Aegis Documentation

Technical Documentation: beemdevelopment/Aegis

ℹ️ Provenance: Multi-Tier Ingestion · CodeWiki Reference

Overview (`README.md`) Copy Section

Aegis Authenticator

Aegis Authenticator is a free, secure and open source 2FA app for Android.
It aims to provide a secure authenticator for your online services, while also
including some features missing in existing authenticator apps, like proper
encryption and backups. Aegis supports HOTP and TOTP, making it compatible with
thousands of services.

For a list of frequently asked questions, please check out the FAQ.

The security design of the app and the vault format is described in detail in
this document.

Features Copy Chapter

• Free and open source
• Secure
  • The vault is encrypted (AES-256-GCM), and can be unlocked with:
    • Password (scrypt)
    • Biometrics (Android Keystore)
  • Screen capture prevention
  • Tap to reveal
• Compatible with Google Authenticator
• Supports industry standard algorithms:
  HOTP and
  TOTP
• Lots of ways to add new entries
  • Scan a QR code or an image of one
  • Enter details manually
  • Import from other authenticator apps: 2FAS Authenticator, Authenticator
    Plus, Authy, andOTP, FreeOTP, FreeOTP+, Google Authenticator, Microsoft
    Authenticator, Plain text, Steam, TOTP Authenticator and WinAuth (root
    access is required for some of these)
• Organization
  • Alphabetic/custom sorting
  • Custom or automatically generated icons
  • Group entries together
  • Advanced entry editing
  • Search by name/issuer
• Material design with multiple themes: Light, Dark, AMOLED
• Export (plaintext or encrypted)
• Automatic backups of the vault to a location of your choosing

Screenshots Copy Chapter

Downloads Copy Chapter

Aegis is available on the Google Play Store and on F-Droid.

Verification Copy Section

APK releases on Google Play and GitHub are signed using the same key. They can
be verified using
apksigner:

apksigner verify --print-certs --verbose aegis.apk

The output should look like:

Verifies
Verified using v1 scheme (JAR signing): true
Verified using v2 scheme (APK Signature Scheme v2): true

The certificate fingerprints should correspond to the ones listed below:

Owner: CN=Beem Development
Issuer: CN=Beem Development
Serial number: 172380c
Valid from: Sat Feb 09 14:05:49 CET 2019 until: Wed Feb 03 14:05:49 CET 2044
Certificate fingerprints:
   MD5:  AA:EE:86:DB:C7:B8:88:9F:1F:C9:D0:7A:EC:37:36:32
   SHA1: 59:FB:63:B7:1F:CE:95:74:6C:EB:1E:1A:CB:2C:2E:45:E5:FF:13:50
   SHA256: C6:DB:80:A8:E1:4E:52:30:C1:DE:84:15:EF:82:0D:13:DC:90:1D:8F:E3:3C:F3:AC:B5:7B:68:62:D8:58:A8:23

Icon packs Copy Section

Aegis supports icon packs to make it easier to assign icons to the entries in
your vault. There are no official icon packs, but the community maintains a
number of third-party icon packs you may want to check out. To learn how to
create your own Aegis-compatible icon pack, see the
documentation.

• aegis-icons

  Unofficial monochrome-styled 2FA icons.

• delta-aegis-icons

  Delta version of the unofficial monochrome-styled 2FA icon pack aegis-icons.

• aegis-simple-icons *

  This project periodically generates an icon pack for Aegis based on Simple
  Icons.

• aegis-simple-icons-outlined *

  This is a variant on the aegis-simple-icons pack where the icons contain no solid background and just the outlines are being used.

* The icons are automatically generated, so
not all of them are as high quality as the ones you'll find in
aegis-icons.

Contributing Copy Chapter

Looking to contribute to Aegis? That's great! There are a couple of ways to help
out. Translations, bug reports and pull requests are all greatly appreciated.
Please refer to our contributing guidelines to get started.

Swing by our Matrix room to interact with other contributors:
#aegis:matrix.org.

License Copy Chapter

This project is licensed under the GNU General Public License v3.0. See the
LICENSE file for details.

A couple of libraries vendored in Aegis' repository are licensed under a
different license:

• TextDrawable
• TrustedIntents

Iconpacks (`docs/iconpacks.md`) Copy Section

Icon packs

The format Copy Section

Icon packs are .ZIP archives with a collection of icons and a pack.json
file. The icon pack definition is a JSON file, formatted like the example below.
All icon packs have a name, a UUID, a version and a list of icons. The version
number is incremented when a new version of the icon pack is released. The UUID
is randomly generated once and stays the same across different versions.

