private string hashPliku(string plik)
{
if (!File.Exists(plik)) throw new Exception();
StringBuilder sb = new StringBuilder();
FileStream fs = new FileStream(plik, FileMode.Open);
MD5 md5 = new MD5CryptoServiceProvider();
byte[] hash = md5.ComputeHash(fs);
fs.Close();
foreach (byte hex in hash)
sb.Append(hex.ToString("x2"));
return sb.ToString();
}