Support fully specified algorithms per RFC 9864

jwcrypto/jwa.py

@@ -2,6 +2,7 @@
 
 import os
 import struct
+import warnings
 from abc import ABCMeta, abstractmethod
 from binascii import hexlify, unhexlify
 
@@ -41,6 +42,15 @@
 actors providing a very high iteration count.
 """
 
+default_warn_deprecated_algorithms = False
+"""When True, emit a DeprecationWarning when instantiating an algorithm
+whose status is 'deprecated'.
+
+Disabled by default so that consumers are not disrupted by warnings for
+algorithms that remain in wide use (e.g. EdDSA). Set to True to audit
+your code for deprecated algorithm usage.
+"""
+
 default_enforce_hmac_key_length = True
 """Enforces that the HMAC key length is at least the size of the hash
 function's output, as recommended by RFC 7518.
@@ -77,6 +87,12 @@ def algorithm_usage_location(self):
     def algorithm_use(self):
         """One of 'sig', 'kex', 'enc'"""
 
+    status = 'active'
+    """Algorithm status: 'active', 'deprecated', or 'prohibited'"""
+
+    deprecated_by = None
+    """Replacement algorithm(s) for deprecated algorithms"""
+
     @property
     def input_keysize(self):
         """The input key size"""
@@ -883,6 +899,8 @@ class _EdDsa(_RawJWS, JWAAlgorithm):
     algorithm_usage_location = 'alg'
     algorithm_use = 'sig'
     keysize = None
+    status = 'deprecated'
+    deprecated_by = 'Ed25519 or Ed448'
 
     def sign(self, key, payload):
         if key['crv'] in ['Ed25519', 'Ed448']:
@@ -1297,6 +1315,14 @@ def instantiate_alg(cls, name, use=None):
         alg = cls.algorithms_registry[name]
         if use is not None and alg.algorithm_use != use:
             raise KeyError
+        if alg.status == 'prohibited':
+            raise InvalidJWAAlgorithm(
+                '%s is prohibited and must not be used' % name)
+        if alg.status == 'deprecated' and default_warn_deprecated_algorithms:
+            msg = '%s is deprecated' % name
+            if alg.deprecated_by:
+                msg += '; use %s instead' % alg.deprecated_by
+            warnings.warn(msg, DeprecationWarning, stacklevel=4)
         return alg()
 
     @classmethod

jwcrypto/tests.py

@@ -2642,3 +2642,30 @@ def test_jws_ed448(self):
         jws_obj.deserialize(serialized_jws, key)
         self.assertTrue(jws_obj.is_valid)
         self.assertEqual(jws_obj.payload, payload)
+
+    def test_eddsa_deprecation_warning(self):
+        import warnings
+        old = jwa.default_warn_deprecated_algorithms
+        try:
+            jwa.default_warn_deprecated_algorithms = True
+            with warnings.catch_warnings(record=True) as w:
+                warnings.simplefilter("always")
+                jwa.JWA.signing_alg('EdDSA')
+                self.assertEqual(len(w), 1)
+                self.assertTrue(issubclass(w[0].category, DeprecationWarning))
+                self.assertIn('EdDSA', str(w[0].message))
+                self.assertIn('Ed25519 or Ed448', str(w[0].message))
+        finally:
+            jwa.default_warn_deprecated_algorithms = old
+
+    def test_eddsa_no_warning_by_default(self):
+        import warnings
+        old = jwa.default_warn_deprecated_algorithms
+        try:
+            jwa.default_warn_deprecated_algorithms = False
+            with warnings.catch_warnings(record=True) as w:
+                warnings.simplefilter("always")
+                jwa.JWA.signing_alg('EdDSA')
+                self.assertEqual(len(w), 0)
+        finally:
+            jwa.default_warn_deprecated_algorithms = old