(C++) ECDSA Sign and Verify Data using Different Hash Algorithms

Demonstrates how to create ECDSA signatures on data using different hash algorithms.

Note: This example requires Chilkat v9.5.0.85 or greater because the SignBd and VerifyBd methods were added in v9.5.0.85.

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#include <CkPrivateKey.h>
#include <CkBinData.h>
#include <CkEcc.h>
#include <CkPrng.h>
#include <CkPublicKey.h>

void ChilkatSample(void)
    {
    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // First load an ECDSA private key to be used for signing.
    CkPrivateKey privKey;
    bool success = privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret");
    if (success == false) {
        std::cout << privKey.lastErrorText() << "\r\n";
        return;
    }

    // Load some data to be signed.
    CkBinData bd;
    success = bd.LoadFile("qa_data/hamlet.xml");
    if (success == false) {
        std::cout << "Failed to load file to be hashed." << "\r\n";
        return;
    }

    CkEcc ecdsa;
    CkPrng prng;

    // Sign the sha256 hash of the data.  Return the ECDSA signature in the base64 encoding.
    std::cout << "ECDSA signing the sha256 hash of the data..." << "\r\n";
    const char *sig = ecdsa.signBd(bd,"sha256","base64",privKey,prng);
    std::cout << "sig = " << sig << "\r\n";

    // Verify the signature against the original data.
    // (We must use the same hash algorithm that was used when signing.)

    // Load the public key that corresponds to the private key used for signing.
    CkPublicKey pubKey;
    success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem");
    if (success == false) {
        std::cout << pubKey.lastErrorText() << "\r\n";
        return;
    }

    CkEcc ecc2;
    int result = ecc2.VerifyBd(bd,"sha256",sig,"base64",pubKey);
    if (result != 1) {
        std::cout << ecc2.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "Verified!" << "\r\n";

    // ----------------------------------------------------------------------------------------
    // Let's do the same thing, but with sha384 hashing...

    std::cout << "--------------------------------------------" << "\r\n";
    std::cout << "ECDSA signing the sha384 hash of the data..." << "\r\n";

    sig = ecdsa.signBd(bd,"sha384","base64",privKey,prng);
    std::cout << "sig = " << sig << "\r\n";

    result = ecc2.VerifyBd(bd,"sha384",sig,"base64",pubKey);
    if (result != 1) {
        std::cout << ecc2.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "Verified!" << "\r\n";
    }