Implement PolicyMappings X.509 extension

Author: ralphje

CHANGELOG.rst

@@ -8,6 +8,8 @@ Changelog
 
 .. note:: This version is not yet released and is under active development.
 
+* Added support for the :class:`~cryptography.x509.PolicyMappings` extension.
+
 .. _v50-0-0:
 
 50.0.0 - 2026-07-31

docs/x509/reference.rst

@@ -2986,6 +2986,26 @@ X.509 Extensions
         mapping may be processed in certificates issued by the subject of this
         certificate, but not in additional certificates in the chain.
 
+.. class:: PolicyMappings(mappings)
+    :canonical: cryptography.x509.extensions.PolicyMappings
+
+    .. versionadded:: 51.0.0
+
+    The policy mappings extension is used in CA certificates to map policy
+    identifiers in the issuer's policy domain to policy identifiers in the
+    subject's policy domain. For more information see :rfc:`5280`.
+
+    :param mappings: A non-empty iterable of 2-tuples. Each tuple contains an
+        issuer domain policy :class:`ObjectIdentifier` followed by a subject
+        domain policy :class:`ObjectIdentifier`.
+
+    .. attribute:: oid
+
+        :type: :class:`ObjectIdentifier`
+
+        Returns :attr:`~cryptography.x509.oid.ExtensionOID.POLICY_MAPPINGS`.
+
+
 .. class:: CRLNumber(crl_number)
     :canonical: cryptography.x509.extensions.CRLNumber
 

src/cryptography/x509/__init__.py

@@ -64,6 +64,7 @@
     OCSPNonce,
     PolicyConstraints,
     PolicyInformation,
+    PolicyMappings,
     PrecertificateSignedCertificateTimestamps,
     PrecertPoison,
     PrivateKeyUsagePeriod,
@@ -233,6 +234,7 @@
     "OtherName",
     "PolicyConstraints",
     "PolicyInformation",
+    "PolicyMappings",
     "PrecertPoison",
     "PrecertificateSignedCertificateTimestamps",
     "PrivateKeyUsagePeriod",

src/cryptography/x509/extensions.py

@@ -37,6 +37,7 @@
 )
 from cryptography.x509.name import Name, RelativeDistinguishedName
 from cryptography.x509.oid import (
+    CertificatePoliciesOID,
     CRLEntryExtensionOID,
     ExtensionOID,
     ObjectIdentifier,
@@ -815,6 +816,52 @@ def public_bytes(self) -> bytes:
         return rust_x509.encode_extension_value(self)
 
 
+class PolicyMappings(ExtensionType):
+    oid = ExtensionOID.POLICY_MAPPINGS
+
+    def __init__(
+        self,
+        mappings: Iterable[tuple[ObjectIdentifier, ObjectIdentifier]],
+    ) -> None:
+        mappings = list(mappings)
+        if not mappings:
+            raise ValueError("mappings must be a non-empty list")
+        if not all(
+            isinstance(mapping, tuple)
+            and len(mapping) == 2
+            and all(isinstance(oid, ObjectIdentifier) for oid in mapping)
+            for mapping in mappings
+        ):
+            raise TypeError(
+                "Every item in the mappings list must be a 2-tuple of "
+                "ObjectIdentifier"
+            )
+        if any(
+            CertificatePoliciesOID.ANY_POLICY in mapping
+            for mapping in mappings
+        ):
+            raise ValueError("Policy mappings must not contain anyPolicy")
+
+        self._mappings = mappings
+
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_mappings")
+
+    def __repr__(self) -> str:
+        return f"<PolicyMappings({self._mappings})>"
+
+    def __eq__(self, other: object) -> bool:
+        if not isinstance(other, PolicyMappings):
+            return NotImplemented
+
+        return self._mappings == other._mappings
+
+    def __hash__(self) -> int:
+        return hash(tuple(self._mappings))
+
+    def public_bytes(self) -> bytes:
+        return rust_x509.encode_extension_value(self)
+
+
 class CertificatePolicies(ExtensionType):
     oid = ExtensionOID.CERTIFICATE_POLICIES
 

src/rust/cryptography-x509/src/extensions.rs

@@ -87,6 +87,14 @@ pub struct PolicyConstraints {
     pub inhibit_policy_mapping: Option<u64>,
 }
 
