Java Security

Hi all,

I'm relatively new to encryption methods, so please excuse me if this question is too simple.

We have a web application that is going to rely on session cookie authentication. The cookie is going to contain some information that we'd like to encrypt, such as a username, email address, stuff like that, so that the client can not (easily) view this information using a cookie viewer (or the like.)

Can someone give me a recommendation on how to do this? Keep in mind that we will need to un-encrypt the data as well so we can identify a user, so I think MD5 won't work since it's a one-way hash.

Thanks,
Derek