Hi David:
Thanks for the speedy follow-up email on your questions re the
security draft.
Just a quick preliminary note on performance:
1) caveat: performance is highly dependent on implementation
platform details, including instruction set, memory and the-like
(and, of course, clever implementation of the crypto itself;
extent to which implementation attack countermeasures have been
implemented, etc.).
2) data point: according to CHES 2004 paper, one has
implementations of 160-bit curve on ATMega128 AVR 8 Mhz processor,
with scalar multiplication taking 0.81s. Although linear scaling
would seem debatable, if one would nevertheless do this,
computational latency of scalar multiplication would come down to
129ms. Note RS: with improvements/new techniques developed since
2004, I estimate one could potentially squeeze this figure down to
roughly 80ms (for 160-bit curve). For curve at 128-bit crypto
strength, this may lead to time latency of roughly 250ms (again,
doing just a backside of a beer coaster estimate; much depends on
implementation platform details).
3) lower bound: the performance of any public-key based scheme
without online TTP using standardized curves has time latency at
least that of roughly one scalar multiplication. (Using RSA has
far higher time latency, so is no option here.)
We can discuss in much more detail offline (by examining your
platform choice).
On 9/21/2012 7:35 PM, David Goodall wrote:
I had an action item to provide my issues
with the draft security text (assume baseline as 1045/r4).
There were two general issues:
1. What functionality or advantages do we
lose when we lose the EAPOL key frames?
A specific example is that the multi-band
operations introduced in 11ad require use of fields which were
added to EAPOL key frames 1-4. If we don’t have the EAPOL key
frames in the 11ai mechanism, and we want the multi-band
operation, then we need to do some extra specification work.
This should be do-able but there may be an ongoing requirement
to maintain this part of the multi-band functionality in more
than one place in the 802.11 specification.
I need to review further to see if there
any other similar issues.
2. Will 11ai fast initial link setup be
fast for low power, CPU-challenged 802.11 devices?
An example is a mobile battery powered
802.11 RFID sensor tag with perhaps a 50 MHz 32 bit CPU. I
gather that the current non-TTP proposal will take perhaps 10
ms on a smart phone with a 1 GHz processor so it does not
appear suitable for low power devices. Rene Struik has
indicated that this issue can be addressed with a different
selection of elliptic curve and various processing techniques.
I have discussed the above with the authors
and expect to communicate further via email when new drafts
are available.
Thanks,
Dave
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