_verify: Check for URI SANs when verifying certificate emails (#288)

* _verify: Check for URI SANs when verifying certificate emails

Signed-off-by: Alex Cameron <asc@tetsuo.sh>

* test: Add unit tests for verifying SANs

Signed-off-by: Alex Cameron <asc@tetsuo.sh>

* test: Update tests to use identity parameter

Signed-off-by: Alex Cameron <asc@tetsuo.sh>

* test: Add test to verify issuer and SAN at the same time

Signed-off-by: Alex Cameron <asc@tetsuo.sh>

* _utils, _verify: Create helper for checking SAN

Signed-off-by: Alex Cameron <asc@tetsuo.sh>

* _utils: Also check `OtherName` in SAN check

Signed-off-by: Alex Cameron <asc@tetsuo.sh>

* _utils: Fix OtherName check

Signed-off-by: Alex Cameron <asc@tetsuo.sh>

Signed-off-by: Alex Cameron <asc@tetsuo.sh>

sigstore/_utils.py

@@ -21,6 +21,14 @@
 
 from cryptography.hazmat.primitives import serialization
 from cryptography.hazmat.primitives.asymmetric import ec, rsa
+from cryptography.x509 import (
+    Certificate,
+    ObjectIdentifier,
+    OtherName,
+    RFC822Name,
+    SubjectAlternativeName,
+    UniformResourceIdentifier,
+)
 
 PublicKey = Union[rsa.RSAPublicKey, ec.EllipticCurvePublicKey]
 
@@ -59,3 +67,19 @@ def key_id(key: PublicKey) -> bytes:
     )
 
     return hashlib.sha256(public_bytes).digest()
+
+
+def cert_contains_identity(cert: Certificate, expected_cert_identity: str) -> bool:
+    """
+    Check that the certificate's SubjectAlternativeName contains a given identity.
+    """
+    san_ext = cert.extensions.get_extension_for_class(SubjectAlternativeName)
+    return (
+        expected_cert_identity in san_ext.value.get_values_for_type(RFC822Name)
+        or expected_cert_identity
+        in san_ext.value.get_values_for_type(UniformResourceIdentifier)
+        or OtherName(
+            ObjectIdentifier("1.3.6.1.4.1.57264.1.7"), expected_cert_identity.encode()
+        )
+        in san_ext.value.get_values_for_type(OtherName)
+    )

sigstore/_verify.py

@@ -34,8 +34,6 @@
     ExtensionNotFound,
     KeyUsage,
     ObjectIdentifier,
-    RFC822Name,
-    SubjectAlternativeName,
     load_pem_x509_certificate,
 )
 from cryptography.x509.oid import ExtendedKeyUsageOID
@@ -53,6 +51,7 @@
 )
 from sigstore._internal.rekor import RekorClient, RekorEntry
 from sigstore._internal.set import InvalidSetError, verify_set
+from sigstore._utils import cert_contains_identity
 
 logger = logging.getLogger(__name__)
 
@@ -207,15 +206,12 @@ def verify(
                 reason="Extended usage does not contain `code signing`"
             )
 
-        if expected_cert_identity is not None:
-            # Check that SubjectAlternativeName contains signer identity
-            san_ext = cert.extensions.get_extension_for_class(SubjectAlternativeName)
-            if expected_cert_identity not in san_ext.value.get_values_for_type(
-                RFC822Name
-            ):
-                return VerificationFailure(
-                    reason=f"Subject name does not contain identity: {expected_cert_identity}"
-                )
+        if expected_cert_identity is not None and not cert_contains_identity(
+            cert, expected_cert_identity
+        ):
+            return VerificationFailure(
+                reason=f"Subject name does not contain identity: {expected_cert_identity}"
+            )
 
         if expected_cert_oidc_issuer is not None:
             # Check that the OIDC issuer extension is present, and contains the expected

test/assets/c.txt

@@ -0,0 +1,5 @@
+DO NOT MODIFY ME!
+
+this is "c.txt", a sample input for sigstore-python's unit tests.
+
+DO NOT MODIFY ME!

