In what way? If I'm storing 255 bytes of username/email/credentials/settings/etc, but pad in some fun way to 512 bytes prior to encryption, what in the world does knowing that the cookie is 512 bytes do you? You have no idea what data is stored. You don't know if there are 512 bytes of actual data, 128 bytes with lots of fluff, or anything at all other than 512 bytes. Hell, it could be 0 bytes of data and 512 bytes of random data that I submit to every single person that visits the site just to fuck with people like you! You seem like you need something to do ;-)

If the contents of the cookie is a JSON array of recently viewed items, then the size is correlated to whether I've been actively viewing items recently.

Adding random padding makes it harder to get a signal, but with a high enough sample size, it's still possible to get some information. If you always pad to a fixed size, then there's probably no useful information.

At the moment, I think I have enough to do, but I'll probably be looking for something new in the next few weeks. Got any novel single player video game recommendations?

>If

That's are really big word in that sentence. You have NO idea, like 0, what is stored in an encrypted cookie. To even think you do is just pure folly.

This is a very simplistic way of looking at things. A lot of the times in security, having an idea of what's not in there can be almost as valuable as having an idea of what's in there.

I will provide a very simple counterpoint to your argument: say I log in, log out and log in again, dumping my two encrypted session cookies in between. If they are perfectly identical, then knowing nothing else about the environment nor the encryption used, I already know that there's no timestamp value in the cookie acting as a time barrier, nor a challenge-response check, nor a nonce value.

Knowing that, I can focus my attention on stealing session cookies from users for trying replay attacks.

I do have ideas. I can strengthen them by reverse-engineering the behavior using my own account. I participate in follies regularly, so that's not a strong disincentive for me.