MD5

using System;
using System.Collections.Generic;
using System.Text;
using System.Security.Cryptography;

public class MD5Helper
{
   public static string ToMD5(string Key, string Value)
   {
        byte[] bytes = Encoding.Default.GetBytes(Key);
        byte[] buffer = Encoding.Default.GetBytes(Value);
        byte[] buffer2 = new HMACMD5(bytes).ComputeHash(buffer);
        //return Encoding.Default.GetString(buffer2);
        StringBuilder bulider= new  StringBuilder(buffer2.Length);

        for (int i = 0; i <= buffer2.Length - 1; i++)
        {
            bulider.Append(buffer2[i].ToString("x"));
        }

        return bulider.ToString();
    }
}