Just emit a warning when verifying with a private key

.travis.yml

@@ -12,7 +12,7 @@ matrix:
   include:
     # Linting
     - python: 3.6
-      env: TOX_ENV=flake8
+      env: TOXENV=flake8
     # CPython 2.7
     - python: 2.7
       env: TOXENV=py27-base

jose/backends/pycrypto_backend.py

@@ -1,6 +1,7 @@
 from base64 import b64encode
 
 import six
+import warnings
 
 import Crypto.Hash.SHA256
 import Crypto.Hash.SHA384
@@ -147,6 +148,9 @@ def sign(self, msg):
             raise JWKError(e)
 
     def verify(self, msg, sig):
+        if not self.is_public():
+            warnings.warn("Attempting to verify a message with a private key. "
+                          "This is not recommended.")
         try:
             return PKCS1_v1_5.new(self.prepared_key).verify(self.hash_alg.new(msg), sig)
         except Exception:

jose/backends/rsa_backend.py

@@ -1,6 +1,8 @@
 import binascii
 
 import six
+import warnings
+
 from pyasn1.error import PyAsn1Error
 
 import rsa as pyrsa
@@ -200,6 +202,9 @@ def sign(self, msg):
         return pyrsa.sign(msg, self._prepared_key, self.hash_alg)
 
     def verify(self, msg, sig):
+        if not self.is_public():
+            warnings.warn("Attempting to verify a message with a private key. "
+                          "This is not recommended.")
         try:
             pyrsa.verify(msg, sig, self._prepared_key)
             return True

jose/utils.py

@@ -1,6 +1,5 @@
 
 import base64
-import hmac
 import six
 import struct
 import sys

pytest.ini

@@ -0,0 +1,7 @@
+[pytest]
+markers =
+    pycrypto: marks tests as applicable with PyCrypto backend
+    pycryptodome: marks tests as applicable with PyCryptodome backend
+    ecdsa: marks tests as applicable with ecdsa backend
+    cryptography: marks tests as applicable with cryptography backend
+    backend_compatibility: mark tests as testing compatibility between backends

setup.py

@@ -3,7 +3,7 @@
 import os
 import platform
 
-import jose
+import jose  # noqa: F401
 
 from setuptools import setup
 

tests/test_jws.py

@@ -1,11 +1,18 @@
 import json
+import warnings
+
+import pytest
 
 from jose import jwk
 from jose import jws
+from jose.backends import RSAKey
 from jose.constants import ALGORITHMS
 from jose.exceptions import JWSError
 
-import pytest
+try:
+    from jose.backends.cryptography_backend import CryptographyRSAKey
+except ImportError:
+    CryptographyRSAKey = None
 
 
 @pytest.fixture
@@ -291,6 +298,20 @@ def test_wrong_key(self, payload):
         with pytest.raises(JWSError):
             jws.verify(token, rsa_public_key, ALGORITHMS.HS256)
 
+    @pytest.mark.skipif(RSAKey is CryptographyRSAKey, reason="Cryptography backend outright fails verification")
+    def test_private_verify_raises_warning(self, payload):
+        token = jws.sign(payload, rsa_private_key, algorithm='RS256')
+
+        # verify with public
+        jws.verify(token, rsa_public_key, algorithms='RS256')
+
+        with warnings.catch_warnings(record=True) as w:
+            # verify with private raises warning
+            jws.verify(token, rsa_private_key, algorithms='RS256')
+
+            assert ("Attempting to verify a message with a private key. "
+                    "This is not recommended.") == str(w[-1].message)
+
 
 ec_private_key = """-----BEGIN EC PRIVATE KEY-----
 MIHcAgEBBEIBzs13YUnYbLfYXTz4SG4DE4rPmsL3wBTdy34JcO+BDpI+NDZ0pqam