# Digital Signature Algorithms

The JWT specification supports several algorithms for cryptographic signing. This library currently supports:

- HS256 - HMAC using SHA-256 hash algorithm (default)

- HS384 - HMAC using SHA-384 hash algorithm

- HS512 - HMAC using SHA-512 hash algorithm

- ES256 - ECDSA signature algorithm using SHA-256 hash algorithm

- ES256K - ECDSA signature algorithm with secp256k1 curve using SHA-256 hash algorithm

- ES384 - ECDSA signature algorithm using SHA-384 hash algorithm

- ES512 - ECDSA signature algorithm using SHA-512 hash algorithm

- RS256 - RSASSA-PKCS1-v1_5 signature algorithm using SHA-256 hash algorithm

- RS384 - RSASSA-PKCS1-v1_5 signature algorithm using SHA-384 hash algorithm

- RS512 - RSASSA-PKCS1-v1_5 signature algorithm using SHA-512 hash algorithm

- PS256 - RSASSA-PSS signature using SHA-256 and MGF1 padding with SHA-256

- PS384 - RSASSA-PSS signature using SHA-384 and MGF1 padding with SHA-384

- PS512 - RSASSA-PSS signature using SHA-512 and MGF1 padding with SHA-512

- EdDSA - Both Ed25519 signature using SHA-512 and Ed448 signature using SHA-3 are supported. Ed25519 and Ed448 provide 128-bit and 224-bit security respectively.

## Asymmetric (Public-key) Algorithms

Usage of RSA (RS*) and EC (EC*) algorithms require a basic understanding of how public-key cryptography is used with regards to digital signatures. If you are unfamiliar, you may want to read this article.

When using the RSASSA-PKCS1-v1_5 algorithms, the key argument in both `jwt.encode()` and `jwt.decode()` (`"secret"` in the examples) is expected to be either an RSA public or private key in PEM or SSH format. The type of key (private or public) depends on whether you are signing or verifying a token.

When using the ECDSA algorithms, the `key` argument is expected to be an Elliptic Curve public or private key in PEM format. The type of key (private or public) depends on whether you are signing or verifying.

## Specifying an Algorithm

You can specify which algorithm you would like to use to sign the JWT by using the algorithm parameter:

    >>> encoded = jwt.encode({"some": "payload"}, "secret", algorithm="HS512")
    >>> print(encoded)
    eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXVCJ9.eyJzb21lIjoicGF5bG9hZCJ9.WTzLzFO079PduJiFIyzrOah54YaM8qoxH9fLMQoQhKtw3_fMGjImIOokijDkXVbyfBqhMo2GCNu4w9v7UXvnpA

When decoding, you can also specify which algorithms you would like to permit when validating the JWT by using the algorithms parameter which takes a list of allowed algorithms:

    >>> jwt.decode(encoded, "secret", algorithms=["HS512", "HS256"])
    {'some': 'payload'}

In the above case, if the JWT has any value for its alg header other than HS512 or HS256, the claim will be rejected with an `InvalidAlgorithmError`.

Warning

Do not compute the `algorithms` parameter based on the `alg` from the token itself, or on any other data that an attacker may be able to influence, as that might expose you to various vulnerabilities (see RFC 8725 §2.1). Instead, either hard-code a fixed value for `algorithms`, or configure it in the same place you configure the `key`. Make sure not to mix symmetric and asymmetric algorithms that interpret the `key` in different ways (e.g. HS* and RS*).