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Fix OCSP.verify_response() to check cert_status #14

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Fix OCSP.verify_response() to check cert_status #14

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33 changes: 33 additions & 0 deletions pyasice/ocsp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,11 @@
from .exceptions import PyAsiceError
from .tsa import default_get_session

# OCSP certificate status values (RFC 6960)
CERT_STATUS_GOOD = "good"
CERT_STATUS_REVOKED = "revoked"
CERT_STATUS_UNKNOWN = "unknown"


class SKHackedTBSRequestExtension(TBSRequestExtension):
"""A workaround class for compatibility with old java libraries used in SK.ee
Expand All @@ -33,6 +38,18 @@ class OCSPError(PyAsiceError):
pass


class OCSPCertificateRevokedError(OCSPError):
"""The certificate has been revoked."""

pass


class OCSPCertificateUnknownError(OCSPError):
"""The certificate status is unknown to the OCSP responder."""

pass


class OCSP(object):
"""
Certificate validation request via the OCSP protocol, using the asn1crypto/ocspbuilder stack.
Expand Down Expand Up @@ -127,6 +144,22 @@ def verify_response(ocsp_response: Union[OCSPResponse, bytes]):

basic_response: ocsp.BasicOCSPResponse = ocsp_response.basic_ocsp_response

# Check cert_status (the actual certificate validity)
single_response = ocsp_response.response_data["responses"][0]
cert_status = single_response["cert_status"]
status_name = cert_status.name

if status_name == CERT_STATUS_GOOD:
pass # Certificate is valid, continue to signature verification
elif status_name == CERT_STATUS_REVOKED:
revoked_info = cert_status.chosen
revocation_time = revoked_info["revocation_time"].native
raise OCSPCertificateRevokedError(f"Certificate was revoked at {revocation_time}")
elif status_name == CERT_STATUS_UNKNOWN:
raise OCSPCertificateUnknownError("Certificate status is unknown to the OCSP responder")
else:
raise OCSPError(f"Unexpected certificate status: {status_name}")

# Signer's certificate
certs = basic_response["certs"]
cert: ASN1Certificate = certs[0]
Expand Down
53 changes: 51 additions & 2 deletions pyasice/tests/test_ocsp.py
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Original file line number Diff line number Diff line change
@@ -1,13 +1,14 @@
from datetime import datetime
from unittest.mock import Mock, patch

import pytest

from asn1crypto.ocsp import OCSPRequest
from asn1crypto.ocsp import OCSPRequest, OCSPResponse
from asn1crypto.x509 import Certificate as ASN1Certificate
from cryptography.hazmat.primitives.serialization import Encoding
from oscrypto.asymmetric import load_certificate

from pyasice.ocsp import OCSP
from pyasice.ocsp import OCSP, OCSPCertificateRevokedError, OCSPCertificateUnknownError

from .conftest import cert_builder

Expand Down Expand Up @@ -63,3 +64,51 @@ def test_ocsp_validate(demo_ocsp_response):

mock_build_ocsp_request.assert_called_once_with(b"subject cert", b"issuer cert", b"some-signature")
mock_post.assert_called_once()


def test_verify_response_rejects_revoked_status(demo_ocsp_response):
ocsp_response = OCSPResponse.load(demo_ocsp_response)
real_response_data = ocsp_response.response_data

mock_cert_status = Mock()
mock_cert_status.name = "revoked"
mock_revoked_info = Mock()
mock_revoked_info.__getitem__ = Mock(
side_effect=lambda key: Mock(native=datetime(2024, 1, 15, 12, 0, 0)) if key == "revocation_time" else None
)
mock_cert_status.chosen = mock_revoked_info

mock_single_response = Mock()
mock_single_response.__getitem__ = Mock(side_effect=lambda key: mock_cert_status if key == "cert_status" else None)

mock_response_data = Mock()
mock_response_data.__getitem__ = Mock(side_effect=lambda key: [mock_single_response] if key == "responses" else None)
mock_response_data.dump = real_response_data.dump

with patch.object(OCSPResponse, "response_data", new_callable=lambda: property(lambda self: mock_response_data)):
with pytest.raises(OCSPCertificateRevokedError, match="Certificate was revoked at"):
OCSP.verify_response(ocsp_response)


def test_verify_response_rejects_unknown_status(demo_ocsp_response):
ocsp_response = OCSPResponse.load(demo_ocsp_response)
real_response_data = ocsp_response.response_data

mock_cert_status = Mock()
mock_cert_status.name = "unknown"

mock_single_response = Mock()
mock_single_response.__getitem__ = Mock(side_effect=lambda key: mock_cert_status if key == "cert_status" else None)

mock_response_data = Mock()
mock_response_data.__getitem__ = Mock(side_effect=lambda key: [mock_single_response] if key == "responses" else None)
mock_response_data.dump = real_response_data.dump

with patch.object(OCSPResponse, "response_data", new_callable=lambda: property(lambda self: mock_response_data)):
with pytest.raises(OCSPCertificateUnknownError, match="Certificate status is unknown"):
OCSP.verify_response(ocsp_response)


def test_verify_response_accepts_good_status(demo_ocsp_response):
# The demo_ocsp_response has a 'good' status
OCSP.verify_response(demo_ocsp_response)