By: Chad Upton
The as3crypto library is packed with the most common encryption and decryption algorithms. In this post, I want to demonstrate how you can use the as3crypto library to encrypt and then decrypt some data that is useful in a variety of real world scenarios.
Encryption is the process used to turn plain text into unreadable information. Decryption is the process of turning unreadable encrypted information back it into plain text. Both operations require an encryption algorithm and key. Anyone who has the key and algorithm can convert the encrypted information back into plain text. This is useful when storing data or transferring data to a place where you don’t want anyone to read it.
There are half a dozen secret key encryption algorithms in as3crypto. Some of these algorithms are better than others, and others are provided because they are common in legacy systems and may be needed for compatibility. I’m going to cover the various algorithms in a future post; for this post I’ll use AES since it is a fast and strong algorithm.
Let’s say you want to write data to an encrypted file. Perhaps, you want to store application settings or software license info in a file, but you don’t want anyone to read it and possibly compromise your licensing system.
Follow the steps below to make an AIR app that will encrypt some data and write it to a file.
- Figure 1
- Start by creating a new AIR project in Flex Builder
- Name the main application file Encrypt.mxml (Figure 1)
- Download the as3crypto library (swc file) from the project on google code
- Place as3crypto.swc in your AIR project’s libs folder (Figure 2)
- Copy the code below and replace everything in Encrypt.mxml with it
- Figure 2
<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication
xmlns:mx="http://www.adobe.com/2006/mxml" layout="horizontal" width="340" height="150" showStatusBar="false" verticalAlign="middle">
<mx:Script>
<![CDATA[
import com.hurlant.crypto.symmetric.AESKey;
import mx.controls.Alert;
import com.hurlant.crypto.symmetric.DESKey;
import com.hurlant.util.Hex;
import mx.charts.CategoryAxis;
private static var stream:FileStream;
private static var file:File;
private function encrypt():void
{
file = File.desktopDirectory.resolvePath("encrypted.txt");
//open a filestream to write to file
stream = new FileStream();
stream.open( file, FileMode.WRITE );
//define the encryption key
var key:ByteArray = Hex.toArray("NewTorontoGroup");
//put plaintext into a bytearray
var plainText:ByteArray = Hex.toArray(Hex.fromString(txtInput.text));
//set the encryption key
var aes:AESKey = new AESKey(key);
//encrypt the text
aes.encrypt( plainText );
//write encrpted text to the file
stream.writeMultiByte( Hex.fromArray(plainText), "utf-8" );
//provide confirmation
Alert.show("Text written to file on desktop","Success");
//close the stream
stream.close();
}
]]>
</mx:Script>
<mx:TextInput id="txtInput" text="Enter text to be encrypted." />
<mx:Button label="Create File" click="encrypt()" />
</mx:WindowedApplication>
Run the Encrypt app. Type some text into the Text Input and click the Create File button. A file called “encrypted.txt” will be written to your desktop. Open the file and look at your text in its encrypted form. If you don’t see anything, check your encrypt application. Try copying the code and clicking the Create File button again. Now we’ll create an app to decrypt the file.
- Start by creating a new MXML Application
- Name the file Decrypt.mxml (Figure 3)
- Copy the code below and replace everything in Decrypt.mxml with it
- Figure 3
<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" initialize="init()" showStatusBar="false">
<mx:Script>
<![CDATA[
import com.hurlant.crypto.symmetric.AESKey;
import com.hurlant.crypto.symmetric.DESKey;
import com.hurlant.util.Hex;
import mx.managers.DragManager;
private function init():void{
addEventListener(NativeDragEvent.NATIVE_DRAG_ENTER, dragEnterHandler);
addEventListener(NativeDragEvent.NATIVE_DRAG_DROP, dragDropHandler);
}
private function dragEnterHandler( event:NativeDragEvent ):void
{
DragManager.acceptDragDrop(this);
}
private function dragDropHandler( event:NativeDragEvent ):void
{
//get the file
var file:File = File(event.clipboard.getData(ClipboardFormats.FILE_LIST_FORMAT)[0]);
//create a FileStream for the file
var fileStream:FileStream = new FileStream();
//open the file to read
fileStream.open(file, FileMode.READ);
//read the file into a string
var encryptedText:String = fileStream.readUTFBytes(fileStream.bytesAvailable);
//close the file
fileStream.close();
//define encryption key
var key:ByteArray = Hex.toArray("NewTorontoGroup");
//set key
var aes:AESKey = new AESKey(key);
//put encrypted text into ByteArray
var decryptedBytes:ByteArray = Hex.toArray( encryptedText );
//decrypt the bytearray
aes.decrypt( decryptedBytes );
//convert the decrypted bytearray to a string and display
txtDecrypted.text += decryptedBytes.toString();
}
]]>
</mx:Script>
<mx:TextArea id="txtDecrypted" text="" wordWrap="true" width="100%" height="100%" />
</mx:WindowedApplication>
Run the Decrypt app. Minimize Flex builder and drag the “Encrypted.txt” file from your desktop and drop it on the Decrypt app. You should see your the encrypted text displayed as decrypted plain text. This illustrated the basic mechanics required to encrypt and decrypt text in ActionScript3 using the as3crypto library.
New Toronto Group
