Finish implementing some encryption in the network protocols with AES

lib/encryption/xtea.dart

@@ -0,0 +1,155 @@
+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);
+  }
+}