.apple.com/app-store/review/guidelines) by Apple. App Store applications are required to use [App Sandbox](https://developer.apple.com/documentation/security/app_sandbox/protecting_user_data_with_app_sandbox) and [Hardened Runtime](https://developer.apple.com/documentation/security/hardened_runtime) (security features restricting what apps can do, making some attacks more difficult). It also offers automatic software updates. Using the App Store requires an Apple Account, which can pose a privacy risk. ## Virtualization Virtualization enables another operating system to run in an isolated virtual machine. On [Apple silicon](https://developer.apple.com/documentation/virtualization), macOS can run supported macOS guests and Windows 11 for ARM using apps such as the following: - [UTM](https://mac.getutm.app/) - Follow the [documentation](https://docs.getutm.app/guest-support/macos) to create macOS and other virtual machines. - [VirtualBuddy](https://github.com/insidegui/VirtualBuddy) - Application for virtualizing macOS 12+ on Apple silicon. - [Bushel](https://getbushel.app/) - A lightweight, free app. On first launch, select "Ask App Not to Track". - [VMware Fusion](https://knowledge.broadcom.com/external/article/315638/download-and-install-vmware-fusion.html) - Now free under Broadcom. Clean UI, easy macOS setup, and supports Windows 11 ARM. - [tart (CLI)](https://tart.run/) - Command‑line application installed with Homebrew. - [Parallels](https://www.parallels.com/) - Paid option with strong integration. > [!WARNING] > VMware requires a Broadcom account and acceptance of agreements before download. > Parallels requires an account, payment details, and other data - see the [privacy notice](https://my.parallels.com/data_reminder). ### Apple containers [Apple Container](https://github.com/apple/container) is a command-line tool for running Linux containers on macOS. Unlike container runtimes that share a single Linux virtual machine, Apple Container runs each container in an isolated, lightweight virtual machine using macOS virtualization capabilities. This provides a stronger isolation boundary between workloads and the host operating system. # First boot When macOS starts for the first time, **Setup Assistant** requires the creation of a primary account. Set a [long and unique password](https://www.eff.org/dice). Leave the password hint field blank. Avoid personally identifiable names: the computer name (such as "John Appleseed's MacBook") is broadcast over local networks and visible to other devices. The system name can be configured in **System Settings > About** or with the commands: ```bash sudo scutil --set ComputerName MacBook sudo scutil --set HostName MacBook sudo scutil --set LocalHostName MacBook ``` # Admin and user accounts The first account created is an administrator account. Administrators can change system-wide settings and run commands with [sudo](https://en.wikipedia.org/wiki/Sudo), which temporarily grants elevated privileges. Any program the administrator runs could obtain the same access; sudo may also have [vulnerabilities](https://bogner.sh/2014/03/another-mac-os-x-sudo-password-bypass/). It is considered a [best practice](https://help.apple.com/machelp/mac/10.12/index.html#/mh11389) to use a dedicated standard account for regular, daily work and only use the administrator account for software and system installation, configuration and updates. It is not required to ever log in with the admin account via the macOS login screen. When a Terminal command requires administrator privileges, the system will prompt for authentication and Terminal continues using those privileges. To that end, Apple provides [recommendations](https://support.apple.com/102099) for hiding the admin account and its home directory. ## Caveats - Only administrators can install applications in the system-wide `/Applications` directory. Finder and Installer ask a standard user to enter an administrator's credentials when approval is required. Some applications can instead be installed in `~/Applications`; applications which do not require admin access should be installed in the user directory. App Store applications are still installed in `/Applications` and require no additional authentication. - A standard user usually is not authorized to use `sudo`. When administrator privileges are required, macOS prompts for an administrator's credentials, or the task can be run from an administrator account. - System Settings and several system utilities (e.g., Wi-Fi Diagnostics) require administrator permission for full functionality. Some System Settings need to be unlocked by selecting the lock icon. Some applications will simply prompt for authentication upon opening, others must be opened by an admin account directly to access all functions (e.g., Console). - Some third-party applications assume the current user is an administrator and will not work from a standard account. - See [issue 167](https://github.com/drduh/macOS-Security-and-Privacy-Guide/issues/167) for additional considerations. ## Setup Accounts be created and managed in System Settings. On existing systems, it is generally easier to create a second admin account and then change the original account from an administrator account to a standard account. Newly-installed systems should instead add a standard account after setup. Demoting an account can be done from the new admin account in System Settings. See also [this post](https://superuser.com/a/395738) for more information about how macOS determines group membership. # Firmware Verify that firmware security is set to [Full Security](https://support.apple.com/guide/mac-help/mchl768f7291/mac) to prevent tampering with the system. This is the default setting. # FileVault Apple silicon Macs use hardware-backed storage encryption by default. [FileVault](https://support.apple.com/guide/mac-help/protect-data-on-your-mac-with-filevault-mh11785/mac) additionally requires an authorized user's password to unlock the startup volume after restart. On Apple silicon, FileVault authorization also protects the [firmware](https://support.apple.com/102384), which prevents booting from anything other than the designated startup disk, accessing [Recovery](https://support.apple.com/guide/mac-help/macos-recovery-a-mac-apple-silicon-mchl82829c17/15.0/mac/15.0#mchl5abfbb29), and [reviving](https://support.apple.com/108900) it with device firmware update (DFU) mode. FileVault will prompt to set a recovery key, which should be stored in a safe location if used. FileVault also offers an option to use iCloud for recovery. Confirm FileVault state: ```bash fdesetup status ``` # Lockdown Mode [Lockdown Mode](https://support.apple.com/105120) significantly reduces attack surface by disabling system and application features commonly exploited in sophisticated attacks. When Lockdown Mode is enabled, Safari has an option to [exclude trusted websites](https://ssd.eff.org/module/how-to-enable-lockdown-mode-on-iphone) from restrictions. # Firewall There are several types of firewalls available for macOS. > [!NOTE] > If malware gains administrator control, it may disable or bypass firewall policies; do not rely on a local firewall as strong protection against a full system compromise. ## Application layer firewall The built-in firewall provides basic protection and blocks incoming connections only. It can neither monitor nor block outgoing connections. It can be controlled by the **Firewall** tab of **Network** in **System Settings**, or with the following commands. Attackers frequently scan networks to identify systems to target. When [stealth mode](https://support.apple.com/guide/mac-help/use-stealth-mode-to-keep-your-mac-more-secure-mh17133/mac) is enabled, responses are not sent to connection attempts from closed ports, making the system more difficult to detect. ### Stealth mode Enable the firewall and stealth mode: ```bash sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setstealthmode on ``` ### Signed apps By default, the firewall allows incoming connections for software signed by Apple or by an identified developer. Disabling these rules makes macOS ask before allowing an application to accept incoming connections: ```bash sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setallowsigned off sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setallowsignedapp off ``` ### Reload firewall After changing settings with `socketfilterfw`, reload the firewall service to apply the new configuration: ```bash sudo pkill -HUP socketfilterfw ``` ### Get state Confirm firewall state: ```console for firewallFlag in \ --getglobalstate \ --getblockall \ --getallowsigned \ --getstealthmode \ --listapps do /usr/libexec/ApplicationFirewall/socketfilterfw "$firewallFlag" done ``` ### AirDrop Enabling the application layer firewall and disabling incoming connections for built-in software prevents [AirDrop](https://support.apple.com/119857) from functioning correctly. For AirDrop to work, both `sharingd` and `rapportd` require firewall exceptions: ```bash sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add /usr/libexec/sharingd sudo /usr/libexec/ApplicationFirewall/socketfilterfw --unblockapp /usr/libexec/sharingd sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add /usr/libexec/rapportd sudo /usr/libexec/ApplicationFirewall/socketfilterfw --unblockapp /usr/libexec/rapportd ``` ## Third-party firewalls Applications such as [Little Snitch](https://www.obdev.at/products/littlesnitch/index.html), [Radio Silence](https://radiosilenceapp.com/), and [LuLu](https://objective-see.com/products/lulu.html) provide a balance between usability and security. These programs are capable of monitoring and blocking both incoming and outgoing connections. However, they may require a closed-source [system extension](https://support.apple.com/HT210999). If frequent allow-or-block prompts are overwhelming, temporarily allow connections while also recording them ([Silent Allow mode](https://help.obdev.at/littlesnitch6/concepts-opmodes) in Little Snitch). Review the configuration to understand and control network activity. ## Packet filter macOS also includes [pf](https://en.wikipedia.org/wiki/PF_(firewall)), a packet-filtering firewall configured from the command line. It is powerful but considerably more complex than the built-in application firewall. pf can also be controlled with a graphical application such as [Murus](https://www.murusfirewall.com/). Many [books](https://nostarch.com/book-of-pf-4e) and [guides](https://www.openbsd.org/faq/pf/) cover the pf firewall. The following example shows how to configure a basic policy. ### Example pf config Add the following rules to a file named `pf.rules`: ```console # Define interface wifi = "en0" # Global options set block-policy drop set skip on lo0 set state-policy if-bound set ruleset-optimization basic scrub in on $wifi all fragment reassemble # Define tables table persist # Default deny both directions and log block log all block quick from no-route to any antispoof quick for $wifi # Blocklist enforcement block log quick on $wifi from { } to any block log quick on $wifi from any to { } # DHCP pass out on $wifi proto udp from any port 68 to any port 67 keep state pass in on $wifi proto udp from any port 67 to any port 68 keep state # Outbound TCP pass out on $wifi proto tcp from ($wifi) to any flags S/SA keep state # Outbound UDP pass out on $wifi proto udp from ($wifi) to any keep state # Outbound ICMP (ping) pass out on $wifi proto icmp from ($wifi) to any keep state ``` ### Firewall commands To control the firewall: Command | Task -: | :- `sudo pfctl -e -f pf.rules` | enable firewall with configuration file `sudo pfctl -t blocklist -T add 1.2.3.4` | add an address to the blocklist `sudo pfctl -d` | disable firewall To monitor the firewall: Command | Task -: | :- `sudo pfctl -t blocklist -T show` | show blocklist `sudo pfctl -sr` | show active rules `sudo pfctl -ss` | show state table `sudo ifconfig pflog0 create` | create packet log interface `sudo tcpdump -ni pflog0` | monitor blocked packets ### Block networks pf can block ranges of network addresses, for example to an entire organization. Query [Merit RADb](https://www.radb.net/) for the list of networks in use by an [autonomous system](https://en.wikipedia.org/wiki/Autonomous_system_(Internet)) (a large network operated by a single organization), such as [Facebook](https://ipinfo.io/AS32934): ```bash whois -h whois.radb.net '!gAS32934' ``` Copy and paste the list of networks returned into the blocklist command: ```bash sudo pfctl -t blocklist -T add 31.13.24.0/21 31.13.64.0/24 157.240.0.0/16 ``` Confirm the addresses were added: ```console $ sudo pfctl -t blocklist -T show No ALTQ support in kernel ALTQ related functions disabled 31.13.24.0/21 31.13.64.0/24 157.240.0.0/16 ``` Confirm network traffic is blocked to those addresses (DNS requests will still work): ```console $ dig a +short facebook.com 157.240.2.35 $ curl --connect-timeout 5 -I https://facebook.com/ * Trying 157.240.2.35... * TCP_NODELAY set * Connection timed out after 5002 milliseconds * Closing connection 0 curl: (28) Connection timed out after 5002 milliseconds $ sudo tcpdump -tqni pflog0 'host 157.240.2.35' IP 192.168.1.1.62771 > 157.240.2.35.443: tcp 0 IP 192.168.1.1.62771 > 157.240.2.35.443: tcp 0 IP 192.168.1.1.62771 > 157.240.2.35.443: tcp 0 ``` The firewall drops the initial packets needed to start the [TCP connection](https://en.wikipedia.org/wiki/Transmission_Control_Protocol#Connection_establishment), so the connection times out. See [drduh/config/scripts/pf-blocklist.sh](https://github.com/drduh/config/blob/main/scripts/pf-blocklist.sh) for more inspiration. # Services Many system and user background services are managed by [launchd](https://en.wikipedia.org/wiki/Launchd). Administrator accounts can modify services and extensions in [System Settings](https://support.apple.com/guide/mac-help/change-login-items-settings-mtusr003). Command | Task -: | :- `launchctl list` | view user jobs `sudo launchctl list` | view system jobs `launchctl list com.apple.Finder` | examine a service `systemextensionsctl list` | list system extensions `ls /System/Library/LaunchDaemons` | list system daemons `ls /System/Library/LaunchAgents` | list system agents To read a service configuration: ```bash defaults read /System/Library/LaunchAgents/com.apple.Finder ``` > [!IMPORTANT] > System services are protected by [SIP](https://github.com/drduh/macOS-Security-and-Privacy-Guide#system-integrity-protection); disabling SIP to modify system services can compromise security and cause system instability. To view the status of services: ```bash find /var/db/com.apple.xpc.launchd \ -type f -print -exec defaults read {} \; 2>/dev/null ``` See [script management with launchd](https://support.apple.com/guide/terminal/script-management-with-launchd-apdc6c1077b-5d5d-4d35-9c19-60f2397b2369) and [launchd.info](https://launchd.info/) for more information. # Siri Suggestions and Spotlight Siri Suggestions and Spotlight may send some queries or usage information to Apple, depending on the enabled features. In System Settings, search for Siri and Spotlight, then disable online suggestions and configure categories to exclude from indexing or suggestion. Review Apple's [Search & Privacy](https://www.apple.com/legal/privacy/data/en/siri-suggestions-search/) policy for more information. # Homebrew If a program is not available through the App Store, consider using [Homebrew](https://brew.sh/). > [!IMPORTANT] > Some Homebrew installation or management workflows may prompt for App Management or [Full Disk Access](https://eclecticlight.co/2025/11/08/explainer-permissions-privacy-and-tcc/). Grant these permissions only when they are fully understood and necessary. Periodically run `brew upgrade` on trusted and secure networks to install software updates. To get information on a package before installation, run `brew info ` and review its formula online. Enable [additional security options](https://github.com/drduh/macOS-Security-and-Privacy-Guide/issues/138), such as `HOMEBREW_NO_INSECURE_REDIRECT=1` According to [Homebrew's Anonymous Analytics](https://docs.brew.sh/Analytics), Homebrew collects anonymous usage analytics and reports them to a self-hosted [InfluxDB](https://en.wikipedia.org/wiki/InfluxDB) instance. To opt out of Homebrew analytics, run `brew analytics off` or set `HOMEBREW_NO_ANALYTICS=1` in the shell startup file. # DNS ## DNS profiles macOS features "DNS configuration profiles" for configuring encrypted DNS, filtering, and [DNSSEC](https://en.wikipedia.org/wiki/Domain_Name_System_Security_Extensions). DNS profiles can be [created](https://dns.notjakob.com/) or obtained from providers such as [Quad9](https://docs.quad9.net/Setup_Guides/MacOS/Big_Sur_and_later_(Encrypted)/#download-profile), [AdGuard](https://adguard-dns.io/en/public-dns.html) and [NextDNS](https://nextdns.io/). ## Hosts file Use the [hosts file](https://en.wikipedia.org/wiki/Hosts_(file)) to block domains associated with malware, advertising, and other unwanted services. To block a domain by [A record](https://en.wikipedia.org/wiki/List_of_DNS_record_types), append any one of the following lines to `/etc/hosts`: ``` 0 example.com 0.0.0.0 example.com 127.0.0.1 example.com ``` > [!NOTE] > IPv6 uses AAAA records rather than A records: block IPv6 connections by including `::1 example.com` entries. Many domain lists are available online. Before appending one to `/etc/hosts`, ensure each entry begins with `0`, `0.0.0.0`, or `127.0.0.1`, and retain the `127.0.0.1 localhost` entry. Popular hosts lists include: - [StevenBlack/hosts](https://github.com/StevenBlack/hosts) - [Sinfonietta/hostfiles](https://github.com/Sinfonietta/hostfiles) - [someonewhocares.org](https://someonewhocares.org/hosts/zero/hosts) To download and append a list to the hosts file, use the [tee](https://man7.org/linux/man-pages/man1/tee.1.html) command: ```bash curl https://raw.githubusercontent.com/StevenBlack/hosts/master/hosts | sudo tee -a /etc/hosts ``` [Little Snitch](#third-party-firewalls) also supports [blocklists](https://help.obdev.at/littlesnitch6/lsc-blocklists). ## DNSCrypt To encrypt DNS traffic, consider [DNSCrypt/dnscrypt-proxy](https://github.com/DNSCrypt/dnscrypt-proxy). When configured with a trusted resolver, DNSCrypt encrypts DNS queries. DNSSEC can additionally validate signed DNS responses where supported. Install DNSCrypt from Homebrew and follow the instructions to configure and start `dnscrypt-proxy`: ```bash brew install dnscrypt-proxy ``` When using DNSCrypt with Dnsmasq, locate the DNSCrypt configuration file by running: ```bash brew info dnscrypt-proxy ``` This command should display a path such as `/usr/local/etc/dnscrypt-proxy.toml`. By default, dnscrypt-proxy listens on `127.0.0.1:53` and sends queries to one or more configured DNS providers. Modify the configuration and change `listen_addresses` to use a port other than 53, such as 5355: ```toml listen_addresses = ['127.0.0.1:5355', '[::1]:5355'] ``` Start DNSCrypt: ```bash sudo brew services restart dnscrypt-proxy ``` Confirm DNSCrypt is running: ```console $ sudo lsof +c 15 -Pni UDP:5355 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME dnscrypt-proxy 15244 nobody 7u IPv4 0x1337f85ff9f8beef 0t0 UDP 127.0.0.1:5355 dnscrypt-proxy 15244 nobody 10u IPv6 0x1337f85ff9f8beef 0t0 UDP [::1]:5355 dnscrypt-proxy 15244 nobody 12u IPv4 0x1337f85ff9f8beef 0t0 UDP 127.0.0.1:5355 dnscrypt-proxy 15244 nobody 14u IPv6 0x1337f85ff9f8beef 0t0 UDP [::1]:5355 ``` Additionally, these pf rules block conventional DNS traffic to port 53 outside the loopback interface, to reduce the risk of [DNS leaks](https://dnsleaktest.com/): ```console block drop quick on !lo0 proto udp from any to any port = 53 block drop quick on !lo0 proto tcp from any to any port = 53 ``` ## Dnsmasq [dnsmasq](https://thekelleys.org.uk/dnsmasq/doc.html) can cache replies, prevent upstream queries for unqualified names, and block entire top-level domains. Use it in combination with DNSCrypt to encrypt DNS traffic. If you do not use DNSCrypt, at minimum choose a DNS resolver other than the one provided by the ISP. Two popular alternatives are [Google DNS](https://developers.google.com/speed/public-dns/) and [OpenDNS](https://www.opendns.com/home-internet-security/). Install Dnsmasq: ```bash brew install dnsmasq ``` Download and edit [drduh/config/dnsmasq.conf](https://github.com/drduh/config/blob/main/dnsmasq.conf) or the default configuration file. See [drduh/config/domains](https://github.com/drduh/config/tree/main/domains) for example domain lists that can be added to block specific destinations. Install and start the program (sudo is required to bind to [privileged port](https://unix.stackexchange.com/questions/16564/why-are-the-first-1024-ports-restricted-to-the-root-user-only) 53): ```bash sudo brew services start dnsmasq ``` To set dnsmasq as the local DNS server, open **System Settings** > **Network** and select the network connection currently in use (such as Wi-Fi), then open the **DNS** tab, select **+**, and add `127.0.0.1`, or use: ```bash sudo networksetup -setdnsservers "Wi-Fi" 127.0.0.1 ``` Confirm Dnsmasq is configured: ```console $ scutil --dns | head DNS configuration resolver #1 search domain[0] : whatever nameserver[0] : 127.0.0.1 flags : Request A records, Request AAAA records reach : 0x00030002 (Reachable,Local Address,Directly Reachable Address) $ networksetup -getdnsservers "Wi-Fi" 127.0.0.1 ``` > [!NOTE] > Some VPN applications override DNS settings on connect. See [issue 24](https://github.com/drduh/macOS-Security-and-Privacy-Guide/issues/24) and [drduh/config/scripts/macos-dns.sh](https://github.com/drduh/config/blob/main/scripts/macos-dns.sh). # Certificate authorities macOS includes a set of trusted root certificate authorities (CAs) operated by corporations, governments and other organizations from around the world. A trusted CA can issue certificates that macOS and browsers may accept for HTTPS connections, making the root CA store a critical part of the system's trust boundary. Inspect **System Roots** to understand the Apple-provided trusted root store using [Keychain Access](https://support.apple.com/guide/keychain-access/welcome/mac) or the [`security`](https://ss64.com/mac/security.html) command-line tool and `/System/Library/Keychains/SystemRootCertificates.keychain` file. Keychain Access can also be launched with the command: ```bash open "/System/Library/CoreServices/Applications/Keychain Access.app" ``` Also review any certificates that may have been added by a user, administrator, VPN client, security product, or mobile device management application in the **login**, **Local Items**, and **System** keychains. To disable a selected certificate, modify its Trust setting to **Never Trust** and close the window to confirm. Doing so may reduce the risk of [MITM](https://wikipedia.org/wiki/Man-in-the-middle_attack) attacks, in which a fraudulent certificate is used to [silently intercept](https://en.wikipedia.org/wiki/DigiNotar#Issuance_of_fraudulent_certificates) encrypted traffic. > [!WARNING] > Removing or modifying certificate authority trust settings can break websites, software updates, enterprise networks, VPNs, captive portals, and other services. See Apple's [available trusted certificates](https://support.apple.com/103723) and [blocked certificates](https://support.apple.com/103247#blocked) lists for current trust-store information. # Privoxy Consider using [Privoxy](https://www.privoxy.org/) as a local proxy to filter web traffic. Install and start Privoxy using Homebrew: ```bash brew install privoxy brew services start privoxy ``` Alternatively, a signed installation package for Privoxy is available from [their website](https://www.privoxy.org/sf-download-mirror/Macintosh%20%28OS%20X%29/) or [Sourceforge](https://sourceforge.net/projects/ijbswa/files/Macintosh%20%28OS%20X%29/). The signed package is [more secure](https://github.com/drduh/macOS-Security-and-Privacy-Guide/issues/65) than the Homebrew version and receives support from the Privoxy project. By default, Privoxy listens on local TCP port 8118. Set the system **HTTP** proxy for the active network interface to `127.0.0.1` and port `8118`: ```bash sudo networksetup -setwebproxy "Wi-Fi" 127.0.0.1 8118 ``` Set the system **HTTPS** proxy: ```bash sudo networksetup -setsecurewebproxy "Wi-Fi" 127.0.0.1 8118 ``` The proxy can also be set in **System Settings** > **Network** > **Details** > **Proxies**. Confirm the proxy is set: ```console $ scutil --proxy { ExceptionsList : { 0 : *.local 1 : 169.254/16 } FTPPassive : 1 HTTPEnable : 1 HTTPPort : 8118 HTTPProxy : 127.0.0.1 } ``` Although most web traffic is encrypted, Privoxy can filter requests by hostname. For example, the following rules block all traffic except traffic to .net, github.com, and Apple domains: ```console { +block{all} } . { -block } .apple. .github.com .net ``` To block Facebook domains: ```console { +block{facebook} } .cdninstagram. .facebook*. .fb. .fbcdn*. .fbinfra. .fbsbx. .fbstatic*. .fbsv. .fburl. .instagr.am .tfbnw. .thefacebook. fb*.akamaihd.net ``` See [drduh/config/privoxy/config](https://github.com/drduh/config/blob/main/privoxy/config) and [drduh/config/privoxy/user.action](https://github.com/drduh/config/blob/main/privoxy/user.action) for additional Privoxy examples. Privoxy does **not** need to be restarted after editing filter rules. To verify traffic is blocked or redirected, use [curl](https://en.wikipedia.org/wiki/CURL) or open the Privoxy interface at in a browser: ```console $ ALL_PROXY=127.0.0.1:8118 curl example.com -IL | head HTTP/1.1 403 Request blocked by Privoxy Content-Length: 9001 Content-Type: text/html Cache-Control: no-cache Pragma: no-cache $ ALL_PROXY=127.0.0.1:8118 curl github.com -IL | head HTTP/1.1 302 Local Redirect from Privoxy Location: https://github.com/ Content-Length: 0 HTTP/1.1 200 Connection established HTTP/2 200 content-type: text/html; charset=utf-8 ``` > [!NOTE] > Applications and services can ignore the proxy settings. pf can redirect traffic through a proxy without configuring each application separately. # Browser Web browsers create significant security and privacy risks because they download and execute untrusted Internet content. A key browser security boundary is the [same-origin policy](https://en.wikipedia.org/wiki/Same-origin_policy) (SOP), which prevents one website from reading another website's data. A bypass can expose data or actions from other sites in the same browser profile. Some browser attacks rely on convincing the user to install software, grant permissions, or use a malicious extension. Be especially careful with unexpected downloads, extension prompts, and requests to run commands in Terminal. Browser extensions also pose a significant security risk: a malicious or poorly-made extension can compromise everything in the browser, including credentials. The use of browser extensions should be limited to critically necessary ones, published by trustworthy developers only. Use separate browser profiles for different identities and purposes. If practical, disable JavaScript and only allow it on trusted sites using browser site permissions. [Mozilla Firefox](https://www.firefox.com/), [Google Chrome](https://www.google.com/chrome), [Safari](https://www.apple.com/safari), and [Tor Browser](https://www.torproject.org/download) are popular browsers, each with unique features and individual purposes. ## Firefox Firefox modernized major parts of its codebase through the [Quantum](https://wiki.mozilla.org/Quantum) and [Photon](https://wiki.mozilla.org/Firefox/Photon/Updates) projects. Quantum includes moving some components from C++ to [Rust](https://rust-lang.org/), a programming language designed to improve memory safety and concurrency safety. Firefox offers a comparable security model to Chrome, including a [bug bounty program](https://www.mozilla.org/security/bug-bounty/) for responsible disclosure of vulnerabilities. Firefox follows a four-week release cycle. See [drduh/config/firefox.user.js](https://github.com/drduh/config/blob/main/firefox.user.js) and [arkenfox/user.js](https://github.com/arkenfox/user.js) for recommended configurations. Also see [NoScript](https://noscript.net/), an extension which allows selective script blocking. Firefox [focuses on user privacy](https://www.mozilla.org/firefox/privacy). It supports [tracking protection](https://developer.mozilla.org/docs/Web/Privacy/Firefox_tracking_protection) in Private Browsing mode. The tracking protection can be enabled for the default account, although it may break the browsing experience on some websites. Firefox in Strict tracking protection mode will [randomize fingerprints](https://support.mozilla.org/kb/firefox-protection-against-fingerprinting) to defend against tracking. Firefox offers separate user [profiles](https://support.mozilla.org/kb/profile-manager-create-remove-switch-firefox-profiles). Browsing can also be delineated with [Multi-Account Containers](https://support.mozilla.org/kb/containers). Firefox only supports Web Extensions through the [WebExtension API](https://developer.mozilla.org/docs/Mozilla/Add-ons/WebExtensions), which is very similar to Chrome. Submission of Web Extensions in Firefox is free. Web Extensions in Firefox most of the time are open-source, although certain Web Extensions are proprietary. ## Chrome [Google Chrome](https://www.google.com/chrome/) is based on the open-source [Chromium project](https://www.chromium.org/). Chrome includes some proprietary components, automatic updates, a PDF viewer, media-codec support, crash reporting, and Google account integration. Review Chrome privacy settings and Google privacy policies for more information. Chrome offers account sync between multiple devices, including credentials; the data is encrypted with the account password. Chrome has the largest share of global usage and is the preferred target platform for the majority of developers. Major technologies are based on Chrome's open-source components, such as [node.js](https://nodejs.org/) which uses [Chrome's V8](https://developers.google.com/v8) Engine and the [Electron](https://electron.atom.io/) framework, which is based on Chromium and node.js. Chrome's vast user base makes it the most attractive target for threat actors and security researchers. Despite constant attacks, Chrome has retained an impressive security track record over the years. This is not a small feat. Chrome offers [separate profiles](https://www.chromium.org/user-experience/multi-profiles), [robust sandboxing](https://chromium.googlesource.com/chromium/src/+/HEAD/docs/design/sandbox.md), [frequent updates](https://chromereleases.googleblog.com/), and carries [impressive credentials](https://www.chromium.org/Home/chromium-security/brag-sheet). In addition, Google offers a very lucrative [bounty program](https://bughunters.google.com/about/rules/5745167867576320/chrome-vulnerability-reward-program-rules) for reporting vulnerabilities, along with its own [Project Zero](https://googleprojectzero.blogspot.com/) team. This means that a large number of highly talented and motivated people are constantly auditing and securing Chrome code. Consider disabling V8 optimization (JavaScript-engine performance features) in browser settings - see [this explanation](https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode) for the security trade-offs. Block trackers with [uBlock Origin Lite](https://chromewebstore.google.com/detail/ublock-origin-lite/ddkjiahejlhfcafbddmgiahcphecmpfh). Disable [DNS prefetching](https://www.chromium.org/developers/design-documents/dns-prefetching) (see [DNS Prefetching and Its Privacy Implications](https://www.usenix.org/legacy/event/leet10/tech/full_papers/Krishnan.pdf)). Chrome [may attempt](https://github.com/drduh/macOS-Security-and-Privacy-Guide/issues/350) to resolve DNS using Google's `8.8.8.8` and `8.8.4.4` public nameservers. See [Chromium Security](https://www.chromium.org/Home/chromium-security) and [Chromium Privacy](https://www.chromium.org/Home/chromium-privacy) for more information. Read [Google's privacy policy](https://policies.google.com/privacy) to understand how personal information is collected and used. ## Safari [Safari](https://www.apple.com/safari) is Apple's built-in browser and is integrated with macOS, providing battery efficiency improvements on Apple hardware. Safari has both open-source and proprietary components. Safari is based on the open-source Web Engine [WebKit](https://webkit.org/), which is ubiquitous among the macOS ecosystem. WebKit is used by Apple apps such as Mail, Books, and the App Store. Chrome's [Blink](https://www.chromium.org/blink) engine is a fork of WebKit and both engines share a number of similarities. Safari supports certain unique features that benefit user security and privacy. [Content blockers](https://webkit.org/blog/3476/content-blockers-first-look) enable the creation of content blocking rules without using JavaScript. This rule based approach greatly improves memory use, security, and privacy. Safari 11 introduced [Intelligent Tracking Prevention](https://webkit.org/blog/7675/intelligent-tracking-prevention), which removes tracking data stored in Safari after a period of non-interaction by the user from the tracker's website. Safari can randomize the browser fingerprint to reduce tracking. Safari does not support certain features such as WebUSB or the Battery API intentionally for security and privacy reasons. Private tabs in Safari have isolated cookies and cache that is destroyed when you close the tab. Safari also support Profiles which are equivalent to Firefox's Multi-Account Containers for separating cookies and browsing. Safari can be made significantly more secure with [lockdown mode](#lockdown-mode), which can be disabled per-site. Read more about [tracking prevention](https://webkit.org/tracking-prevention/) in Safari. Web Extensions in Safari have an additional option to use native code in Safari's sandbox environment, in addition to Web Extension APIs. Web Extensions in Safari are also distributed through Apple App Store. App Store submission comes with the added benefit of Web Extension code being audited by Apple. On the other hand App Store submission comes at a steep cost. Yearly [developer subscription](https://developer.apple.com/support/compare-memberships) fee costs 100 USD (in contrast to Chrome's 5 USD fee and Firefox's free submission). The high cost is prohibitive for the majority of open-source