Verify an Argon2 Password with a Secret and Memory Guard

Demonstrates Crypt2.Argon2VerifyPassword when the hash was created with a secret (pepper) or ad, and the use of maxMemoryKb to guard against untrusted hash strings.

import 'package:chilkat/chilkat.dart';

void main() {
  final crypt = CkCrypt2();

  // The password should come from a secure source rather than being hard-coded.
  final password = 'correct horse battery staple';

  final phcHash = '\$argon2id\$v=19\$m=131072,t=4,p=2\$c29tZXJhbmRvbXNhbHQ\$3fJ7v1qKcVJ0lHqXjBQZ8mYm3sNTfSPRt0bqDl9kEyM';

  // When the hash was created with a secret (pepper) or ad, the same values must be supplied to verify.
  // Only the secret, ad, encoding, passwordCharset, and maxMemoryKb members of the options are used;
  // everything else is ignored.
  final json = CkJsonObject();
  json.updateString('secret', 'application-wide-pepper');
  json.updateString('secretEncoding', 'utf-8');

  // maxMemoryKb guards against a hash from an untrusted source claiming an enormous memory cost.  The
  // memory cost is taken from the hash string, so this limit is checked before any memory is allocated.
  // It defaults to 2 GB.
  json.updateInt('maxMemoryKb', 262144);

  // Argon2VerifyPassword returns 1 if the password matched, 0 if it did not match, and -1 if the
  // verification could not be performed.  Always test for a match with == 1.
  final verifyResult = crypt.argon2VerifyPassword(password, json.emit(), phcHash);
  if (verifyResult == 1) {
    print('The password is verified.');
  } else {
    if (verifyResult == 0) {
      print('The password does not match.');
    } else {
      print('The verification could not be performed: ${crypt.lastErrorText}');
    }
  }
}