Dart

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

See more ECC Examples

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.

Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // 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.

  final sb = CkStringBuilder();
  sb.append('The quick brown fox jumps over the lazy dog');
  final hash = sb.getHash('sha256', 'base64', 'utf-8');

  // Load the ECDSA key to be used for signing.
  final privKey = CkPrivateKey();
  try {
    privKey.loadPemFile('qa_data/ecc/secp256r1-key-pkcs8.pem');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  final prng = CkPrng();
  final ecdsa = CkEcc();

  // 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;

  final String ecdsaSigBase64;
  try {
    ecdsaSigBase64 = ecdsa.signHashENC(hash, 'base64', privKey, prng);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('ECDSA signature = $ecdsaSigBase64');

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

  final pubKey = CkPublicKey();
  try {
    pubKey.loadFromFile('qa_data/ecc/secp256r1-pubkey.pem');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Note: When verifying, Chilkat will auto-detect the format for both kinds of ECDSA signatures (ASN.1 or binary r+s)
  final result = ecdsa.verifyHashENC(hash, ecdsaSigBase64, 'base64', pubKey);
  if (result == 1) {
    print('Signature is valid.');
    return;
  }

  if (result == 0) {
    print('Signature is invalid.');
    return;
  }

  if (result < 0) {
    print(ecdsa.lastErrorText);
    print('The VerifyHashENC method call failed.');
    return;
  }
}