In this series of three articles on the topic of Encryption in Flex Applications, we’ll first cover a basic data encryption and storage example in a Flex application. In article two, we’ll look at using an interface and doing some minimal encryption on a SWC file to protect an example commercial library we want to sell. In the final installment, we’ll take a look at using some of the features of NitroLM.com which is a commercial API for user registration, management, and entire application encryption.

In Adobe’s newly-released version of AIR 1.0, they provide an API for storing encrypted data to the hard drive. The flash.data.EncryptedLocalStore class uses the Windows DPAPI or KeyChain on MacOS to store and retrieve encrypted data as a ByteArray. Unfortunately, this capability isn’t available to us in a Flex application. In this example, I’ll demonstrate creating similar functionality by encrypting data stored in a local SharedObject.

The first thing we need is to download an encryption library to use in our Flex application. I’m using AS3Crypto (http://crypto.hurlant.com) created by Henri Torgemane. I recommend downloading the source code so you can debug easier and see how the encryption is working.

In this example (view-source enabled), the user can save a username and password between runs of the application to be used by a web service. It’s not totally secure since the randomly generated key is stored along with the encrypted data. I’ll leave it as an exercise for the reader to come up with clever ways to obfuscate the key or use alternative server-side repositories that are more secure.

FlexEncryptionExample1 example

Let’s walk through the code. We have two main methods, encryptedLoad() and encryptedSave(). encryptedSave() generates a random 16 byte key, and runs the AES-128 encryption algorithm on our username and password that we’ve packaged into a ByteArray.

 

private function encryptedSave():void
{
 	//create or retrieve the current shared object
 	var so:SharedObject = SharedObject.getLocal("encryptedStore");
 				
 	//generate a random key
 	var key:ByteArray = new ByteArray();
 	var random:Random = new Random();
 	random.nextBytes(key, 16);
 				
 	//store our data to encrypt into a ByteArray
 	var cleartextBytes:ByteArray = new ByteArray();
 	cleartextBytes.writeUTF(username.text);
 	cleartextBytes.writeUTF(password.text);
 				
 	//encrypt using 128b AES encryption using a random key
 	var aes:ICipher = Crypto.getCipher("aes-ecb", key, Crypto.getPad("pkcs5"));
 	aes.encrypt(cleartextBytes);
 				
 	//store key along with the data to decrypt
 	//Note: normally you'd never do this for security reasons,
 	//      but I'll leave it to the reader to handle additional
 	//      security and/or obvuscation.
 	var dataToStore:ByteArray = new ByteArray();
 	dataToStore.writeBytes(key);
 	dataToStore.writeBytes(cleartextBytes);
 
 	//save the blob of encrypted stuff in the SharedObject
 	so.data.ws_creds = dataToStore;
 	so.flush();
 				
 	//clear out the fields
 	username.text="";
 	password.text="";
}

encryptedLoad() reads in our key and uses it to decrypt the rest of the ByteArray. The values are then loaded into their respective form fields from the decrypted ByteArray.

 

private function encryptedLoad():void
{
 	//create or retrieve the current shared object
 	var so:SharedObject = SharedObject.getLocal("encryptedStore");
 				
 	var dataToLoad:ByteArray = so.data.ws_creds;
 				
 	//read in our key
 	var key:ByteArray = new ByteArray();
 	dataToLoad.readBytes(key, 0, 16);
 				
 	//read in our encryptedText
 	var encryptedBytes:ByteArray = new ByteArray();
 	dataToLoad.readBytes(encryptedBytes);
 				
 	//decrypt using 128b AES encryption
 	var aes:ICipher = Crypto.getCipher("aes-ecb", key, Crypto.getPad("pkcs5"));
 	aes.decrypt(encryptedBytes);
 				
 	encryptedBytes.position = 0;
 				
 	username.text = encryptedBytes.readUTF();
 	password.text = encryptedBytes.readUTF();
}

Hopefully with this example, you can start to see some of the possibilities for encrypting your data using Adobe Flex/AIR.