Support Subject Alternative Name in the OpenSSL backend

Adds only DNS support first

2 files changed, 47 insertions, 0 deletions

diff --git a/src/cryptography/hazmat/backends/openssl/x509.py b/src/cryptography/hazmat/backends/openssl/x509.py
index 57e6146b..363d3df1 100644
--- a/src/cryptography/hazmat/backends/openssl/x509.py
+++ b/src/cryptography/hazmat/backends/openssl/x509.py
@@ -15,6 +15,8 @@ from __future__ import absolute_import, division, print_function
 
 import datetime
 
+import idna
+
 from cryptography import utils, x509
 from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.primitives import hashes
@@ -57,6 +59,14 @@ def _build_x509_name(backend, x509_name):
     return x509.Name(attributes)
 
 
+def _build_general_name(backend, gn):
+    if gn.type == backend._lib.GEN_DNS:
+        data = backend._ffi.buffer(
+            gn.d.dNSName.data, gn.d.dNSName.length
+        )[:].decode("ascii")
+        return x509.DNSName(idna.decode(data))
+
+
 @utils.register_interface(x509.Certificate)
 class _Certificate(object):
     def __init__(self, backend, x509):
@@ -173,6 +183,8 @@ class _Certificate(object):
                 value = self._build_subject_key_identifier(ext)
             elif oid == x509.OID_KEY_USAGE:
                 value = self._build_key_usage(ext)
+            elif oid == x509.OID_SUBJECT_ALTERNATIVE_NAME:
+                value = self._build_subject_alt_name(ext)
             elif critical:
                 raise x509.UnsupportedExtension(
                     "{0} is not currently supported".format(oid), oid
@@ -254,6 +266,24 @@ class _Certificate(object):
             decipher_only
         )
 
+    def _build_subject_alt_name(self, ext):
+        gns = self._backend._ffi.cast(
+            "GENERAL_NAMES *", self._backend._lib.X509V3_EXT_d2i(ext)
+        )
+        assert gns != self._backend._ffi.NULL
+        gns = self._backend._ffi.gc(gns, self._backend._lib.GENERAL_NAMES_free)
+        num = self._backend._lib.sk_GENERAL_NAME_num(gns)
+        general_names = []
+
+        for i in range(0, num):
+            gn = self._backend._lib.sk_GENERAL_NAME_value(gns, i)
+            assert gn != self._backend._ffi.NULL
+            value = _build_general_name(self._backend, gn)
+
+            general_names.append(value)
+
+        return x509.SubjectAlternativeName(general_names)
+
 
 @utils.register_interface(x509.CertificateSigningRequest)
 class _CertificateSigningRequest(object):
diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index cdc0e430..9e4b5eea 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -70,6 +70,19 @@ _OID_NAMES = {
 }
 
 
+_GENERAL_NAMES = {
+    0: "otherName",
+    1: "rfc822Name",
+    2: "dNSName",
+    3: "x400Address",
+    4: "directoryName",
+    5: "ediPartyName",
+    6: "uniformResourceIdentifier",
+    7: "iPAddress",
+    8: "registeredID",
+}
+
+
 class Version(Enum):
     v1 = 0
     v3 = 2
@@ -115,6 +128,10 @@ class ExtensionNotFound(Exception):
         self.oid = oid
 
 
+class UnsupportedGeneralNameType(Exception):
+    pass
+
+
 class NameAttribute(object):
     def __init__(self, oid, value):
         if not isinstance(oid, ObjectIdentifier):