Dart Requires Chilkat v11.0.0+

Verify an RSA Signature Against the Signed String

See more Apple Keychain Examples

Demonstrates how to validate an RSA Signature against the string that was signed. Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Create the same string we previously signed in this example: 
  // RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

  final sb = CkStringBuilder();
  final crlfLineEnding = true;
  for (var i = 0; i <= 10; i++) {
    sb.appendLine('This is a test.', crlfLineEnding);
  }

  final base64RsaSig = 'gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ==';

  // Get the public key to be used for signature verification.
  final pubKey = CkPublicKey();
  try {
    pubKey.loadFromFile('rsaKeys/chilkat-rsa-2048.pem');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  final rsa = CkRsa();
  try {
    rsa.usePublicKey(pubKey);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Verify the string against the signature.
  // We signed the utf-8 byte representation of the string, so we must indicate
  // to also validate against the utf-8 byte representation.
  rsa.charset = 'utf-8';
  rsa.encodingMode = 'base64';
  final signedString = sb.getAsString();

  try {
    rsa.verifyStringENC(signedString, 'sha256', base64RsaSig);
    print('Signature valid.');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    print('Signature invalid.');
  }
}