一：字符串加密：

public static String GetMD5(string input)

        {

           System.Security.Cryptography.MD5CryptoServiceProvider  x=newSystem.Security.Cryptography.MD5CryptoServiceProvider();

            byte[]bs =System.Text.Encoding.UTF8.GetBytes(input);

            bs =x.ComputeHash(bs);

            System.Text.StringBuilder s =newSystem.Text.StringBuilder();

            foreach(byte b inbs)

            {

                s.Append(b.ToString("x2").ToLower());

            }

            returns.ToString();

        }

public static string GetMD5(string sDataIn)
        {
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            byte[] bytValue, bytHash;
            bytValue = System.Text.Encoding.UTF8.GetBytes(sDataIn);
            bytHash = md5.ComputeHash(bytValue);
            md5.Clear();
            string sTemp = "";
            for (int i = 0; i < bytHash.Length; i++)
            {
                sTemp += bytHash[i].ToString("X").PadLeft(2, '0');
            }
            return sTemp.ToLower();
        }

二：文件加密：

/// <summary>
        /// 计算文件MD5值
        /// </summary>
        /// <param name="str">需要计算的文件路径</param>
        /// <returns>MD5值</returns>
        public static string MD5Value(String filepath)
        {
            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] md5ch;
            using (FileStream fs = File.OpenRead(filepath))
            {
                md5ch = md5.ComputeHash(fs);
            }           
            md5.Clear();
            string strMd5 = "";
            for (int i = 0; i < md5ch.Length - 1; i++)
            {
                strMd5 += md5ch[i].ToString("x").PadLeft(2, '0');
            }
            return strMd5;
        }