one less onion skin

[James Muir]

Nick Mathewson wrote:
> On Wed, Mar 07, 2007 at 09:29:43AM -0500, Paul Syverson wrote:
>  [...]
>> My kneejerk response is
>> that (a) the overhead from this vs. everything else in Tor is very
>> small,
> 
> This was one of the major reasons for not doing it at the same time as
> CREATE_FAST.  Assuming that TLS conns are mostly longer-lived than
> circuits, then circuit PK should strongly dominate link PK.  The same
> amount of data, however, goes over TLS as over circuits.
> 
> Given those (fuzzy, inaccurate) assumptions, it follows using
> CREATE_FAST should have been sufficient to get rid of 33% of the
> server-side PK.  Dumping the first circuit hop's AES, however, would
> only get rid (at best) of 12.5% of server-side AES, so it wasn't as
> immediately clear of a win.  (There are 8 server-side AES operations
> on all the data now: the first two servers in the circuit need to a
> TLS decrypt, a circuit decrypt, and a TLS encrypt; the third server
> does a TLS decrypt and a circuit decrypt.)
> 
> AES was between 8 and 20% of server CPU time the last time I looked;
> this change would save at most 2.5% of server CPU, which doesn't
> really make it seem like low-hanging fruit to me.

Is the 8 to 20% AES CPU time true even for Entry Guards?

When I checked a couple of weeks ago, the network-status documents 
listed only 279 Entry Guards (out of 1301 total nodes).  My thought was 
that it makes sense to make their burden lighter since they handle more 
circuits.  Can't we eliminate 33% of the Entry Guards AES operations by 
dropping the outer onion skin?

-James