using System;    public string CreateMD5Hash (string input)  {     // Use input string to calculate MD5 hash     MD5 md5 = System.Security.Cryptography.MD5.Create();     byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes (input);     byte[] hashBytes  = md5.ComputeHash (inputBytes);       // Convert the byte array to hexadecimal string     StringBuilder sb = new StringBuilder();     for (int i = 0; i < hashBytes.Length; i++)     {         sb.Append (hashBytes[i].ToString ("X2"));         // To force the hex string to lower-case letters instead of         // upper-case, use he following line instead:         // sb.Append(hashBytes[i].ToString("x2"));      }     return sb.ToString();  }

用法：

string md5hash = CreateMD5Hash("abcdefghijklmnopqrstuvwxyz");

执行结果

md5hash will contain this string: "C3FCD3D76192E4007DFB496CCA67E13B".

C#里也可以直接使用System.Web.Security 命名空间 生成MD5

FormsAuthentication.HashPasswordForStoringInConfigFile (string, "MD5")