developers. As a result, Safari has very few extensions to choose from. However, keep the high cost in mind when installing extensions. It is expected that most Web Extensions will have some way of monetizing usage to cover development costs. Avoid Web Extensions without open-source code available for review. Safari syncs user preferences and passwords with [iCloud Keychain](https://support.apple.com/HT202303). Viewing a saved password requires authentication with the current device account password or another configured authentication method. Safari implements new web features more slowly than Chrome or Firefox, but security patches are delivered promptly through system updates. See also [el1t/uBlock-Safari](https://github.com/el1t/uBlock-Safari/wiki/Disable-hyperlink-auditing-beacon) to disable hyperlink auditing beacons. ## Web browser privacy Websites infer information about the [browser and device](https://developer.mozilla.org/docs/Web/API/Navigator) from settings, fonts, screen size, language, IP address, and browser behavior. This information contributes to [browser fingerprinting](https://en.wikipedia.org/wiki/Device_fingerprint). For more information about security-conscious browsing and what data is sent by the browser, see [HowTo: Privacy & Security Conscious Browsing](https://gist.github.com/atcuno/3425484ac5cce5298932), [browserleaks.com](https://browserleaks.com/), [Am I Unique?](https://amiunique.org/fingerprint) and [EFF Cover Your Tracks](https://coveryourtracks.eff.org/) resources. To reduce cross-site tracking, block [third-party cookies](https://en.wikipedia.org/wiki/Third-party_cookies). Also be aware of [WebRTC](https://en.wikipedia.org/wiki/WebRTC#Concerns), which may reveal local or public (if connected to a VPN) IP address(es). In Firefox and Chrome/Chromium, this feature can be disabled with [uBlock Origin](https://github.com/gorhill/uBlock/wiki/Prevent-WebRTC-from-leaking-local-IP-address). [Lockdown mode](#lockdown-mode) also [disables WebRTC](https://www.sevarg.net/2022/07/20/ios16-lockdown-mode-browser-analysis) in Safari. # Tor [Tor](https://en.wikipedia.org/wiki/Tor_(network)) is an anonymity network that can provide additional privacy while browsing. Tor Browser is a modified Firefox-based browser configured to use the Tor network. Download Tor Browser from [Tor Project](https://www.torproject.org/download/), both `dmg` and `asc` files for [verification](https://support.torproject.org/tor-browser/getting-started/verifying-tor-browser/): ```console $ cd ~/Downloads $ file tor-browser-macos-* tor-browser-macos-15.0.17.dmg: XZ compressed data, checksum NONE tor-browser-macos-15.0.17.dmg.asc: PGP signature Signature (old) $ gpg --verify tor-browser-macos-*.asc [...] gpg: Can't check signature: No public key $ gpg --auto-key-locate nodefault,wkd --locate-keys torbrowser@torproject.org gpg: key 0x4E2C6E8793298290: public key "Tor Browser Developers (signing key) " imported gpg: Total number processed: 1 gpg: imported: 1 pub rsa4096/0x4E2C6E8793298290 2014-12-15 [C] [expires: 2027-07-15] Key fingerprint = EF6E 286D DA85 EA2A 4BA7 DE68 4E2C 6E87 9329 8290 uid [ unknown] Tor Browser Developers (signing key) sub rsa4096/0x157432CF78A65729 2024-07-15 [S] [expires: 2026-10-26] Key fingerprint = CAAE 408A EBE2 288E 96FC 5D5E 1574 32CF 78A6 5729 $ gpg --verify tor-browser-macos-*.asc gpg: assuming signed data in 'tor-browser-macos-15.0.17.dmg' gpg: Signature made Sun Jun 28 15:35:20 2026 PDT gpg: using RSA key CAAE408AEBE2288E96FC5D5E157432CF78A65729 gpg: Good signature from "Tor Browser Developers (signing key) " [unknown] gpg: WARNING: This key is not certified with a trusted signature! gpg: There is no indication that the signature belongs to the owner. Primary key fingerprint: EF6E 286D DA85 EA2A 4BA7 DE68 4E2C 6E87 9329 8290 Subkey fingerprint: CAAE 408A EBE2 288E 96FC 5D5E 1574 32CF 78A6 5729 ``` Make sure `Good signature from "Tor Browser Developers (signing key) "` appears in the output. The warning is expected, as the key has not been personally verified and added to a trusted keyring. See [How can I verify Tor Browser's signature?](https://support.torproject.org/tbb/how-to-verify-signature/) for more information. To finish installing Tor Browser, open the disk image and drag it to the Applications folder, or use the commands: ```bash hdiutil mount tor-browser-macos-15.0.17.dmg cp -r /Volumes/Tor\ Browser/Tor\ Browser.app/ ~/Applications/ ``` Verify the application was signed by The Tor Project's Apple Developer ID `MADPSAYN6T` using the `spctl -a -v` or `pkgutil --check-signature` commands: ```console $ spctl -a -vv ~/Applications/Tor\ Browser.app /Users/user1/Applications/Tor Browser.app: accepted source=Notarized Developer ID origin=Developer ID Application: The Tor Project, Inc (MADPSAYN6T) $ pkgutil --check-signature ~/Applications/Tor\ Browser.app Package "Tor Browser.app": Status: signed by a certificate trusted by macOS Certificate Chain: 1. Developer ID Application: The Tor Project, Inc (MADPSAYN6T) Expires: 2028-10-11 17:57:46 +0000 SHA256 Fingerprint: 76 3C 89 02 ED CB AD 8E 59 86 1E 93 D3 05 5B 28 F9 04 0C 96 03 8B 16 28 9F 38 64 ED 53 45 B4 DA ------------------------------------------------------------------------ 2. Developer ID Certification Authority Expires: 2031-09-17 00:00:00 +0000 SHA256 Fingerprint: F1 6C D3 C5 4C 7F 83 CE A4 BF 1A 3E 6A 08 19 C8 AA A8 E4 A1 52 8F D1 44 71 5F 35 06 43 D2 DF 3A ------------------------------------------------------------------------ 3. Apple Root CA Expires: 2035-02-09 21:40:36 +0000 SHA256 Fingerprint: B0 B1 73 0E CB C7 FF 45 05 14 2C 49 F1 29 5E 6E DA 6B CA ED 7E 2C 68 C5 BE 91 B5 A1 10 01 F0 24 ``` The command `codesign` can also be used to examine an application's code signature: ```console $ codesign -dvv ~/Applications/Tor\ Browser.app Executable=/Users/user1/Applications/Tor Browser.app/Contents/MacOS/firefox Identifier=org.torproject.torbrowser Format=app bundle with Mach-O universal (x86_64 arm64) CodeDirectory v=20500 size=805 flags=0x10000(runtime) hashes=14+7 location=embedded Signature size=9054 Authority=Developer ID Application: The Tor Project, Inc (MADPSAYN6T) Authority=Developer ID Certification Authority Authority=Apple Root CA Timestamp=Jun 28, 2026 at 14:01:57 Notarization Ticket=stapled Info.plist entries=27 TeamIdentifier=MADPSAYN6T Runtime Version=15.5.0 Sealed Resources version=2 rules=13 files=208 Internal requirements count=1 size=188 ``` To view full certificate details for a signed application, extract with `codesign` and decode with `openssl`: ```console $ codesign -d --extract-certificates ~/Applications/Tor\ Browser.app Executable=/Users/user1/Applications/Tor Browser.app/Contents/MacOS/firefox $ file codesign* codesign0: Certificate, Version=3 codesign1: Certificate, Version=3 codesign2: Certificate, Version=3 Certificate, Version=02 $ openssl x509 -inform der -in codesign0 -subject -issuer -startdate -enddate -noout subject= /UID=MADPSAYN6T/CN=Developer ID Application: The Tor Project, Inc (MADPSAYN6T)/OU=MADPSAYN6T/O=The Tor Project, Inc/C=US issuer= /CN=Developer ID Certification Authority/OU=G2/O=Apple Inc./C=US notBefore=Oct 11 17:57:47 2023 GMT notAfter=Oct 11 17:57:46 2028 GMT $ openssl x509 -inform der -in codesign0 -fingerprint -noout SHA256 Fingerprint=76:3C:89:02:ED:CB:AD:8E:59:86:1E:93:D3:05:5B:28:F9:04:0C:96:03:8B:16:28:9F:38:64:ED:53:45:B4:DA ``` Tor Browser can use special connection methods called [pluggable transports](https://support.torproject.org/tor-browser/circumvention/) to make traffic harder to identify or block. This can be done by setting up a [relay](https://support.torproject.org/relays/) or using an existing [bridge](https://bridges.torproject.org/). The Tor network provides [anonymity](https://www.privateinternetaccess.com/blog/2013/10/how-does-privacy-differ-from-anonymity-and-why-are-both-important/), which is not necessarily the same as privacy. The network does not defend against a global observer capable of traffic analysis and correlation. See also [Seeking Anonymity in an Internet Panopticon](https://bford.info/pub/net/panopticon-cacm.pdf) and [Traffic Correlation on Tor by Realistic Adversaries](https://www.ohmygodel.com/publications/usersrouted-ccs13.pdf). See [Tor Protocol Specification](https://spec.torproject.org/tor-spec/) for more information. Also see [Invisible Internet Project (I2P)](https://geti2p.net/en/about/intro) and its [Tor comparison](https://geti2p.net/en/comparison/tor). # VPN Choose a VPN provider or self-hosted setup with a documented, modern protocol and well-audited clients. Avoid obsolete protocols such as [PPTP](https://en.wikipedia.org/wiki/Point-to-Point_Tunneling_Protocol#Security) in favor of [OpenVPN](https://en.wikipedia.org/wiki/OpenVPN) or [WireGuard](https://www.wireguard.com/) [on a Linux VM](https://github.com/mrash/Wireguard-macOS-LinuxVM) or via a set of [cross platform tools](https://www.wireguard.com/xplatform/). Some VPN clients may send traffic over the next available network interface when the connection is interrupted or disconnected. See [scy/8122924](https://gist.github.com/scy/8122924) for an example on how to allow traffic only over VPN. See guides to set up an [IPsec](https://en.wikipedia.org/wiki/Ipsec) VPN on a virtual machine ([hwdsl2/setup-ipsec-vpn](https://github.com/hwdsl2/setup-ipsec-vpn)) or a Docker container ([hwdsl2/docker-ipsec-vpn-server](https://github.com/hwdsl2/docker-ipsec-vpn-server)). It may be worthwhile to consider the geographical location of the VPN provider. See further discussion in [issue 114](https://github.com/drduh/macOS-Security-and-Privacy-Guide/issues/114). Also see this [technical overview](https://blog.timac.org/2018/0717-macos-vpn-architecture/) of the macOS built-in VPN L2TP/IPsec and [IKEv2](https://en.wikipedia.org/wiki/IKEv2) client. # PGP/GPG PGP is a standard for encrypting and signing data, especially email. It can protect message content between correspondents who correctly exchange and verify keys, but it does not protect metadata such as email recipients and subject lines. GPG (GNU Privacy Guard) is a GPL-licensed, open-source program compliant with the PGP standard. It can verify software signatures and encrypt files [symmetrically](https://en.wikipedia.org/wiki/Symmetric-key_algorithm) or using [public keys](https://en.wikipedia.org/wiki/Public-key_cryptography). Install GnuPG with Homebrew (`brew install gnupg`) or install [GPG Suite](https://gpgtools.org/). Download [gpg.conf](https://github.com/drduh/YubiKey-Guide/blob/main/config/gpg.conf) to use recommended settings: ```bash curl -o ~/.gnupg/gpg.conf \ https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/config/gpg.conf ``` See [drduh/YubiKey-Guide](https://github.com/drduh/YubiKey-Guide) to generate and manage credentials. # Email Email is not designed to provide strong privacy by default: message content may be retained by service providers, copied to recipients' mailboxes, forwarded, or exposed through account compromise. Metadata (including recipient, subject, timestamps, and mail server information) generally remains visible even when message content is encrypted. ## Thunderbird [Thunderbird](https://www.thunderbird.net/) is a free and open-source email client with standard [IMAP](https://en.wikipedia.org/wiki/Internet_Message_Access_Protocol), [POP](https://en.wikipedia.org/wiki/Post_Office_Protocol), [CalDAV](https://en.wikipedia.org/wiki/CalDAV), and [CardDAV](https://en.wikipedia.org/wiki/CardDAV) support. It is a suitable choice for accessing mail and retaining local copies rather than depending exclusively on a provider's remote server. Thunderbird includes support for [OpenPGP](https://support.mozilla.org/kb/openpgp-thunderbird-howto-and-faq) email encryption, which can protect message content and provide cryptographic [signatures](https://www.gnupg.org/gph/en/manual/x135.html). Always verify public-key fingerprints through an independent channel before relying on a key for sensitive communication. The [archived messages feature](https://support.mozilla.org/kb/archived-messages) can move messages out of remote mail servers to a **Local Folder**, improving privacy. # Messengers ## XMPP [XMPP](https://en.wikipedia.org/wiki/XMPP) is an [open protocol](https://xmpp.org/extensions/) developed by the [IETF](https://www.ietf.org/) that supports cross-platform, federated messaging. There are many [client options](https://xmpp.org/getting-started/). Consider using one of the browser-based clients to take advantage of the browser's sandbox. Depending on the provider, you might not need anything other than a username and password to set up an account. XMPP is not end-to-end encrypted (E2EE) by default; use [OMEMO](https://omemo.top/) with a compatible client. ## Signal [Signal](https://signal.org/) is a popular E2EE messenger whose [double-ratchet](https://signal.org/docs/specifications/doubleratchet/) protocol is used by many other applications including WhatsApp, Google Messages, and Facebook Messenger. To use the Signal desktop app, Signal must first be installed on a phone. See EFF's [Signal guide](https://ssd.eff.org/module/how-to-use-signal) for additional guidance. ## iMessage [iMessage](https://en.wikipedia.org/wiki/IMessage) is Apple's first-party messenger. It requires an [Apple Account](#apple-account) to use. Enable [Contact Key Verification](https://support.apple.com/118246) and verify contacts. iMessage can be used with either a [phone number or an email](https://support.apple.com/108758#help). > [!WARNING] > By default, iCloud backup is enabled, which stores copies of message encryption keys on [Apple's servers](https://support.apple.com/102651) without E2EE. Either [disable iCloud backup](https://support.apple.com/guide/icloud/view-and-manage-backups-mm122d3ef202/1.0/icloud/1.0) or enable [Advanced Data Protection](https://support.apple.com/guide/security/advanced-data-protection-for-icloud-sec973254c5f) to prevent this. Remind messaging recipients to do the same. # Viruses and malware See [Methods of malware persistence on Mac OS X](https://www.virusbtn.com/pdf/conference/vb2014/VB2014-Wardle.pdf) and [Malware Persistence on OS X Yosemite](https://www.rsaconference.com/events/us15/agenda/sessions/1591/malware-persistence-on-os-x-yosemite) to learn how common macOS malware persists. For examples of advanced macOS malware capabilities, see the [Hacking Team material](https://www.schneier.com/blog/archives/2015/07/hacking_team_is.html). For further analysis, see [root installation for MacOS](https://github.com/hackedteam/vector-macos-root), [support driver for Mac Agent](https://github.com/hackedteam/driver-macos) and [RCS Agent for Mac](https://github.com/hackedteam/core-macos). Also see [A Brief Analysis of an RCS Implant Installer](https://objective-see.com/blog/blog_0x0D.html) and [reverse.put.as](https://reverse.put.as/2016/02/29/the-italian-morons-are-back-what-are-they-up-to-this-time/). ## Downloading Software Applications from the App Store or [notarized by Apple](https://support.apple.com/guide/security/app-code-signing-process-sec3ad8e6e53/web) may reduce malware risk, but neither process guarantees safety. Apple performs automated checks on notarized apps, and App Store apps [undergo review](https://developer.apple.com/app-store/review/guidelines/). Otherwise, obtain software from sources identified by the developer as official, and verify the website or command-line download uses HTTPS. ## App Sandbox Check if a program uses [App Sandbox](https://developer.apple.com/documentation/security/app_sandbox/protecting_user_data_with_app_sandbox): ```bash codesign -dvvv --entitlements - /path/to/application.app ``` With App Sandbox enabled, output will include: ```console [Key] com.apple.security.app-sandbox [Value] [Bool] true ``` **Activity Monitor** can also indicate whether it is enabled with the "Sandbox" column displayed: ```bash defaults write com.apple.ActivityMonitor "UserColumnsPerTab v6.0" \ -dict-add 0 '(Command, CPUUsage, CPUTime, Threads, IdleWakeUps, Architecture, GPUUsage, GPUTime, PID, UID, Sandbox, restricted)' ``` App Store software is required to use App Sandbox. Applications such as Google Chrome use their own [sandbox](https://chromium.googlesource.com/chromium/src/+/HEAD/docs/design/sandbox.md) and might not use App Sandbox. > [!NOTE] > Sandboxing limits an application's default access, but entitlements and user-granted permissions can expand access. ## Hardened Runtime Check if a program uses the [Hardened Runtime](https://developer.apple.com/documentation/security/hardened_runtime) before running it using the command: ```bash codesign --display --verbose /path/to/application.app ``` If Hardened Runtime is enabled, `flags=0x10000(runtime)` will appear in output. **Activity Monitor** has the option to display a "Restricted" column which indicates a program is restricted from injecting code via macOS's [dynamic linker](https://pewpewthespells.com/blog/blocking_code_injection_on_ios_and_os_x.html). The Hardened Runtime is a prerequisite for notarization of distributed apps. ## Antivirus To scan files and applications, consider uploading them to [VirusTotal](https://www.virustotal.com/gui/home/upload), keeping in mind this makes them publicly-viewable. macOS includes built-in antivirus software called [XProtect](https://support.apple.com/guide/security/protecting-against-malware-sec469d47bd8), which runs in the background and updates signatures used to detect malware automatically. If malware is detected, XProtect attempts to remove and quarantine it. Applications such as [BlockBlock](https://objective-see.com/products/blockblock.html) or [hazcod/maclaunch](https://github.com/hazcod/maclaunch) might help prevent or detect persistent malware. Antivirus software can help detect common malware, but it may also increase attack surface because it often runs with extensive system privileges. Some products may also send telemetry or samples to the vendor. See [Sophail: Applied attacks against Antivirus](https://lock.cmpxchg8b.com/sophailv2.pdf), [Analysis and Exploitation of an ESET Vulnerability](https://googleprojectzero.blogspot.ro/2015/06/analysis-and-exploitation-of-eset.html), [Popular Security Software Came Under Relentless NSA and GCHQ Attacks](https://theintercept.com/2015/06/22/nsa-gchq-targeted-kaspersky/), and [How Israel Caught Russian Hackers Scouring the World for U.S. Secrets](https://www.nytimes.com/2017/10/10/technology/kaspersky-lab-israel-russia-hacking.html). ## Gatekeeper [Gatekeeper](https://support.apple.com/guide/security/gatekeeper-and-runtime-protection-sec5599b66df/web) verifies software notarization and provenance. Gatekeeper warns when opening an application without notarization. It can be bypassed by selecting the application listed in **System Settings** > **Privacy & Security** after a failed attempt. # System Integrity Protection To verify System Integrity Protection is enabled, use the command `csrutil status`, which should return: `System Integrity Protection status: enabled.