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feat: PKCS#7 extension policies
added tests accordingly adapted the pkcs7 certificate adapted EE policy do not know if a CA policy is needed! added SAN checking (incomplete though)
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‎docs/development/test-vectors.rst‎

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@@ -1001,6 +1001,8 @@ Custom PKCS7 Test Vectors
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* ``pkcs7/enveloped-no-content.der``- A DER encoded PKCS7 file with
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enveloped data, without encrypted content, with key encrypted under the
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public key of ``x509/custom/ca/rsa_ca.pem``.
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* ``pkcs7/ca.pem`` - A certificate adapted for S/MIME signature & verification.
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Its private key is ``pkcs7/ca_key.pem`` .
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Custom OpenSSH Test Vectors
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~~~~~~~~~~~~~~~~~~~~~~~~~~~

‎src/cryptography/hazmat/primitives/serialization/pkcs7.py‎

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@@ -21,6 +21,12 @@
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algorithms,
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)
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from cryptography.utils import _check_byteslike
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from cryptography.x509 import Certificate
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from cryptography.x509.verification import (
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Criticality,
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ExtensionPolicy,
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Policy,
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)
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load_pem_pkcs7_certificates = rust_pkcs7.load_pem_pkcs7_certificates
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@@ -53,6 +59,108 @@ class PKCS7Options(utils.Enum):
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NoCerts = "Don't embed signer certificate"
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def pkcs7_x509_extension_policies() -> tuple[ExtensionPolicy, ExtensionPolicy]:
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"""
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Gets the default X.509 extension policy for S/MIME. Some specifications
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that differ from the standard ones:
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- Certificates used as end entities (i.e., the cert used to sign
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a PKCS#7/SMIME message) should not have ca=true in their basic
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constraints extension.
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- EKU_CLIENT_AUTH_OID is not required
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- EKU_EMAIL_PROTECTION_OID is required
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"""
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# CA policy - TODO: is there any?
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ca_policy = ExtensionPolicy.webpki_defaults_ca()
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# EE policy
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def _validate_basic_constraints(
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policy: Policy, cert: Certificate, bc: x509.BasicConstraints | None
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) -> None:
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if bc is not None and bc.ca:
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raise ValueError("Basic Constraints CA must be False.")
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def _validate_key_usage(
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policy: Policy, cert: Certificate, ku: x509.KeyUsage | None
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) -> None:
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if ku is not None:
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# Content commitment used to be named non repudiation
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if not ku.digital_signature or ku.content_commitment:
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raise ValueError(
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"Key Usage, if specified, must have at least one of the "
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"digital signature or content commitment (formerly non "
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"repudiation) bits set."
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)
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def _validate_subject_alternative_name(
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policy: Policy,
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cert: Certificate,
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san: x509.SubjectAlternativeName,
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) -> None:
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"""
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For each general name in the SAN, for those which are email addresses:
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- If it is an RFC822Name, general part must be ascii.
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- If it is an OtherName, general part must be non-ascii.
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"""
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for general_name in san:
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if (
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isinstance(general_name, x509.RFC822Name)
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and "@" in general_name.value
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and not general_name.value.split("@")[0].isascii()
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):
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raise ValueError(
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f"RFC822Name {general_name.value} contains non-ASCII "
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"characters."
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)
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if (
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isinstance(general_name, x509.OtherName)
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and "@" in general_name.value.decode()
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and general_name.value.decode().split("@")[0].isascii()
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):
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raise ValueError(
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f"OtherName {general_name.value.decode()} is ASCII, "
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"so must be stored in RFC822Name."
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)
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def _validate_extended_key_usage(
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policy: Policy, cert: Certificate, eku: x509.ExtendedKeyUsage | None
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) -> None:
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if eku is not None:
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ep = x509.ExtendedKeyUsageOID.EMAIL_PROTECTION in eku # type: ignore[attr-defined]
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aeku = x509.ExtendedKeyUsageOID.ANY_EXTENDED_KEY_USAGE in eku # type: ignore[attr-defined]
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if not (ep or aeku):
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raise ValueError(
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"Extended Key Usage, if specified, must include "
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"emailProtection or anyExtendedKeyUsage."
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)
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ee_policy = (
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ExtensionPolicy.webpki_defaults_ee()
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.may_be_present(
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x509.BasicConstraints,
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Criticality.AGNOSTIC,
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_validate_basic_constraints,
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)
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.may_be_present(
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x509.KeyUsage,
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Criticality.CRITICAL,
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_validate_key_usage,
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)
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.require_present(
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x509.SubjectAlternativeName,
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Criticality.AGNOSTIC,
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_validate_subject_alternative_name,
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)
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.may_be_present(
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x509.ExtendedKeyUsage,
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Criticality.AGNOSTIC,
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_validate_extended_key_usage,
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)
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)
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return ca_policy, ee_policy
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class PKCS7SignatureBuilder:
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def __init__(
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self,

