De-duplicate verify methods

signxml/verifier.py

@@ -2,6 +2,7 @@
 from dataclasses import dataclass, replace
 from typing import Callable, FrozenSet, List, Optional, Union
 
+import cryptography.exceptions
 from cryptography import x509
 from cryptography.hazmat.primitives.asymmetric import dsa, ec, rsa, utils
 from cryptography.hazmat.primitives.asymmetric.padding import MGF1, PSS, AsymmetricPadding, PKCS1v15
@@ -114,14 +115,20 @@ def _get_signature(self, root):
 
     def _verify_signature_with_pubkey(
         self,
+        *,
         signed_info_c14n: bytes,
         raw_signature: bytes,
-        key_value: etree._Element,
-        der_encoded_key_value: Optional[etree._Element],
         signature_alg: SignatureMethod,
+        key_value: Optional[etree._Element] = None,
+        der_encoded_key_value: Optional[etree._Element] = None,
+        signing_certificate: Optional[x509.Certificate] = None,
     ) -> None:
         if der_encoded_key_value is not None:
             key = load_der_public_key(b64decode(der_encoded_key_value.text))  # type: ignore
+        elif signing_certificate is not None:
+            key = signing_certificate.public_key()
+        elif key_value is None:
+            raise InvalidInput("Expected one of key_value, der_encoded_key_value, or signing_certificate to be set")
 
         digest_alg_impl = digest_algorithm_implementations[signature_alg]()
         if signature_alg.name.startswith("ECDSA_"):
@@ -137,8 +144,8 @@ def _verify_signature_with_pubkey(
                 key = ecpn.public_key()
             elif not isinstance(key, ec.EllipticCurvePublicKey):
                 raise InvalidInput("DER encoded key value does not match specified signature algorithm")
-            dss_signature = self._encode_dss_signature(raw_signature, key.key_size)
-            key.verify(dss_signature, data=signed_info_c14n, signature_algorithm=ec.ECDSA(digest_alg_impl))
+            signature_for_ecdsa = self._encode_dss_signature(raw_signature, key.key_size)
+            key.verify(signature_for_ecdsa, data=signed_info_c14n, signature_algorithm=ec.ECDSA(digest_alg_impl))
         elif signature_alg.name.startswith("DSA_"):
             if key_value is not None:
                 dsa_key_value = self._find(key_value, "DSAKeyValue")
@@ -167,7 +174,7 @@ def _verify_signature_with_pubkey(
                 padding = PSS(mgf=MGF1(algorithm=digest_alg_impl), salt_length=digest_alg_impl.digest_size)
             key.verify(raw_signature, data=signed_info_c14n, padding=padding, algorithm=digest_alg_impl)
         else:
-            raise NotImplementedError()
+            raise InvalidInput(f"Unsupported signature algorithm {signature_alg}")
 
     def _encode_dss_signature(self, raw_signature: bytes, key_size_bits: int) -> bytes:
         want_raw_signature_len = bits_to_bytes_unit(key_size_bits) * 2
@@ -226,16 +233,6 @@ def _apply_transforms(self, payload, *, transforms_node: etree._Element, signatu
     def get_cert_chain_verifier(self, ca_pem_file, ca_path):
         return X509CertChainVerifier(ca_pem_file=ca_pem_file, ca_path=ca_path)
 
-    def _verify_signature_with_public_key_impl(self, *, signature, data, public_key, signature_alg_impl):
-        verify_args = dict(signature=signature, data=data)
-        if isinstance(public_key, rsa.RSAPublicKey):
-            verify_args.update(padding=PKCS1v15(), algorithm=signature_alg_impl)
-        elif isinstance(public_key, dsa.DSAPublicKey):
-            verify_args.update(algorithm=signature_alg_impl)
-        elif isinstance(public_key, ec.EllipticCurvePublicKey):
-            verify_args.update(signature_algorithm=ec.ECDSA(signature_alg_impl))
-        public_key.verify(**verify_args)
-
     def verify(
         self,
         data,
@@ -406,17 +403,15 @@ def verify(
                 if subject_cn_from_signing_cert != cert_subject_name:
                     raise InvalidSignature("Certificate subject common name mismatch")
 
-            if signature_alg.name.startswith("ECDSA"):
-                raw_signature = self._encode_dss_signature(raw_signature, signing_cert.public_key().key_size)
-
-            cert_public_key = signing_cert.public_key()
-            signature_alg_impl = digest_algorithm_implementations[signature_alg]()
-            self._verify_signature_with_public_key_impl(
-                signature=raw_signature,
-                data=signed_info_c14n,
-                public_key=cert_public_key,
-                signature_alg_impl=signature_alg_impl,
-            )
+            try:
+                self._verify_signature_with_pubkey(
+                    signed_info_c14n=signed_info_c14n,
+                    raw_signature=raw_signature,
+                    signing_certificate=signing_cert,
+                    signature_alg=signature_alg,
+                )
+            except cryptography.exceptions.InvalidSignature as e:
+                raise InvalidSignature(f"Signature verification failed: {e}")
 
             # If both X509Data and KeyValue are present, match one against the other and raise an error on mismatch
             if key_value is not None: