How to encrypt data in javascript and decrypt in php?

You could use AES + Base64, there's a JS aes library at http://www.movable-type.co.uk/scripts/aes.html, should be doable in php as well http://www.movable-type.co.uk/scripts/aes-php.html.

What you are probably looking for is RSA encryption. You generate a key for your server to use which has a public version and a private version. Your javascript will contain the public version which can be used to encrypt the data, and your php will use the private version to decrypt the data.

As a jumping off point, you can start here for javascript public/private key examples: http://shop-js.sourceforge.net/crypto2.htm

And here for the PHP side: http://www.webtatic.com/blog/2009/07/php-public-key-cryptography/

I'm not sure what you would gain by doing encryption in javascript. Your entire routine and encryption key are effectively available to the public. If you are trying to protect against sniffing, you should use SSL.

I think you will have to use SSL to encrypt everything.