(Mono 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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// 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.

Chilkat.StringBuilder sb = new Chilkat.StringBuilder();
sb.Append("The quick brown fox jumps over the lazy dog");
string hash = sb.GetHash("sha256","base64","utf-8");

// Load the ECDSA key to be used for signing.
Chilkat.PrivateKey privKey = new Chilkat.PrivateKey();
bool success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem");
if (success != true) {
    Debug.WriteLine(privKey.LastErrorText);
    return;
}

Chilkat.Prng prng = new Chilkat.Prng();
Chilkat.Ecc ecdsa = new Chilkat.Ecc();

// 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.AsnFormat = false;

string ecdsaSigBase64 = ecdsa.SignHashENC(hash,"base64",privKey,prng);
if (ecdsa.LastMethodSuccess != true) {
    Debug.WriteLine(ecdsa.LastErrorText);
    return;
}

Debug.WriteLine("ECDSA signature = " + ecdsaSigBase64);

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

Chilkat.PublicKey pubKey = new Chilkat.PublicKey();
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pubkey.pem");
if (success != true) {
    Debug.WriteLine(pubKey.LastErrorText);
    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) {
    Debug.WriteLine("Signature is valid.");
    return;
}

if (result == 0) {
    Debug.WriteLine("Signature is invalid.");
    return;
}

if (result < 0) {
    Debug.WriteLine(ecdsa.LastErrorText);
    Debug.WriteLine("The VerifyHashENC method call failed.");
    return;
}