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python implementation of JSON Web Signatures
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A Python implementation of JSON Web Signatures draft 02


$ git://
$ python install


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

  • HS256 – HMAC using SHA-256 hash algorithm
  • HS384 – HMAC using SHA-384 hash algorithm
  • HS512 – HMAC using SHA-512 hash algorithm
  • RS256 – RSA using SHA-256 hash algorithm *caveat, read below
  • 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.

NOTE: you must use the version of pycrypto in vendor/pycrypto to get RSA256 support. However if you don't ever plan on using RSA, you don't have to worry about it – all crypto libraries are lazily loaded so you won't even notice it's not there.

If you want to know why RSA support is limited, read this:


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')
>>> 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)

Advanced Usage

Make this file

# file:
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>')
>>> jws.verify(header, payload, sig, 'y u no verify?')
Traceback (most recent call last):
jws.exceptions.SignatureError: nope

Other Stuff

Check out for a 14-line implemention of JWT.

See for a rage-comic inspired cryptography extension.


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


use nosetests



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