+#[derive(asn1::Asn1Read, asn1::Asn1Write)]
+pub struct PolicyMapping {
+    pub issuer_domain_policy: asn1::ObjectIdentifier,
+    pub subject_domain_policy: asn1::ObjectIdentifier,
+}
+
+pub type PolicyMappings<'a, Op> = <Op as Asn1Operation>::SequenceOfVec<'a, PolicyMapping>;
+
 #[derive(asn1::Asn1Read, asn1::Asn1Write)]
 pub struct AccessDescription<'a> {
     pub access_method: asn1::ObjectIdentifier,

src/rust/cryptography-x509/src/oid.rs

@@ -38,6 +38,7 @@ pub const CERTIFICATE_ISSUER_OID: asn1::ObjectIdentifier = asn1::oid!(2, 5, 29,
 pub const NAME_CONSTRAINTS_OID: asn1::ObjectIdentifier = asn1::oid!(2, 5, 29, 30);
 pub const CRL_DISTRIBUTION_POINTS_OID: asn1::ObjectIdentifier = asn1::oid!(2, 5, 29, 31);
 pub const CERTIFICATE_POLICIES_OID: asn1::ObjectIdentifier = asn1::oid!(2, 5, 29, 32);
+pub const POLICY_MAPPINGS_OID: asn1::ObjectIdentifier = asn1::oid!(2, 5, 29, 33);
 pub const AUTHORITY_KEY_IDENTIFIER_OID: asn1::ObjectIdentifier = asn1::oid!(2, 5, 29, 35);
 pub const POLICY_CONSTRAINTS_OID: asn1::ObjectIdentifier = asn1::oid!(2, 5, 29, 36);
 pub const EXTENDED_KEY_USAGE_OID: asn1::ObjectIdentifier = asn1::oid!(2, 5, 29, 37);

src/rust/src/types.rs

@@ -153,6 +153,8 @@ pub static INHIBIT_ANY_POLICY: LazyPyImport =
 pub static OCSP_NO_CHECK: LazyPyImport = LazyPyImport::new("cryptography.x509", &["OCSPNoCheck"]);
 pub static POLICY_CONSTRAINTS: LazyPyImport =
     LazyPyImport::new("cryptography.x509", &["PolicyConstraints"]);
+pub static POLICY_MAPPINGS: LazyPyImport =
+    LazyPyImport::new("cryptography.x509", &["PolicyMappings"]);
 pub static CERTIFICATE_POLICIES: LazyPyImport =
     LazyPyImport::new("cryptography.x509", &["CertificatePolicies"]);
 pub static SUBJECT_INFORMATION_ACCESS: LazyPyImport =

src/rust/src/x509/certificate.rs

@@ -11,7 +11,7 @@ use cryptography_x509::extensions::{
     Admission, Admissions, AuthorityKeyIdentifier, BasicConstraints, DisplayText,
     DistributionPoint, DistributionPointName, DuplicateExtensionsError, ExtendedKeyUsage,
     Extension, IssuerAlternativeName, KeyUsage, MSCertificateTemplate, NameConstraints,
-    NamingAuthority, PolicyConstraints, PolicyInformation, PolicyQualifierInfo,
+    NamingAuthority, PolicyConstraints, PolicyInformation, PolicyMappings, PolicyQualifierInfo,
     PrivateKeyUsagePeriod, ProfessionInfo, Qualifier, RawExtensions, SequenceOfAccessDescriptions,
     SequenceOfSubtrees, SubjectAlternativeName, UserNotice,
 };
@@ -889,6 +889,17 @@ pub fn parse_cert_ext<'p>(
                 pc.inhibit_policy_mapping,
             ))?))
         }
+        oid::POLICY_MAPPINGS_OID => {
+            let mappings = ext.value::<PolicyMappings<'_, Asn1Read>>()?;
+            let py_mappings = pyo3::types::PyList::empty(py);
+            for mapping in mappings {
+                py_mappings.append((
+                    oid_to_py_oid(py, &mapping.issuer_domain_policy)?,
+                    oid_to_py_oid(py, &mapping.subject_domain_policy)?,
+                ))?;
+            }
+            Ok(Some(types::POLICY_MAPPINGS.get(py)?.call1((py_mappings,))?))
+        }
         oid::OCSP_NO_CHECK_OID => {
             ext.value::<()>()?;
             Ok(Some(types::OCSP_NO_CHECK.get(py)?.call0()?))

