As a builder of web applications, I'm interested to see how others do it. This morning I received a promotional email from Snapfish about printing Facebook photos, and noticed the "view this email as a web page" link at the top. I figured the URL had to be unique enough to identify the campaign and the recipient, and it had to be obscure enough to prevent hacking so that I couldn't peek in on others' emails.
The typical way to do this is to include some keys in the URL, and then to also include a hash of those keys that includes a secret only the server has. The URL can be checked for authenticity, and the keys can be used to retrieve the data to display. The URL can't be hacked, because if I fiddle with the keys, the hash won't compute properly.
This is the actual URL (broken to fit):
The odd thing here are the almost-words that appear in it: "tnapfith", "Racebooj", and "nedzgnedbauchekdes9col". That's almost "Snapfish", "Facebook", and my email address. And there's the tell-tale "://" sequence with "olli" before it, which looks like ROT-13 "http" but is not.
I understand why the URL is so long: if you can store all of the data about the message in the URL itself, then you don't need to store it on your server and then retrieve it by key when the link is clicked. But what's with the grade-school encryption going on here?