decrypt method

String decrypt(String encryptedText, { int saltLength = 4, CharClass charClass = CharClass.chars95, String? charSetMembers, })

Decrypts the encryptedText encrypted by encrypt(). saltLength: this is the length of the salt preceding the encryptedText.

Implementation

String decrypt(String encryptedText,
    {int saltLength = 4,
    CharClass charClass = CharClass.chars95,
    String? charSetMembers}) {
  var rc = '';
  final salt = encryptedText.substring(0, saltLength);
  final encryptedText2 = encryptedText.substring(saltLength);
  final currentState = firstState.toList();
  currentState[0] =
      random.maskOperand(random.maskOperand(salt.hashCode) + currentState[0]);
  random.restoreState(currentState);
  charSetMembers ??= BaseRandom.getCharClassMembers(charClass);
  if (charClass == CharClass.chars95 || charClass == CharClass.chars96) {
    // the charset is ordered like ASCII:
    final upperBound = charClass == CharClass.chars95 ? 127 : 128;
    final max = charClass == CharClass.chars95 ? 95 : 96;
    for (var ix = 0; ix < encryptedText2.length; ix++) {
      final code = encryptedText2.codeUnitAt(ix);
      if (code < 32 || code >= upperBound) {
        rc += encryptedText2[ix];
      } else {
        final rand = random.nextInt(max: max);
        final value = 32 + (code - 32 + max - rand) % max;
        rc += String.fromCharCode(value);
      }
    }
  } else {
    // the charset is not ordered like ASCII:
    // charSetMembers cannot be null!
    final membersLength = charSetMembers?.length ?? 1;
    for (var ix = 0; ix < encryptedText2.length; ix++) {
      final index = charSetMembers?.indexOf(encryptedText2[ix]) ?? -1;
      if (index < 0) {
        rc += encryptedText2[ix];
      } else {
        final rand = random.nextInt(max: membersLength);
        final value = (index + membersLength - rand) % membersLength;
        // charSetMembers cannot be null!
        rc += charSetMembers == null ? '' : charSetMembers[value];
      }
    }
  }
  return rc;
}