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pythonpycryptocrypto++

Decrypt cipher text encrypted with PyCrypto using cryptopp

My server encrypts files using pycrypto with AES in CTR mode. My counter is a simple counter like this:

\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01
\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02
\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x03

I wanna decrypt the cipher text with c++'s cryptopp library in my clients. How should I do so?

Python code:

encryptor = AES.new(
    CRYPTOGRAPHY_KEY,
    AES.MODE_CTR,
    counter=Counter.new(128),
)
cipher = encryptor.encrypt(plain_text)

C++ code so far:

byte ctr[] = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01"
mDecryptor = new CryptoPP::CTR_Mode<CryptoPP::AES>::Decryption(key, 32, ctr);
std::string plain;
CryptoPP::StringSource(std::string(data, len), true, new CryptoPP::StreamTransformationFilter(*mDecryptor, new CryptoPP::StringSink(plain)));

but after running this plain is garbage.

Update:

Sample encrypted data you can try to decrypt with crypto++ so that you can help me even if you don't know python and you're just experienced with crypto++:

Try to decrypt this base64 encoded text:

2t0lLuSBY7NkfK5I4kML0qjcZl3xHcEQBPbDo4TbvQaXuUT8W7lNbRCl8hfSGJA00wgUXhAjQApcuTCZckb9e6EVOwsa+eLY78jo2CqYWzhGez9zn0D2LMKNmZQi88WuTFVw9r1GSKIHstoDWvn54zISmr/1JgjC++mv2yRvatcvs8GhcsZVZT8dueaNK6tXLd1fQumhXCjpMyFjOlPWVTBPjlnsC5Uh98V/YiIa898SF4dwfjtDrG/fQZYmWUzJ8k2AslYLKGs=

with this key:

12341234123412341234123412341234

with counter function described in the beginning of this post using crypto++. If you succeed post the decrypted text (which contains only numbers) and your solution please.

Update2: I'm not providing an IV in python code, the python module ignores IV. I the IV thing is what causing the problem.

Solution

  • As I read their source codes I can say PyCrypto and Crypto++ Both are perfect libraries for cryptography for Python and C++. The problem was that I was prefixing the encrypted data with some meta information about file and I totally forgot about that, after handling these meta data in client Crypto++ decrypted my files.

    As I didn't find this documented explicitly anywhere (not even in Wikipedia) I write it here: Any combination of Nonce, IV and Counter like concatenation, xor, or likes will work for CTR mode, but the standard that most libraries implement is to concatenate these values in order. So the value that is used in block cipher algorithm is usually: Nonce + IV + Counter. And counter usually starts from 1 (not 0).