verify openssl signature using crypto++ library

Question

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

Also see ECDSA sign with OpenSSL, verify with Crypto++ and ECDSA sign with BouncyCastle and verify with Crypto++. — jww
– jww, Commented Aug 10, 2018 at 22:40

alk · Accepted Answer · 2013-12-28 11:19:35Z

1

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

edited Dec 28, 2013 at 11:19

answered Dec 28, 2013 at 11:12

alk

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1 Comment

adnan kamili Over a year ago

Thanks a ton! I was about to pull out my hair.

Ashish Singhal · Accepted Answer · 2014-02-26 05:34:52Z

0

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

answered Feb 26, 2014 at 5:34

Ashish Singhal

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