public class EncryptMethods
    {
        /// <summary>
        /// Md5加密
        /// </summary>
        /// <param name="str">时间+随机数+令牌</param>
        /// <returns></returns>
        public string EncryptToMD5(string str)
        {
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            byte[] str1 = Encoding.UTF8.GetBytes(str);
            byte[] str2 = md5.ComputeHash(str1, 0, str1.Length);
            md5.Clear();
            (md5 as IDisposable).Dispose();
            return Convert.ToBase64String(str2);
        }
　　}

EncryptMethods ec = new EncryptMethods();//实例化
dto.PassWord = ec.EncryptToMD5(dto.PassWord);