StringHelpers

public class StringHelpers
{
    public const char QUERY_STRING_DELIMITER = '&';

    private static RijndaelManaged _cryptoProvider;
    //128 bit encyption: DO NOT CHANGE
    private static readonly byte[] Key = { , , , , , , , , , , , , , , ,  };
    private static readonly byte[] IV = { , , , , , , , , , , , , , , ,  };
    static StringHelpers()
    {
        _cryptoProvider = new RijndaelManaged();
        _cryptoProvider.Mode = CipherMode.CBC;
        _cryptoProvider.Padding = PaddingMode.PKCS7;
    }

    public static string Encrypt(string unencryptedString)
    {
        return Encrypt(unencryptedString, string.Empty);
    }

    public static string Encrypt(string unencryptedString, string myKey)
    {

        //byte[] bytIn = ASCIIEncoding.ASCII.GetBytes(unencryptedString);
        //如果內容有unicode的話，要用utf8編碼
        byte[] bytIn = UTF8Encoding.UTF8.GetBytes(unencryptedString);
        byte[] bytKey;
        if(string.IsNullOrEmpty(myKey)){
            bytKey = Key;
        }else{
            bytKey = ASCIIEncoding.ASCII.GetBytes(myKey);
            Array.Resize(ref bytKey, );
        }
        // Create a MemoryStream
        MemoryStream ms = new MemoryStream();
        // Create Crypto Stream that encrypts a stream
        CryptoStream cs = new CryptoStream(ms, _cryptoProvider.CreateEncryptor(bytKey, IV), CryptoStreamMode.Write);
        // Write content into MemoryStream
        cs.Write(bytIn, , bytIn.Length);
        cs.FlushFinalBlock();
        byte[] bytOut = ms.ToArray();
        //因為url不能吃+所以要轉成@@@
        return Convert.ToBase64String(bytOut).Replace("+", "@@@");
    }

    public static string Decrypt(string encryptedString)
    {
        return Decrypt(encryptedString, string.Empty);
    }

    public static string Decrypt(string encryptedString, string myKey)
    {
        if (encryptedString.Trim().Length != )
        {
            //如果有人改加密字串的話，解就會發生錯誤，所以錯誤就回傳空字串
            try
            {
                // Convert from Base64 to binary 在解開前要先將@@@轉成+
                byte[] bytIn = Convert.FromBase64String(encryptedString.Replace("@@@", "+"));
                byte[] bytKey;
                if(string.IsNullOrEmpty(myKey)){
                    bytKey = Key;
                }else{
                    bytKey = ASCIIEncoding.ASCII.GetBytes(myKey);
                    Array.Resize(ref bytKey, );
                }
                // Create a MemoryStream
                MemoryStream ms = new MemoryStream(bytIn, , bytIn.Length);
                // Create a CryptoStream that decrypts the data
                CryptoStream cs = new CryptoStream(ms, _cryptoProvider.CreateDecryptor(bytKey, IV), CryptoStreamMode.Read);

                // Read the Crypto Stream
                StreamReader sr = new StreamReader(cs);
                return sr.ReadToEnd();
            }
            catch
            {
                return "";
            }
        }
        else
        {
            return "";
        }
    }

    public static NameValueCollection DecryptQueryString(string queryString)
    {
        return DecryptQueryString(queryString, string.Empty);
    }

    public static NameValueCollection DecryptQueryString(string queryString, string myKey)
    {
        if (queryString.Length != )
        {
            //Decode the string
            string decodedQueryString = HttpUtility.UrlDecode(queryString);
            //Decrypt the string
            string decryptedQueryString = StringHelpers.Decrypt(decodedQueryString, myKey );
            //Now split the string based on each parameter
            string[] actionQueryString = decryptedQueryString.Split(new char[] { QUERY_STRING_DELIMITER });
            NameValueCollection newQueryString = new NameValueCollection();
            //loop around for each name value pair.
            for (int index = ; index < actionQueryString.Length; index++)
            {
                string[] queryStringItem = actionQueryString[index].Split(new char[] { '=' });
                if(queryStringItem.Length > )
                    newQueryString.Add(queryStringItem[], queryStringItem[]);
            }
            return newQueryString;
        }
        else
        {
            //No query string was passed in.
            return null;
        }
    }

    public static string EncryptQueryString(NameValueCollection queryString)
    {
        return EncryptQueryString(queryString, string.Empty);
    }

    public static string EncryptQueryString(NameValueCollection queryString, string myKey)
    {
        //create a string for each value in the query string passed in.
        string tempQueryString = "";
        for (int index = ; index < queryString.Count; index++)
        {
            tempQueryString += queryString.GetKey(index) + "=" + queryString[index];
            if (index != queryString.Count - )
            {
                tempQueryString += QUERY_STRING_DELIMITER;
            }
        }
        return EncryptQueryString(tempQueryString, myKey);
    }

    public static string EncryptQueryString(string queryString)
    {
        return EncryptQueryString(queryString, string.Empty);
    }

    public static string EncryptQueryString(string queryString, string myKey)
    {
        return "?" + HttpUtility.UrlEncode(StringHelpers.Encrypt(queryString, myKey));
    }
}