feat: Use cryptography based JWT parser for increased speed

Switches to using python cryptography library instead of jose/jwt
(which relied on python ecdsa library). Also discovered lots of fun
discrepencies between how ecdsa and libssl sign things.

closes #785

autopush/jwt.py

@@ -0,0 +1,107 @@
+import base64
+import binascii
+import json
+
+from cryptography.exceptions import InvalidSignature
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives.asymmetric import ec, utils
+from cryptography.hazmat.primitives import hashes
+from pyasn1.error import PyAsn1Error
+from twisted.logger import Logger
+
+
+def repad(string):
+    # type: (str) -> str
+    """Adds padding to strings for base64 decoding"""
+    if len(string) % 4:
+        string += '===='[len(string) % 4:]
+    return string
+
+
+class VerifyJWT(object):
+    """Minimally verify a Vapid JWT object.
+
+        Why hand roll? Most python JWT libraries either use a python elliptic
+        curve library directly, or call one that does, or is abandoned, or a
+        dozen other reasons.
+
+        After spending half a day looking for reasonable replacements, I
+        decided to just write the functions we need directly.
+
+        THIS IS NOT A FULL JWT REPLACEMENT.
+
+    """
+
+    @staticmethod
+    def extract_signature(auth):
+        # type: (str) -> tuple()
+        """Fix the JWT auth token.
+
+        The JWA spec defines the signature to be a pair of 32octet encoded
+        longs.
+        The `ecdsa` library signs using a raw, 32octet pair of values (s, r).
+        Cryptography, which uses OpenSSL, uses a DER sequence of (s, r).
+        This function converts the raw ecdsa to DER.
+
+        :param auth: A JWT authorization token.
+        :type auth: str
+
+        :return tuple containing the signature material and signature
+
+        """
+        payload, asig = auth.encode('utf8').rsplit(".", 1)
+        sig = base64.urlsafe_b64decode(repad(asig))
+        if len(sig) != 64:
+            return payload, sig
+
+        encoded = utils.encode_dss_signature(
+            s=int(binascii.hexlify(sig[32:]), 16),
+            r=int(binascii.hexlify(sig[:32]), 16)
+        )
+        return payload, encoded
+
+    @staticmethod
+    def decode(token, key):
+        # type (str, str) -> dict()
+        """Decode a web token into a assertion dictionary.
+
+        This attempts to rectify both ecdsa and openssl generated
+        signatures. We use the built-in cryptography library since it wraps
+        libssl and is faster than the python only approach.
+
+        :param token: VAPID auth token
+        :type token: str
+        :param key: bitarray containing public key
+        :type key: str or bitarray
+
+        :return dict of the VAPID claims
+
+        :raise InvalidSignature
+
+        """
+        # convert the signature if needed.
+        try:
+            sig_material, signature = VerifyJWT.extract_signature(token)
+            pkey = ec.EllipticCurvePublicNumbers.from_encoded_point(
+                ec.SECP256R1(),
+                key
+            ).public_key(default_backend())
+            # NOTE: verify() will take any string as the signature. It appears
+            # to be doing lazy verification and matching strings rather than
+            # comparing content values. If the signatures start failing for
+            # some unknown reason in the future, decode the signature and
+            # make sure it matches how we're reconstructing it.
+            # This will raise an InvalidSignature exception if failure.
+            # It will be captured externally.
+            pkey.verify(
+                signature,
+                sig_material.encode('utf8'),
+                ec.ECDSA(hashes.SHA256()))
+            return json.loads(
+                base64.urlsafe_b64decode(
+                    repad(sig_material.split('.')[1]).encode('utf8')))
+        except (ValueError, TypeError, binascii.Error, PyAsn1Error):
+            raise InvalidSignature()
+        except Exception:  # pragma: no cover
+            Logger().failure("Unexpected error processing JWT")
+            raise InvalidSignature()

autopush/tests/test_endpoint.py

@@ -1,11 +1,10 @@
 import json
 import uuid
 
-import jose
 import twisted.internet.base
 from cryptography.fernet import Fernet, InvalidToken
 from cyclone.web import Application
-from mock import Mock, patch
+from mock import Mock
 from moto import mock_dynamodb2
 from nose.tools import eq_, ok_
 from twisted.internet.defer import Deferred
@@ -538,28 +537,6 @@ def restore(*args, **kwargs):
                                      chid=str(dummy_chid)))
         return self.finish_deferred
 
-    @patch('jose.jws.verify', side_effect=jose.exceptions.JWTError)
-    def test_post_bad_jwt(self, *args):
-        self.reg.request.body = json.dumps(dict(
-            channelID=str(dummy_chid),
-        ))
-
-        def handle_finish(value):
-            self._check_error(401, 109, 'Unauthorized')
-
-        def restore(*args, **kwargs):
-            uuid.uuid4 = old_func
-
-        old_func = uuid.uuid4
-        uuid.uuid4 = lambda: dummy_uaid
-        self.finish_deferred.addBoth(restore)
-        self.finish_deferred.addCallback(handle_finish)
-        self.reg.request.headers["Authorization"] = "WebPush Dummy"
-        self.reg.post(self._make_req(router_type="webpush",
-                                     uaid=dummy_uaid.hex,
-                                     chid=str(dummy_chid)))
-        return self.finish_deferred
-
     def test_post_uaid_chid(self, *args):
         self.reg.request.body = json.dumps(dict(
             type="simplepush",

