3 files changed, 9 insertions, 4 deletions
diff --git a/src/_cffi_src/openssl/bignum.py b/src/_cffi_src/openssl/bignum.py
index ae035007..455afdc1 100644
--- a/src/_cffi_src/openssl/bignum.py
+++ b/src/_cffi_src/openssl/bignum.py
@@ -71,6 +71,8 @@ int BN_mask_bits(BIGNUM *, int);
 """
 
 MACROS = """
+int BN_num_bytes(const BIGNUM *);
+
 int BN_zero(BIGNUM *);
 int BN_one(BIGNUM *);
 int BN_mod(BIGNUM *, const BIGNUM *, const BIGNUM *, BN_CTX *);
diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index 0dd9a2e3..c0c9ebe2 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -919,17 +919,14 @@ class Backend(object):
         assert bn != self._ffi.NULL
         if six.PY3:
             # Python 3 has constant time from_bytes, so use that.
-
-            bn_num_bytes = (self._lib.BN_num_bits(bn) + 7) // 8
+            bn_num_bytes = self._lib.BN_num_bytes(bn)
             bin_ptr = self._ffi.new("unsigned char[]", bn_num_bytes)
             bin_len = self._lib.BN_bn2bin(bn, bin_ptr)
             # A zero length means the BN has value 0
             self.openssl_assert(bin_len >= 0)
             return int.from_bytes(self._ffi.buffer(bin_ptr)[:bin_len], "big")
-
         else:
             # Under Python 2 the best we can do is hex()
-
             hex_cdata = self._lib.BN_bn2hex(bn)
             self.openssl_assert(hex_cdata != self._ffi.NULL)
             hex_str = self._ffi.string(hex_cdata)
diff --git a/src/cryptography/x509/extensions.py b/src/cryptography/x509/extensions.py
index 10b8da41..4dee72f0 100644
--- a/src/cryptography/x509/extensions.py
+++ b/src/cryptography/x509/extensions.py
@@ -961,6 +961,9 @@ class IssuerAlternativeName(object):
     def __ne__(self, other):
         return not self == other
 
+    def __getitem__(self, idx):
+        return self._general_names[idx]
+
 
 @utils.register_interface(ExtensionType)
 class CertificateIssuer(object):
@@ -990,6 +993,9 @@ class CertificateIssuer(object):
     def __ne__(self, other):
         return not self == other
 
+    def __getitem__(self, idx):
+        return self._general_names[idx]
+
 
 @utils.register_interface(ExtensionType)
 class CRLReason(object):