Why can't I verify a C++ signature made in Python?

Question

Python

I create public private keys in Python, after which I sign a private string, send a signature hex and a public key over the network, on the other side I check with C ++ code or Openssl / RSA_verify. And writes that the signature is not valid. I tried on the pluses to make the signature the same private and the same line, then the hex from the signature is generally different. I understand the algorithms are different for different lib / languages?
Here is how I create keys in Python:

public, private = rsa.newkeys(len_key)
    pub = public.save_pkcs1()
    pri = private.save_pkcs1()

I'm making a signature

signatur = rsa.sign(data, rsa.PrivateKey.load_pkcs1(privateKey), 'SHA-512')

I check on the pluses:

RSA_verify(NID_sha512, (const unsigned char*) text.c_str(), text.length(), (const unsigned char*) sign.c_str(), sign.length(), publicRSA);

I tried to use pyOpenSSL in Python, but it did not help.
Who will tell you what? what's the bug?

Answer 1

Because the RSA_verify input should be a hash of the data, not the data itself.

std::string text = "hello world";
SHA512_CTX sha_ctx = { 0 };
unsigned char digest[SHA512_DIGEST_LENGTH];
SHA512_Init(&sha_ctx);
SHA512_Update(&sha_ctx, text.data(), text.length());
SHA512_Final(digest, &sha_ctx);

if (RSA_verify(NID_sha512, digest, SHA512_DIGEST_LENGTH, (const unsigned char*)sign.data(), sign.length(), publicRSA) == 1) {
   // Успех
}

Answer 2

It seems to me that there is a jamb in these constructions
A line in C ends with a \0 character
Before passing these parameters, trim 1 last character, or try specifying the length as text.length()-1