novyronst/lib/common/help/help_encrypt.dart

import 'dart:async';
import 'dart:convert';
import 'dart:typed_data';
import 'dart:math';

class HelpEncrypt {
  static const int bfSize = 2048;
  static const String enStrTag = r'$';

  // Generates a random salt of size between 16 and 64 bytes
  static Uint8List randSalt() {
    final rand = Random.secure();
    final size = rand.nextInt(49) + 16; // 16..64
    return Uint8List.fromList(List.generate(size, (_) => rand.nextInt(256)));
  }

  // Encrypts the given data with a random salt
  static Uint8List en(Uint8List data) {
    if (data.isEmpty) return data;
    final salt = randSalt();
    final encryptedData = enWithSalt(data, salt);
    return Uint8List.fromList([salt.length, ...salt, ...encryptedData]);
  }

  // Decrypts the given encrypted data
  static Uint8List de(Uint8List data) {
    if (data.isEmpty) return data;
    final saltLen = data[0];
    final salt = data.sublist(1, 1 + saltLen);
    final encrypted = data.sublist(1 + saltLen);
    return deWithSalt(encrypted, salt);
  }

  // Encrypts data with a specified salt
  static Uint8List enWithSalt(Uint8List data, Uint8List salt) {
    final mixedData = mixSalt(data, salt);
    return cxEd(mixedData);
  }

  // Decrypts data with a specified salt
  static Uint8List deWithSalt(Uint8List data, Uint8List salt) {
    final decryptedData = cxEd(data);
    return removeSalt(decryptedData, salt);
  }

  // Simple XOR-based encryption/decryption (bitwise negation)
  static Uint8List cxEd(Uint8List data) {
    return Uint8List.fromList(data.map((b) => b ^ 0xFF).toList());
  }

  // Apply salt to the data for encryption
  static Uint8List mixSalt(Uint8List data, Uint8List salt) {
    if (salt.isEmpty) return data;
    return Uint8List.fromList(
      List.generate(data.length, (i) {
        final s = salt[i % salt.length];
        return calSalt(data[i], s);
      }),
    );
  }

  // Remove salt from the data after decryption
  static Uint8List removeSalt(Uint8List data, Uint8List salt) {
    if (salt.isEmpty) return data;
    return Uint8List.fromList(
      List.generate(data.length, (i) {
        final s = salt[i % salt.length];
        return calRemoveSalt(data[i], s);
      }),
    );
  }

  // Calculate a modified value after mixing salt (for encryption)
  static int calSalt(int v, int s) {
    final r = v ^ 0xFF;
    return s > r ? (s - r - 1) & 0xFF : (v + s) & 0xFF;
  }

  // Reverse the salt mixing process for decryption
  static int calRemoveSalt(int v, int s) {
    return v >= s ? (v - s) & 0xFF : (0xFF - (s - v) + 1) & 0xFF;
  }

  // Encrypt a string and return the hex representation
  static String cxEStr(String data) {
    return cxEStrAsBytes(
      data,
    ).map((b) => b.toRadixString(16).padLeft(2, '0')).join();
  }

  // Encrypt string and return as bytes
  static Uint8List cxEStrAsBytes(String data) {
    return cxEd(Uint8List.fromList(utf8.encode(data)));
  }

  // Decrypt a hex string to a regular string
  static String cxDStr(String data) {
    final bytes = Uint8List.fromList([
      for (int i = 0; i < data.length; i += 2)
        int.parse(data.substring(i, i + 2), radix: 16),
    ]);
    return utf8.decode(cxEd(bytes));
  }

  // Encrypt string data and return in the form of hex string with prefix
  static String enStr(String data) {
    return enBytesStr(Uint8List.fromList(utf8.encode(data)));
  }

  // Encrypt bytes and return as hex string with prefix
  static String enBytesStr(Uint8List data) {
    final encrypted = en(data);
    return '$enStrTag${encrypted.map((b) => b.toRadixString(16).padLeft(2, '0')).join()}';
  }

  // Decrypt a string with encoded prefix (e.g., "$" symbol)
  static String deStr(String data) {
    return utf8.decode(deStrBytes(data));
  }

  // Decrypt the byte array extracted from a string
  static Uint8List deStrBytes(String data) {
    if (!data.startsWith(enStrTag)) {
      throw ArgumentError("Invalid encoded string");
    }
    final hexData = data.substring(1);
    final bytes = Uint8List.fromList([
      for (int i = 0; i < hexData.length; i += 2)
        int.parse(hexData.substring(i, i + 2), radix: 16),
    ]);
    return de(bytes);
  }

  // Copy encrypted data from a stream to another stream
  static Future<int> copy(
      Stream<List<int>> reader,
      StreamSink<List<int>> writer,
      ) async {
    int total = 0;
    await for (final chunk in reader) {
      total += chunk.length;
      final encrypted = chunk.map((b) => b ^ 0xFF).toList();
      writer.add(encrypted);
    }
    await writer.close();
    return total;
  }

  // Custom encryption with condition (even and odd byte values handled differently)
  static Uint8List cxEd1(Uint8List data) {
    return Uint8List.fromList(
      data.map((b) => (b % 2 == 1) ? (b ^ 0xFF) : b).toList(),
    );
  }
}