Getting exception “RSA/OAEP-MGF1(SHA-1): ciphertext length of 154 doesn't match the required length of 192 for this key” during decrypting session key

问题

I am getting "RSA/OAEP-MGF1(SHA-1): ciphertext length of 154 doesn't match the required length of 192 for this key" when I try to decrypt encrypted session key which uses crypto++ library.

Following are code snippets for the same:

std::string encrypt_session_key(PAES_KEY_WITH_IV pKey)
{
        std::string ciphered;
        CryptoPP::SecByteBlock block(pKey->key.size());

        try {
                CryptoPP::RSAES< CryptoPP::OAEP<CryptoPP::SHA> >::Encryptor enc(RSA_master_pubKey);
                enc.Encrypt(rng, pKey->key, pKey->key.size(), block);
                ciphered.assign((char *)block.BytePtr());
        }
        catch (const CryptoPP::Exception& e)
        {
                std::cerr << e.what() << std::endl;
                b_success = false;
        }
        return ciphered;
}

PAES_KEY_WITH_IV decrypt_session_key(std::string & ciphered)
{
        CryptoPP::SecByteBlock rec(ciphered.size());
        CryptoPP::SecByteBlock block((const byte *)ciphered.data(), ciphered.size());
        PAES_KEY_WITH_IV pKey = new AES_KEY_WITH_IV;
        try {
                CryptoPP::RSAES< CryptoPP::OAEP<CryptoPP::SHA> >::Decryptor dec(RSA_master_privKey);
                dec.Decrypt(rng, block, block.size(), rec);

                pKey->key = rec;
        }
        catch (const CryptoPP::Exception& e)
        {
                std::cerr << e.what() << std::endl;
                b_success = false;
        }
        return pKey;
}

Here I have given both code for encrypting and decrypting session key.

Can some one tell me Why I am getting above exception ?

Please note that : I am using Version 5.6.3 of crypto++ library.

Thanks in Advance.

回答1:

ciphered.assign((char *)block.BytePtr());

The cipher text will likely have an embedded NULL. You cannot treat it like a char*.

Use the fourth append overload instead, which provides the pointer and the length of a buffer:

ciphered.assign((char *)block.BytePtr(), block.SizeInBytes());

You are still casting it to a char* to get it into the std::string object. But its really a more like a Rope - its a string of octets without character traits.

来源：https://stackoverflow.com/questions/38545180/getting-exception-rsa-oaep-mgf1sha-1-ciphertext-length-of-154-doesnt-match

标签

c++

crypto++