环境：vs.net2005/sql server2000/xp测试通过
1.MD5　16位加密实例
       using System;
using System.Collections.Generic;
using System.Text;
using System.Security.Cryptography;

namespace md5
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(UserMd5("8"));
            Console.WriteLine(GetMd5Str("8"));
        }
        /**//// <summary>
        /// MD5 16位加密
        /// </summary>
        /// <param name="ConvertString"></param>
        /// <returns></returns>
        public static string GetMd5Str(string ConvertString)
        {
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            string t2 = BitConverter.ToString(md5.ComputeHash(UTF8Encoding.Default.GetBytes(ConvertString)), 4, 8);
            t2 = t2.Replace("-", "");
            return t2;
        }
http://www.cnblogs.com/sopper/archive/2007/01/08/615111.html
        /**//// <summary>
        /// MD5　32位加密
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
       static  string UserMd5(string str)
        {
            string cl = str;
            string pwd = "";
            MD5 md5 = MD5.Create();//实例化一个md5对像
            // 加密后是一个字节类型的数组，这里要注意编码UTF8/Unicode等的选择　
            byte[] s = md5.ComputeHash(Encoding.UTF8.GetBytes(cl));
            // 通过使用循环，将字节类型的数组转换为字符串，此字符串是常规字符格式化所得
            for (int i = 0; i < s.Length; i++)
            {
                // 将得到的字符串使用十六进制类型格式。格式后的字符是小写的字母，如果使用大写（X）则格式后的字符是大写字符

                pwd = pwd + s[i].ToString("X");
               
            }
            return pwd;
        }
    }
}