PyJWT

A Python implementation of JSON Web Token draft 01.

Installing

sudo easy_install PyJWT

Note: The RSASSA-PKCS1-v1_5 algorithms depend on PyCrypto. If you plan on using any of those algorithms you'll need to install it as well.

sudo easy_install PyCrypto

Usage

import jwt
jwt.encode({"some": "payload"}, "secret")

Note the resulting JWT will not be encrypted, but verifiable with a secret key.

jwt.decode("someJWTstring", "secret")

If the secret is wrong, it will raise a jwt.DecodeError telling you as such. You can still get the payload by setting the verify argument to False.

jwt.decode("someJWTstring", verify=False)

Algorithms

The JWT spec 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
• 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

Change the algorithm with by setting it in encode:

jwt.encode({"some": "payload"}, "secret", "HS512")

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 an RSA private key as imported with Crypto.PublicKey.RSA.importKey().

Tests

You can run tests from the project root after cloning with:

python tests/test_jwt.py

Support of reserved claim names

JSON Web Token defines some reserved claim names and defines how they should be used. PyJWT supports these reserved claim names:

• "exp" (Expiration Time) Claim

Expiration Time Claim

From draft 01 of the JWT spec:

The exp (expiration time) claim identifies the expiration time on or after which the JWT MUST NOT be accepted for processing. The processing of the exp claim requires that the current date/time MUST be before the expiration date/time listed in the exp claim. Implementers MAY provide for some small leeway, usually no more than a few minutes, to account for clock skew. Its value MUST be a number containing an IntDate value. Use of this claim is OPTIONAL.

You can pass the expiration time as a UTC UNIX timestamp (an int) or as a datetime, which will be converted into an int. For example:

jwt.encode({"exp": 1371720939}, "secret")

jwt.encode({"exp": datetime.utcnow()}, "secret")

Expiration time is automatically verified in jwt.decode() and raises jwt.ExpiredSignature if the expiration time is in the past:

import jwt
try:
    jwt.decode('JWT_STRING', "secret")
except jwt.ExpiredSignature:
    # Signature has expired

Expiration time will be compared to the current UTC time (as given by timegm(datetime.utcnow().utctimetuple())), so be sure to use a UTC timestamp or datetime in encoding.

You can turn off expiration time verification with the verify_expiration argument.

PyJWT also supports the leeway part of the expiration time definition, which means you can validate a expiration time which is in the past but not very far. For example, if you have a JWT payload with a expiration time set to 30 seconds after creation but you know that sometimes you will process it after 30 seconds, you can set a leeway of 10 seconds in order to have some margin:

import jwt, time
jwt_payload = jwt.encode({'exp': datetime.utcnow() + datetime.timedelta(seconds=30)}, 'secret')
time.sleep(32)
# Jwt payload is now expired
# But with some leeway, it will still validate
jwt.decode(jwt_payload, 'secret', leeway=10)

License

MIT