{
    "uuid": "c553f06f-2a17-46ca-87f5-56af90dd0500",
    "name": "Alex' Icon Pack",
    "version": 1,
    "icons": [
        {
            "name": "Google",
            "filename": "services/Google.png",
            "category": "Services",
            "issuer": [ "google" ]
        },
        {
            "name": "Blizzard",
            "filename": "services/Blizzard.png",
            "category": "Gaming",
            "issuer": [ "blizzard", "battle.net" ]
        }
    ]
}

Every icon definition contains the filename of the icon file, relative to the
root of the .ZIP archive. Icon definitions also have a list of strings that the
Issuer field in Aegis is matched against for automatic selection of an icon for
new entries. Matching is done in a case-insensitive manner. There's also a
category field. Optionally, icons can also have a name.

The following image formats are supported, in order of preference:

Any files in the .ZIP archive that are not the pack.json file or referred to
in the icons list are ignored. Such files are not extracted when importing the
icon pack into Aegis.

Using icon packs in Aegis Copy Section

Users can download an icon pack from the internet and import it into Aegis
through the settings menu. Aegis extracts the icon pack to
icons/{uuid}/{version}, relative to its internal storage directory. So for
the example icon pack above, that'd be:
icons/c553f06f-2a17-46ca-87f5-56af90dd0500/1. If it has an old version of
the icon pack, it will be removed after successful extraction of the newer
version.

After that, Aegis will start proposing icons for new entries if the issuer
matches with one of the icons in the pack. We'll also have an icon selection
dialog, where all of the icons in the pack appear. When the user selects an
icon, it is copied and stored in the vault file.

Vault (`docs/vault.md`) Copy Section

Aegis Vault

Aegis persists the user's token secrets and related information to a file. This
file is referred to as the vault. Users can configure the app to store the
vault in plain text or to encrypt it with a password.

This document describes Aegis' security design and file format. It's split up
into two parts. First, the cryptographic primitives and use of them for
encryption are discussed. The second section documents the details of the file
format of the vault.

Security Copy Chapter

Primitives Copy Section

Two cryptographic primitives were selected for use in Aegis. An Authenticated
Encryption with Associated Data
(AEAD)
cipher and a Key Derivation Function
(KDF).

AEAD

AES-256 in GCM mode is used as the AEAD cipher to ensure the
confidentiality, integrity and authenticity of the vault contents.

This cipher requires a unique 96-bit nonce for each invocation with the same
key. This is not ideal, because 96 bits is not large enough to comfortably
generate an unlimited amount of random numbers without getting collisions at
some point. It is not possible to use a monotonically increasing counter in this
case, because a future use case could involve using the vault on multiple
devices simultaneously, which would almost certainly result in nonce reuse. As a
repeat of the nonce would have catastrophic consequences for the confidentiality
of the ciphertext, NIST strongly recommends not exceeding 2³²
invocations when using random nonces with GCM. As such, the security of the
Aegis vault also relies on the assumption that this limit is never exceeded.
This is a reasonable assumption to make, because it's highly unlikely that an
Aegis user will ever come close to saving the vault 2³² times.

Switching to a nonce misuse-resistant cipher like AES-GCM-SIV or a cipher with
a larger (192 bits) nonce like XChaCha-Poly1305 will be considered in the
future.

KDF

scrypt is used as the KDF to derive
a key from a user-provided password, with the following parameters:

These are the same parameters as Android itself uses to derive a key for
full-disk encryption. Because of the memory limitations Android apps have, it's
not possible to increase these parameters without running into OOM conditions on
most devices.

Argon2 is a more modern KDF that's a bit more flexible than scrypt, because it
allows tweaking the memory-hardness parameter and CPU-hardness parameter
separately, whereas scrypt ties those together into one cost parameter (N). It
will be considered as an alternative option to switch to in the future.

Encryption Copy Section

When a vault is first created, a random 256-bit key is generated that is used to
encrypt the contents with AES in GCM mode. This key is referred to as the
master key.

Aegis supports unlocking a vault with multiple different credentials. The main
credential is a key derived from a user-provided password. In addition to that,
users can also add a key backed by the Android KeyStore as a credential, which
is only usable after biometrics authentication.

Slots

Each credential that should be able to encrypt/decrypt the contents of a vault
has its own slot. Every slot contains a copy of the master key that is
encrypted with its credential. The process of encrypting a key with another key
is known as key wrapping. This allows obtaining the master key by providing
any of the credentials. An important consequence is that the master key is only
as secure as the weakest credential.

This design is similar to and largely inspired by LUKS' key slot system.

Integrity

Because of the use of an AEAD for encryption, the vault contents and encrypted
master keys in the slots are checked for integrity and authenticity. The rest of
the file is not.

Overview Copy Section

Format Copy Chapter

The vault is stored in JSON and encoded in UTF-8. The upper-level structure is
shown below:

{
    "version": 1,
    "header": {},
    "db": {}
}

It starts with a version number. If a forwards incompatible change is
introduced to the vault format, the version number will be incremented. The
current version of the vault format is 1.

