(C++) ECDSA Sign Data and Verify Signature

Demonstrates using the Elliptic Curve Digital Signature Algorithm to hash data and sign it. Also demonstrates how to verify the ECDSA signature.

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#include <CkCrypt2.h>
#include <CkPrivateKey.h>
#include <CkPrng.h>
#include <CkEcc.h>
#include <CkPublicKey.h>

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

    // To create an ECDSA signature, the data first needs to be hashed.  Then the hash
    // is signed.

    // Use Chilkat Crypt2 to generate a hash for any of the following
    // hash algorithms: SHA256, SHA384, SHA512, SHA1, MD5, MD2, HAVAL, RIPEMD128/160/256/320

    CkCrypt2 crypt;
    crypt.put_HashAlgorithm("SHA256");
    crypt.put_Charset("utf-8");
    crypt.put_EncodingMode("base64");

    // Hash a string.
    const char *hash1 = crypt.hashStringENC("The quick brown fox jumps over the lazy dog");
    std::cout << "hash1 = " << hash1 << "\r\n";

    // Or hash a file..
    const char *hash2 = crypt.hashFileENC("qa_data/hamlet.xml");
    std::cout << "hash2 = " << hash2 << "\r\n";

    // (The Crypt2 API provides many other ways to hash data..)

    // -----------------------------------------------------------
    // An ECDSA private key is used for signing.  The public key is for signature verification.
    // Load our ECC private key.
    // Our private key file contains this:

    // 	// -----BEGIN PRIVATE KEY-----
    // 	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
    // 	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
    // 	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
    // 	-----END PRIVATE KEY-----

    CkPrivateKey privKey;
    bool success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem");
    if (success != true) {
        std::cout << privKey.lastErrorText() << "\r\n";
        return;
    }

    // We'll need a PRNG source for random number generation.
    // Use Chilkat's PRNG (for the Fortuna PRNG algorithm).
    CkPrng prng;

    // Sign the hash..
    CkEcc ecdsa;
    const char *ecdsaSigBase64 = ecdsa.signHashENC(hash1,"base64",privKey,prng);
    if (ecdsa.get_LastMethodSuccess() != true) {
        std::cout << ecdsa.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "ECDSA signature = " << ecdsaSigBase64 << "\r\n";

    // -----------------------------------------------------------
    // Now let's verify the signature using the public key.

    CkPublicKey pubKey;
    success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem");
    if (success != true) {
        std::cout << pubKey.lastErrorText() << "\r\n";
        return;
    }

    int result = ecdsa.VerifyHashENC(hash1,ecdsaSigBase64,"base64",pubKey);
    if (result == 1) {
        std::cout << "Signature is valid." << "\r\n";
        return;
    }

    if (result == 0) {
        std::cout << "Signature is invalid." << "\r\n";
        return;
    }

    if (result < 0) {
        std::cout << ecdsa.lastErrorText() << "\r\n";
        std::cout << "The VerifyHashENC method call failed." << "\r\n";
        return;
    }
    }