‎tests/hazmat/primitives/test_pkcs7.py‎

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@@ -18,6 +18,11 @@
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from cryptography.hazmat.primitives.asymmetric import ed25519, padding, rsa
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from cryptography.hazmat.primitives.ciphers import algorithms
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from cryptography.hazmat.primitives.serialization import pkcs7
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from cryptography.x509.verification import (
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PolicyBuilder,
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Store,
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VerificationError,
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)
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from tests.x509.test_x509 import _generate_ca_and_leaf
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from ...hazmat.primitives.fixtures_rsa import (
@@ -125,20 +130,129 @@ def test_load_pkcs7_empty_certificates(self):
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def _load_cert_key():
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key = load_vectors_from_file(
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os.path.join("x509", "custom", "ca", "ca_key.pem"),
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os.path.join("pkcs7", "ca_key.pem"),
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lambda pemfile: serialization.load_pem_private_key(
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pemfile.read(), None, unsafe_skip_rsa_key_validation=True
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),
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mode="rb",
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)
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cert = load_vectors_from_file(
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os.path.join("x509", "custom", "ca", "ca.pem"),
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os.path.join("pkcs7", "ca.pem"),
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loader=lambda pemfile: x509.load_pem_x509_certificate(pemfile.read()),
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mode="rb",
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)
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return cert, key
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class TestPKCS7VerifyCertificate:
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def test_verify_pkcs7_certificate(self):
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certificate, _ = _load_cert_key()
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ca_policy, ee_policy = pkcs7.pkcs7_x509_extension_policies()
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verifier = (
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PolicyBuilder()
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.store(Store([certificate]))
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.extension_policies(ca_policy, ee_policy)
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.build_client_verifier()
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)
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verifier.verify(certificate, [])
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@pytest.fixture(name="certificate_builder")
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def fixture_certificate_builder(self) -> x509.CertificateBuilder:
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certificate, private_key = _load_cert_key()
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return (
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x509.CertificateBuilder()
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.serial_number(certificate.serial_number)
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.subject_name(certificate.subject)
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.issuer_name(certificate.issuer)
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.public_key(private_key.public_key())
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.not_valid_before(certificate.not_valid_before)
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.not_valid_after(certificate.not_valid_after)
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)
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def test_verify_pkcs7_certificate_wrong_bc(self, certificate_builder):
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certificate, private_key = _load_cert_key()
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# Add an invalid extension
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extension = x509.BasicConstraints(ca=True, path_length=None)
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certificate_builder = certificate_builder.add_extension(
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extension, True
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)
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# Build the certificate
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pkcs7_certificate = certificate_builder.sign(
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private_key, certificate.signature_hash_algorithm, None
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)
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# Verify the certificate
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self.verify_invalid_pkcs7_certificate(pkcs7_certificate)
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def test_verify_pkcs7_certificate_wrong_ku(self, certificate_builder):
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certificate, private_key = _load_cert_key()
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# Add an invalid extension
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extension = x509.KeyUsage(
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digital_signature=False,
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content_commitment=False,
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key_encipherment=True,
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data_encipherment=True,
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key_agreement=True,
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key_cert_sign=True,
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crl_sign=True,
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encipher_only=False,
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decipher_only=False,
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)
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certificate_builder = certificate_builder.add_extension(
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extension, True
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)
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# Build the certificate
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pkcs7_certificate = certificate_builder.sign(
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private_key, certificate.signature_hash_algorithm, None
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)
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# Verify the certificate
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self.verify_invalid_pkcs7_certificate(pkcs7_certificate)
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def test_verify_pkcs7_certificate_wrong_eku(self, certificate_builder):
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certificate, private_key = _load_cert_key()
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# Add an invalid extension
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usages = [x509.ExtendedKeyUsageOID.CLIENT_AUTH] # type: ignore[attr-defined]
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extension = x509.ExtendedKeyUsage(usages)
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certificate_builder = certificate_builder.add_extension(
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extension, True
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)
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# Add an invalid extension
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usages = [x509.ExtendedKeyUsageOID.CLIENT_AUTH] # type: ignore[attr-defined]
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extension = x509.ExtendedKeyUsage(usages)
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certificate_builder = certificate_builder.add_extension(
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extension, True
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)
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# Build the certificate
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pkcs7_certificate = certificate_builder.sign(
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private_key, certificate.signature_hash_algorithm, None
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)
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# Verify the certificate
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self.verify_invalid_pkcs7_certificate(pkcs7_certificate)
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@staticmethod
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def verify_invalid_pkcs7_certificate(certificate: x509.Certificate):
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ca_policy, ee_policy = pkcs7.pkcs7_x509_extension_policies()
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verifier = (
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PolicyBuilder()
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.store(Store([certificate]))
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.extension_policies(ca_policy, ee_policy)
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.build_client_verifier()
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)
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with pytest.raises(VerificationError):
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verifier.verify(certificate, [])
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@pytest.mark.supported(
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only_if=lambda backend: backend.pkcs7_supported(),
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skip_message="Requires OpenSSL with PKCS7 support",

