WebApp Sec: Re: Whitepaper "SESSION RIDING - A Widespread Vulnerability in To day's Web Applications"

[Florian Weimer <fw () deneb enyo de>]

* Jim Weiler:

> Couldn't the secret be any unpredictable value that the server can
> come up with, like a GUID or the timestamp of the user login, and
> not something that uses encryption?
Yes, and a HMAC provides that.  You have to make the value depending
on the web application user (and preferably the time), otherwise users
could attack each other.  Of course, you can also use a decent PRNG to
generate a token, and store it in the user's session object on the
server side.  But this might be more complicated to implement.

A HMAC is not really encryption---but thanks to chaffing and
winnowing, all authentication schemes also permit encryption, albeit
with a significant overhead.