sigstore: add new verification policies for missing extensions (#1004)

* sigstore: add new verification policies for missing extensions Signed-off-by: Facundo Tuesca <facundo.tuesca@trailofbits.com> * Rename policy class Signed-off-by: Facundo Tuesca <facundo.tuesca@trailofbits.com> * Update pyproject.toml Co-authored-by: William Woodruff <william@yossarian.net> Signed-off-by: Facundo Tuesca <facu@tuesca.com> --------- Signed-off-by: Facundo Tuesca <facundo.tuesca@trailofbits.com> Signed-off-by: Facundo Tuesca <facu@tuesca.com> Co-authored-by: William Woodruff <william@yossarian.net>
sigstore · May 7, 2024 · e136352 · e136352
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commit e136352
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diff --git a/pyproject.toml b/pyproject.toml
@@ -28,6 +28,7 @@ dependencies = [
   "cryptography >= 42",
   "id >= 1.1.0",
   "importlib_resources ~= 5.7; python_version < '3.11'",
+  "pyasn1 ~= 0.6",
   "pydantic >= 2,< 3",
   "pyjwt >= 2.1",
   "pyOpenSSL >= 23.0.0",

diff --git a/sigstore/verify/policy.py b/sigstore/verify/policy.py
@@ -32,6 +32,8 @@
     SubjectAlternativeName,
     UniformResourceIdentifier,
 )
+from pyasn1.codec.der.decoder import decode as der_decode
+from pyasn1.type.char import UTF8String
 
 from sigstore.errors import VerificationError
 
@@ -45,6 +47,23 @@
 _OIDC_GITHUB_WORKFLOW_REPOSITORY_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.5")
 _OIDC_GITHUB_WORKFLOW_REF_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.6")
 _OTHERNAME_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.7")
+_OIDC_ISSUER_V2_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.8")
+_OIDC_BUILD_SIGNER_URI_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.9")
+_OIDC_BUILD_SIGNER_DIGEST_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.10")
+_OIDC_RUNNER_ENVIRONMENT_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.11")
+_OIDC_SOURCE_REPOSITORY_URI_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.12")
+_OIDC_SOURCE_REPOSITORY_DIGEST_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.13")
+_OIDC_SOURCE_REPOSITORY_REF_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.14")
+_OIDC_SOURCE_REPOSITORY_IDENTIFIER_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.15")
+_OIDC_SOURCE_REPOSITORY_OWNER_URI_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.16")
+_OIDC_SOURCE_REPOSITORY_OWNER_IDENTIFIER_OID = ObjectIdentifier(
+    "1.3.6.1.4.1.57264.1.17"
+)
+_OIDC_BUILD_CONFIG_URI_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.18")
+_OIDC_BUILD_CONFIG_DIGEST_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.19")
+_OIDC_BUILD_TRIGGER_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.20")
+_OIDC_RUN_INVOCATION_URI_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.21")
+_OIDC_SOURCE_REPOSITORY_VISIBILITY_OID = ObjectIdentifier("1.3.6.1.4.1.57264.1.22")
 
 
 class _SingleX509ExtPolicy(ABC):
@@ -93,6 +112,41 @@ def verify(self, cert: Certificate) -> None:
             )
 