‎vectors/cryptography_vectors/pkcs7/ca.pem‎

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-----BEGIN CERTIFICATE-----
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MIIBhjCCASygAwIBAgICAwkwCgYIKoZIzj0EAwIwJzELMAkGA1UEBhMCVVMxGDAW
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BgNVBAMMD2NyeXB0b2dyYXBoeSBDQTAgFw0xNzAxMDEwMTAwMDBaGA8yMTAwMDEw
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MTAwMDAwMFowJzELMAkGA1UEBhMCVVMxGDAWBgNVBAMMD2NyeXB0b2dyYXBoeSBD
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QTBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABBj/z7v5Obj13cPuwECLBnUGq0/N
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2CxSJE4f4BBGZ7VfFblivTvPDG++Gve0oQ+0uctuhrNQ+WxRv8GC177F+QWjRjBE
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MCEGA1UdEQEB/wQXMBWBE2V4YW1wbGVAZXhhbXBsZS5jb20wHwYDVR0jBBgwFoAU
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/Ou02BLyyT2Zwzxn9H03feYT7fowCgYIKoZIzj0EAwIDSAAwRQIgUwIdC0Emkd6f
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17DeOXTlmTAhwSDJ2FTuyHESwei7wJcCIQCnr9NpBxbtJfEzxHGGyd7PxgpOLi5u
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rk+8QfzGMmg/fw==
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-----END CERTIFICATE-----

‎vectors/cryptography_vectors/pkcs7/ca_key.pem‎

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-----BEGIN PRIVATE KEY-----
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MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgA8Zqz5vLeR0ePZUe
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jBfdyMmnnI4U5uAJApWTsMn/RuWhRANCAAQY/8+7+Tm49d3D7sBAiwZ1BqtPzdgs
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UiROH+AQRme1XxW5Yr07zwxvvhr3tKEPtLnLboazUPlsUb/Bgte+xfkF
5+
-----END PRIVATE KEY-----

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