Hi Mike,

the signature size of RSA is an issue even in the 1024 bit version. The main 
wireless protocol, 802.15.4 has a PHY/MAC packet size of 127 bytes so we will 
have to fragment IP packets (Bluetooth LE is even smaller at just 27 bytes). 
This makes it very difficult to meet the time to light requirements. This is 
also a concern for the 70-80 byte overhead of ECC but we can probably just 
about manage.


Abhinav

________________________________
From: Ace <ace-boun...@ietf.org> on behalf of Michael StJohns 
<mstjo...@comcast.net>
Sent: Wednesday, February 8, 2017 3:55:22 AM
To: ace@ietf.org
Subject: [Ace] Asymmetric signature performance

Hi -

This is sort of non-obvious, but one or two articles I read suggest that
RSA 1024 performance may be better than the ECDSA equivalent.

The tradeoff here is obviously the size of the signature and the
transmission thereof, but...

While 1024 bits isn't an ideal security strength for RSA, using any
asymmetric key system for source authentication in group systems is
going to be much better than trying to pretend that symmetric group key
systems have any authentication properties at all.

I saw a PPT presentation by Hannes that  didn't include any RSA
performance numbers for the ARM processors even though the key sizes
were compared. My guess is that someone has numbers for 1024 RSA
signatures on the tiny ARM processors that might be useful to throw into
the mix.

https://www.cryptopp.com/benchmarks.html has comparison values for a
specific library.

What I'm suggesting is that we figure out how to meet the "can't cost
anything" requirement with weaker asymmetric keys rather than accepting
a low end fantasy of symmetric key multicast authentication.

Mike




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