public partial class MainPage : PhoneApplicationPage
{
   string FileName = "SecuredFile";

Step 3: Place below method in MainPage.xaml.cs which will write the encrypted data to a file and store in IsolatedStorage.

private void WriteTextToFile(byte[] textData)
{
   IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication();
   IsolatedStorageFileStream writestream = new IsolatedStorageFileStream(FileName, System.IO.FileMode.Create, System.IO.FileAccess.Write, file);
   Stream stream = new StreamWriter(writestream).BaseStream;
   stream.Write(textData, 0, textData.Length);
   stream.Close();
   writestream.Close();
}

Step 4: Place below method in MainPage.xaml.cs which will read the encrypted data from file placed in IsolatedStorage.

private byte[] ReadTextFromFile()
{
   IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication();
   IsolatedStorageFileStream readstream = new IsolatedStorageFileStream(FileName, System.IO.FileMode.Open, FileAccess.Read, file);
   Stream reader = new StreamReader(readstream).BaseStream;
   byte[] textArray = new byte[reader.Length];
   reader.Read(textArray, 0, textArray.Length);
   reader.Close();
   readstream.Close();
   return textArray;
}

Step 5: Place below method which will be triggered on click of Encrypt button. Protect method of ProtectedData takes two arguments first the text to be encrypted and second takes entropy to add additional complexity of encryption

private void Encrypt_Click(object sender, RoutedEventArgs e)
{
   byte[] TextByte = Encoding.UTF8.GetBytes(txtText.Text);
   byte[] entropyByte = Encoding.UTF8.GetBytes(txtEntropy.Text);
   byte[] ProtectedTextByte = ProtectedData.Protect(TextByte, entropyByte);
   this.WriteTextToFile(ProtectedTextByte);
   txtEncrypted.Text = Encoding.UTF8.GetString(ProtectedTextByte, 0, ProtectedTextByte.Length);
}

Step 6: Place below methond also in MainPage.xaml.cs to decrypt encrypted data. Unprotect method of ProtectedData takes two arguments first the text to decrypted and second takes entropy to decrypt the encrypted data.

private void Decrypt_Click(object sender, RoutedEventArgs e)
{
   byte[] entropyByte = Encoding.UTF8.GetBytes(txtEntropy.Text);
   byte[] ProtectedTextByte = this.ReadTextFromFile();
   byte[] TextByte = ProtectedData.Unprotect(ProtectedTextByte, entropyByte);
   txtDecrypted.Text = Encoding.UTF8.GetString(TextByte, 0, TextByte.Length);
}

Step 7: Now run the application and the screen shown below will appear where text can be encrypted and decrypted.