LibAC-dart/lib/encryption/xtea.dart

import 'dart:convert';

import 'package:libac_dart/utils/Hashing.dart';

class XTEA {
  static const int XTEA_DELTA = 0x9E3779B9; // (sqrt(5) - 1) * 2^31
  static const int xteaNumRounds = 6;
  List<int> _xteaKey = [0, 0, 0, 0];

  /// Used as part of testsuite to compare provided keys.
  ///
  /// This function will sequentially check each entry.
  ///
  /// Returns: -1 on success, or which entry failed verification.
  ///
  /// On failure it will print to the console what failed
  int testKey(List<int> key) {
    for (int i = 0; i < key.length; i++) {
      int v0 = _xteaKey[i];
      int v1 = key[i];

      if (v0 != v1) {
        print(
            "FATAL: TestKey XTEA failed at position ${i}.\nExpected: ${v1}\nActual: ${v0}");

        return i;
      }
    }

    return -1;
  }

  XTEA(String password) {
    _xteaKey = _xteaKeyFromString(password);
  }

  List<int> _xteaKeyFromString(String str) {
    // Convert string to MD5 and split into 4 integers
    str = md5(str); // Assume md5 function exists
    return [
      int.parse(str.substring(0, 8), radix: 16),
      int.parse(str.substring(8, 16), radix: 16),
      int.parse(str.substring(16, 24), radix: 16),
      int.parse(str.substring(24, 32), radix: 16)
    ];
  }

  List<int> encipher(List<int> data) {
    int v0 = data[0];
    int v1 = data[1];
    int sum = 0;

    for (int i = 0; i < xteaNumRounds; i++) {
      v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + _xteaKey[sum & 3]);
      sum += XTEA_DELTA;
      v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + _xteaKey[(sum >> 11) & 3]);
    }

    return [v0 & 0xFFFFFFFF, v1 & 0xFFFFFFFF]; // Ensure 32-bit integers
  }

  List<int> decipher(List<int> data) {
    int v0 = data[0];
    int v1 = data[1];
    int sum = XTEA_DELTA * xteaNumRounds;

    for (int i = 0; i < xteaNumRounds; i++) {
      v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + _xteaKey[(sum >> 11) & 3]);
      sum -= XTEA_DELTA;
      v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + _xteaKey[sum & 3]);
    }

    return [v0 & 0xFFFFFFFF, v1 & 0xFFFFFFFF]; // Ensure 32-bit integers
  }

  String encryptString(String plaintext) {
    List<int> data = utf8.encode(plaintext).toList();
    while (data.length % 8 != 0) {
      data = [...data, 0]; // Zero padding
    }

    List<int> encrypted = [];
    for (int i = 0; i < data.length; i += 8) {
      List<int> block = encipher([
        (data[i] << 24) |
            (data[i + 1] << 16) |
            (data[i + 2] << 8) |
            data[i + 3],
        (data[i + 4] << 24) |
            (data[i + 5] << 16) |
            (data[i + 6] << 8) |
            data[i + 7]
      ]);
      encrypted.addAll([
        (block[0] >> 24) & 0xFF,
        (block[0] >> 16) & 0xFF,
        (block[0] >> 8) & 0xFF,
        block[0] & 0xFF,
        (block[1] >> 24) & 0xFF,
        (block[1] >> 16) & 0xFF,
        (block[1] >> 8) & 0xFF,
        block[1] & 0xFF
      ]);
    }

    return base64.encode(encrypted);
  }

  String decryptString(String ciphertext) {
    List<int> data = base64.decode(ciphertext).toList();
    List<int> decrypted = [];

    for (int i = 0; i < data.length; i += 8) {
      List<int> block = decipher([
        (data[i] << 24) |
            (data[i + 1] << 16) |
            (data[i + 2] << 8) |
            data[i + 3],
        (data[i + 4] << 24) |
            (data[i + 5] << 16) |
            (data[i + 6] << 8) |
            data[i + 7]
      ]);
      decrypted.addAll([
        (block[0] >> 24) & 0xFF,
        (block[0] >> 16) & 0xFF,
        (block[0] >> 8) & 0xFF,
        block[0] & 0xFF,
        (block[1] >> 24) & 0xFF,
        (block[1] >> 16) & 0xFF,
        (block[1] >> 8) & 0xFF,
        block[1] & 0xFF
      ]);
    }

    // Find the index of the last non-zero byte
    int paddingStart = decrypted.lastIndexWhere((byte) => byte != 0);

    // If padding was added, remove only trailing zero bytes
    if (paddingStart != -1 && paddingStart + 1 < decrypted.length) {
      decrypted = decrypted.sublist(0, paddingStart + 1);
    }

    // Attempt to decode as UTF-8
    try {
      return utf8.decode(decrypted);
    } catch (e) {
      throw FormatException('Decrypted data is not valid UTF-8: $e');
    }
  }

  String md5(String input) {
    return Hashing.llMD5String(input, 0);
  }
}