C# MD5加密

/// <summary>
        /// 返回MD5加密字符串
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string getMd5(string str)
        {
            if (str == null)
                return null;
            string result = "";
            MD5 md5 = MD5.Create();
            byte[] s = md5.ComputeHash(Encoding.UTF8.GetBytes(str));
            for (int i = 0; i < s.Length; i++)
            {
                result+=s[i].ToString("X2");
            }
            return result;
        }