moxxy/lib/service/cryptography/implementations.dart

import 'dart:convert';
import 'dart:io';
import 'package:cryptography/cryptography.dart';
import 'package:moxxmpp/moxxmpp.dart';
import 'package:moxxyv2/service/cryptography/types.dart';

Future<List<int>> hashFileImpl(HashRequest request) async {
  final data = await File(request.path).readAsBytes();

  return CryptographicHashManager.hashFromData(data, request.hash);
}

Future<EncryptionResult> encryptFileImpl(EncryptionRequest request) async { 
  Cipher algorithm;
  switch (request.encryption) {
    case SFSEncryptionType.aes128GcmNoPadding:
      algorithm = AesGcm.with128bits();
      break;
    case SFSEncryptionType.aes256GcmNoPadding:
      algorithm = AesGcm.with256bits();
      break;
    case SFSEncryptionType.aes256CbcPkcs7:
      // TODO(Unknown): Implement
      throw Exception();
      // ignore: dead_code
      break;
  }

  // Generate a key and an IV for the file
  final key = await algorithm.newSecretKey();
  final iv = algorithm.newNonce();
  final plaintext = await File(request.source).readAsBytes();
  final secretBox = await algorithm.encrypt(
    plaintext,
    secretKey: key,
    nonce: iv,
  );
  final ciphertext = [
    ...secretBox.cipherText,
    ...secretBox.mac.bytes,
  ];

  // Write the file
  await File(request.dest).writeAsBytes(ciphertext);

  return EncryptionResult(
    await key.extractBytes(),
    iv,
    {
      hashSha256: base64Encode(
        await CryptographicHashManager.hashFromData(plaintext, HashFunction.sha256),
      ),
    },
    {
      hashSha256: base64Encode(
        await CryptographicHashManager.hashFromData(ciphertext, HashFunction.sha256),
      ),
    },
  );
}

// TODO(PapaTutuWawa): Somehow fail when the ciphertext hash is not matching the provided data
Future<DecryptionResult> decryptFileImpl(DecryptionRequest request) async {
  Cipher algorithm;
  switch (request.encryption) {
    case SFSEncryptionType.aes128GcmNoPadding:
      algorithm = AesGcm.with128bits();
      break;
    case SFSEncryptionType.aes256GcmNoPadding:
      algorithm = AesGcm.with256bits();
      break;
    case SFSEncryptionType.aes256CbcPkcs7:
      // TODO(Unknown): Implement
      throw Exception();
      // ignore: dead_code
      break;
  }
  
  final ciphertextRaw = await File(request.source).readAsBytes();
  final mac = List<int>.empty(growable: true);
  final ciphertext = List<int>.empty(growable: true);
  // TODO(PapaTutuWawa): Somehow handle aes256CbcPkcs7
  if (request.encryption == SFSEncryptionType.aes128GcmNoPadding ||
      request.encryption == SFSEncryptionType.aes256GcmNoPadding) {
    mac.addAll(ciphertextRaw.sublist(ciphertextRaw.length - 16));
    ciphertext.addAll(ciphertextRaw.sublist(0, ciphertextRaw.length - 16));
  }

  var passedCiphertextIntegrityCheck = true;
  var passedPlaintextIntegrityCheck = true;
  // Try to find one hash we can verify
  for (final entry in request.ciphertextHashes.entries) {
    if ([hashSha256, hashSha512, hashBlake2b512].contains(entry.key)) {
      final hash = await CryptographicHashManager.hashFromData(
        ciphertext,
        hashFunctionFromName(entry.key),
      );

      if (base64Encode(hash) == entry.value) {
        passedCiphertextIntegrityCheck = true;
      } else {
        passedCiphertextIntegrityCheck = false;
      }
      break;
    }
  }
  
  final secretBox = SecretBox(
    ciphertext,
    nonce: request.iv,
    mac: Mac(mac),
  );

  try {
    final data = await algorithm.decrypt(
      secretBox,
      secretKey: SecretKey(request.key),
    );

    for (final entry in request.plaintextHashes.entries) {
      if ([hashSha256, hashSha512, hashBlake2b512].contains(entry.key)) {
        final hash = await CryptographicHashManager.hashFromData(
          data,
          hashFunctionFromName(entry.key),
        );

        if (base64Encode(hash) == entry.value) {
          passedPlaintextIntegrityCheck = true;
        } else {
          passedPlaintextIntegrityCheck = false;
        }
        break;
      }
    }

    await File(request.dest).writeAsBytes(data);
  } catch (_) {
    return DecryptionResult(
      false,
      passedPlaintextIntegrityCheck,
      passedCiphertextIntegrityCheck,
    );
  }

  return DecryptionResult(
    true,
    passedPlaintextIntegrityCheck,
    passedCiphertextIntegrityCheck,
  );
}