[Python] NDT files decryptor

procedure TForm1.Encrypt;
var
  key: Byte;
  c, new_size: integer;
  size: string;
  myfile: file;
  inp_file: string;
  directory: string;
  size_2: integer;
begin
  Memo1.Lines.SaveToFile(ExePath + '3.txt', Tencoding.Unicode);
  inp_file := ExePath + '3.txt';
  // Set Key to 51
  key := $51;
  SetLength(Source, 0);
  // Select file to Crypt
  // Read File
  ReadBytesFromFile(inp_file);
  // Encrypt
  new_size := length(Source);
  for c := new_size - 2 downto 0 do
    Source[c] := (Source[c] xor Source[c + 1]) + key;
  SetLength(Dest, new_size + 24);
  move(Source[0], Dest[24], new_size);
  Dest[$0] := $4E;
  Dest[$1] := $43;
  Dest[$2] := $52;
  Dest[$3] := $00;
  Dest[$4] := $01;
  Dest[$5] := $00;
  Dest[$6] := $01;
  Dest[$7] := $00;
  size := IntToHex(new_size, 8);
  Dest[$8] := strtoint('$' + copy(size, 7, 2));
  Dest[$9] := strtoint('$' + copy(size, 5, 2));
  Dest[$A] := strtoint('$' + copy(size, 3, 2));
  Dest[$B] := strtoint('$' + copy(size, 1, 2));
  Dest[$C] := key;
  Dest[$D] := $00;
  Dest[$E] := $00;
  Dest[$F] := $00;
  Dest[$10] := $00;
  Dest[$11] := $00;
  Dest[$12] := $00;
  Dest[$13] := $00;
  Dest[$14] := $00;
  Dest[$16] := $00;
  Dest[$17] := $00;
  // Write to file
  directory := IniFile.ReadString('Directories', 'File_2', '');
  AssignFile(myfile, directory + Label2.Caption);
  size_2 := length(Dest);
  ReWrite(myfile, size_2);
  BlockWrite(myfile, Dest[0], 1);
  CloseFile(myfile);
end;