Re: Load Balancing

[Roger Dingledine <arma@xxxxxxx>]

On Sat, Sep 22, 2007 at 03:51:07PM -0400, Anthony DiPierro wrote:
> > If the user started churning through circuits at five times the current
> > rate, we may end up forced to move the "10 minute" value back even farther
> > to compensate, resulting in even more user connections becoming linkable.
> >
> Why does new circuit creation use up so much CPU?  Are you spawning a
> new thread for each circuit, or something?  If so, maybe there's a way
> to be more efficient instead?

It's because of the crypto. Each server on the path needs to do two
public key operations for each new circuit -- one to ensure perfect
forward secrecy, and the other for authentication.

See e.g.
https://tor.eff.org/svn/trunk/doc/design-paper/tor-design.html#subsec:circuits
or Section 5.1 of
https://tor.eff.org/svn/trunk/doc/spec/tor-spec.txt

If you still want to read after those, also see
http://freehaven.net/anonbib/#overlier-pet2007
and
http://freehaven.net/anonbib/full/date.html#kate-pet2007

--Roger