#jwt #json #tokens #key-pair #authentication #jws


Easy to use, secure, non opinionated JWT (JSON Web Tokens) implementation for Rust

3 releases

0.12.9 Jan 13, 2024
0.12.8 Jan 13, 2024
0.12.7 Jan 13, 2024

#614 in Web programming

ISC license


GitHub CI Docs.rs crates.io


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

jwt-simple is unopinionated and supports all commonly deployed authentication and signature algorithms:

JWT algorithm name Description
HS256 HMAC-SHA-256
HS384 HMAC-SHA-384
HS512 HMAC-SHA-512
RS256 RSA with PKCS#1v1.5 padding / SHA-256
RS384 RSA with PKCS#1v1.5 padding / SHA-384
RS512 RSA with PKCS#1v1.5 padding / SHA-512
PS256 RSA with PSS padding / SHA-256
PS384 RSA with PSS padding / SHA-384
PS512 RSA with PSS padding / SHA-512
ES256 ECDSA over p256 / SHA-256
ES384 ECDSA over p384 / SHA-384
ES256K ECDSA over secp256k1 / SHA-256
EdDSA Ed25519

jwt-simple can be compiled out of the box to WebAssembly/WASI. It is fully compatible with Fastly Compute service.

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



jwt-simple = "0.12"


use jwt_simple::prelude::*;

Errors are returned as jwt_simple::Error values (alias for the Error type of the thiserror crate).

Authentication (symmetric, HS* JWT algorithms) example

Authentication schemes use the same key for creating and verifying tokens. In other words, both parties need to ultimately trust each other, or else the verifier could also create arbitrary tokens.

Keys and tokens creation

Key creation:

use jwt_simple::prelude::*;

// create a new key for the `HS256` JWT algorithm
let key = HS256Key::generate();

A key can be exported as bytes with key.to_bytes(), and restored with HS256Key::from_bytes().

Token creation:

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

-> Done!

Token verification

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

-> Done! No additional steps required.

Key expiration, start time, authentication tags, etc. are automatically verified. The function fails with JWTError::InvalidAuthenticationTag if the authentication tag is invalid for the given key.

The full set of claims can be inspected in the claims object if necessary. NoCustomClaims means that only the standard set of claims is used by the application, but application-defined claims can also be supported.

Extra verification steps can optionally be enabled via the ValidationOptions structure:

let mut options = VerificationOptions::default();
// Accept tokens that will only be valid in the future
options.accept_future = true;
// Accept tokens even if they have expired up to 15 minutes after the deadline,
// and/or they will be valid within 15 minutes.
options.time_tolerance = Some(Duration::from_mins(15));
// Reject tokens if they were issued more than 1 hour ago
options.max_validity = Some(Duration::from_hours(1));
// Reject tokens if they don't include an issuer from that set
options.allowed_issuers = Some(HashSet::from_strings(&["example app"]));

// see the documentation for the full list of available options

let claims = key.verify_token::<NoCustomClaims>(&token, Some(options))?;

Note that allowed_issuers and allowed_audiences are not strings, but sets of strings (using the HashSet type from the Rust standard library), as the application can allow multiple return values.

Signatures (asymmetric, RS*, PS*, ES* and EdDSA algorithms) example

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:


use jwt_simple::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();


use jwt_simple::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 data 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");

But application-defined claims can also be defined. These simply 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 useful prior to tag or signature verification in order 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: neither the key ID nor the algorithm can be trusted. This is an unfixable design flaw of the JWT standard.

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 made for the same algorithm.

At the bare minimum, verification using HS* must be prohibited if a signature scheme was originally used to create the token.

Creating and attaching key identifiers

Key identifiers indicate to verifiers what public key (or shared key) should be used for verification. They can be attached at any time to existing shared keys, key pairs and public keys:

let public_key_with_id = public_key.with_key_id(&"unique key identifier");

Instead of delegating this to applications, jwt-simple can also create such an identifier for an existing key:

let key_id = public_key.create_key_id();

This creates an text-encoded identifier for the key, attaches it, and returns it.

If an identifier has been attached to a shared key or a key pair, tokens created with them will include it.

Mitigations against replay attacks

jwt-simple includes mechanisms to mitigate replay attacks:

  • Nonces can be created and attached to new tokens using the create_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 what their expiration date is. This prevents tokens from malicious (or compromised) signers from being used for 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.

CWT (CBOR) support

The development code includes a cwt cargo feature that enables experimental parsing and validation of CWT tokens.

Please note that CWT doesn't support custom claims. The required identifiers haven't been standardized yet.

Also, the existing Rust crates for JSON and CBOR deserialization are not safe. An untrusted party can send a serialized object that requires a lot of memory and CPU to deserialize. Band-aids have been added for JSON, but with the current Rust tooling, it would be tricky to do for CBOR.

As a mitigation, we highly recommend rejecting tokens that would be too large in the context of your application. That can be done by with the max_token_length verification option.

Working around compilation issues with the boring crate

As a temporary workaround for portability issues with one of the dependencies (the boring crate), this library can be compiled to use only Rust implementations.

In order to do so, import the crate with default-features=false, features=["pure-rust"] in your Cargo configuration.

Do not do it unconditionally. This is only required for very specific setups and targets, and only until issues with the boring crate have been solved. The way to configure this in Cargo may also change in future versions.

Static builds targeting the musl library don't require that workaround. Just use cargo-zigbuild to build your project.

Usage in Web browsers

The wasm32-freestanding target (still sometimes called wasm32-unknown-unknown in Rust) is supported (as in "it compiles").

However, using a native JavaScript implementation is highly recommended instead. There are high-quality JWT implementations in JavaScript, leveraging the WebCrypto API, that provide better performance and security guarantees than a WebAssembly module.

Why yet another JWT crate

This crate is not an endorsement of JWT. JWT is an awful design, and one of the many examples that "but this is a standard" doesn't necessarily mean that it is good.

I would highly recommend PASETO or Biscuit instead if you control both token creation and verification.

However, JWT is still widely used in the industry, and remains absolutely mandatory to communicate with popular APIs.

This crate was designed to:

  • Be simple to use, even to people who are new to Rust
  • Avoid common JWT API pitfalls
  • Support features widely in use. I'd love to limit the algorithm choices to Ed25519, but other methods are required to connect to existing APIs, so just provide them (with the exception of the None signature method for obvious reasons).
  • Minimize code complexity and external dependencies
  • Automatically perform common tasks to prevent misuse. Signature verification and claims validation happen automatically instead of relying on applications.
  • Still allow power users to access everything JWT tokens include if they really need to
  • Work out of the box in a WebAssembly environment, so that it can be used in function-as-a-service platforms.


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