The header, if not empty, contains the list of slots and the
encryption parameters used for decrypting the vault.

The vault contents are stored under db. Its value depends on whether the
vault is encrypted or not. If it is, the value is a string containing the Base64
encoded (with padding) ciphertext of the vault contents. Otherwise, the value is
a JSON object. See vault content for details.

Full examples of a plain text
vault
and an encrypted
vault
are available in the test
data folder.
There's also an example Python script that can decrypt an Aegis vault given the
password: decrypt.py.

Header Copy Section

The header starts with the list of slots. Each slot contains the
master key in an encrypted form together with the key wrapping parameters.

It also has a params object that holds the nonce and tag that were
produced during the AES-GCM encryption, encoded as a hexadecimal string. These
encryption parameters together with the master key (which can be retrieved by
decrypting the key from one of the slots) are used to decrypt the vault
contents found in the db field.

Setting slots and params to null indicates that the vault is not
encrypted and Aegis will try to parse it as such.

{
    "slots": [],
    "params": {
        "nonce": "0123456789abcdef01234567",
        "tag": "0123456789abcdef0123456789abcdef"
    }
}

Slots

The different slot types are identified with a numerical ID.

Raw

This slot type is used for raw AES key credentials. It is not used directly in
the app, but all other slots are based on this slot type, so this section
applies to all of them.

Each slot transforms its credential in a way that it can be used to encrypt the
master key with AES-256 in GCM mode. The nonce, tag and encrypted
key are encoded as a hexadecimal string and stored together. Slots also have
a unique randomly generated UUID (version 4).

{
    "type": 0,
    "uuid": "01234567-89ab-cdef-0123-456789abcdef",
    "key": "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef",
    "key_params": {
        "nonce": "0123456789abcdef01234567",
        "tag": "0123456789abcdef0123456789abcdef"
    }
}

Biometric

The structure of the Biometric slot is exactly the same as the Raw slot. The
difference is that the wrapper key is backed by the Android KeyStore, whereas
Raw slots don't imply use of a particular storage type.

Password

As noted earlier, scrypt is used to derive a 256-bit key from a user-provided
password. A random 256-bit salt is generated and passed to scrypt to protect
against rainbow table attacks. It's stored along with the N, r and p
parameters.

{
    "type": 1,
    "uuid": "01234567-89ab-cdef-0123-456789abcdef",
    "key": "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef",
    "key_params": {
        "nonce": "0123456789abcdef01234567",
        "tag": "0123456789abcdef0123456789abcdef"
    },
    "n": 32768,
    "r": 8,
    "p": 1,
    "salt": "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"
}

Vault content Copy Section

The content is a JSON object encoded in UTF-8.

{
    "version": 3,
    "entries": [],
    "groups": []
}

It has a version number, a list of entries and a list of groups. If
a forwards incompatible change is introduced to the content format, the version
number will be incremented. The current version of the vault content format is
3.

Entries

Each entry has a unique randomly generated UUID, as well as a name and
issuer to identify the account name and service that the token is for.

Entries hold the following fields:

The info object contains different fields depending on the type of the OTP.

There are a number of supported types:

Common info fields for all types:

Example of a TOTP entry:

{
    "type": "totp",
    "uuid": "01234567-89ab-cdef-0123-456789abcdef",
    "name": "Bob",
    "issuer": "Google",
    "note": "Main account",
    "favorite": false,
    "icon": null,
    "icon_mime": null,
    "icon_hash": null,
    "info": {
        "secret": "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567",
        "algo": "SHA1",
        "digits": 6,
        "period": 30
    },
    "groups": [
        "01234567-89ab-cdef-0123-456789abcdef"
    ]
}

HOTP and TOTP

TOTP uses the period field, which is the time step in seconds. HOTP uses the
counter field, which is incremented every time a token is generated.

The following algorithms are supported for HOTP and TOTP:

Steam

There is no specification available for Steam's OTP algorithm. It's essentially
the same as TOTP, but it uses a different final encoding step. Aegis'
implementation of it can be found in
crypto/otp/OTP.java.

A couple of fields have fixed values:

MOTP

There is no specification available for MOTP. Aegis' implementation of it can be
found in
crypto/otp/MOTP.java.

A couple of fields have fixed values:

MOTP-specific fields:

Yandex

There is no specification available for Yandex's OTP algorithm. Aegis'
implementation can be found in
crypto/otp/YAOTP.java

A couple of fields have fixed values:

Yandex-specific fields:

Groups

A group consists of a name and a randomly generated uuid (version 4).

Example:

{
    "uuid": "01234567-89ab-cdef-0123-456789abcdef",
    "name": "Personal"
}

--- METRICS ---

• Files Extracted: 3
• Estimated Token Budget: ~6016 tokens
• Canonical Reference: https://codewiki.google/github.com/beemdevelopment/Aegis