ppkMacCheck static method

void ppkMacCheck(String? privateMac, PpkMacData macData, String? password)

This method performs the mac check against the privateMac to validate the files content. It is also capable of testing whether the password was wrong or not. The macData is data used to compute the mac and to compare it to the given privateMac

Implementation

static void ppkMacCheck(
  String? privateMac,
  PpkMacData macData,
  String? password,
) {
  var sha1Hash = SHA1Digest()
    ..update(
      Uint8List.fromList('putty-private-key-file-mac-key'.codeUnits),
      0,
      'putty-private-key-file-mac-key'.codeUnits.length,
    );
  if (password != null) {
    sha1Hash.update(
      Uint8List.fromList(password.codeUnits),
      0,
      password.codeUnits.length,
    );
  }
  var key = Uint8List(20);
  sha1Hash.doFinal(key, 0);

  var macResult = Uint8List(20);
  var mac = HMac(SHA1Digest(), 64);
  mac.init(KeyParameter(key));
  mac.update(
    Uint8List.fromList([0, 0, 0, macData.algorithm.codeUnits.length]),
    0,
    4,
  );
  mac.update(
    utf8.encode(macData.algorithm),
    0,
    macData.algorithm.codeUnits.length,
  );
  mac.update(
    Uint8List.fromList([0, 0, 0, macData.encryption.codeUnits.length]),
    0,
    4,
  );
  mac.update(utf8.encode(macData.encryption), 0, macData.encryption.length);
  mac.update(
    Uint8List.fromList([0, 0, 0, macData.comment.codeUnits.length]),
    0,
    4,
  );
  mac.update(utf8.encode(macData.comment), 0, macData.comment.length);
  mac.update(Uint8List.fromList([0, 0, 0, macData.publicKey.length]), 0, 4);
  mac.update(macData.publicKey, 0, macData.publicKey.length);
  mac.update(Uint8List.fromList([0, 0, 0, macData.privateKey.length]), 0, 4);
  mac.update(macData.privateKey, 0, macData.privateKey.length);
  mac.doFinal(macResult, 0);
  if (Base16Encoder.instance.encode(ByteList(macResult)) != privateMac) {
    if (password == null) {
      throw Exception('Mac check failed, file is corrupt!');
    } else {
      throw Exception('Wrong password!');
    }
  }
}