add tbsCertList and signature interfaces to CRLs

docs/x509/reference.rst

@@ -504,6 +504,26 @@ X.509 CRL (Certificate Revocation List) Object
 
         The extensions encoded in the CRL.
 
+    .. attribute:: signature
+
+        .. versionadded:: 1.2
+
+        :type: bytes
+
+        The bytes of the CRL's signature.
+
+    .. attribute:: tbs_certlist_bytes
+
+        .. versionadded:: 1.2
+
+        :type: bytes
+
+        The DER encoded bytes payload (as defined by :rfc:`5280`) that is hashed
+        and then signed by the private key of the CRL's issuer. This data may be
+        used to validate a signature, but use extreme caution as CRL validation
+        is a complex problem that involves much more than just signature checks.
+
+
 X.509 Certificate Builder
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 

src/_cffi_src/openssl/x509.py

@@ -65,6 +65,7 @@
 typedef struct {
     X509_CRL_INFO *crl;
     X509_ALGOR *sig_alg;
+    ASN1_BIT_STRING *signature;
     ...;
 } X509_CRL;
 
@@ -259,6 +260,8 @@
 
 MACROS = """
 int i2d_X509_CINF(X509_CINF *, unsigned char **);
+int i2d_X509_CRL_INFO(X509_CRL_INFO *, unsigned char **);
+
 long X509_get_version(X509 *);
 
 ASN1_TIME *X509_get_notBefore(X509 *);

src/cryptography/hazmat/backends/openssl/x509.py

@@ -818,6 +818,21 @@ def last_update(self):
         self._backend.openssl_assert(lu != self._backend._ffi.NULL)
         return self._backend._parse_asn1_time(lu)
 
+    @property
+    def signature(self):
+        return self._backend._asn1_string_to_bytes(self._x509_crl.signature)
+
+    @property
+    def tbs_certlist_bytes(self):
+        pp = self._backend._ffi.new("unsigned char **")
+        # the X509_CRL_INFO struct holds the tbsCertList data
+        res = self._backend._lib.i2d_X509_CRL_INFO(self._x509_crl.crl, pp)
+        self._backend.openssl_assert(res > 0)
+        pp = self._backend._ffi.gc(
+            pp, lambda pointer: self._backend._lib.OPENSSL_free(pointer[0])
+        )
+        return self._backend._ffi.buffer(pp[0], res)[:]
+
     def _revoked_certificates(self):
         revoked = self._backend._lib.X509_CRL_get_REVOKED(self._x509_crl)
         self._backend.openssl_assert(revoked != self._backend._ffi.NULL)

src/cryptography/x509/base.py

@@ -194,6 +194,18 @@ def extensions(self):
         Returns an Extensions object containing a list of CRL extensions.
         """
 
+    @abc.abstractproperty
+    def signature(self):
+        """
+        Returns the signature bytes.
+        """
+
+    @abc.abstractproperty
+    def tbs_certlist_bytes(self):
+        """
+        Returns the tbsCertList payload bytes as defined in RFC 5280.
+        """
+
     @abc.abstractmethod
     def __eq__(self, other):
         """

tests/test_x509.py

@@ -184,6 +184,44 @@ def test_extensions(self, backend):
         with pytest.raises(NotImplementedError):
             crl.extensions
 
+    def test_signature(self, backend):
+        crl = _load_cert(
+            os.path.join("x509", "custom", "crl_all_reasons.pem"),
+            x509.load_pem_x509_crl,
+            backend
+        )
+
+        assert crl.signature == binascii.unhexlify(
+            b"536a5a0794f68267361e7bc2f19167a3e667a2ab141535616855d8deb2ba1af"
+            b"9fd4546b1fe76b454eb436af7b28229fedff4634dfc9dd92254266219ae0ea8"
+            b"75d9ff972e9a2da23d5945f073da18c50a4265bfed9ca16586347800ef49dd1"
+            b"6856d7265f4f3c498a57f04dc04404e2bd2e2ada1f5697057aacef779a18371"
+            b"c621edc9a5c2b8ec1716e8fa22feeb7fcec0ce9156c8d344aa6ae8d1a5d99d0"
+            b"9386df36307df3b63c83908f4a61a0ff604c1e292ad63b349d1082ddd7ae1b7"
+            b"c178bba995523ec6999310c54da5706549797bfb1230f5593ba7b4353dade4f"
+            b"d2be13a57580a6eb20b5c4083f000abac3bf32cd8b75f23e4c8f4b3a79e1e2d"
+            b"58a472b0"
+        )
+
+    def test_tbs_certlist_bytes(self, backend):
+        crl = _load_cert(
+            os.path.join("x509", "PKITS_data", "crls", "GoodCACRL.crl"),
+            x509.load_der_x509_crl,
+            backend
+        )
+
+        ca_cert = _load_cert(
+            os.path.join("x509", "PKITS_data", "certs", "GoodCACert.crt"),
+            x509.load_der_x509_certificate,
+            backend
+        )
+
+        verifier = ca_cert.public_key().verifier(
+            crl.signature, padding.PKCS1v15(), crl.signature_hash_algorithm
+        )
+        verifier.update(crl.tbs_certlist_bytes)
+        verifier.verify()
+
 
 @pytest.mark.requires_backend_interface(interface=X509Backend)
 class TestRevokedCertificate(object):