(C++) Create ECSDA Signature using Raw r and s Format (not ASN.1)

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Demonstrates how to create an ECDSA signature using the raw r/s format.

ECDSA signatures have two equal sized parts, r and s. There are two common formats for encoding the signature:

(a) Concatenating the raw byte array of r and s
(b) Encoding both into a structured ASN.1 / DER sequence.

This example demonstrates how to create a signature that is a byte array of r and s concatenated.

Note: This example requires Chilkat v9.5.0.97 or greater.

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#include <CkStringBuilder.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.

    CkStringBuilder sb;
    sb.Append("The quick brown fox jumps over the lazy dog");
    const char *hash = sb.getHash("sha256","base64","utf-8");

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

    CkPrng prng;
    CkEcc ecdsa;

    // Produce a signature that is not ASN.1, but is instead the concatenation
    // of the raw r and s signature parts.
    // This feature was added in Chilkat v9.5.0.97
    ecdsa.put_AsnFormat(false);

    const char *ecdsaSigBase64 = ecdsa.signHashENC(hash,"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;
    }

    // Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
    int result = ecdsa.VerifyHashENC(hash,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;
    }
    }