Windows Phone Data Protection

To encrypt the PIN

 　 // Convert the PIN to a byte[].
    byte[] PinByte = Encoding.UTF8.GetBytes(TBPin.Text);

    // Encrypt the PIN by using the Protect() method.
    byte[] ProtectedPinByte = ProtectedData.Protect(PinByte, null);

    // Store the encrypted PIN in isolated storage.
    this.WritePinToFile(ProtectedPinByte);

Write PIN to file

    // Create a file in the application's isolated storage.
    IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication();
    IsolatedStorageFileStream writestream = new IsolatedStorageFileStream(FilePath, System.IO.FileMode.Create, System.IO.FileAccess.Write, file);

    // Write pinData to the file.
    Stream writer = new StreamWriter(writestream).BaseStream;
    writer.Write(pinData, 0, pinData.Length);
    writer.Close();
    writestream.Close();

To decrypt the data

    // Retrieve the PIN from isolated storage.
    byte[] ProtectedPinByte = this.ReadPinFromFile();

    // Decrypt the PIN by using the Unprotect method.
    byte[] PinByte = ProtectedData.Unprotect(ProtectedPinByte, null);

    // Convert the PIN from byte to string and display it in the text box.
    TBPin.Text = Encoding.UTF8.GetString(PinByte, 0, PinByte.Length);

Read PIN from file

    // Access the file in the application's isolated storage.
    IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication();
    IsolatedStorageFileStream readstream = new IsolatedStorageFileStream(FilePath, System.IO.FileMode.Open, FileAccess.Read, file);

    // Read the PIN from the file.
    Stream reader =  new StreamReader(readstream).BaseStream;
    byte[] pinArray = new byte[reader.Length];

    reader.Read(pinArray, 0, pinArray.Length);
    reader.Close();
    readstream.Close();

    return pinArray;