test/assets/c.txt.crt

@@ -0,0 +1,23 @@
+-----BEGIN CERTIFICATE-----
+MIIDwTCCA0igAwIBAgIUdXPCI40ren/SEkqxmHcCc6lIV7MwCgYIKoZIzj0EAwMw
+NzEVMBMGA1UEChMMc2lnc3RvcmUuZGV2MR4wHAYDVQQDExVzaWdzdG9yZS1pbnRl
+cm1lZGlhdGUwHhcNMjIxMTAzMDc0NTM1WhcNMjIxMTAzMDc1NTM1WjAAMHYwEAYH
+KoZIzj0CAQYFK4EEACIDYgAELVUlqi4FjTw4mHzuyE8sOsK6mVvzOTv0EX7ot+aZ
+ftaf+ato9xuemqA69qARscFPwG15It1F9PVdKUOeJkTPjZC+lRHNAIeamJpilskz
+xqR6fisI7q72zHY8OhgMnSSHo4ICSjCCAkYwDgYDVR0PAQH/BAQDAgeAMBMGA1Ud
+JQQMMAoGCCsGAQUFBwMDMB0GA1UdDgQWBBREb7Dfm1g8gILV3K9rT9WSF7GnzzAf
+BgNVHSMEGDAWgBRxhjCmFHxib/n31vQFGn9f/+tvrDBmBgNVHREBAf8EXDBahlho
+dHRwczovL2dpdGh1Yi5jb20vc2lnc3RvcmUvc2lnc3RvcmUtcHl0aG9uLy5naXRo
+dWIvd29ya2Zsb3dzL2NpLnltbEByZWZzL3B1bGwvMjg4L21lcmdlMDkGCisGAQQB
+g78wAQEEK2h0dHBzOi8vdG9rZW4uYWN0aW9ucy5naXRodWJ1c2VyY29udGVudC5j
+b20wGgYKKwYBBAGDvzABAgQMcHVsbF9yZXF1ZXN0MDYGCisGAQQBg78wAQMEKDNi
+ZTcyMzU2ZWY0NTE3YmI4ZTUwZjI5Njg4N2Y5YzU3ODZmOTAzMTYwEAYKKwYBBAGD
+vzABBAQCQ0kwJgYKKwYBBAGDvzABBQQYc2lnc3RvcmUvc2lnc3RvcmUtcHl0aG9u
+MCEGCisGAQQBg78wAQYEE3JlZnMvcHVsbC8yODgvbWVyZ2UwgYoGCisGAQQB1nkC
+BAIEfAR6AHgAdgArMLzcaIjJ4uHYJiledB9IOTGWAvKcM8teQ0D+sqyGegAAAYQ8
+c9igAAAEAwBHMEUCIQCn/JSbLxs0ds3Nycn0yINUQABeltbAmcYDFEn/sdm50gIg
+fm4lKdhXJoWHJRC8IS7MxYI3yR/oNzX6dntuqpHJ24YwCgYIKoZIzj0EAwMDZwAw
+ZAIwE0F3B/HgHn+ov6axOY0TMR/hv2DUVlC3qkGBQEEMtglf5qtT+a9g7aQ5g4pG
+of+JAjB+qUeUdSAyGPDK+5Ti6aROy0oAbwl+B3bH7QmmZ/i5M++PXIW4l4lcuAmA
+UkjTgLw=
+-----END CERTIFICATE-----

test/assets/c.txt.sig

@@ -0,0 +1 @@
+MGUCMAQYRaYOdZEOT3C3WP22sC9+2euiFGYbC4VNefWVL31+MAL7oKMWsHsBwh1ngjTZHAIxALuUf+mzlACBqYUSTTwl3LFIGUGl8g3Z6wkTMsqdI1NrtHj0rVpcWA1DIO4GhGOM5w==

test/test_verify.py

@@ -64,3 +64,57 @@ def test_verify_result_boolish():
     assert not VerificationFailure(reason="foo")
     assert not CertificateVerificationFailure(reason="foo", exception=ValueError("bar"))
     assert VerificationSuccess()
+
+
+@pytest.mark.online
+def test_verifier_issuer(signed_asset):
+    a_assets = signed_asset("a.txt")
+
+    verifier = Verifier.staging()
+    assert verifier.verify(
+        a_assets[0],
+        a_assets[1],
+        a_assets[2],
+        expected_cert_oidc_issuer="https://github.com/login/oauth",
+    )
+
+
+@pytest.mark.online
+def test_verifier_san_email(signed_asset):
+    a_assets = signed_asset("a.txt")
+
+    verifier = Verifier.staging()
+    assert verifier.verify(
+        a_assets[0],
+        a_assets[1],
+        a_assets[2],
+        expected_cert_identity="william@yossarian.net",
+    )
+
+
+@pytest.mark.online
+def test_verifier_san_uri(signed_asset):
+    a_assets = signed_asset("c.txt")
+
+    verifier = Verifier.staging()
+    assert verifier.verify(
+        a_assets[0],
+        a_assets[1],
+        a_assets[2],
+        expected_cert_identity="https://github.com/sigstore/"
+        "sigstore-python/.github/workflows/ci.yml@refs/pull/288/merge",
+    )
+
+
+@pytest.mark.online
+def test_verifier_issuer_and_san(signed_asset):
+    a_assets = signed_asset("a.txt")
+
+    verifier = Verifier.staging()
+    assert verifier.verify(
+        a_assets[0],
+        a_assets[1],
+        a_assets[2],
+        expected_cert_identity="william@yossarian.net",
+        expected_cert_oidc_issuer="https://github.com/login/oauth",
+    )