The example below uses my 100% JavaScript multiple-precision math library. The encryption exponent is small-ish, making for faster encryption. Presumably, decryption would be handled on the server, where things aren't as slow.

In a nutshell, here are the JavaScript files you need:

• Multiple-precision library
• Barrett modular reduction library
• RSA library

Additionally, I wrote a Windows application that generates random keys for use with the JavaScript library. It even generates the JavaScript source code. Paste and go!

• RSA Key Generator
• RSA Key Generator source code

Note: The RSA key generator application is written in Delphi 4, which is Object Pascal. This includes a re-implementation of the multiple-precision library and the Miller-Rabin test for primality. Keys are generated using Algorithm 8.1 from the Handbook of Applied Cryptography. However, the actual random-number generation is not particularly robust. I just use the built-in functions in Delphi, seeded from the system clock. If you want to get fancy, you should write a better random-number generator.