Encrypt/Decrypt in Windows store app.

Question

Hi

I am using below code in my web application to encrypt and Decrypt the text. but when I try to use the same code in Windows Store app it not working and show missing some classes.

Can you please help me get the most equivalent code in WinRT.  

 public static string Encrypt(string plainSourceStringToEncrypt, string passPhrase)
        {
            //Set up the encryption objects
            using (AesCryptoServiceProvider acsp = GetProvider(Encoding.Default.GetBytes(passPhrase)))
            {
                byte[] sourceBytes = Encoding.ASCII.GetBytes(plainSourceStringToEncrypt);
                ICryptoTransform ictE = acsp.CreateEncryptor();

                //Set up stream to contain the encryption
                MemoryStream msS = new MemoryStream();

                //Perform the encrpytion, storing output into the stream
                CryptoStream csS = new CryptoStream(msS, ictE, CryptoStreamMode.Write);
                csS.Write(sourceBytes, 0, sourceBytes.Length);
                csS.FlushFinalBlock();

                //sourceBytes are now encrypted as an array of secure bytes
                byte[] encryptedBytes = msS.ToArray(); //.ToArray() is important, don't mess with the buffer

                //return the encrypted bytes as a BASE64 encoded string
                return Convert.ToBase64String(encryptedBytes);
            }
        }

    public static string Decrypt(string base64StringToDecrypt, string passphrase)
        {
            //Set up the encryption objects
            using (AesCryptoServiceProvider acsp = GetProvider(Encoding.Default.GetBytes(passphrase)))
            {
                byte[] RawBytes = Convert.FromBase64String(base64StringToDecrypt);
                ICryptoTransform ictD = acsp.CreateDecryptor();

                //RawBytes now contains original byte array, still in Encrypted state

                //Decrypt into stream
                MemoryStream msD = new MemoryStream(RawBytes, 0, RawBytes.Length);
                CryptoStream csD = new CryptoStream(msD, ictD, CryptoStreamMode.Read);
                //csD now contains original byte array, fully decrypted

                //return the content of msD as a regular string
                return (new StreamReader(csD)).ReadToEnd();
            }
        }