py_hmac_validator: Formencode Hmac Validator.

hmac_validator.py

class HmacValidator(formencode.validators.FancyValidator):
    """

    """

    hashalg = hashlib.sha512

    messages = {
        'malformed': 'Malformed challenge hash.'
    }

    def __init__(self, key, *args, **kwa):
        for k in ('hashalg', ):
            if k in kwa:
                setattr(self, k, kwa.pop(k))
        self.key = key
        self.digest_size = self.hashalg().digest_size
        formencode.validators.FancyValidator.__init__(self, *args, **kwa)

    def _convert_to_python(self, value, state):
        value = base64.urlsafe_b64decode(value)
        return value[:self.digest_size], value[self.digest_size:]

    def _convert_from_python(self, value, state):
        alg = hmac.new(self.key, msg=value, digestmod=self.hashalg)
        return base64.urlsafe_b64encode(alg.digest() + value)

    def _validate_python(self, value, state):
        challenge_digest, value = value
        alg = hmac.new(self.key, msg=value, digestmod=self.hashalg)
        digest = alg.digest()

        if len(challenge_digest) < self.digest_size:
            raise formencode.Invalid(self.message('malformed', state), value,
                                     state)

        if not hmac.compare_digest(digest, challenge_digest) is True:
            raise formencode.Invalid(self.message('malformed', state), value,
                                     state)