public string GetMD5Str(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().ToLower();
        }
原文:http://www.cnblogs.com/ilrc/p/6266852.html