c# 自定义加密解密工具，避免MD5加密不可逆或者DES对称加密容易被破解问题。

    /// <summary>
    /// 加密密钥（8位）
    /// </summary>
    public static string KEY_64 = "00000000";

    /// <summary>
    /// 加密初始化向量（8位）
    /// </summary>
    public static string IV_64 = "88888888";

    /// <summary>
    /// 加密
    /// </summary>
    /// <param name="data"></param>
    /// <returns></returns>
    public static string Encode(string data)
    {
        byte[] byKey = System.Text.ASCIIEncoding.ASCII.GetBytes(KEY_64);
        byte[] byIV = System.Text.ASCIIEncoding.ASCII.GetBytes(IV_64);

        DESCryptoServiceProvider cryptoProvider = new DESCryptoServiceProvider();
        int i = cryptoProvider.KeySize;
        MemoryStream ms = new MemoryStream();
        CryptoStream cst = new CryptoStream(ms, cryptoProvider.CreateEncryptor(byKey, byIV), CryptoStreamMode.Write);

        StreamWriter sw = new StreamWriter(cst);
        sw.Write(data);
        sw.Flush();
        cst.FlushFinalBlock();
        sw.Flush();
        return Convert.ToBase64String(ms.GetBuffer(), 0, (int)ms.Length).Replace("=", "φ");

    }

    /// <summary>
    /// 解密
    /// </summary>
    /// <param name="data"></param>
    /// <returns></returns>
    public static string Decode(string data)
    {
        try
        {
            byte[] byKey = System.Text.ASCIIEncoding.ASCII.GetBytes(KEY_64);
            byte[] byIV = System.Text.ASCIIEncoding.ASCII.GetBytes(IV_64);

            byte[] byEnc;
            try
            {
                byEnc = Convert.FromBase64String(data.Replace("φ", "="));
            }
            catch
            {
                return null;
            }

            DESCryptoServiceProvider cryptoProvider = new DESCryptoServiceProvider();
            MemoryStream ms = new MemoryStream(byEnc);
            CryptoStream cst = new CryptoStream(ms, cryptoProvider.CreateDecryptor(byKey, byIV), CryptoStreamMode.Read);
            StreamReader sr = new StreamReader(cst);
            return sr.ReadToEnd();
        }
        catch
        { return ""; }
    }