• keygate-jwt
  • Usage
  • Signatures
    • Key pairs and tokens creation
      • ES256
      • ES384
  • Advanced usage
    • Custom claims
    • Peeking at metadata before verification
    • Mitigations against replay attacks
  • Why yet another JWT crate
  • Credits

keygate-jwt

A new JWT (JSON Web Tokens) implementation for Rust that focuses on simplicity while avoiding common JWT security pitfalls.

keygate-jwt is opinionated and only supports secure signature algorithms:

Whenever possible, you should use EdDSA, however not all JWT libraries support it yet, so ecdsa is also supported.

keygate-jwt uses only pure Rust implementations and can be compiled out of the box to WebAssembly/WASI.

Important: JWT's purpose is to verify that data has been created by a party knowing a secret key. It does not provide any confidentiality: JWT data is simply encoded as BASE64 and is not encrypted.

Usage

cargo.toml:

[dependencies]
keygate-jwt = "1.0"

Errors are returned as keygate-jwt::Error values

Signatures

A signature requires a key pair: a secret key used to create tokens and a public key that can only verify them.

Always use a signature scheme if both parties do not ultimately trust each other, such as tokens exchanged between clients and API providers.

Key pairs and tokens creation

Key creation:

ES256

use keygate_jwt::prelude::*;

// create a new key pair for the `ES256` JWT algorithm
let key_pair = ES256KeyPair::generate();

// a public key can be extracted from a key pair:
let public_key = key_pair.public_key();

ES384

use keygate_jwt::prelude::*;

// create a new key pair for the `ES384` JWT algorithm
let key_pair = ES384KeyPair::generate();

// a public key can be extracted from a key pair:
let public_key = key_pair.public_key();

Keys can be exported as bytes for later reuse and imported from bytes or, for RSA, from individual parameters, DER-encoded or PEM-encoded data.

RSA key pair creation, using OpenSSL and PEM importation of the secret key:

openssl genrsa -out private.pem 2048
openssl rsa -in private.pem -outform PEM -pubout -out public.pem

let key_pair = RS384KeyPair::from_pem(private_pem_file_content)?;
let public_key = RS384PublicKey::from_pem(public_pem_file_content)?;

Token creation and verification work the same way as with HS* algorithms, except that tokens are created with a key pair and verified using the corresponding public key.

Token creation:

/// create claims valid for 2 hours
let claims = Claims::create(Duration::from_hours(2));
let token = key_pair.sign(claims)?;

Token verification:

let claims = public_key.verify_token::<NoCustomClaims>(&token, None)?;

Available verification options are identical to the ones used with symmetric algorithms.

Advanced usage

Custom claims

Claim objects support all the standard claims by default, and they can be set directly or via convenient helpers:

let claims = Claims::create(Duration::from_hours(2)).
    with_issuer("Example issuer").with_subject("Example subject");

You can also define your own claims. These have to be present in a serializable type (this requires the serde crate):

#[derive(Serialize, Deserialize)]
struct MyAdditionalData {
   user_is_admin: bool,
   user_country: String,
}
let my_additional_data = MyAdditionalData {
   user_is_admin: false,
   user_country: "FR".to_string(),
};

Claim creation with custom data:

let claims = Claims::with_custom_claims(my_additional_data, Duration::from_secs(30));

Claim verification with custom data. Note the presence of the custom data type:

let claims = public_key.verify_token::<MyAdditionalData>(&token, None)?;
let user_is_admin = claims.custom.user_is_admin;

Peeking at metadata before verification

Properties such as the key identifier can be helpful before tag or signature verification to pick the right key out of a set.

let metadata = Token::decode_metadata(&token)?;
let key_id = metadata.key_id();
let algorithm = metadata.algorithm();
// all other standard properties are also accessible

IMPORTANT: You can't trust the key ID, nor the algorithm

As a result, algorithm should be used only for debugging purposes and never to select a key type. Similarly, key_id should be used only to select a key in a set of keys for the same algorithm.

Mitigations against replay attacks

keygate-jwt includes mechanisms to mitigate replay attacks:

• Nonces can be attached to new tokens using the with_nonce() claim function. The verification procedure can later reject any token that doesn't include the expected nonce (required_nonce verification option).
• The verification procedure can reject tokens created too long ago, no matter their expiration date. This prevents tokens from malicious (or compromised) signers from being used too long.
• The verification procedure can reject tokens created before a date. For a given user, the date of the last successful authentication can be stored in a database and used later, along with this option, to reject older (replayed) tokens.

Why yet another JWT crate

There are already several JWT crates for Rust, but none of them satisfied our needs:

• no insecure algorithms (such as RSA or HS256) and hash functions (such as SHA1) are supported
• minimal, rust-only dependencies

Credits

This crate is based on the jwt-simple project by Frank Denis. Notable changes include introducing cargo feature flags and unneeded dependencies and removing support for insecure algorithms. 1