Simplest way to encrypt / decrypt a string?

Ben Johnson wrote:

I have done multiple google searches and searched the mailing list. All
of the solutions I found seemed kind of heavy / complicated. I just want
a very simple way to encrypt and decrypt a string. Something like:

encrypt("fdsfdsfdsf", "some key");
decrypt("fdsfdsfsdf", "some key");

A quick Google for "Ruby AES encrypt" reveled several examples.

This one looks fine to me. (completely untested):