(EC)DSA signature fix (#670)
* Write a test - signatures with EC keys (#609)
* Ask for signature length before allocating a buffer.
This fixes a potential heap buffer overflow that may happen when a signature
is longer than the private key, as with X9.62 ECDSA (#609).
* change approach to EVP_PKEY_size and add changelog
* add a small assert
diff --git a/src/OpenSSL/crypto.py b/src/OpenSSL/crypto.py
index 20cf183..4f7e4d8 100644
--- a/src/OpenSSL/crypto.py
+++ b/src/OpenSSL/crypto.py
@@ -2801,9 +2801,10 @@
_lib.EVP_SignInit(md_ctx, digest_obj)
_lib.EVP_SignUpdate(md_ctx, data, len(data))
- pkey_length = (PKey.bits(pkey) + 7) // 8
- signature_buffer = _ffi.new("unsigned char[]", pkey_length)
- signature_length = _ffi.new("unsigned int*")
+ length = _lib.EVP_PKEY_size(pkey._pkey)
+ _openssl_assert(length > 0)
+ signature_buffer = _ffi.new("unsigned char[]", length)
+ signature_length = _ffi.new("unsigned int *")
final_result = _lib.EVP_SignFinal(
md_ctx, signature_buffer, signature_length, pkey._pkey)
_openssl_assert(final_result == 1)