 
+class _SingleX509ExtPolicyV2(_SingleX509ExtPolicy):
+    """
+    An base class for verification policies that boil down to checking a single
+    X.509 extension's value, where the value is formatted as a DER-encoded string,
+    the ASN.1 tag is UTF8String (0x0C) and the tag class is universal.
+    """
+
+    def verify(self, cert: Certificate) -> None:
+        """
+        Verify this policy against `cert`.
+
+        Raises `VerificationError` on failure.
+        """
+        try:
+            ext = cert.extensions.get_extension_for_oid(self.oid).value
+        except ExtensionNotFound:
+            raise VerificationError(
+                (
+                    f"Certificate does not contain {self.__class__.__name__} "
+                    f"({self.oid.dotted_string}) extension"
+                )
+            )
+
+        # NOTE(ww): mypy is confused by the `Extension[ExtensionType]` returned
+        # by `get_extension_for_oid` above.
+        ext_value = der_decode(ext.value, UTF8String)[0].decode()  # type: ignore[attr-defined]
+        if ext_value != self._value:
+            raise VerificationError(
+                (
+                    f"Certificate's {self.__class__.__name__} does not match "
+                    f"(got {ext_value}, expected {self._value})"
+                )
+            )
+
+
 class OIDCIssuer(_SingleX509ExtPolicy):
     """
     Verifies the certificate's OIDC issuer, identified by
@@ -147,6 +201,145 @@ class GitHubWorkflowRef(_SingleX509ExtPolicy):
     oid = _OIDC_GITHUB_WORKFLOW_REF_OID
 
 
+class OIDCIssuerV2(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC issuer, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.8`.
+    The difference with `OIDCIssuer` is that the value for
+    this extension is formatted to the RFC 5280 specification
+    as a DER-encoded string.
+    """
+
+    oid = _OIDC_ISSUER_V2_OID
+
+
+class OIDCBuildSignerURI(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Build Signer URI, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.9`.
+    """
+
+    oid = _OIDC_BUILD_SIGNER_URI_OID
+
+
+class OIDCBuildSignerDigest(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Build Signer Digest, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.10`.
+    """
+
+    oid = _OIDC_BUILD_SIGNER_DIGEST_OID
+
+
+class OIDCRunnerEnvironment(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Runner Environment, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.11`.
+    """
+
+    oid = _OIDC_RUNNER_ENVIRONMENT_OID
+
+
+class OIDCSourceRepositoryURI(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Source Repository URI, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.12`.
+    """
+
+    oid = _OIDC_SOURCE_REPOSITORY_URI_OID
+
+
+class OIDCSourceRepositoryDigest(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Source Repository Digest, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.13`.
+    """
+
+    oid = _OIDC_SOURCE_REPOSITORY_DIGEST_OID
+
+
+class OIDCSourceRepositoryRef(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Source Repository Ref, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.14`.
+    """
+
+    oid = _OIDC_SOURCE_REPOSITORY_REF_OID
+
+
+class OIDCSourceRepositoryIdentifier(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Source Repository Identifier, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.15`.
+    """
+
+    oid = _OIDC_SOURCE_REPOSITORY_IDENTIFIER_OID
+
+
+class OIDCSourceRepositoryOwnerURI(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Source Repository Owner URI, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.16`.
+    """
+
+    oid = _OIDC_SOURCE_REPOSITORY_OWNER_URI_OID
+
+
+class OIDCSourceRepositoryOwnerIdentifier(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Source Repository Owner Identifier, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.17`.
+    """
+
+    oid = _OIDC_SOURCE_REPOSITORY_OWNER_IDENTIFIER_OID
+
+
+class OIDCBuildConfigURI(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Build Config URI, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.18`.
+    """
+
+    oid = _OIDC_BUILD_CONFIG_URI_OID
+
+
+class OIDCBuildConfigDigest(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Build Config Digest, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.19`.
+    """
+
+    oid = _OIDC_BUILD_CONFIG_DIGEST_OID
+
+
+class OIDCBuildTrigger(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Build Trigger, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.20`.
+    """
+
+    oid = _OIDC_BUILD_TRIGGER_OID
+
+
+class OIDCRunInvocationURI(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Run Invocation URI, identified by
+    an X.509v3 extension tagged with `1.3.6.1.4.1.57264.1.21`.
+    """
+
+    oid = _OIDC_RUN_INVOCATION_URI_OID
+
+
+class OIDCSourceRepositoryVisibility(_SingleX509ExtPolicyV2):
+    """
+    Verifies the certificate's OIDC Source Repository Visibility
+    At Signing, identified by an X.509v3 extension tagged with
+    `1.3.6.1.4.1.57264.1.22`.
+    """
+
+    oid = _OIDC_SOURCE_REPOSITORY_VISIBILITY_OID
+
+
 class VerificationPolicy(Protocol):
     """
     A protocol type describing the interface that all verification policies

