Over the last couple of years I have used encryption on many Flash projects and until the other day, this was always a straight forward task. Cryptography has been particularly useful when to protect a server side script from fraudulent attacks. This has included things like a high score board or the progress of players through out a game.
Actionscript AES Encryption
So here is a simple example demo with just pure Actionscript AES encryption and decryption with a block cipher of 256 bits.
PHP AES Encryption from Flash
And here is another example demonstrating Actionscript to PHP AES encryption and decryption with the same block cipher of 256 bits. Both demonstrations use the same key so if you change the keys so they do not match then they will not be able to decrypt between each other. Also in this demonstration I post the key with the text to either encrypt or decrypt, you would of course never do this when using AES normally.
I hope this is sunshine on a rainny day for someone out there, you can download the source code from the Lost In Actionscript code.google repository or download an archived version.