` Otherwise, [enable SIP](https://developer.apple.com/documentation/security/disabling_and_enabling_system_integrity_protection) using [Recovery Mode](https://support.apple.com/102518). # Metadata and artifacts macOS attaches metadata ([APFS extended attributes](https://en.wikipedia.org/wiki/Extended_file_attributes#macOS)) to files. Metadata attributes can be viewed and removed with the `mdls` and `xattr` commands. Other metadata and artifacts may be found in the directories including, but not limited to, `~/Library/Preferences/`, `~/Library/Containers//Data/Library/Preferences`, `/Library/Preferences`, some of which is detailed below. `~/Library/Preferences/com.apple.sidebarlists.plist` contains historical list of volumes attached. To clear it, use the command `/usr/libexec/PlistBuddy -c "delete :systemitems:VolumesList" ~/Library/Preferences/com.apple.sidebarlists.plist` `/Library/Preferences/com.apple.Bluetooth.plist` contains Bluetooth metadata, including device history. If Bluetooth is not used, the metadata can be cleared with: ```bash sudo defaults delete /Library/Preferences/com.apple.Bluetooth.plist DeviceCache sudo defaults delete /Library/Preferences/com.apple.Bluetooth.plist IDSPairedDevices sudo defaults delete /Library/Preferences/com.apple.Bluetooth.plist PANDevices sudo defaults delete /Library/Preferences/com.apple.Bluetooth.plist PANInterfaces sudo defaults delete /Library/Preferences/com.apple.Bluetooth.plist SCOAudioDevices ``` `/var/spool/cups` contains the CUPS printer job cache. To clear it, use the commands: ```bash sudo rm -rfv /var/spool/cups/c0* sudo rm -rfv /var/spool/cups/tmp/* sudo rm -rfv /var/spool/cups/cache/job.cache* ``` To clear the list of iOS devices connected, use: ```bash sudo defaults delete /Users/$USER/Library/Preferences/com.apple.iPod.plist "conn:128:Last Connect" sudo defaults delete /Users/$USER/Library/Preferences/com.apple.iPod.plist Devices sudo defaults delete /Library/Preferences/com.apple.iPod.plist "conn:128:Last Connect" sudo defaults delete /Library/Preferences/com.apple.iPod.plist Devices sudo rm -rfv /var/db/lockdown/* ``` Quicklook thumbnail data can be cleared using the `qlmanage -r cache` command, but this writes to the file `resetreason` in the Quicklook directories, and states that the Quicklook cache was manually cleared. Disable the thumbnail cache with `qlmanage -r disablecache` It can also be cleared by getting the directory names with `getconf DARWIN_USER_CACHE_DIR` and `sudo getconf DARWIN_USER_CACHE_DIR`, then removing them: ```bash rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/exclusive rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/index.sqlite rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/index.sqlite-shm rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/index.sqlite-wal rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/resetreason rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/thumbnails.data ``` Similarly, for the root user: ```bash sudo rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/thumbnails.fraghandler sudo rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/exclusive sudo rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/index.sqlite sudo rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/index.sqlite-shm sudo rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/index.sqlite-wal sudo rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/resetreason sudo rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/thumbnails.data sudo rm -rfv $(getconf DARWIN_USER_CACHE_DIR)/com.apple.QuickLook.thumbnailcache/thumbnails.fraghandler ``` Also see ['quicklook' cache may leak encrypted data](https://objective-see.com/blog/blog_0x30.html). To clear Finder preferences: ```bash defaults delete ~/Library/Preferences/com.apple.finder.plist FXDesktopVolumePositions defaults delete ~/Library/Preferences/com.apple.finder.plist FXRecentFolders defaults delete ~/Library/Preferences/com.apple.finder.plist RecentMoveAndCopyDestinations defaults delete ~/Library/Preferences/com.apple.finder.plist RecentSearches defaults delete ~/Library/Preferences/com.apple.finder.plist SGTRecentFileSearches ``` Additional diagnostic files may be found in the following directories - but caution should be taken before removing any, as it may break logging or cause other issues: ``` /var/db/CoreDuet/ /var/db/diagnostics/ /var/db/systemstats/ /var/db/uuidtext/ /var/log/DiagnosticMessages/ ``` macOS may collect spelling and language suggestions. To list them and prevent them from being created again, use the commands: ```bash ls ~/Library/LanguageModeling/ ~/Library/Spelling/ ~/Library/Suggestions/ chmod -R 000 ~/Library/LanguageModeling ~/Library/Spelling ~/Library/Suggestions chflags -R uchg ~/Library/LanguageModeling ~/Library/Spelling ~/Library/Suggestions ``` QuickLook application support metadata can be cleared and locked with the commands: ```bash rm -rfv "$HOME/Library/Application Support/Quick Look/*" chmod -R 000 "$HOME/Library/Application Support/Quick Look" chflags -R uchg "$HOME/Library/Application Support/Quick Look" ``` > [!WARNING] > Clearing or locking this directory can break core macOS applications and prevent document-version recovery. Document revision metadata can be cleared and disabled with the commands: ```bash sudo rm -rfv /.DocumentRevisions-V100/* sudo chmod -R 000 /.DocumentRevisions-V100 sudo chflags -R uchg /.DocumentRevisions-V100 ``` Saved application state metadata can be listed and locked with the commands: ```bash ls ~/Library/Saved\ Application\ State/* ls ~/Library/Containers//Data/Library/Saved\ Application\ State chmod -R 000 ~/Library/Saved\ Application\ State/ chmod -R 000 ~/Library/Containers//Data/Library/Saved\ Application\ State chflags -R uchg ~/Library/Saved\ Application\ State/ chflags -R uchg ~/Library/Containers//Data/Library/Saved\ Application\ State ``` Autosave metadata can be listed and locked with the commands: ```bash ls "$HOME/Library/Containers//Data/Library/Autosave Information" ls "$HOME/Library/Autosave Information" chmod -R 000 "~/Library/Containers//Data/Library/Autosave Information" chmod -R 000 "~/Library/Autosave Information" chflags -R uchg "~/Library/Containers//Data/Library/Autosave Information" chflags -R uchg "~/Library/Autosave Information" ``` The Siri analytics database, which is created even if the Siri launch agent is disabled, can be cleared and locked with the commands: ```bash rm -rfv ~/Library/Assistant/SiriAnalytics.db chmod -R 000 ~/Library/Assistant/SiriAnalytics.db chflags -R uchg ~/Library/Assistant/SiriAnalytics.db ``` Media played in QuickTime Player can be found in: ```bash ~/Library/Containers/com.apple.QuickTimePlayerX/Data/Library/Preferences/com.apple.QuickTimePlayerX.plist ``` Additional metadata may exist in the following files: ```bash ~/Library/Containers/com.apple.appstore/Data/Library/Preferences/com.apple.commerce.knownclients.plist ~/Library/Preferences/com.apple.commerce.plist ~/Library/Preferences/com.apple.QuickTimePlayerX.plist ``` # Authentication The [Passwords](https://support.apple.com/guide/passwords/the-passwords-app-mchl901b1b95/mac) app creates [secure credentials](https://support.apple.com/guide/security/automatic-strong-passwords-secc84c811c4/web). It supports [passkeys](https://fidoalliance.org/passkeys/), which are credentials designed to resist phishing when used with compatible services. [KeePassXC](https://keepassxc.org/) is an open-source, cross-platform password manager to consider. It supports strong authentication with compatible hardware tokens and a browser extension for entering credentials automatically. Memorable passwords can be created with [Diceware](https://secure.research.vt.edu/diceware/). Ensure online accounts have [multi-factor authentication](https://en.wikipedia.org/wiki/Multi-factor_authentication) enabled. Prefer phishing-resistant authentication, such as hardware tokens or passkeys with supported services. Authenticator apps are preferable to SMS codes, but any MFA is better than password-only authentication. [YubiKey](https://www.yubico.com/products/) is a popular hardware authentication token. It can also store keys for encryption, signing and authentication tasks - see [drduh/YubiKey-Guide](https://github.com/drduh/YubiKey-Guide). GnuPG can also manage passwords and other encrypted files - see [drduh/Purse](https://github.com/drduh/Purse) and [drduh/pwd.sh](https://github.com/drduh/pwd.sh). # Backup Encrypt files locally before backing them up to external media or online services. Follow the [3-2-1 backup model](https://www.cisa.gov/sites/default/files/publications/data_backup_options.pdf): keep three copies of important data, store them on at least two different types of media, and keep at least one copy in a separate physical location. ## Time Machine [Time Machine](https://support.apple.com/104984) is the built-in tool for handling backups on macOS. Use an external drive or network storage to create [encrypted](https://support.apple.com/guide/mac-help/keep-your-time-machine-backup-disk-secure-mh21241) backups. ## GnuPG GnuPG can be used with a password or public key, with the private key stored on [YubiKey](https://github.com/drduh/YubiKey-Guide). Compress and encrypt a directory using a password: ```bash tar zcvf - ~/Downloads | gpg -c > ~/Downloads/backup-$(date +%F-%H%M).tar.gz.gpg ``` Decrypt and decompress the directory: ```bash gpg -o ~/Downloads/decrypted-backup.tar.gz -d ~/Downloads/backup-*.tar.gz.gpg tar zxvf ~/Downloads/decrypted-backup.tar.gz ``` ## Disk Utility Encrypted volumes can be created using [Disk Utility](https://support.apple.com/guide/disk-utility/toc) or `hdiutil`: ```bash hdiutil create ~/Downloads/encrypted.dmg -encryption -size 50M -volname "secretStuff" hdiutil mount ~/Downloads/encrypted.dmg cp -v ~/Documents/passwords.txt /Volumes/secretStuff hdiutil eject /Volumes/secretStuff ``` ## Other [Tresorit](https://tresorit.com/) and [restic](https://restic.net/) may also be of interest. # Wi-Fi Wi-Fi network names, called SSIDs, and device probe behavior can reveal information about nearby and previously-used networks. [Hidden networks](https://support.apple.com/guide/security/wi-fi-privacy-with-apple-devices-sec31e483abf/web#sec059998a98) do not provide meaningful privacy and can cause devices to actively probe for them. Set a [private Wi-Fi address](https://support.apple.com/guide/mac-help/use-a-private-wi-fi-address-on-mac-mchlb1cb3eb4/mac) to reduce network tracking. Set wireless network security to [WPA3](https://en.wikipedia.org/wiki/WPA3#WPA3). Follow [Apple guidance](https://support.apple.com/102766) to set recommended settings for routers and access points. # SSH For remote SSH connections, use a unique SSH key protected by a passphrase or a hardware token, verify server host keys, and avoid password-based authentication. See [drduh/config/ssh_config](https://github.com/drduh/config/blob/main/ssh_config) for recommended client options. An SSH tunnel can securely route traffic through another computer, similar to a VPN. To use Privoxy running on a remote host on port 8118: ```bash ssh -C -L 5555:127.0.0.1:8118 you@remote-host.tld sudo networksetup -setwebproxy "Wi-Fi" 127.0.0.1 5555 sudo networksetup -setsecurewebproxy "Wi-Fi" 127.0.0.1 5555 ``` Or to use an SSH connection as a [SOCKS proxy](https://www.mikeash.com/ssh_socks.html): ```bash ssh -NCD 3000 you@remote-host.tld ``` By default, macOS does not have [Remote Login](https://support.apple.com/guide/mac-help/allow-a-remote-computer-to-access-your-mac-mchlp1066/mac) (SSH server) enabled. To enable SSH and allow incoming connections, use **System Settings** > **General** > **Sharing** or the command: ```bash sudo launchctl load -w /System/Library/LaunchDaemons/ssh.plist ``` Disable password authentication and consider further [hardening](https://stribika.github.io/2015/01/04/secure-secure-shell.html) the SSH server configuration. See [drduh/config/sshd_config](https://github.com/drduh/config/blob/main/sshd_config) for recommended options. Confirm the SSH server is running: ```bash sudo lsof -Pni TCP:22 ``` # Physical access Do not leave the computer unattended in unsafe locations. A skilled attacker with unsupervised physical access could install a [hardware keylogger](https://trmm.net/Thunderstrike_31c3) to record keystrokes, including passwords. Using a Mac with a built-in keyboard or a bluetooth keyboard makes this more difficult as many off-the-shelf versions of this attack are designed to be plugged in between a USB keyboard and the computer. To reduce the consequences of theft while a Mac is in use, consider using [buskill/buskill-app](https://github.com/buskill/buskill-app) or [Lennolium/swiftGuard](https://github.com/Lennolium/swiftGuard). Consider purchasing a privacy screen/filter for use in public. [Nail polish](https://trmm.net/Glitter) and tamper-evidence seals can be applied to components to detect tampering. # Monitoring ## Logs Monitor system logs with [Console](https://support.apple.com/guide/console/toc) or the `log stream` command. Print all system logs from the last 5 minutes in classic syslog format: ```bash log show --last 5m --style syslog ``` Output as JSON array: ```bash log show --last 5m --style json ``` Output newline-delimited JSON (one JSON object per line); required for [jq](https://jqlang.org/download/): ```bash log show --last 5m --style ndjson ``` Filter messages by subsystem, for example from `com.apple.SoftwareUpdate`: ```bash log show --last 1h --style json \ --predicate 'subsystem == "com.apple.SoftwareUpdate"' ``` Filter messages by content, for example containing `failed`: ```bash log show --last 1h --predicate 'eventMessage CONTAINS "failed"' ``` Case-insensitive message filtering: ```bash log show --last 1h --predicate 'eventMessage CONTAINS[c] "error"' ``` Count distinct error messages with jq: ```bash log show --last 1h --style ndjson \ --predicate 'eventMessage CONTAINS[c] "error"' | jq -r '.eventMessage' | sort | uniq -c | sort -nr | head -100 ``` Export logs to an archive, which can be opened with Console: ```bash log collect --last 1h --output ~/Downloads/logs-$(date +%F-%H%M).logarchive ``` ## DTrace [System Integrity Protection](https://github.com/drduh/macOS-Security-and-Privacy-Guide#system-integrity-protection) interferes with [DTrace](https://en.wikipedia.org/wiki/DTrace) and must be [partially disabled](https://eclecticlight.co/2024/08/21/controlling-system-integrity-protection-using-csrutil-a-reference/) before use. - `iosnoop` monitors disk I/O - `opensnoop` monitors file opens - `execsnoop` monitors processes - `errinfo` monitors failed system calls - `dtruss` monitors all system calls See `man -k dtrace` for more information. ## Processes List running processes with [Activity Monitor](https://support.apple.com/guide/activity-monitor/toc) or the `ps` command. ## Network List open network connections: ```bash sudo lsof -Pni ``` List the contents of various network-related data structures: ```bash sudo netstat -atln ``` [Wireshark](https://www.wireshark.org/) can be used from the command line with [`tshark`](https://www.wireshark.org/docs/man-pages/tshark.html). Replace `en0` with the active interface shown by `networksetup -listallhardwareports`. > [!IMPORTANT] > Capture traffic only on networks and systems you are authorized to monitor. Monitor DNS: ```bash /Applications/Wireshark.app/Contents/MacOS/tshark -i en0 \ -Y "dns.flags.response == 1" -Tfields \ -e frame.time_delta \ -e dns.qry.name \ -e dns.a \ -Eseparator=, ``` Monitor HTTP: ```bash /Applications/Wireshark.app/Contents/MacOS/tshark -i en0 \ -Y "http.request or http.response" -Tfields \ -e ip.dst \ -e http.request.full_uri \ -e http.request.method \ -e http.response.code \ -e http.response.phrase \ -Eseparator=/s ``` Monitor x509/TLS certificates: ```bash /Applications/Wireshark.app/Contents/MacOS/tshark -i en0 \ -Y "ssl.handshake.certificate" -Tfields \ -e ip.src \ -e x509sat.uTF8String \ -e x509sat.printableString \ -e x509sat.universalString \ -e x509sat.IA5String \ -e x509sat.teletexString \ -Eseparator=/s -Equote=d ``` # Miscellaneous ## Diagnostic data Disable [Diagnostics & Usage Data](https://support.apple.com/guide/mac-help/share-analytics-information-mac-apple-mh27990). Disable crash reporter (the dialog which appears after an application crashes and prompts to report the problem to Apple): ```bash defaults write com.apple.CrashReporter DialogType none ``` ## Media player Use [QuickTime Player](https://en.wikipedia.org/wiki/Quicktime_player), the built-in media application, for playing music and video files. It uses [App Sandbox](https://developer.apple.com/documentation/security/app_sandbox/protecting_user_data_with_app_sandbox), [Hardened Runtime](https://developer.apple.com/documentation/xcode/configuring-the-hardened-runtime), and benefits from the [Signed System Volume](https://support.apple.com/guide/security/signed-system-volume-security-secd698747c9/web) as part of the base system. ## File handlers Manage [default file handlers](https://support.apple.com/guide/mac-help/choose-an-app-to-open-a-file-on-mac-mh35597) to reduce risk of opening certain file types. Change the default app for script files so that opening them displays their contents instead of executing them. In Finder, locate and select any .sh file, right-click on it and select Get Info or press Command + I. In the "Open with" section, select TextEdit from the dropdown menu. If it is not listed, select "Other..." and Applications > TextEdit.app. Select "Change All..." and confirm by selecting Continue. ## Screensaver Set the screen to lock as soon as the screensaver starts: ```bash defaults write com.apple.screensaver askForPassword -int 1 defaults write com.apple.screensaver askForPasswordDelay -int 0 ``` ## Finder options Show hidden files and the Library folder in Finder: ```bash defaults write com.apple.finder AppleShowAllFiles -bool true chflags nohidden ~/Library ``` Show all filename extensions: ```bash defaults write NSGlobalDomain AppleShowAllExtensions -bool true ``` Do not default to saving documents to iCloud: ```bash defaults write NSGlobalDomain NSDocumentSaveNewDocumentsToCloud -bool false ``` ## umask Set a [custom umask](https://support.apple.com/101914): ```bash sudo launchctl config user umask 077 ``` Reboot, then create a file/directory and verify permissions (macOS default allows 'group/other' read access): ```console $ ls -ld umask* drwx------@ 2 user1 staff 64 Jul 26 12:00 umask.dir -rw-------@ 1 user1 staff 32 Jul 26 12:00 umask.txt ``` ## Keyboard entry Enable [secure keyboard entry](https://support.apple.com/guide/terminal/use-secure-keyboard-entry-trml109) in Terminal (this may interfere with applications such as [TextExpander](https://smilesoftware.com/textexpander/secure-input)). ## Networking Disable [Bonjour multicast advertisements](https://www.tenable.com/audits/items/CIS_Apple_macOS_10.13_v1.1.0_Level_2.audit:d9dcee7e4d2b8d2ee54f437158992d88) (this also disables AirPlay and AirPrint features): ```bash sudo defaults write /Library/Preferences/com.apple.mDNSResponder \ NoMulticastAdvertisements -bool YES ``` [Disable Handoff](https://support.apple.com/guide/mac-help/change-airdrop-handoff-settings-mchl6a407f99) and [Bluetooth](https://support.apple.com/guide/mac-help/turn-bluetooth-on-or-off-blth1008) features. ## Sudoers macOS comes with this line in `/etc/sudoers`: ```bash Defaults env_keep += "HOME MAIL" ``` This prevents sudo from changing HOME when privileges are elevated. As a result, programs run with sudo may use configuration files from the invoking user's home directory. Consider removing `HOME` from `env_keep` unless this behavior is specifically required. To retain the convenience of the root user having a non-root user's home directory, append an export line to `/var/root/.zshrc`, e.g.: ```bash export HOME=/Users/user1 ``` # Related software Software | Category | Description :-: | :-: | :- [lynis](https://github.com/CISOfy/lynis) | Audit scanner | Cross-platform security-auditing tool that checks system configuration and suggests hardening improvements. [zentral](https://github.com/zentralopensource/zentral) | Monitoring & configuration platform | Fleet-management server for macOS endpoints; collects inventory, events, audits, and osquery results. Best suited to managed environments. [osquery](https://github.com/osquery/osquery) | Monitoring engine | Exposes operating-system state as SQL tables, enabling repeatable checks of processes, users, launch items, network connections, and more. [pareto-mac](https://github.com/paretoSecurity/pareto-mac) | Audit scanner | Menu-bar application that checks a Mac against common baseline security recommendations. # Additional resources - [iCloud security and privacy overview](https://support.apple.com/102651) - [EFF Surveillance Self-Defense Guide](https://ssd.eff.org/) - [beerisgood/macOS_Hardening](https://github.com/beerisgood/macOS_Hardening) - [Reverse Engineering macOS blog](https://reverse.put.as/) - [Reverse Engineering Resources](http://samdmarshall.com/re.html) - [Malwarebytes Blog](https://www.malwarebytes.com/blog) - [Objective-See's Blog](https://objective-see.com/blog.html) - [CIS Benchmarks](https://www.cisecurity.org/benchmark/apple_os/) - [Apple Open Source](https://opensource.apple.com/) - [iOS, The Future Of macOS, Freedom, Security And Privacy In An Increasingly Hostile Global Environment](https://gist.github.com/iosecure/357e724811fe04167332ef54e736670d) ## 2. Official Technical Reference & Guides (drduh/YubiKey-Guide) This guide demonstrates how to store credentials on a [YubiKey](https://www.yubico.com/products/identifying-your-yubikey/). The private keys cannot be copied back out of the device; a separate offline "Certify" key is retained only to replace or renew them. - [Purchase YubiKey](#purchase-yubikey) - [Prepare setup environment](#prepare-setup-environment) - [Download and verify Debian](#download-and-verify-debian) - [Create bootable USB device](#create-bootable-usb-drive) - [Prepare hardware](#prepare-hardware) - [Install software](#install-software) - [Prepare GnuPG](#prepare-gnupg) - [Configuration](#configuration) - [Identity](#identity) - [Key algorithm](#key-algorithm) - [Expiration](#expiration) - [Passphrase](#passphrase) - [Create Certify key](#create-certify-key) - [Create Subkeys](#create-subkeys) - [Verify keys](#verify-keys) - [Backup keys](#backup-keys) - [Export public key](#export-public-key) - [Configure YubiKey](#configure-yubikey) - [Change PIN](#change-pin) - [Set attributes](#set-attributes) - [Transfer Subkeys](#transfer-subkeys) - [Signature key](#signature-key) - [Encryption key](#encryption-key) - [Authentication key](#authentication-key) - [Verify transfer](#verify-transfer) - [Finish setup](#finish-setup) - [Using YubiKey](#using-yubikey) - [Encryption](#encryption) - [Signature](#signature) - [Configure touch](#configure-touch) - [SSH](#ssh) - [Replace agents](#replace-agents) - [Copy public key](#copy-public-key) - [Import SSH keys](#import-ssh-keys) - [SSH agent forwarding](#ssh-agent-forwarding) - [Use ssh-agent](#use-ssh-agent) - [Use S.gpg-agent.ssh](#use-sgpg-agentssh) - [Chained forwarding](#chained-forwarding) - [GitHub](#github) - [GnuPG agent forwarding](#gnupg-agent-forwarding) - [Legacy distributions](#legacy-distributions) - [Chained GnuPG agent forwarding](#chained-gnupg-agent-forwarding) - [Using multiple YubiKeys](#using-multiple-yubikeys) - [Email](#email) - [Thunderbird](#thunderbird) - [Mailvelope](#mailvelope) - [Mutt](#mutt) - [Keyserver](#keyserver) - [Updating keys](#updating-keys) - [Renew Subkeys](#renew-subkeys) - [Rotate Subkeys](#rotate-subkeys) - [Reset YubiKey](#reset-yubikey) - [Optional hardening](#optional-hardening) - [Improving entropy](#improving-entropy) - [Enable KDF](#enable-kdf) - [Network considerations](#network-considerations) - [Notes](#notes) - [Troubleshooting](#troubleshooting) - [Alternative solutions](#alternative-solutions) - [Additional resources](#additional-resources) --- # Purchase YubiKey Choose a [YubiKey model](https://www.yubico.com/store/compare/) that includes the OpenPGP application. YubiKey Security Key and YubiKey Bio models do not include OpenPGP support and cannot be used with this guide. Verify the YubiKey at [yubico.com/genuine](https://www.yubico.com/genuine/). Select Verify Device, touch the key when prompted, and allow the site to identify the device model. This can help detect some [supply chain tampering](https://media.defcon.org/DEF%20CON%2025/DEF%20CON%2025%20presentations/DEF%20CON%2025%20-%20r00killah-and-securelyfitz-Secure-Tokin-and-Doobiekeys.pdf). Have at least two USB drives or microSD cards for storing encrypted offline backups in different physical locations. # Prepare setup environment Use a dedicated, hardened environment to generate the keys and backups. The following environments are ordered from least to most secure for this task: 1. Public, shared or other computer owned by someone else 1. Daily-use personal operating system with unrestricted network access 1. Virtualized system with limited capabilities (using [virt-manager](https://virt-manager.org/), VirtualBox or VMware, for example) 1. Dedicated and hardened [Debian](https://www.debian.org/) or [OpenBSD](https://www.openbsd.org/) installation 1. Ephemeral [Debian Live](https://www.debian.org/CD/live/) or [Tails](https://tails.boum.org/index.en.html) booted without primary storage attached 1. Hardened hardware and firmware (e.g., [Coreboot](https://www.coreboot.org/), [Intel ME removed](https://github.com/corna/me_cleaner)) 1. Air-gapped system without network capabilities, preferably ARM-based Raspberry Pi or other architecturally diverse equivalent Network isolation and dedicated hardware generally provide stronger protection than a daily-use online system. For most people, booting Debian Live from USB on a personal computer is a practical baseline. ## Download and verify Debian Download the latest Debian Live image and signature files. These commands download the checksum file, its signature, and the current 64-bit XFCE Live ISO: ```bash imageUrl="https://cdimage.debian.org/debian-cd/current-live/amd64/iso-hybrid/" curl -sfL -O "$imageUrl/SHA512SUMS" -O "$imageUrl/SHA512SUMS.sign" curl -sfLO "$imageUrl/$(awk '/xfce\.iso$/ {print $NF}' SHA512SUMS)" ``` Download the Debian signing public key: ```bash gpg --keyserver hkps://keyring.debian.org \ --recv DF9B9C49EAA9298432589D76DA87E80D6294BE9B ``` If the public key cannot be received, use a different keyserver or DNS server: ```bash gpg --keyserver hkps://keyserver.ubuntu.com:443 \ --recv DF9B9C49EAA9298432589D76DA87E80D6294BE9B ``` The Debian Live signing public key is also available for import in [pubkeys](https://github.com/drduh/YubiKey-Guide/tree/main/pubkeys): ```bash gpg --import pubkeys/debian-DA87E80D6294BE9B.asc ``` Verify the signature: ```bash gpg --verify SHA512SUMS.sign SHA512SUMS ``` Confirm the fingerprint matches Debian's published fingerprint: ```console gpg: Good signature from "Debian CD signing key " ``` Verify the image hash matches the signed sums file: ```bash grep $(sha512sum debian-live-*-amd64-xfce.iso) SHA512SUMS ``` See [Verifying authenticity of Debian CDs](https://www.debian.org/CD/verify) for more information. ## Create bootable USB device Connect a storage device and identify the device path. This guide uses `/dev/sdc` throughout, but this value may differ on your system. > [!WARNING] > The following `dd` commands erase and overwrite the selected device. Check the device path before continuing! **Linux** ```console $ sudo dmesg | tail usb-storage 3-2:1.0: USB Mass Storage device detected sd 2:0:0:0: [sdc] Attached SCSI removable disk ``` Copy the Debian image to the device: ```bash sudo dd if=debian-live-*-amd64-xfce.iso of=/dev/sdc bs=4M status=progress ; sync ``` **OpenBSD** ```console $ dmesg | tail -n2 sd2 at scsibus4 targ 1 lun 0: SCSI4 0/direct removable serial.0000000000000 sd2: 15193MB, 512 bytes/sector, 31116288 sectors $ doas dd if=debian-live-*-amd64-xfce.iso of=/dev/rsd2c bs=4m 465+1 records in 465+1 records out 1951432704 bytes transferred in 139.125 secs (14026448 bytes/sec) ``` ## Prepare hardware Shut down the computer that will be used to generate keys. Disconnect internal storage and unnecessary peripherals, such as the wireless card. # Install software Boot the computer from the Debian Live USB drive. Configure networking to install the required software; see [Network considerations](#network-considerations) for optional restrictions. > [!TIP] > If the screen locks on Debian Live, unlock with `user` / `live` Open a terminal and install the required software. **Debian/Ubuntu** ```bash sudo apt update sudo apt -y upgrade sudo apt -y install \ wget gnupg2 gnupg-agent dirmngr \ cryptsetup scdaemon pcscd \ yubikey-personalization yubikey-manager ``` **OpenBSD** ```bash doas pkg_add gnupg pcsc-tools ``` **macOS** Download and install [Homebrew](https://brew.sh/) and the following packages: ```bash brew install gnupg yubikey-personalization ykman pinentry-mac wget ``` Or using [MacPorts](https://www.macports.org/install.php), install the following packages: ```bash sudo port install gnupg2 yubikey-manager pinentry wget ``` **NixOS** Use this repository's purpose-built live ISO instead of Debian Live. Copy the resulting ISO to a USB drive, boot from it, and keep the system offline while generating keys. ```bash ref=$(git ls-remote https://github.com/drduh/Yubikey-Guide refs/heads/main | awk '{print $1}') nix build --experimental-features "nix-command flakes" \ github:drduh/YubiKey-Guide/$ref?dir=nix#nixosConfigurations.yubikeyLive.x86_64-linux.config.system.build.isoImage ``` If you have this repository checked out: Recommended, but optional: update `nixpkgs` and `drduh/config`: ```bash nix flake update --commit-lock-file ``` Build the image: ```bash nix build --experimental-features "nix-command flakes" nix#nixosConfigurations.yubikeyLive.x86_64-linux.config.system.build.isoImage ``` Copy to USB drive: ```bash sudo cp -v result/iso/yubikeyLive.iso /dev/sdc ; sync ``` Skip steps to create a temporary working directory and a hardened configuration, as they are already part of the image. Test builds using virtualization tools like QEMU. A virtual machine provides less isolation than a booted live system. To test the image in QEMU with 4 GiB of RAM, two CPUs, and KVM enabled: ```bash qemu-system-x86_64 -enable-kvm -m 4G -smp 2 \ -drive readonly=on,media=cdrom,format=raw,file=result/iso/yubikeyLive.iso ``` **Arch Linux** ```bash sudo pacman -Syu --needed gnupg pcsclite ccid yubikey-personalization ``` **Red Hat Enterprise Linux (RHEL)** ```bash sudo yum install -y gnupg2 pinentry pcsc-lite pcsc-lite-libs gnupg2-smime ``` **Fedora** ```bash sudo dnf install --skip-unavailable \ wget gnupg2 \ cryptsetup gnupg2-scdaemon pcsc-lite \ yubikey-personalization-gui yubikey-manager ``` # Prepare GnuPG Create a temporary directory for [GnuPG configuration](https://www.gnupg.org/documentation/manuals/gnupg/Configuration-Options.html): ```bash export GNUPGHOME=$(mktemp -d "${TMPDIR:-/tmp}/$(date +%Y.%m.%d)-XXXXXXXX") printf "\nTemporary directory:\t%s\n\n" "$GNUPGHOME" ``` > [!NOTE] > This directory is cleared by reboot only when it is stored on a memory-backed filesystem such as [tmpfs](https://en.wikipedia.org/wiki/Tmpfs). > > If it is stored on persistent disk, remove it after completing the guide with `rm -rf "$GNUPGHOME"` and then reboot. ## Configuration Download the recommended [GnuPG configuration](https://github.com/drduh/YubiKey-Guide/blob/main/config/gpg.conf) into the temporary GnuPG directory. ```bash wget https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/config/gpg.conf \ -P $GNUPGHOME ``` Review the configuration before using it. It selects modern cryptographic defaults and privacy-oriented options, such as hiding recipient key IDs: ```console $ grep -v "^#" $GNUPGHOME/gpg.conf personal-cipher-preferences AES256 AES192 AES personal-digest-preferences SHA512 SHA384 SHA256 personal-compress-preferences ZLIB BZIP2 ZIP Uncompressed default-preference-list SHA512 SHA384 SHA256 AES256 AES192 AES ZLIB BZIP2 ZIP Uncompressed cert-digest-algo SHA512 s2k-digest-algo SHA512 s2k-cipher-algo AES256 charset utf-8 no-comments no-emit-version no-greeting keyid-format 0xlong list-options show-uid-validity verify-options show-uid-validity with-fingerprint require-cross-certification require-secmem no-symkey-cache armor use-agent throw-keyids ``` > [!IMPORTANT] > Networking should be disabled for the remainder of the setup. ## Identity Create a user ID - the public label attached to the key. Use a random label if the key does not need to be publicly identified: ```bash export IDENTITY="yk.