diff --git a/test/unit/assets/bundle_v3_github.whl b/test/unit/assets/bundle_v3_github.whl
diff --git a/test/unit/assets/bundle_v3_github.whl.sigstore b/test/unit/assets/bundle_v3_github.whl.sigstore
@@ -0,0 +1 @@
+{"mediaType": "application/vnd.dev.sigstore.bundle+json;version=0.2", "verificationMaterial": {"x509CertificateChain": {"certificates": [{"rawBytes": "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"}]}, 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"messageSignature": {"messageDigest": {"algorithm": "SHA2_256", "digest": "xOkunsyCi+8qp9uh3orJg1EfdTKg3xHHcNOQmaJc8gE="}, "signature": "MEYCIQCeH6E3MpZngWA6RPg8HAl/Z764hTFYycNyF3R+mPTSbAIhAPgMS8qBM8lCEU2XW765myMMz2zuyu9iTF40PH+XZlJQ"}}
diff --git a/test/unit/verify/test_policy.py b/test/unit/verify/test_policy.py
@@ -151,3 +151,43 @@ def test_fails_no_san_match(self, signing_bundle):
             match="Certificate's SANs do not match",
         ):
             policy_.verify(bundle.signing_certificate)
+
+
+class TestSingleExtPolicy:
+    def test_succeeds(self, signing_bundle):
+        _, bundle = signing_bundle("bundle_v3_github.whl")
+
+        verification_policy_extensions = [
+            policy.OIDCIssuer("https://token.actions.githubusercontent.com"),
+            policy.GitHubWorkflowTrigger("release"),
+            policy.GitHubWorkflowSHA("d8b4a6445f38c48b9137a8099706d9b8073146e4"),
+            policy.GitHubWorkflowName("release"),
+            policy.GitHubWorkflowRepository("trailofbits/rfc8785.py"),
+            policy.GitHubWorkflowRef("refs/tags/v0.1.2"),
+            policy.OIDCIssuerV2("https://token.actions.githubusercontent.com"),
+            policy.OIDCBuildSignerURI(
+                "https://github.com/trailofbits/rfc8785.py/.github/workflows/release.yml@refs/tags/v0.1.2"
+            ),
+            policy.OIDCBuildSignerDigest("d8b4a6445f38c48b9137a8099706d9b8073146e4"),
+            policy.OIDCRunnerEnvironment("github-hosted"),
+            policy.OIDCSourceRepositoryURI("https://github.com/trailofbits/rfc8785.py"),
+            policy.OIDCSourceRepositoryDigest(
+                "d8b4a6445f38c48b9137a8099706d9b8073146e4"
+            ),
+            policy.OIDCSourceRepositoryRef("refs/tags/v0.1.2"),
+            policy.OIDCSourceRepositoryIdentifier("768213997"),
+            policy.OIDCSourceRepositoryOwnerURI("https://github.com/trailofbits"),
+            policy.OIDCSourceRepositoryOwnerIdentifier("2314423"),
+            policy.OIDCBuildConfigURI(
+                "https://github.com/trailofbits/rfc8785.py/.github/workflows/release.yml@refs/tags/v0.1.2"
+            ),
+            policy.OIDCBuildConfigDigest("d8b4a6445f38c48b9137a8099706d9b8073146e4"),
+            policy.OIDCBuildTrigger("release"),
+            policy.OIDCRunInvocationURI(
+                "https://github.com/trailofbits/rfc8785.py/actions/runs/8351058501/attempts/1"
+            ),
+            policy.OIDCSourceRepositoryVisibility("public"),
+        ]
+
+        policy_ = policy.AllOf(verification_policy_extensions)
+        policy_.verify(bundle.signing_certificate)