I am developing a site where users send an e-mail to their friends, etc, to come and view "Their Page". Which is a generic page which lists dates, and times the the user input.

The key to this is getting the members ID out of the e-mail. I want it encoded, so as to keep information secure etc...

The only thing I could think of doing was a
HTTP://URL/page.php?id=[md5 string] where [md5 string] is a md5 of memberID.

Now I see a lot of issues with just doing that... Do any of you guys have any ideas? Simple crypto classes/ruitines?

thanks a lot