短信发送AZDG加密算法

public static string passport_encrypt(string txt, string key)
        {
            //   使用随机数发生器产生   0~32000   的值并   MD5()
            Random rnd = new Random(100);
            int int_encrypt_key = rnd.Next(0, 32000);
            string encrypt_key = int_encrypt_key.ToString();

int ctr = 0;
            string tmp = "";
            byte[] encodebyte = new byte[txt.Length];
            for (int i = 0; i < txt.Length; i++)
            {
                ctr = ctr == encrypt_key.Length ? 0 : ctr;
                char prefix = encrypt_key[ctr];
                char left = txt[i];
                char right = encrypt_key[ctr++];

encodebyte[i] = (byte)(left ^ right);
                char[] block = new char[2];
                block[0] = prefix;
                block[1] = Convert.ToChar(encodebyte[i]);
                tmp += new string(block);
            }
            //////用base64编码
            string complicatedstring = passport_key(tmp, key);/////先和key加一次密？

byte[] inputbytes = System.Text.Encoding.Default.GetBytes(complicatedstring);

string string_64 = Convert.ToBase64String(inputbytes, 0, inputbytes.Length);/////再和随机key加密

return string_64;
        }
        public static string passport_decrypt(string txt, string key)
        {
            byte[] array_64 = Convert.FromBase64String(txt);
            string txt_64 = System.Text.Encoding.Default.GetString(array_64);
            txt = passport_key(txt_64, key);

string temp = "";
            byte[] encodebyte = new byte[txt.Length];
            for (int i = 0; i < txt.Length; i++)
            {

char left = txt[i];
                char right = txt[++i];
                encodebyte[i] = (byte)(left ^ right);
            }
            temp = System.Text.Encoding.Default.GetString(encodebyte);
            return temp;
        }