CODEWITHSUNDEEP
c++cencryptionopensslrsa
adnan kamili
adnan kamili

Reputation: 9465

verify openssl signature using crypto++ library

I am trying to verify open-ssl signature using crypto++, here is the open-ssl part:

$ openssl genrsa 1024 >priv.pem

$ openssl rsa -in priv.pem -pubout -out pubkey.pem

$ openssl dgst -sha1 -sign privkey.pem data.txt > sign

$ openssl dgst -sha1 -verify pubkey.pem -signature sign data.txt
  Verified OK

Now in my C++ code:

int main(int argc, char* argv[])
{
    try
    {
        RSA::PublicKey publicKey;
        const char * pubFilename = "pubkey.pem";
    FileSource pubFile(pubFilename,true,new PEMStripper(new Base64Decoder()));
    RSASSA_PKCS1v15_SHA_Verifier pub(pubFile);
        cout << "n: " << pub.GetTrapdoorFunction().GetModulus() << endl;
        cout << "e: " << pub.GetTrapdoorFunction().GetPublicExponent() << endl;
        string message = "data that is to be hashed and signed.";  //same as data.txt

        ifstream file ("sign", ios::in | ios::binary | ios::ate);
    ifstream::pos_type sigSize;
    char* sig;
    if(file.is_open())
    {
          sigSize = file.tellg();
          sig = new char[sigSize];
          file.seekg(0, ios::beg);
          if(!file.read(sig, sigSize))
          {
          cout << "fail to read" << endl;
          }
          file.close();
    }
        bool result = pub.VerifyMessage( (const byte*)message.c_str(),
            message.length(), (const byte*)sig, sigSize );

        // Result
        if( true == result ) {
            cout << "Signature on message verified" << endl;
        } else {
            cout << "Message verification failed" << endl;
        }

    } // try

    catch( CryptoPP::Exception& e ) {
        std::cerr << "Error: " << e.what() << std::endl;
    }

    return 0;
}

But I always get Message verification failed

Upvotes: 0

Views: 2256

Answers (2)

Ashish Singhal
Ashish Singhal

Reputation: 425

Openssl take limited length of string data so first hash using sha1 and then send data to opensssl

Upvotes: 0

alk
alk

Reputation: 70981

Are you sure data.txt doesn't contain a final trailing \n?

If not so append one to the string lietrale in this line like so:

string message = "data that is to be hashed and signed.\n";  //same as data.txt

Upvotes: 1

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