add subjectkeyidentifier support

2 files changed, 38 insertions, 0 deletions

diff --git a/src/cryptography/hazmat/backends/openssl/x509.py b/src/cryptography/hazmat/backends/openssl/x509.py
index 6a7032ba..8b77a11b 100644
--- a/src/cryptography/hazmat/backends/openssl/x509.py
+++ b/src/cryptography/hazmat/backends/openssl/x509.py
@@ -170,6 +170,8 @@ class _Certificate(object):
                 )
             elif oid == x509.OID_BASIC_CONSTRAINTS:
                 value = self._build_basic_constraints(ext)
+            elif oid == x509.OID_SUBJECT_KEY_IDENTIFIER:
+                value = self._build_subject_key_identifier(ext)
             elif oid == x509.OID_KEY_USAGE and critical:
                 # TODO: remove this obviously.
                 warnings.warn(
@@ -217,6 +219,16 @@ class _Certificate(object):
 
         return x509.BasicConstraints(ca, path_length)
 
+    def _build_subject_key_identifier(self, ext):
+        asn1_string = self._backend._lib.X509V3_EXT_d2i(ext)
+        assert asn1_string != self._backend._ffi.NULL
+        asn1_string = self._backend._ffi.cast(
+            "ASN1_OCTET_STRING *", asn1_string
+        )
+        return x509.SubjectKeyIdentifier(
+            self._backend._ffi.buffer(asn1_string.data, asn1_string.length)[:]
+        )
+
 
 @utils.register_interface(x509.CertificateSigningRequest)
 class _CertificateSigningRequest(object):
diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index 697d7d6e..df37934a 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -5,6 +5,7 @@
 from __future__ import absolute_import, division, print_function
 
 import abc
+import binascii
 from enum import Enum
 
 import six
@@ -346,6 +347,31 @@ class KeyUsage(object):
             return self._decipher_only
 
 
+class SubjectKeyIdentifier(object):
+    def __init__(self, digest):
+        self._digest = digest
+
+    digest = utils.read_only_property("_digest")
+
+    @property
+    def hexdigest(self):
+        return binascii.hexlify(self.digest).decode("ascii")
+
+    def __repr__(self):
+        return "<SubjectKeyIdentifier(value={0})>".format(self.hexdigest)
+
+    def __eq__(self, other):
+        if not isinstance(other, SubjectKeyIdentifier):
+            return NotImplemented
+
+        return (
+            self.digest == other.digest
+        )
+
+    def __ne__(self, other):
+        return not self == other
+
+
 OID_COMMON_NAME = ObjectIdentifier("2.5.4.3")
 OID_COUNTRY_NAME = ObjectIdentifier("2.5.4.6")
 OID_LOCALITY_NAME = ObjectIdentifier("2.5.4.7")