//метод для генерации md5 hash
public string EncodePassword(string originalPassword)
        {
            //Declarations
            Byte[] originalBytes;
            Byte[] encodedBytes;
            MD5 md5;

            //Instantiate MD5CryptoServiceProvider, get   bytes for original password and compute hash (encoded password)
            md5 = new MD5CryptoServiceProvider();
            originalBytes = ASCIIEncoding.Default.GetBytes(originalPassword);
            encodedBytes = md5.ComputeHash(originalBytes);

            //Convert encoded bytes back to a 'readable' string
            return BitConverter.ToString(encodedBytes);
        }

using System.Security.Cryptography;
 public string MD5Hash(string instr)
        {
            string strHash = string.Empty;
            foreach (byte b in new MD5CryptoServiceProvider().ComputeHash(Encoding.Default.GetBytes(instr)))
            {
                strHash += b.ToString("X2");
            }
            return strHash;
        }