security(jose): treat a non-string kid as a typed error

CHANGELOG.md

@@ -72,6 +72,10 @@ All notable changes to **openvc** are documented here. The format follows
   (RFC 9901 §7.1 step 6). A selectively disclosed validity claim is now
   enforced when the holder presents it, not only when it stays in the
   issuer-JWT body.
+- **A non-string JOSE `kid` is a typed error, not `AttributeError`**
+  ([#175](https://github.com/luisgf/openvc/issues/175)). `peek_issuer`
+  and `DidDocument.key_by_kid` now reject it, so `verify_many` isolates
+  the item instead of aborting the batch.
 
 ## [1.24.0] — 2026-07-29
 

src/openvc/did/base.py

@@ -65,6 +65,8 @@ def key_by_kid(self, kid: str | None) -> VerificationMethod | None:
         may carry either). If kid is None, fall back to the sole key if unique."""
         if kid is None:
             return self.verification_methods[0] if len(self.verification_methods) == 1 else None
+        if not isinstance(kid, str):
+            return None
         fragment = kid.split("#", 1)[-1]
         return next(
             (vm for vm in self.verification_methods if vm.id == kid or vm.kid == fragment),

src/openvc/proof/sd_jwt.py

@@ -219,7 +219,10 @@ def peek_issuer(self, sd_jwt: str) -> tuple[str, str | None]:
         iss = payload.get("iss")
         if not iss or not isinstance(iss, str):
             raise MalformedToken("no iss in the issuer-signed JWT")
-        return iss, header.get("kid")
+        kid = header.get("kid")
+        if kid is not None and not isinstance(kid, str):
+            raise MalformedToken("kid must be a string")
+        return iss, kid
 
     # -- issuance --------------------------------------------------------- #
 

src/openvc/proof/vc_jwt.py

@@ -161,7 +161,10 @@ def peek_issuer(self, token: str) -> tuple[str, str | None]:
             iss = iss.get("id")
         if not iss or not isinstance(iss, str):
             raise MalformedToken("no issuer (iss / vc.issuer) present")
-        return iss, header.get("kid")
+        kid = header.get("kid")
+        if kid is not None and not isinstance(kid, str):
+            raise MalformedToken("kid must be a string")
+        return iss, kid
 
     def peek_claims(self, token: str) -> dict[str, Any]:
         """Decode the full claim set WITHOUT verifying the signature. UNTRUSTED.

tests/test_hostile_input.py

@@ -101,6 +101,45 @@ def test_vc_jwt_peek_typed_on_non_string_iss_and_non_object_vc():
         VcJwtProofSuite().peek_issuer(_jose({"alg": "ES256"}, {"vc": [1, 2]}))
 
 
+def test_vc_jwt_peek_typed_on_non_string_kid():
+    with pytest.raises(OpenvcError):
+        VcJwtProofSuite().peek_issuer(
+            _jose({"alg": "ES256", "kid": 1}, {"iss": "did:example:iss"}))
+    with pytest.raises(OpenvcError):
+        SdJwtVcProofSuite().peek_issuer(
+            _jose({"alg": "EdDSA", "typ": "vc+sd-jwt", "kid": 1},
+                  {"iss": "did:example:iss"}) + "~")
+
+
+def test_verify_many_isolates_a_non_string_kid():
+    # #175. kid:1 used to AttributeError in DidDocument.key_by_kid and abort
+    # the batch. A sibling "not.a.jwt" must still become a typed BatchResult.
+    from openvc.keys import Ed25519SigningKey
+    from openvc.multibase import encode_multibase
+    from openvc.proof._jws import sign_compact
+
+    def _leb128(code: int) -> bytes:
+        out = bytearray()
+        while True:
+            b, code = code & 0x7F, code >> 7
+            out.append(b | (0x80 if code else 0))
+            if not code:
+                return bytes(out)
+
+    key = Ed25519SigningKey.generate(kid="k")
+    raw = base64.urlsafe_b64decode(key.public_jwk()["x"] + "==")
+    did = "did:key:" + encode_multibase(_leb128(0xED) + raw)
+    token = sign_compact(
+        {"alg": key.alg, "typ": "JWT", "kid": 1},
+        {"iss": did, "vc": {"type": ["VerifiableCredential"], "issuer": did,
+                            "credentialSubject": {"id": "did:example:alice"}}},
+        signing_key=key,
+    )
+    results = verify_many([token, "not.a.jwt"])
+    assert len(results) == 2
+    assert all((not r.ok) and isinstance(r.error, OpenvcError) for r in results)
+
+
 def test_verify_many_isolates_a_non_object_payload():
     """The A1 regression: a hostile non-object-payload token must become a fail-closed
     BatchResult, never abort the sibling that follows it."""