Re: TCP timestamp starting value

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Thu, Jul 21, 2016 at 11:13:21AM +0200, Edgar Fuß wrote:
> > Wouldn't a better idea be to compute HASH(cookie,src,dst) + uptime for
> > some random cookie created at boot time? Essentially, you give each
> > target a unique monotonic time base, without leaking any data about the
> > perceived local time.
> I thought about something like that, but then the peer would be able to tell 
> when you booted (because the timebase changed). The elegance (or so I think) 
> of using real time is that the peer can't tell a reboot from an intermediate 
> network failure.
> On the other hand, what's so bad about "leaking" information on my perception 
> of UTC time?

You are assuming a clock is synchronised. It may or may not be. Given
that ntpdate is often run on boot as well, there are lots of
environments where leaking the real time can be useful or where a reboot
is just as visible. The cookie can be updated automatically every couple
of hours. The other issue remaining is that the real time is not
monotonic.

Joerg