autopush/tests/test_web_validation.py

@@ -8,8 +8,8 @@
     ItemNotFound,
 )
 from cryptography.fernet import InvalidToken
+from cryptography.exceptions import InvalidSignature
 from jose import jws
-from jose.exceptions import JWTClaimsError
 from marshmallow import Schema, fields
 from mock import Mock, patch
 from moto import mock_dynamodb2
@@ -1005,7 +1005,7 @@ def test_invalid_encryption_header(self, mock_jwt):
     def test_invalid_encryption_jwt(self, mock_jwt):
         schema = self._make_fut()
         # use a deeply superclassed error to make sure that it gets picked up.
-        mock_jwt.side_effect = JWTClaimsError("invalid claim")
+        mock_jwt.side_effect = InvalidSignature("invalid signature")
 
         header = {"typ": "JWT", "alg": "ES256"}
         payload = {"aud": "https://push.example.com",

autopush/utils.py

@@ -7,7 +7,6 @@
 import time
 import uuid
 
-import ecdsa
 import requests
 from attr import (
     Factory,
@@ -16,7 +15,6 @@
 )
 from boto.dynamodb2.items import Item  # noqa
 from cryptography.fernet import Fernet  # noqa
-from jose import jwt
 from typing import (  # noqa
     Any,
     Dict,
@@ -27,6 +25,7 @@
 from ua_parser import user_agent_parser
 
 from autopush.exceptions import InvalidTokenException
+from autopush.jwt import repad, VerifyJWT as jwt
 
 
 # Remove trailing padding characters from complex header items like
@@ -122,14 +121,6 @@ def base64url_encode(string):
     return base64.urlsafe_b64encode(string).strip('=')
 
 
-def repad(string):
-    # type: (str) -> str
-    """Adds padding to strings for base64 decoding"""
-    if len(string) % 4:
-        string += '===='[len(string) % 4:]
-    return string
-
-
 def base64url_decode(string):
     # type: (str) -> str
     """Decodes a Base64 URL-encoded string per RFC 7515.
@@ -171,11 +162,11 @@ def decipher_public_key(key_data):
     # key data is actually a raw coordinate pair
     key_data = base64url_decode(key_data)
     key_len = len(key_data)
-    if key_len == 64:
+    if key_len == 65 and key_data[0] == '\x04':
         return key_data
     # Key format is "raw"
-    if key_len == 65 and key_data[0] == '\x04':
-        return key_data[-64:]
+    if key_len == 64:
+        return '\04' + key_data
     # key format is "spki"
     if key_len == 88 and key_data[:3] == '0V0':
         return key_data[-64:]
@@ -188,18 +179,7 @@ def extract_jwt(token, crypto_key):
     # first split and convert the jwt.
     if not token or not crypto_key:
         return {}
-
-    key = decipher_public_key(crypto_key)
-    vk = ecdsa.VerifyingKey.from_string(key, curve=ecdsa.NIST256p)
-    # jose offers jwt.decode(token, vk, ...) which does a full check
-    # on the JWT object. Vapid is a bit more creative in how it
-    # stores data into a JWT and breaks expectations. We would have to
-    # turn off most of the validation in order for it to be useful.
-    return jwt.decode(token, dict(keys=[vk]), options=dict(
-        verify_aud=False,
-        verify_sub=False,
-        verify_exp=False,
-    ))
+    return jwt.decode(token, decipher_public_key(crypto_key))
 
 
 def parse_user_agent(agent_string):

autopush/web/webpush.py

@@ -3,7 +3,7 @@
 
 from boto.dynamodb2.exceptions import ItemNotFound
 from cryptography.fernet import InvalidToken
-from jose import JOSEError
+from cryptography.exceptions import InvalidSignature
 from marshmallow import (
     Schema,
     fields,
@@ -321,7 +321,7 @@ def validate_auth(self, d):
 
         try:
             jwt = extract_jwt(token, public_key)
-        except (AssertionError, ValueError, JOSEError):
+        except (ValueError, InvalidSignature, Exception):
             raise InvalidRequest("Invalid Authorization Header",
                                  status_code=401, errno=109,
                                  headers={"www-authenticate": PREF_SCHEME})

docs/api.rst

@@ -31,3 +31,4 @@ documentation is organized alphabetically by module name.
    api/ssl
    api/utils
    api/websocket
+   api/jwt

docs/api/jwt.rst

@@ -0,0 +1,10 @@
+.. _jwt_module:
+
+:mod:`autopush.jwt`
+------------------------
+
+.. automodule:: autopush.jwt
+
+.. autoclass:: VerifyJWT
+    :members:
+    :member-order: bysource

requirements.txt

@@ -13,7 +13,6 @@ cryptography==1.7.2
 cyclone==1.1
 datadog==0.13.0
 decorator==4.0.10
-ecdsa==0.13
 enum34==1.1.6
 future==0.15.2
 futures==3.0.5
@@ -32,7 +31,6 @@ pycparser==2.17
 pycrypto==2.6.1
 pyfcm==1.0.4
 python-dateutil==2.5.3
-python-jose==1.3.2
 raven==5.25.0
 requests==2.11.0
 service-identity==16.0.0

test-requirements.txt

@@ -1,6 +1,8 @@
 -r requirements.txt
 nose
 coverage
+ecdsa==0.13
+python-jose==1.3.2
 mock>=1.0.1
 funcsigs==1.0.2
 pbr==1.10.0