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(EC)DSA signature fix #670

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merged 4 commits into from
Jul 20, 2017
Merged

(EC)DSA signature fix #670

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8cb1d25
Write a test - signatures with EC keys (#609)
Jul 19, 2017
36f8d81
Ask for signature length before allocating a buffer.
Jul 19, 2017
0be1eee
change approach to EVP_PKEY_size and add changelog
reaperhulk Jul 20, 2017
e9b6f82
add a small assert
reaperhulk Jul 20, 2017
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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).
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@reaperhulk
Jakub Zakrzewski authored and reaperhulk committed Jul 20, 2017
commit 36f8d81b1d82add6ee6dcfbc80cc50c52127c722
10 changes: 7 additions & 3 deletions src/OpenSSL/crypto.py
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Expand Up @@ -2801,9 +2801,13 @@ def sign(pkey, data, digest):
_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*")
# obtain the length of the signature.
signature_length = _ffi.new("unsigned int[]", 1)
len_result = _lib.EVP_SignFinal(
md_ctx, _ffi.NULL, signature_length, pkey._pkey)
_openssl_assert(len_result == 1)

signature_buffer = _ffi.new("unsigned char[]", signature_length[0])
final_result = _lib.EVP_SignFinal(
md_ctx, signature_buffer, signature_length, pkey._pkey)
_openssl_assert(final_result == 1)
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