jws

python-jws

A Python implementation of JSON Web Signatures draft 02

Also now works on Python 3.3+ as well as Python 2.7+. However, it's a naive conversion to support both Python 2 and Python 3 so there may well be hidden bugs.

Installing

$ pip install jws

Algorithms

The JWS spec reserves several algorithms for cryptographic signing. Out of the 9, this library currently supports 7:

HMAC – native

• HS256 – HMAC using SHA-256 hash algorithm
• HS384 – HMAC using SHA-384 hash algorithm
• HS512 – HMAC using SHA-512 hash algorithm

RSA – requires pycrypto >= 2.5: pip install pycrypto

• RS256 – RSA using SHA-256 hash algorithm

ECDSA – requires ecdsa lib: pip install ecdsa

• ES256 – ECDSA using P-256 curve and SHA-256 hash algorithm
• ES384 – ECDSA using P-384 curve and SHA-384 hash algorithm
• ES512 – ECDSA using P-521 curve and SHA-512 hash algorithm

There is also a mechanism for extending functionality by adding your own algorithms without cracking open the whole codebase. See the advanced usage section for an example.

For RSA and ECDSA, all crypto libraries are lazily loaded so you won't need the dependencies unless you try to use the functionality.

Usage

Let's check out some examples.

>>> import jws
>>> header  = { 'alg': 'HS256' }
>>> payload = { 'claim': 'JSON is the raddest.', 'iss': 'brianb' }
>>> signature = jws.sign(header, payload, 'secret')
>>> jws.verify(header, payload, signature, 'secret')
True
>>> jws.verify(header, payload, signature, 'badbadbad')
Traceback (most recent call last):
...
jws.exceptions.SignatureError: Could not validate signature

Now with a real key!

>>> import ecdsa
>>> sk256 = ecdsa.SigningKey.generate(curve=ecdsa.NIST256p)
>>> vk = sk256.get_verifying_key()
>>> header = { 'alg': 'ES256' }
>>> sig = jws.sign(header, payload, sk256)
>>> jws.verify(header, payload, sig, vk)
True

Advanced Usage

Make this file

# file: sillycrypto.py
import jws
from jws.algos import AlgorithmBase, SignatureError
class FXUY(AlgorithmBase):
    def __init__(self, x, y):
        self.x = int(x)
        self.y = int(y)
    def sign(self, msg, key):
        return 'verysecure' * self.x + key * self.y

    def verify(self, msg, sig, key):
        if sig != self.sign(msg, key):
            raise SignatureError('nope')
        return True

jws.algos.CUSTOM += [
   # a regular expression with two named matching groups. (x and y)
    # named groups will be sent to the class constructor
    (r'^F(?P<x>\d)U(?P<y>\d{2})$',  FXUY),
]

And in an interpreter:

>>> import jws
>>> header = { 'alg': 'F7U12' }
>>> payload = { 'claim': 'wutt' }
>>> sig = jws.sign(header, payload, '<trollface>')
Traceback (most recent call last):
  ....
jws.exceptions.AlgorithmNotImplemented: "F7U12" not implemented.
>>>
>>> import sillycrypto
>>> sig = jws.sign(header, payload, '<trollface>')
>>> jws.verify(header, payload, sig, '<trollface>')
True
>>> jws.verify(header, payload, sig, 'y u no verify?')
Traceback (most recent call last):
....
jws.exceptions.SignatureError: nope

Other Stuff

Check out https://github.com/brianloveswords/python-jws/blob/master/examples/minijwt.py for a 14-line implemention of JWT.

See https://github.com/brianloveswords/python-jws/blob/master/examples/ragecrypto.py for a rage-comic inspired cryptography extension.

TODO

• Write about all the rad stuff that can be done around headers (as extensible as crypto algos)
• Pull in JWK support

Tests

use nosetests

License

MIT