A complete set of the basic cryptographic algorithms can be found in the Crypto-js open source library. Almost complete as RSA is not yet featured. But its OpenSSL interoperability aligned with its simplicity of use make it a standard in run-time encryption. If you still want to use the RSA algorithm, then you will have to turn to the Titaniumcore Project maintained by Atsushi Oka. The Titaniumcore library allow the processing of a 65536bit RSA key generation without killing your CPU. The computing is based on an asynchronous function call. This allow an average 4096bit RSA key to be generated in an human/consumer space time.
As the encryption itself is a CPU killer task, Adobe is developing its own actionscript package flash.crypto in its incubating new beta version of as3. The package is by now only providing a stronger random number generator, which would insure a better, stronger encryption.
A realistic IT use of run-time client-side encryption should be adapted for small and sensible data. Let’s say login/password communication for example. By separating key and message, as well as signing the data itself you can get a sniffing way more complex that it is actually in the small business IT ecosystem. Skylink Lab get its hand on the Titaniumcore library and will soon open an “on-the-fly” key generation combined with message delivery. We will update soon.