the check_cert_signature() method was attempting to compare RSA and ECC signatures.

If a ec public-key certificate is signed with an RSA key, then it can't be a self-signed certificate, in which case we just raise InvalidSignature.

lemur/common/utils.py

@@ -147,6 +147,8 @@ def generate_private_key(key_type):
 def check_cert_signature(cert, issuer_public_key):
     """
     Check a certificate's signature against an issuer public key.
+    Before EC validation, make sure public key and signature are of the same type,
+    otherwise verification not possible (raise InvalidSignature)
     On success, returns None; on failure, raises UnsupportedAlgorithm or InvalidSignature.
     """
     if isinstance(issuer_public_key, rsa.RSAPublicKey):
@@ -160,9 +162,10 @@ def check_cert_signature(cert, issuer_public_key):
         else:
             padder = padding.PKCS1v15()
         issuer_public_key.verify(cert.signature, cert.tbs_certificate_bytes, padder, cert.signature_hash_algorithm)
-    else:
-        # EllipticCurvePublicKey or DSAPublicKey
+    elif isinstance(issuer_public_key, ec.EllipticCurvePublicKey) and isinstance(cert.signature_hash_algorithm, ec.ECDSA):
             issuer_public_key.verify(cert.signature, cert.tbs_certificate_bytes, cert.signature_hash_algorithm)
+    else:
+        raise InvalidSignature
 
 
 def is_selfsigned(cert):
@@ -176,6 +179,8 @@ def is_selfsigned(cert):
         return True
     except InvalidSignature:
         return False
+    except UnsupportedAlgorithm as e:
+        raise Exception(e)
 
 
 def is_weekend(date):

lemur/tests/test_utils.py

@@ -1,6 +1,6 @@
 import pytest
 
-from lemur.tests.vectors import SAN_CERT, INTERMEDIATE_CERT, ROOTCA_CERT
+from lemur.tests.vectors import SAN_CERT, INTERMEDIATE_CERT, ROOTCA_CERT, EC_CERT_EXAMPLE
 
 
 def test_generate_private_key():
@@ -83,3 +83,4 @@ def test_is_selfsigned(selfsigned_cert):
     assert is_selfsigned(INTERMEDIATE_CERT) is False
     # Root CA certificates are also technically self-signed
     assert is_selfsigned(ROOTCA_CERT) is True
+    assert is_selfsigned(EC_CERT_EXAMPLE) is False

lemur/tests/vectors.py

@@ -394,3 +394,31 @@ zm3Cn4Ul8DO26w9QS4fmZjmnPOZFXYMWoOR6osHzb62PWQ8FBMqXcdToBV2Q9Iw4
 PiFAxlc0tVjlLqQ=
 -----END CERTIFICATE REQUEST-----
 """
+
+
+EC_CERT_STR = """
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
+"""
+EC_CERT_EXAMPLE = parse_certificate(EC_CERT_STR)