$(LC_ALL=C tr -dc 'a-z0-9' < /dev/urandom | head -c 16)" printf "\nIdentity:\t\t%s\n\n" "$IDENTITY" ``` If email encryption or Git verification use is anticipated, set the Identity label to a name and email address: ```bash export IDENTITY="YubiKey User " ``` > [!TIP] > Use single quotes to wrap double quote characters (`"`): > > `export IDENTITY='My Identity (a.k.a. "YubiKey User") '` ## Key algorithm Set the key algorithm and size - RSA 4096 is recommended: ```bash export KEY_TYPE=rsa4096 ``` ## Expiration The Certify key is the offline primary key and should not have an expiration date.[^1] The signing, encryption, and authentication Subkeys will be stored on YubiKey. Assign Subkeys an expiration date so a lost or obsolete YubiKey becomes inoperable after that date. A two-year expiration for Subkeys is recommended, balancing security and usability. Longer expiration durations reduce maintenance frequency. > [!NOTE] > After a Subkey expires, GnuPG can still use it to decrypt existing messages, and SSH may still use it for authentication. However, the expired Subkey cannot encrypt new data or create new signatures! Subkeys are renewed or rotated using the Certify key. See [Updating keys](#updating-keys). Set Subkeys to expire on a planned date: ```bash export KEY_EXPIRATION=2028-08-01 ``` The expiration date may also be relative, for example set to two years from today: ```bash export KEY_EXPIRATION=2y ``` ## Passphrase Create a passphrase for the offline Certify key. This passphrase protects the backup copy of the Certify key and is required to manage Subkeys. A passphrase consisting only of uppercase letters and numbers is recommended: the limited character set makes handwritten storage easier to write and read. The following commands will generate and print a strong passphrase[^2]: ```bash export CERTIFY_PASS=$(LC_ALL=C tr -dc "A-Z3-9" < /dev/urandom | tr -d "IOUS5" | head -c ${PASS_LENGTH:-24} | fold -w ${PASS_GROUPSIZE:-4} | paste -sd ${PASS_DELIMITER:--} -) printf "\nCertify passphrase:\t%s\n\n" "$CERTIFY_PASS" ``` To change the passphrase length, delimiter character or group size, export the respective variable(s) prior to running the passphrase generation command, for example: ```bash export PASS_GROUPSIZE=6 export PASS_DELIMITER=+ export PASS_LENGTH=48 ``` Record the Certify key passphrase on durable media and store it separately from the encrypted backup containing the key material, or memorize it. The included [passphrase.html](https://github.com/drduh/YubiKey-Guide/blob/main/templates/passphrase.html) and [passphrase.txt](https://github.com/drduh/YubiKey-Guide/blob/main/templates/passphrase.txt) templates can assist with accurate transcription. Save the [html file](https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/templates/passphrase.html), open in a browser to render and print. Mark the corresponding character on sequential rows for each passphrase character. [passphrase.txt](https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/templates/passphrase.txt) can also be printed for use without a browser: ```bash lp -d Printer-Name passphrase.txt ``` [Diceware](https://secure.research.vt.edu/diceware) is another popular method for creating memorable passphrases. # Create Certify key The Certify key is the primary OpenPGP key: it authorizes the signing, encryption, and authentication Subkeys. Keep it offline and use it only in a secure environment to create, renew, revoke, or replace Subkeys. Generate the Certify key: ```bash printf '%s' "$CERTIFY_PASS" | gpg --batch --passphrase-fd 0 \ --quick-generate-key "$IDENTITY" "$KEY_TYPE" cert never ``` Set and print `KEY_FP` (the full key fingerprint) and `KEY_ID` (the last 16 characters of the fingerprint - a shorter identifier commonly accepted by GnuPG): ```bash export KEY_FP=$(gpg -k --with-colons $IDENTITY | awk -F: '/^fpr:/ { print $10; exit }') export KEY_ID="${KEY_FP: -16}" printf "\nKey ID/Fingerprint:\t%s\n%s\n\n" "$KEY_ID" "$KEY_FP" ``` Additional identities (optional) Skip this section unless the OpenPGP key must have [multiple public identities](https://github.com/drduh/YubiKey-Guide/issues/445). Examples include addresses used for different languages or Git providers. Do not add both personal and professional addresses if linking those identities would reduce privacy - use separate YubiKeys instead. Define a Bash array of additional user IDs. Put each complete user ID in quotes and separate array entries with spaces: ```bash declare -a additional_uids additional_uids=("Super Cool YubiKey 2026" "uid 1 ") ``` Add the additional UIDs to the Identity. ```bash for uid in "${additional_uids[@]}" ; do \ printf '%s' "$CERTIFY_PASS" | gpg --batch --passphrase-fd 0 \ --pinentry-mode loopback --quick-add-uid "$KEY_FP" "$uid" done ``` Set UID trust levels to *ultimate*: ```bash gpg --command-fd 0 --pinentry-mode loopback --edit-key "$KEY_FP" < [!NOTE] > Some SSH servers do not accept RSA authentication keys. To use [Ed25519](https://ed25519.cr.yp.to/) instead, run the following command before creating the Authentication Subkey: > > `export KEY_TYPE=ed25519` ```bash printf '%s' "$CERTIFY_PASS" | gpg --batch --pinentry-mode loopback --passphrase-fd 0 \ --quick-add-key "$KEY_FP" "$KEY_TYPE" auth "$KEY_EXPIRATION" ``` # Verify keys List available secret keys: ```bash gpg -K ``` The output should display **[C]ertify, [S]ignature, [E]ncryption and [A]uthentication** keys: ```console sec rsa4096/0xF0F2CFEB04341FB5 2026-08-01 [C] Key fingerprint = 4E2C 1FA3 372C BA96 A06A C34A F0F2 CFEB 0434 1FB5 uid [ultimate] yk.pn8wgfx67khlhext ssb rsa4096/0xB3CD10E502E19637 2026-08-01 [S] [expires: 2028-08-01] ssb rsa4096/0x30CBE8C4B085B9F7 2026-08-01 [E] [expires: 2028-08-01] ssb rsa4096/0xAD9E24E1B8CB9600 2026-08-01 [A] [expires: 2028-08-01] ``` # Backup keys Export the public key: ```bash gpg --output $GNUPGHOME/public-$KEY_ID-$(date +%F).asc \ --armor --export $KEY_ID ``` Export the Certify key: ```bash printf '%s' "$CERTIFY_PASS" | gpg --batch --pinentry-mode loopback --passphrase-fd 0 \ --output $GNUPGHOME/secret-$KEY_ID-Certify.key \ --armor --export-secret-keys $KEY_ID ``` Export the Subkeys: ```bash printf '%s' "$CERTIFY_PASS" | gpg --batch --pinentry-mode loopback --passphrase-fd 0 \ --output $GNUPGHOME/secret-$KEY_ID-Subkeys.key \ --armor --export-secret-subkeys $KEY_ID ``` > [!IMPORTANT] > The exported `.key` files contain secret keys. Anyone who obtains these files and the Certify key passphrase can create Subkeys and sign or decrypt data encrypted to those keys. Create a backup on encrypted storage to be kept offline in a secure and durable location. Repeat the process several times on multiple portable storage devices, as they may fail over time. As an additional backup measure, [Paperkey](https://www.jabberwocky.com/software/paperkey/) can create a physical copy of key materials for improved durability. > [!TIP] > [ext2](https://en.wikipedia.org/wiki/Ext2) file systems (without encryption) can be mounted on Linux and OpenBSD. > Use [FAT32](https://en.wikipedia.org/wiki/Fat32) or [NTFS](https://en.wikipedia.org/wiki/Ntfs) file systems for macOS and Windows compatibility instead. > [!WARNING] > Confirm the destination (`of`) before issuing `dd` commands as they are destructive! This guide uses `/dev/sdc` - this value may be different on your system. **Linux** Attach a portable storage device and confirm its label - in this example `/dev/sdc`: ```console $ sudo dmesg | tail usb-storage 3-2:1.0: USB Mass Storage device detected sd 2:0:0:0: [sdc] Attached SCSI removable disk $ sudo fdisk -l /dev/sdc Disk /dev/sdc: 14.9 GiB, 15931539456 bytes, 31116288 sectors ``` Clear the first 4 MiB so the operating system does not retain previous partition tables: ```bash sudo dd if=/dev/zero of=/dev/sdc bs=4M count=1 ``` Remove and reconnect the storage device so the operating system reads the cleared partition table before the next command. Create a new GPT partition table: ```bash sudo fdisk /dev/sdc < SCSI4 0/direct removable serial.00000000000000000000 ``` Print the existing partitions to make sure it's the right device: ```bash doas disklabel -h sd2 ``` Create an `a` partition of FS type `RAID` and size of 25 Megabytes: ```console $ doas fdisk -giy sd2 Writing MBR at offset 0. Writing GPT. $ doas disklabel -E sd2 Label editor (enter '?' for help at any prompt) sd2> a a offset: [64] size: [31101776] 25M FS type: [4.2BSD] RAID sd2*> w sd2> q No label changes ``` Encrypt with bioctl using a unique [Passphrase](#passphrase): ```console $ doas bioctl -c C -l sd2a softraid0 New passphrase: Re-type passphrase: softraid0: CRYPTO volume attached as sd3 ``` Create an `i` partition on the new crypto volume and the filesystem: ```console $ doas fdisk -giy sd3 Writing MBR at offset 0. Writing GPT. $ doas disklabel -E sd3 Label editor (enter '?' for help at any prompt) sd3> a i offset: [64] size: [16001] FS type: [4.2BSD] sd3*> w sd3> q No label changes. $ doas newfs sd3i ``` Mount the filesystem and copy the temporary directory with the keyring: ```bash doas mkdir -p /mnt/encrypted-storage doas mount /dev/sd3i /mnt/encrypted-storage doas cp -av $GNUPGHOME /mnt/encrypted-storage ``` Unmount and remove the encrypted volume: ```bash doas umount /mnt/encrypted-storage doas bioctl -d sd3 ``` See [OpenBSD FAQ#14](https://www.openbsd.org/faq/faq14.html#softraidCrypto) for more information. # Export public key > [!IMPORTANT] > YubiKey stores the transferred private Subkeys. Each computer also needs the public key and its metadata to identify and use them with GnuPG. Without the public key, it is **not** be possible to use GnuPG to decrypt and sign. However, YubiKey can still be used for SSH authentication. Connect another portable storage device or create a new partition on the existing one. **Linux** Using the same `/dev/sdc` device as in the previous step, create a small (at least 20 MB is recommended) partition for storing materials: ```bash sudo fdisk /dev/sdc < a b offset: [32130] size: [31069710] 25M FS type: [swap] 4.2BSD sd2*> w sd2> q No label changes. ``` Create a filesystem and export the public key to it: ```bash doas newfs sd2b doas mkdir -p /mnt/public doas mount /dev/sd2b /mnt/public gpg --armor --export $KEY_ID | doas tee /mnt/public/$KEY_ID-$(date +%F).asc ``` Unmount and remove the storage device: ```bash doas umount /mnt/public ``` # Configure YubiKey Connect YubiKey and confirm its status: ```bash gpg --card-status ``` If the YubiKey is locked, follow [Reset YubiKey](#reset-yubikey) to permanently delete any existing keys stored on it. ## Change PIN YubiKey contains several independent [applications](https://developers.yubico.com/). This guide uses the [OpenPGP application](https://developers.yubico.com/PGP/), whose PINs are separate from PINs used by [PIV](https://developers.yubico.com/PIV/), FIDO, and other card features. Name | Default | Capability :-: | :-: | - User PIN | `123456` | routine key operations (decrypt, sign, authenticate) Admin PIN | `12345678` | manage card settings (reset PIN, change Reset Code, add keys and owner information) Reset Code | None | reset PIN ([more information](https://forum.yubico.com/viewtopicd01c.html?p=9055#p9055)) The *User PIN* must be at least 6 characters and the *Admin PIN* must be at least 8 characters. A maximum of 127 ASCII characters are allowed. See [Managing PINs](https://www.gnupg.org/howtos/card-howto/en/ch03s02.html) for more information. YubiKey limits failed PIN attempts, which reduces guessing risk, allowing the User PIN to be short and convenient for regular use. Generate convenient numeric PINs: an 8-digit Admin PIN and a 6-digit User PIN. These meet the minimum lengths but can be increased: ```bash PINS=$(LC_ALL=C tr -dc '0-9' < /dev/urandom | head -c 14) export ADMIN_PIN=${PINS:0:8} export USER_PIN=${PINS:8:6} printf "\nAdmin PIN:\t\t%s\nUser PIN:\t\t%s\n\n" "$ADMIN_PIN" "$USER_PIN" ``` Change the Admin PIN: ```bash gpg --command-fd 0 --pinentry-mode loopback --change-pin < [!CAUTION] > Three incorrect *User PIN* entries will cause it to become blocked and must be unblocked with either the *Admin PIN* or *Reset Code*. Three incorrect *Admin PIN* or *Reset Code* entries will destroy data on YubiKey. Increase PIN limits if the risk of accidental lockout outweighs the increased opportunity for guessing. This command sets five attempts for the User PIN, Reset Code, and Admin PIN: ```bash ykman openpgp access set-retries 5 5 5 -f -a $ADMIN_PIN ``` ## Set attributes > [!IMPORTANT] > OpenPGP card metadata is readable without authentication by anyone with physical access to the YubiKey. This includes the card serial number, key fingerprints, public-key data, and other card attributes. Do not store a name, email address, account name, or other personal identifier in Login data, except for deliberate lost-and-found or asset-management purposes. Set the card Login attribute. The random label generated by the following command is intentionally non-identifying: ```bash export CARD_ATTR_LOGIN="yk.$(LC_ALL=C tr -dc 'a-z0-9' < /dev/urandom | head -c 16)" printf "\nLogin attribute:\t%s\n\n" "$CARD_ATTR_LOGIN" ``` Apply the attribute: ```bash gpg --command-fd 0 --pinentry-mode loopback --edit-card < [!NOTE] > After each transfer, GnuPG deletes its usable local copy of the private key and retains only a record that the Subkey is on this YubiKey. The Subkey cannot be copied back from the YubiKey. Confirm that offline backups exist before continuing. The Certify key passphrase and Admin PIN are required to transfer keys. ## Signature key Transfer the Signature key: ```bash gpg --command-fd 0 --pinentry-mode loopback --edit-key $KEY_FP <` - the `>` indicates the private key is on the smart card: ```console sec rsa4096/0xF0F2CFEB04341FB5 2026-08-01 [C] Key fingerprint = 4E2C 1FA3 372C BA96 A06A C34A F0F2 CFEB 0434 1FB5 uid [ultimate] yk.pn8wgfx67khlhext ssb> rsa4096/0xB3CD10E502E19637 2026-08-01 [S] [expires: 2028-08-01] ssb> rsa4096/0x30CBE8C4B085B9F7 2026-08-01 [E] [expires: 2028-08-01] ssb> rsa4096/0xAD9E24E1B8CB9600 2026-08-01 [A] [expires: 2028-08-01] ``` # Finish setup Confirm that each of the following steps was successfully completed: - [ ] Memorized or recorded the Certify key passphrase and stored it in a secure, durable location separate from the encrypted backup. - Run `echo $CERTIFY_PASS` to display it again. - Use [`passphrase.html`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/templates/passphrase.html) or [`passphrase.txt`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/templates/passphrase.txt) to record it. - [ ] Memorized or recorded the passphrase for the encrypted backup volume and stored it separately from that volume. - Run `echo $LUKS_PASS` to display it again. - Use [`passphrase.html`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/templates/passphrase.html) or [`passphrase.txt`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/templates/passphrase.txt) to record it. - [ ] Saved the Certify key and Subkeys to encrypted portable storage and stored the backups offline. - Keep at least two backups. - Store the backups in separate physical locations. - [ ] Exported a copy of the public key to a location that is easy to access later. - Use a separate device or a non-encrypted partition. - [ ] Memorized or recorded the unique User PIN and Admin PIN after changing them from their default values. - Run `echo $USER_PIN $ADMIN_PIN` to display them again. - Use [`passphrase.html`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/templates/passphrase.html) or [`passphrase.txt`](https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/templates/passphrase.txt) to record them. - [ ] Transferred the Encryption, Signature, and Authentication Subkeys to the YubiKey. - Confirm that `gpg -K` shows `ssb>` for all three Subkeys. - [ ] Cleared the temporary GnuPG working directory by rebooting or by removing it. # Using YubiKey Create or inspect the local GnuPG keyring. This command lists public keys and initializes `~/.gnupg` if needed: ```bash gpg -k ``` Import the [recommended configuration](https://github.com/drduh/YubiKey-Guide/blob/main/config/gpg.conf): ```bash cd ~/.gnupg wget https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/config/gpg.conf ``` Set the following option. This avoids the problem where GnuPG will repeatedly prompt for the insertion of an already-inserted YubiKey: ```bash touch scdaemon.conf echo "disable-ccid" >>scdaemon.conf ``` Install the required packages: **Debian/Ubuntu** ```bash sudo apt update sudo apt install -y gnupg gnupg-agent scdaemon pcscd ``` **Arch** ```bash sudo pacman -S --needed gnupg pcsc-tools sudo systemctl enable --now pcscd.service ``` **macOS** ```bash brew install gnupg ``` Or using MacPorts ```bash sudo port install gnupg2 pcsc-tools ``` **OpenBSD** ```bash doas pkg_add gnupg pcsc-tools doas rcctl enable pcscd doas reboot ``` Mount the non-encrypted volume with the public key: **Debian/Ubuntu** ```bash sudo mkdir -p /mnt/public sudo mount /dev/sdc2 /mnt/public ``` **OpenBSD** ```bash doas mkdir -p /mnt/public doas mount /dev/sd3i /mnt/public ``` Import the public key: ```bash gpg --import /mnt/public/public-*.asc ``` Or download the public key from a keyserver: ```bash gpg --recv $KEY_ID ``` Or with the URL on YubiKey, retrieve the public key: ```bash printf "fetch" | gpg --command-fd 0 --pinentry-mode loopback --card-edit ``` Determine the key ID: ```bash gpg -k export KEY_ID=0xF0F2CFEB04341FB5 ``` Assign ultimate trust by typing `trust` and selecting option `5` then `quit`: ```bash gpg --command-fd 0 --pinentry-mode loopback --edit-key $KEY_ID < rsa4096/0xB3CD10E502E19637 created: 2026-08-01 expires: 2028-08-01 card-no: 0006 05553211 ssb> rsa4096/0x30CBE8C4B085B9F7 created: 2026-08-01 expires: 2028-08-01 card-no: 0006 05553211 ssb> rsa4096/0xAD9E24E1B8CB9600 created: 2026-08-01 expires: 2028-08-01 card-no: 0006 05553211 ``` `sec#` indicates the corresponding key is not available (the Certify key is offline). YubiKey is now ready for use! ## Encryption Encrypt a message to yourself (useful for storing credentials or protecting backups): ```bash printf "test message string\n" | gpg --encrypt --armor \ --recipient $KEY_ID --output encrypted.txt ``` Decrypt the message - a prompt for the User PIN will appear: ```bash gpg --decrypt --armor encrypted.txt ``` To encrypt to multiple recipients/keys, set the preferred key ID last: ```bash printf "test message string\n" | gpg --encrypt --armor \ --recipient $KEY_ID3 \ --recipient $KEY_ID2 \ --recipient $KEY_ID1 \ --output encrypted.txt ``` Use a [shell function](https://github.com/drduh/config/blob/main/zshrc) to make encrypting files easier: ```bash secret() { local file="${1}" local output="${file}.$(date +%s).enc" gpg --encrypt --armor --recipient "${KEY_ID}" \ --output "${output}" -- "${file}" && printf '%s -> %s' "${file}" "${output}" } reveal() { local file="${1}" local output="${file%.[0-9]*.enc}" gpg --decrypt --output "${output}" -- "${file}" && printf '%s -> %s' "${file}" "${output}" } ``` Example output: ```console $ secret document.pdf document.pdf -> document.pdf.1780000000.enc $ reveal document.pdf.1780000000.enc gpg: encrypted with RSA key, ID 0x0000000000000000 gpg: anonymous recipient; trying secret key 0xF0F2CFEB04341FB5 ... gpg: okay, we are the anonymous recipient. document.pdf.1780000000.enc -> document.pdf ``` [drduh/Purse](https://github.com/drduh/Purse) is a secrets manager implemented with GnuPG and YubiKey. ## Signature Sign a message: ```bash printf "test message string\n" | gpg --armor --clearsign > signed.txt ``` Verify the signature: ```bash gpg --verify signed.txt ``` The output will be similar to: ```console gpg: Signature made Sat 01 Aug 2026 12:00:00 PM UTC gpg: using RSA key CF5A305B808B7A0F230DA064B3CD10E502E19637 gpg: Good signature from "yk.pn8wgfx67khlhext" [ultimate] Primary key fingerprint: 4E2C 1FA3 372C BA96 A06A C34A F0F2 CFEB 0434 1FB5 Subkey fingerprint: CF5A 305B 808B 7A0F 230D A064 B3CD 10E5 02E1 9637 ``` ## Configure touch By default, cryptographic operations do not require any action from the user after YubiKey is unlocked with the User PIN. To require a touch for each operation, use [YubiKey Manager](https://developers.yubico.com/yubikey-manager/) and the Admin PIN to set key policy. Encryption: ```bash ykman openpgp keys set-touch dec on ``` > [!NOTE] > YubiKey Manager prior to version 5.1.0 uses `enc` instead of `dec` for encryption: ```bash ykman openpgp keys set-touch enc on ``` > [!NOTE] > Legacy versions of YubiKey Manager use `touch` instead of `set-touch`. Signature: ```bash ykman openpgp keys set-touch sig on ``` Authentication: ```bash ykman openpgp keys set-touch aut on ``` To view the configured touch policy: ```bash ykman openpgp info ``` To adjust the policy, see available options with: ```bash ykman openpgp keys set-touch --help ``` `Cached` or `Cached-Fixed` may be desirable for YubiKey use with email clients. YubiKey blinks when waiting for a touch. On Linux, [maximbaz/yubikey-touch-detector](https://github.com/maximbaz/yubikey-touch-detector) can also be used for indication. ## SSH Create or import a [hardened configuration](https://github.com/drduh/YubiKey-Guide/blob/main/config/gpg-agent.conf): ```bash cd ~/.gnupg wget https://raw.githubusercontent.com/drduh/YubiKey-Guide/main/config/gpg-agent.conf ``` > [!NOTE] > `cache-ttl` options do **not** apply when using YubiKey as a smart card, because the PIN is [cached by the smart card itself](https://dev.gnupg.org/T3362). To clear the PIN from cache (equivalent to `default-cache-ttl` and `max-cache-ttl`), remove YubiKey, or set `forcesig` when editing the card to be prompted for the PIN each time. > [!TIP] > Set `pinentry-program` to `/usr/bin/pinentry-gnome3` for a GUI-based prompt. **macOS** Install pinentry with `brew install pinentry-mac` or `sudo port install pinentry` then edit `gpg-agent.conf` to set the `pinentry-program` path to: - Apple Silicon Macs: `/opt/homebrew/bin/pinentry-mac` - Intel Macs: `/usr/local/bin/pinentry-mac` or `/opt/local/bin/pinentry` (MacPorts) - MacGPG Suite: `/usr/local/MacGPG2/libexec/pinentry-mac.app/Contents/MacOS/pinentry-mac` Then run `gpgconf --kill gpg-agent` for the change to take effect. To use graphical applications on macOS, [additional setup is required](https://jms1.net/yubikey/make-ssh-use-gpg-agent.md). Create `$HOME/Library/LaunchAgents/gnupg.gpg-agent.plist` with the following contents: ```xml Label gnupg.gpg-agent RunAtLoad KeepAlive EnvironmentVariables PATH /opt/homebrew/bin:/usr/local/bin:/usr/bin:/usr/local/MacGPG2/bin:/bin ProgramArguments /usr/bin/env gpg-connect-agent /bye ``` Load it: ```bash launchctl load $HOME/Library/LaunchAgents/gnupg.gpg-agent.plist ``` Create `$HOME/Library/LaunchAgents/gnupg.gpg-agent-symlink.plist` with the following contents: ```xml Label gnupg.gpg-agent-symlink ProgramArguments /bin/sh -c /bin/ln -sf $HOME/.gnupg/S.gpg-agent.ssh $SSH_AUTH_SOCK RunAtLoad ``` Load it: ```bash launchctl load $HOME/Library/LaunchAgents/gnupg.gpg-agent-symlink.plist ``` Reboot to activate changes. **Windows** Windows can already have some virtual smart card readers installed, like the one provided for Windows Hello. To verify YubiKey is the correct one used by scdaemon, add it to its configuration. Find the YubiKey label using PowerShell: ```powershell PS C:\WINDOWS\system32> Get-PnpDevice -Class SoftwareDevice | Where-Object {$_.FriendlyName -like "*YubiKey*"} | Select-Object -ExpandProperty FriendlyName Yubico YubiKey OTP+FIDO+CCID 0 ``` See [How to setup Signed Git Commits with a YubiKey NEO and GPG and Keybase on Windows (2018)](https://www.hanselman.com/blog/HowToSetupSignedGitCommitsWithAYubiKeyNEOAndGPGAndKeybaseOnWindows.aspx) for more information. Edit `%APPDATA%/gnupg/scdaemon.conf` to add: ```console reader-port ``` Edit `%APPDATA%/gnupg/gpg-agent.conf` to add: ```console enable-ssh-support enable-putty-support ``` Restart the agent: ```bash gpg-connect-agent killagent /bye gpg-connect-agent /bye ``` Verify YubiKey details: ```bash gpg --card-status ``` Import the public key and set ultimate trust: ```bash gpg --import ``` Retrieve the public key id: ```bash gpg --list-public-keys ``` Export the SSH public key: ```bash gpg --export-ssh-key ``` Copy the public SSH key to a file - it corresponds to the secret key on YubiKey and can be copied to SSH destination hosts. Create a shortcut that points to `gpg-connect-agent /bye` and place it in the startup folder `shell:startup` to make sure the agent starts after reboot. Modify the shortcut properties so it starts in a "Minimized" window. PuTTY can now be used for public-key SSH authentication. When the server asks for public-key verification, PuTTY will forward the request to GnuPG, which will prompt for a PIN to authorize the operation. **WSL** The goal is to configure SSH client inside WSL work together with the Windows agent, such as gpg-agent.exe. See the [WSL agent architecture](media/schema_gpg.png) illustration for an overview. GnuPG forwarding for cryptographic operations is not supported. See [vuori/weasel-pageant](https://github.com/vuori/weasel-pageant) for more information. One way to forward is just `ssh -A` (still need to eval weasel to setup local ssh-agent), and only relies on OpenSSH. In this track, `ForwardAgent` and `AllowAgentForwarding` in ssh/sshd config may be involved. However, when using ssh socket forwarding, do not enable `ForwardAgent` in ssh config. See [SSH Agent Forwarding](#ssh-agent-forwarding) for more information. This requires Ubuntu 16.04 or newer for WSL and Kleopatra. Download [vuori/weasel-pageant](https://github.com/vuori/weasel-pageant). Add `eval $(/mnt/c//weasel-pageant -r -a /tmp/S.weasel-pageant)` to the shell rc file. Use a named socket here so it can be used in the `RemoteForward` directive of `~/.ssh/config`. Source it with `source ~/.bashrc`. Display the SSH key with `ssh-add -l`. Edit `~/.ssh/config` to add the following for each agent forwarding host: ```console RemoteForward /tmp/S.weasel-pageant ``` The remote SSH socket path can be found with `gpgconf --list-dirs agent-ssh-socket` Add the following to the shell rc file: ```bash export SSH_AUTH_SOCK=$(gpgconf --list-dirs agent-ssh-socket) ``` Add the following to `/etc/ssh/sshd_config`: ```console StreamLocalBindUnlink yes ``` Reload SSH daemon: ```bash sudo service sshd reload ``` Remove YubiKey and reboot. Log back into Windows, open a WSL console and enter `ssh-add -l` - no output should appear. Plug in YubiKey, enter the same command to display the SSH key. Connect to the remote host and use `ssh-add -l` to confirm forwarding works. Agent forwarding may be chained through multiple hosts. Follow the same [protocol](#remote-host-configuration) to configure each host. An alternate method is the [usbipd-win](https://github.com/dorssel/usbipd-win) library. If you encounter issues with accessing the YubiKey in WSL after configuring usbipd-win, you may need to add custom polkit rules to ensure proper permissions for the pcscd service. Here's an example configuration using a scard group (the group logic is optional): Create a new rule file at /etc/polkit-1/rules.d/99-pcscd.rules: ```bash polkit.addRule(function(action, subject) { if (action.id == "org.debian.pcsc-lite.access_card" && subject.isInGroup("scard")) { return polkit.Result.YES; } }); polkit.addRule(function(action, subject) { if (action.id == "org.debian.pcsc-lite.access_pcsc" && subject.isInGroup("scard")) { return polkit.Result.YES; } }); ``` ### Replace agents To launch `gpg-agent` for SSH, use `gpg-connect-agent /bye` or `gpgconf --launch gpg-agent` commands. Add the following to the shell rc file: ```bash export GPG_TTY=$(tty) export SSH_AUTH_SOCK=$(gpgconf --list-dirs agent-ssh-socket) gpgconf --launch gpg-agent gpg-connect-agent updatestartuptty /bye > /dev/null ``` For fish, `config.fish` should look like this (consider putting them into the `is-interactive` block): ```fish set -x GPG_TTY (tty) set -x SSH_AUTH_SOCK (gpgconf --list-dirs agent-ssh-socket) gpgconf --launch gpg-agent ``` When using `ForwardAgent` for ssh-agent forwarding, `SSH_AUTH_SOCK` only needs to be set on the *local* host, where YubiKey is connected. On the *remote* host, `ssh` will set `SSH_AUTH_SOCK` to something like `/tmp/ssh-mXzCzYT2Np/agent.7541` upon connection. Do **not** set `SSH_AUTH_SOCK` on the remote host - doing so will break [SSH Agent Forwarding](#ssh-agent-forwarding). For `S.gpg-agent.ssh` (see [SSH Agent Forwarding](#ssh-agent-forwarding) for more info), `SSH_AUTH_SOCK` should also be set on the *remote*. However, `GPG_TTY` should not be set on the *remote*, explanation specified in that section. ### Copy public key > [!TIP] > It is **not** necessary to import the GnuPG public key in order to use SSH only. Copy and paste the output from `ssh-add` to the server's `authorized_keys` file: ```console $ ssh-add -L ssh-rsa AAAAB4NzaC1yc2EAAAADAQABAAACAz[...]zreOKM+HwpkHzcy9DQcVG2Nw== cardno:000605553211 ``` **Optional** Save the public key for identity file configuration. By default, SSH attempts to use all the identities available via the agent. It's often a good idea to manage exactly which keys SSH will use to connect to a server, for example to separate different roles or [to avoid being fingerprinted by untrusted ssh servers](https://words.filippo.io/ssh-whoami-filippo-io/). To do this you'll need to use the command line argument `-i [identity_file]` or the `IdentityFile` and `IdentitiesOnly` options in `.ssh/config`. The argument provided to `IdentityFile` is traditionally the path to the _private_ key file (for example `IdentityFile ~/.ssh/id_rsa`). For YubiKey, `IdentityFile` must point to the _public_ key file, and `ssh` will select the appropriate private key from those available via ssh-agent. To prevent `ssh` from trying all keys in the agent, use `IdentitiesOnly yes` along with one or more `-i` or `IdentityFile` options for the target host. To reiterate, with `IdentitiesOnly yes`, `ssh` will not enumerate public keys loaded into `ssh-agent` or `gpg-agent`. This means public-key authentication will not proceed unless explicitly named by `ssh -i [identity_file]` or in `.ssh/config` on a per-host basis. In the case of YubiKey usage, to extract the public key from the ssh agent: ```bash ssh-add -L | grep "cardno:000605553211" > ~/.ssh/id_rsa_yubikey.pub ``` Then explicitly associate this YubiKey-stored key for use with a host - `github.com` for example, as follows: ```console $ cat << EOF >> ~/.ssh/config Host github.com IdentitiesOnly yes IdentityFile ~/.ssh/id_rsa_yubikey.pub EOF ``` Connect with public key authentication: ```console $ ssh git@github.com -vvv [...] debug2: key: cardno:000605553211 (0x1234567890), debug1: Authentications that can continue: publickey debug3: start over, passed a different list publickey debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password debug3: authmethod_lookup publickey debug3: remaining preferred: keyboard-interactive,password debug3: authmethod_is_enabled publickey debug1: Next authentication method: publickey debug1: Offering RSA public key: cardno:000605553211 debug3: send_pubkey_test debug2: we sent a publickey packet, wait for reply debug1: Server accepts key: pkalg ssh-rsa blen 535 debug2: input_userauth_pk_ok: fp e5:de:a5:74:b1:3e:96:9b:85:46:e7:28:53:b4:82:c3 debug3: sign_and_send_pubkey: RSA e5:de:a5:74:b1:3e:96:9b:85:46:e7:28:53:b4:82:c3 debug1: Authentication succeeded (publickey). [...] ``` > [!TIP] > To enable multiple SSH connections, use the [ControlMaster](https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing) option. ### Import SSH keys If there are existing SSH keys to make available via `gpg-agent`, they will need to be imported. Then, remove the original private keys. When importing the key, `gpg-agent` uses the key filename as the label - this makes it easier to follow where the key originated from. In this example, we're starting with just the YubiKey in place and importing `~/.ssh/id_rsa`: ```console $ ssh-add -l 4096 SHA256:... cardno:00060123456 (RSA) $ ssh-add ~/.ssh/id_rsa && rm ~/.ssh/id_rsa ``` When invoking `ssh-add`, a prompt for the SSH key passphrase will appear, then the `pinentry` program will prompt and confirm a new passphrase to encrypt the converted key within the GnuPG key store. The migrated key will be listed in `ssh-add -l`: ```console $ ssh-add -l 4096 SHA256:... cardno:00060123456 (RSA) 2048 SHA256:... /Users/username/.ssh/id_rsa (RSA) ``` To show MD5 fingerprints, as used by `gpg-connect-agent`'s `KEYINFO` and `DELETE_KEY` commands: ```console $ ssh-add -E md5 -l 4096 MD5:... cardno:00060123456 (RSA) 2048 MD5:... /Users/username/.ssh/id_rsa (RSA) ``` When using the key `pinentry` will be invoked to request the key passphrase. The passphrase will be cached for up to 10 idle minutes between uses, up to a maximum of 2 hours. ### SSH agent forwarding > [!CAUTION] > SSH Agent Forwarding can [add additional risk](https://matrix.org/blog/2019/05/08/post-mortem-and-remediations-for-apr-11-security-incident/#ssh-agent-forwarding-should-be-disabled) - proceed with caution! There are two methods for ssh-agent forwarding, one is provided by OpenSSH and the other is provided by GnuPG. The latter one may be more insecure as raw socket is just forwarded (not like `S.gpg-agent.extra` with only limited functionality; if `ForwardAgent` implemented by OpenSSH is just forwarding the raw socket, then they are insecure to the same degree). But for the latter one, one convenience is that one may forward once and use this agent everywhere in the remote. So again, proceed with caution! For example, tmux does not have environment variables such as `$SSH_AUTH_SOCK` when connecting to remote hosts and attaching an existing session. For each shell, find the socket and `export SSH_AUTH_SOCK=/tmp/ssh-agent-xxx/xxxx.socket`. However, with `S.gpg-agent.ssh` in a fixed place, it can be used as the ssh-agent in shell rc files. #### Use ssh-agent Run `ssh -A remote` from the local host. On the remote host, `ssh-add -l` should list the public key from the YubiKey as a `cardno:` entry. Enable `ForwardAgent yes` only for explicitly trusted hosts! #### Use S.gpg-agent.ssh Before continuing, configure [GnuPG agent forwarding](gnupg-agent-forwarding) and record the local and remote values of `gpgconf --list-dirs agent-ssh-socket`. Edit `~/.ssh/config` to add the remote host: ```console Host Hostname remote-host.tld StreamLocalBindUnlink yes RemoteForward /run/user/1000/gnupg/S.gpg-agent.ssh /run/user/1000/gnupg/S.gpg-agent.ssh #RemoteForward [remote socket] [local socket] #Note that ForwardAgent is not wanted here! ``` After successfully connecting to the remote host, confirm `/run/user/1000/gnupg/S.gpg-agent.ssh` exists and configure `SSH_AUTH_SOCK`: ```bash export SSH_AUTH_SOCK="/run/user/$UID/gnupg/S.gpg-agent.ssh" ``` `ssh-add -l` should now return the correct public key. In this process no gpg-agent in the remote is involved, hence `gpg-agent.conf` in the remote is of no use. Also pinentry is invoked locally. #### Chained forwarding To use `ssh-agent` provided by OpenSSH to forward into a *third* host, use `ssh -A third` on the *remote* host. If you use `S.gpg-agent.ssh`, assume you have gone through the steps above and have `S.gpg-agent.ssh` on the *remote*, and you would like to forward this agent into a *third* box, first configure `sshd_config` and `SSH_AUTH_SOCK` of *third* in the same way as *remote*, then configure SSH of *remote* by adding the following lines: ```console Host third Hostname third-host.tld StreamLocalBindUnlink yes RemoteForward /run/user/1000/gnupg/S.gpg-agent.ssh /run/user/1000/gnupg/S.gpg-agent.ssh #RemoteForward [remote socket] [local socket] #Note that ForwardAgent is not wanted here! ``` The path must be set according to `gpgconf --list-dirs agent-ssh-socket` on *remote* and *third* hosts. ## GitHub Use YubiKey to sign Git commits and tags and to authenticate to GitHub over SSH. To authenticate, first add the exported SSH public key to [GitHub SSH keys](https://github.com/settings/keys). Configure the signing key: ```bash git config --global user.signingkey $KEY_ID ``` Alternatively, if you are using the aforementioned `IdentityFile` (SSH key) for signing: ```bash git config --global gpg.format ssh git config --global user.signingkey ~/.ssh/id_rsa_yubikey.pub ``` Configure the `user.name` and `user.email` options to match the identity associated with this key: ```bash git config --global user.name 'YubiKey User' git config --global user.email yubikey@example.com ``` To sign commits or tags, use the `-S` option, or consider enabling commit and tag signing by default: ```bash git config --global commit.gpgsign true git config --global tag.gpgSign true ``` **Windows** Configure authentication: ```bash git config --global core.sshcommand "plink -agent" git config --global gpg.program 'C:\Program Files (x86)\GnuPG\bin\gpg.exe' ``` Then update the repository URL to `git@github.com:USERNAME/repository` ## GnuPG agent forwarding YubiKey can sign Git commits and decrypt files on remote hosts by forwarding GnuPG agent operations. To connect through an intermediate host and then access GitHub over SSH, see [SSH agent forwarding](#ssh-agent-forwarding). After forwarding is configured, GnuPG on the remote host communicates through a forwarded socket to gpg-agent on the local host. The local agent accesses the YubiKey and displays any PIN prompt locally. On the remote host, edit `/etc/ssh/sshd_config` to set `StreamLocalBindUnlink yes`. **Optional** Without root access on the remote host to edit `/etc/ssh/sshd_config`, socket located at `gpgconf --list-dir agent-socket` on the remote host will need to be removed before forwarding works. See [AgentForwarding GNUPG wiki page](https://wiki.gnupg.org/AgentForwarding) for more information. Import the public key on the remote host. On the local host, copy the public keyring to the remote host: ```bash scp ~/.gnupg/pubring.kbx remote:~/.gnupg/ ``` On modern distributions, such as Fedora 30, there is no need to set `RemoteForward` in `~/.ssh/config` ### Legacy distributions On the local host, run: ```bash gpgconf --list-dirs agent-extra-socket ``` This should return a path to agent-extra-socket - `/run/user/1000/gnupg/S.gpg-agent.extra` - though on some Linux distros (and macOS) it may be `/home//.gnupg/S.gpg-agent.extra` Find the agent socket on the **remote** host: ```bash gpgconf --list-dirs agent-socket ``` This should return a path such as `/run/user/1000/gnupg/S.gpg-agent` Finally, enable agent forwarding for a given host by adding the following to the local host's `~/.ssh/config` (agent sockets may differ): ``` Host Hostname remote-host.tld StreamLocalBindUnlink yes RemoteForward /run/user/1000/gnupg/S.gpg-agent /run/user/1000/gnupg/S.gpg-agent.extra #RemoteForward [remote socket] [local socket] ``` It may be necessary to edit `gpg-agent.conf` on the *local* host to add the following information: ``` pinentry-program /usr/bin/pinentry-gtk-2 extra-socket /run/user/1000/gnupg/S.gpg-agent.extra ``` > [!IMPORTANT] > The pinentry program starts on the *local* host, not remote. Any pinentry program except `pinentry-tty` or `pinentry-curses` may be used. This is because local `gpg-agent` may start headlessly (by systemd without `$GPG_TTY` set locally telling which tty it is on), thus failed to obtain the pin. Errors on the remote may be misleading saying that there is *IO Error*. (Yes, internally there is actually an *IO Error* since it happens when writing to/reading from tty while finding no tty to use, but for end users this is not friendly.) See [Issue 85](https://github.com/drduh/YubiKey-Guide/issues/85) for more information and troubleshooting. ### Chained GnuPG agent forwarding Assume you have gone through the steps above and have `S.gpg-agent` on the *remote*, and you would like to forward this agent into a *third* box, first you may need to configure `sshd_config` of *third* in the same way as *remote*, then in the ssh config of *remote*, add the following lines: ```console Host third Hostname third-host.tld StreamLocalBindUnlink yes RemoteForward /run/user/1000/gnupg/S.gpg-agent /run/user/1000/gnupg/S.gpg-agent #RemoteForward [remote socket] [local socket] ``` You should change the path according to `gpgconf --list-dirs agent-socket` on *remote* and *third*. On *local* you have `S.gpg-agent.extra` whereas on *remote* and *third*, you only have `S.gpg-agent`. ## Using multiple YubiKeys When a GnuPG key is added to YubiKey using `keytocard`, the credential is deleted from the keyring and a local reference ('stub') pointing to the card is added. The stub identifies the GnuPG key ID and YubiKey serial number. When a Subkey is added to an additional YubiKey, the stub is overwritten and will now point to the latest YubiKey. GnuPG will request a specific YubiKey by serial number, as referenced by the stub, and will not recognize another YubiKey with a different serial number. To scan an additional YubiKey and recreate the correct stub: ```bash gpg-connect-agent "scd serialno" "learn --force" /bye ``` Alternatively, use a script to delete the GnuPG shadowed key, where the serial number is stored (see [GnuPG #T2291](https://dev.gnupg.org/T2291)): ```bash mkdir -p ~/scripts && cat >> ~/scripts/remove-keygrips.sh <&2; exit 1; } KEYGRIPS=$(gpg --with-keygrip --list-secret-keys "$@" | awk '/Keygrip/ { print $3 }') for keygrip in $KEYGRIPS do rm "$HOME/.gnupg/private-keys-v1.d/$keygrip.key" 2> /dev/null done gpg --card-status EOF chmod +x ~/scripts/remove-keygrips.sh ~/scripts/remove-keygrips.sh $KEY_ID ``` See discussion in [#19](https://github.com/drduh/YubiKey-Guide/issues/19) and [#112](https://github.com/drduh/YubiKey-Guide/issues/112) for more information. ## Email YubiKey can decrypt and sign emails and attachments using [Thunderbird](https://www.thunderbird.net/) and [Mutt](http://www.mutt.org/). Thunderbird supports OAuth and can be used with Gmail. See [this EFF guide](https://ssd.eff.org/en/module/how-use-pgp-linux) for more information. ### Thunderbird Follow [Mozilla instructions](https://wiki.mozilla.org/Thunderbird:OpenPGP:Smartcards#Configure_an_email_account_to_use_an_external_GnuPG_key) to setup YubiKey with Thunderbird using the external GPG provider. > [!NOTE] > Thunderbird will [fail to decrypt](https://github.com/drduh/YubiKey-Guide/issues/448) messages if the `armor` option is configured. > If you see the error `gpg: [don't know]: invalid packet (ctb=2d)` or `message cannot be decrypted (there are unknown problems with this encrypted message)`, remove `armor` from `~/.gnupg/gpg.conf`, then restart Thunderbird. ### Mailvelope [Mailvelope](https://www.mailvelope.com/en) allows YubiKey to be used with Gmail and others. > [!NOTE] > Mailvelope [does not work](https://github.com/drduh/YubiKey-Guide/issues/178) with the `throw-keyids` option set in `gpg.conf` On macOS, install gpgme using Homebrew: ```bash brew install gpgme ``` To allow Chrome to run gpgme, edit `~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/gpgmejson.json` to add: ```json { "name": "gpgmejson", "description": "Integration with GnuPG", "path": "/usr/local/bin/gpgme-json", "type": "stdio", "allowed_origins": [ "chrome-extension://kajibbejlbohfaggdiogboambcijhkke/" ] } ``` Edit the default path to allow Chrome to find GnuPG: ```bash sudo launchctl config user path /usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin ``` Finally, install the [Mailvelope extension](https://chromewebstore.google.com/detail/mailvelope/kajibbejlbohfaggdiogboambcijhkke) from the Chrome web store. ### Mutt Mutt can be used from the command line or its text-based interface. To enable OpenPGP support, copy the sample GnuPG configuration file (`/usr/share/doc/mutt/samples/gpg.rc`), set `pgp_default_key`, `pgp_sign_as`, and `pgp_autosign` in that file, then add a source line for it in the Mutt configuration file (`~/.muttrc`). > [!NOTE] > `pinentry-tty` set as the pinentry program in `gpg-agent.conf` may cause problems with Mutt because it uses curses; use `pinentry-curses` or other graphic pinentry program instead. ## Keyserver Optionally, publish the public key to a keyserver so others can find it. Select a server to send it to: ```bash gpg --send-key $KEY_ID gpg --keyserver keys.gnupg.net --send-key $KEY_ID gpg --keyserver hkps://keyserver.ubuntu.com:443 --send-key $KEY_ID ``` Or if [uploading to keys.openpgp.org](https://keys.openpgp.org/about/usage): ```bash gpg --export $KEY_ID | curl -T - https://keys.openpgp.org ``` A retrieval URL can also be stored on YubiKey: ```bash URL="hkps://keyserver.ubuntu.com:443/pks/lookup?op=get&search=${KEY_ID}" ``` Edit YubiKey with `gpg --edit-card` and the Admin PIN: ```console gpg/card> admin gpg/card> url URL to retrieve public key: hkps://keyserver.ubuntu.com:443/pks/lookup?op=get&search=0xFF00000000000000 gpg/card> quit ``` # Updating keys OpenPGP does not provide [forward secrecy](https://en.wikipedia.org/wiki/Forward_secrecy): if an encryption key is compromised, an attacker may be able to decrypt messages encrypted to that key in the past. Renewing or replacing Subkeys limits future use of a lost or obsolete key, but it may not protect previously encrypted data. Choose an expiration and renewal schedule to meet individual risk tolerance and maintenance capacity preferences. When a Subkey expires, it can either be renewed or replaced. Both actions require access to the Certify key. - Renewal preserves existing Subkeys and is generally simpler to operate. - Replacement creates new Subkeys and may be more secure: new Subkeys will **not** be able to decrypt previous data, authenticate with SSH, etc. The public key will need to be updated and any encrypted data must be decrypted and re-encrypted to new Subkeys. This process is functionally equivalent to provisioning a new YubiKey. Neither rotation method is superior and it is up to personal philosophy on identity management and individual threat modeling to decide which one to use, or whether to expire Subkeys at all. Ideally, Subkeys would be ephemeral: used only once for each unique encryption, signature and authentication event, however in practice that is not really practical nor worthwhile with YubiKey. Advanced users may dedicate an air-gapped machine for frequent credential rotation. To renew or rotate Subkeys, follow the same process as generating keys: boot to a secure environment, install required software and disable networking. Connect the portable storage device with the Certify key and identify the device path. Decrypt and mount the encrypted volume: ```bash sudo cryptsetup luksOpen /dev/sdc1 gnupg-secrets sudo mkdir -p /mnt/encrypted-storage sudo mount /dev/mapper/gnupg-secrets /mnt/encrypted-storage ``` Mount the non-encrypted public partition: ```bash sudo mkdir -p /mnt/public sudo mount /dev/sdc2 /mnt/public ``` Copy the original private key materials (after updating the encrypted storage directory name) to a temporary working directory: ```bash export GNUPGHOME=$(mktemp -d "${TMPDIR:-/tmp}/$(date +%Y.%m.%d)-XXXXXXXX") cp -avi /mnt/encrypted-storage/2026.*/* $GNUPGHOME/ ``` Confirm the identity is available, set the key ID and fingerprint values: ```bash gpg -K export KEY_FP=$(gpg -k --with-colons $IDENTITY | awk -F: '/^fpr:/ { print $10; exit }') export KEY_ID="${KEY_FP: -16}" printf "\nKey ID/Fingerprint:\t%s\n%s\n\n" "$KEY_ID" "$KEY_FP" ``` Recall the Certify key passphrase and set it, for example: ```bash export CERTIFY_PASS="ABCD-0123-IJKL-4567-QRST-UVWX" ``` ## Renew Subkeys Set the updated expiration date: ```bash export KEY_EXPIRATION=2028-09-01 ``` Renew the Subkeys: ```bash printf '%s' "$CERTIFY_PASS" | gpg --batch --pinentry-mode loopback \ --passphrase-fd 0 --quick-set-expire "$KEY_FP" "$KEY_EXPIRATION" \ $(gpg -K --with-colons | awk -F: '$1=="fpr" { if (++n > 1) printf "%s ", $10 } END { print "" }') ``` Export the updated public key: ```bash gpg --armor --export $KEY_ID | sudo tee /mnt/public/public-$KEY_ID-$(date +%F).asc ``` Transfer the public key to the destination host and import it: ```bash gpg --import /mnt/public/*.asc ``` Alternatively, publish to a public key server and download it: ```bash gpg --send-key $KEY_ID gpg --recv $KEY_ID ``` The validity of the GnuPG identity will be extended, enabling encryption and signature operations. The SSH public key does **not** need to be updated on remote hosts. ## Rotate Subkeys Follow the original procedure to [Create Subkeys](#create-subkeys). Previous Subkeys can be deleted from the identity. Finish by transferring new Subkeys to YubiKey. Copy the **new** temporary working directory to encrypted storage, which is still mounted: ```bash sudo cp -avi $GNUPGHOME /mnt/encrypted-storage ``` Unmount and close the encrypted volume: ```bash sudo umount /mnt/encrypted-storage sudo cryptsetup luksClose gnupg-secrets ``` Export the updated public key: ```bash sudo mkdir -p /mnt/public sudo mount /dev/sdc2 /mnt/public gpg --armor --export $KEY_ID | sudo tee /mnt/public/$KEY_ID-$(date +%F).asc sudo umount /mnt/public ``` Remove the storage device and follow the original steps to transfer new Subkeys (`4`, `5` and `6`) to YubiKey, replacing existing ones. Reboot or securely erase the temporary working directory. # Reset YubiKey If PIN attempts are exceeded, the YubiKey is locked and must be [Reset](https://developers.yubico.com/ykneo-openpgp/ResetApplet.html) and set up again using the encrypted backup. Use YubiKey Manager to reset the OpenPGP application: ```bash ykman openpgp reset ``` YubiKey can also be reset with [scripts/resetCard.sh](https://github.com/drduh/YubiKey-Guide/blob/main/scripts/resetCard.sh), or by copying the following commands to a file and running `gpg-connect-agent -r `: ```console /hex scd serialno scd apdu 00 20 00 81 08 40 40 40 40 40 40 40 40 scd apdu 00 20 00 81 08 40 40 40 40 40 40 40 40 scd apdu 00 20 00 81 08 40 40 40 40 40 40 40 40 scd apdu 00 20 00 81 08 40 40 40 40 40 40 40 40 scd apdu 00 20 00 83 08 40 40 40 40 40 40 40 40 scd apdu 00 20 00 83 08 40 40 40 40 40 40 40 40 scd apdu 00 20 00 83 08 40 40 40 40 40 40 40 40 scd apdu 00 20 00 83 08 40 40 40 40 40 40 40 40 scd apdu 00 e6 00 00 scd apdu 00 44 00 00 /echo Card has been successfully reset. /bye ``` Remove and reinsert the YubiKey to complete reset. # Optional hardening The following steps may improve the security and privacy of YubiKey. ## Improving entropy Generating cryptographic keys requires high-quality [randomness](https://www.random.org/randomness/), measured as entropy. Most operating systems use software-based pseudorandom number generators or CPU-based hardware random number generators (HRNG). Optionally, a device such as [OneRNG](https://onerng.info/onerng/) may be used to [increase the speed](https://lwn.net/Articles/648550/) and possibly the quality of available entropy. Before creating keys, configure [rng-tools](https://wiki.archlinux.org/title/Rng-tools): ```bash sudo apt -y install at rng-tools python3-gnupg openssl wget https://github.com/OneRNG/onerng.github.io/raw/master/sw/onerng_3.7-1_all.deb ``` Verify the package: ```bash sha256sum onerng_3.7-1_all.deb ``` The value must match: ```console b7cda2fe07dce219a95dfeabeb5ee0f662f64ba1474f6b9dddacc3e8734d8f57 ``` Install the package: ```bash sudo dpkg -i onerng_3.7-1_all.deb echo "HRNGDEVICE=/dev/ttyACM0" | sudo tee /etc/default/rng-tools ``` Insert the device and restart rng-tools: ```bash sudo atd sudo service rng-tools restart ``` ## Enable KDF > [!IMPORTANT] > This feature is not compatible with legacy GnuPG versions, especially mobile clients, and may cause the PIN to always be rejected. This step must be completed before changing PINs or moving keys or an error will occur: `gpg: error for setup KDF: Conditions of use not satisfied` A key derivation function (KDF) derives a value from the PIN before it is sent to the card, reducing its exposure. Enable KDF using the default Admin PIN of `12345678`: ```bash gpg --command-fd 0 --pinentry-mode loopback --card-edit <