Merge pull request #1780 from reaperhulk/allow-zero-bn
allow zero value bn using _bn_to_int in the openssl backend
diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index 59503bd..60aa453 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -327,7 +327,8 @@
bn_num_bytes = (self._lib.BN_num_bits(bn) + 7) // 8
bin_ptr = self._ffi.new("unsigned char[]", bn_num_bytes)
bin_len = self._lib.BN_bn2bin(bn, bin_ptr)
- assert bin_len > 0
+ # A zero length means the BN has value 0
+ assert bin_len >= 0
assert bin_ptr != self._ffi.NULL
return int.from_bytes(self._ffi.buffer(bin_ptr)[:bin_len], "big")
diff --git a/tests/hazmat/backends/test_openssl.py b/tests/hazmat/backends/test_openssl.py
index 73316f8..867c5dd 100644
--- a/tests/hazmat/backends/test_openssl.py
+++ b/tests/hazmat/backends/test_openssl.py
@@ -210,6 +210,10 @@
assert bn == bn_ptr
assert backend._bn_to_int(bn_ptr) == value
+ def test_bn_to_int(self):
+ bn = backend._int_to_bn(0)
+ assert backend._bn_to_int(bn) == 0
+
class TestOpenSSLRandomEngine(object):
def teardown_method(self, method):