As3Crypto
This is a bit of old news as the latest version of AS3Crypto came out in November, but I've only had the time to post about it now.
So what is As3Crypto? Well it's the Swiss Knife of AS3 Cryptography, I've been using it for a while now to manage secure communications for highscores and other sensitive data.
And guess what, a new version just (in November) came out, with support for TLS! Yes TLS in AS3, also version 1.3 has a lot of new improvements ( check the list ).
So to wrap things up, I prefer to use AS3Crypto over Adobe's crypto library because it has more features, a nice wrapper class and from my experience it's usually faster. Be sure to check out this great tool to check if your encryption is working well.
Expect a tutorial on how to use it with PHP soon 
November 7th, 2008 at 12:34 am
Any luck on how to use the AS3Crypto with RSA / OpenSSL in PHP - that would really be awesome - I’ve been trying to get flex and PHP to talk using this library and the php openssl but ive not had any luck
November 7th, 2008 at 9:51 am
Not really no, specially with php I found that was a bit of a mess because of special characters, but if you base16 or 8 encode it i’m sure it will help. Most of the issues i had were due to special characters being handled wrong in either flash or php.
But you might want to check directly with hurlant.