src/rust/src/x509/extensions.rs

@@ -595,6 +595,18 @@ pub(crate) fn encode_extension(
             };
             Ok(Some(asn1::write_single(&pc)?))
         }
+        &oid::POLICY_MAPPINGS_OID => {
+            let mut mappings = vec![];
+            for py_mapping in ext.try_iter()? {
+                let py_mapping = py_mapping?;
+                mappings.push(extensions::PolicyMapping {
+                    issuer_domain_policy: py_oid_to_oid(py_mapping.get_item(0)?)?,
+                    subject_domain_policy: py_oid_to_oid(py_mapping.get_item(1)?)?,
+                });
+            }
+            let mappings = asn1::SequenceOfWriter::new(mappings);
+            Ok(Some(asn1::write_single(&mappings)?))
+        }
         &oid::NAME_CONSTRAINTS_OID => {
             let ka_bytes = cryptography_keepalive::KeepAlive::new();
             let ka_str = cryptography_keepalive::KeepAlive::new();

tests/x509/test_x509_ext.py

@@ -28,6 +28,7 @@
 )
 from cryptography.x509.oid import (
     AuthorityInformationAccessOID,
+    CertificatePoliciesOID,
     ExtendedKeyUsageOID,
     ExtensionOID,
     NameOID,
@@ -3124,6 +3125,73 @@ def test_public_bytes(self):
         assert ext.public_bytes() == b"\x30\x03\x81\x01\x00"
 
 
+class TestPolicyMappings:
+    issuer_policy = ObjectIdentifier("1.2.3.4")
+    subject_policy = ObjectIdentifier("1.2.3.5")
+    mapping = ((issuer_policy, subject_policy),)
+
+    def test_invalid_mappings(self):
+        with pytest.raises(TypeError):
+            x509.PolicyMappings(
+                [(self.issuer_policy, typing.cast(typing.Any, "invalid"))]
+            )
+        with pytest.raises(TypeError):
+            x509.PolicyMappings(
+                [typing.cast(typing.Any, (self.issuer_policy,))]
+            )
+
+    def test_empty_mappings(self):
+        with pytest.raises(ValueError):
+            x509.PolicyMappings([])
+
+    @pytest.mark.parametrize("position", [0, 1])
+    def test_any_policy(self, position):
+        mapping = list(self.mapping[0])
+        mapping[position] = CertificatePoliciesOID.ANY_POLICY
+        with pytest.raises(ValueError, match="must not contain anyPolicy"):
+            x509.PolicyMappings([tuple(mapping)])  # type: ignore[list-item]
+
+    def test_iter_len_index(self):
+        mappings = x509.PolicyMappings(self.mapping)
+        assert len(mappings) == 1
+        assert list(mappings) == list(self.mapping)
+
+    def test_repr(self):
+        assert repr(x509.PolicyMappings(self.mapping)) == (
+            "<PolicyMappings([(<ObjectIdentifier(oid=1.2.3.4, name=Unknown "
+            "OID)>, <ObjectIdentifier(oid=1.2.3.5, name=Unknown OID)>)])>"
+        )
+
+    def test_eq_hash(self):
+        iss_to_sub = [(self.issuer_policy, self.subject_policy)]
+        sub_to_iss = [(self.subject_policy, self.issuer_policy)]
+
+        mappings = x509.PolicyMappings(iss_to_sub)
+        mappings2 = x509.PolicyMappings(iss_to_sub)
+        mappings3 = x509.PolicyMappings(sub_to_iss)
+        assert mappings == mappings2
+        assert mappings != mappings3
+        assert mappings != object()
+        assert hash(mappings) == hash(mappings2)
+        assert hash(mappings) != hash(mappings3)
+
+    def test_public_bytes(self):
+        mappings = x509.PolicyMappings(self.mapping)
+        assert mappings.public_bytes() == (
+            b"\x30\x0c\x30\x0a\x06\x03\x2a\x03\x04\x06\x03\x2a\x03\x05"
+        )
+
+    def test_certbuilder(self, rsa_key_2048: rsa.RSAPrivateKey):
+        cert = (
+            _make_certbuilder(rsa_key_2048)
+            .add_extension(x509.PolicyMappings(self.mapping), critical=True)
+            .sign(rsa_key_2048, hashes.SHA256())
+        )
+        ext = cert.extensions.get_extension_for_class(x509.PolicyMappings)
+        assert ext.critical is True
+        assert list(ext.value) == list(self.mapping)
+
+
 class TestAuthorityInformationAccess:
     def test_invalid_descriptions(self):
         with pytest.raises(TypeError):