Hi Matt,
Thank you for your interest. I put the modified files, here:
https://github.com/bvwelch/dropbear
If you prefer a fork, or other approach, let me know and I will revise the
upload.
I can go back to my microblaze and capture the dropbear race output, and
probably could run gprof on the Microblaze as well.
Since this all started by selecting dropbear versus openssh from the
typical Buildroot, that means that the same toolchain
is used, so my guess is that openssh just has a different algorithm. By
the way I tried various versions of gcc toolchains.
I did notice that if I disabled group14, I saw about the same login time as
dropbear 0.52 -- 45 seconds, and if I switched
to fastmath, the time dropped to 30 seconds.
But the 'footprint' of dropbear, built with tomsfastmath, is large, since
it has a lot of unrolled loops. It may be about as large
as openssh.
I will check out your other suggestions.
Thank you,
William
On Saturday, June 1, 2013, Matt Johnston wrote:
Hi William,
That's puzzling. I wonder if the hotspot is different on the Microblaze
device versus what you see with valgrind - googling I came across a setup
that sounds similar to yours [1], they thought the SDRAM interface was the
bottleneck. Do you know what kind of memory setup your CPU has? Perhaps
OpenSSL is better at keeping everything in registers, or something like
that. It could be worth asking on the libtom google group if anyone has
ideas?
[1] bottom of
https://groups.google.com/forum/#!msg/sci.crypt/3pg1ngSaQpc/Tr-gcbqxfvEJ
I'd be keen to see your modifications to integrate them into the main tree
- for more normal slow CPUs I think tomsfastmath will be worthwhile.
Cheers,
Matt
On Sat 1/6/2013, at 5:15 am, William Welch bvwe...@gmail.com wrote:
Greetings,
I completed a first cut of the fast math version -- sadly, it did not
help much. I went back to my linux PC and did some testing with
valgrind/callgrind -- and, according to callgrind, for both the tommath and
the fast math versions, the hot spots are in tight loops inside of
fp_montgomery_reduce and fast_mp_montgomery_reduce. The 2nd hot spot is in
fast_s_mp_sqr and the similar routine in fast math.
I am pondering my next step -- I guess I will study those inner loops
and see why they are so slow on the microblaze -- but I am a bit confused
by the fact that openssh / sshd completes in 5 to 10 seconds on the same
system...
If there is interest in these modifications to dropbox for fast math,
let me know and I will send them or put them online. The changes are
pretty clean -- just a couple of things as mentioned previously.
Suggestions welcome!
William
On Sat, May 25, 2013 at 10:19 AM, Matt Johnston m...@ucc.asn.au wrote:
I'd start from 2013.58. It's mostly a case of search/replace
of function calls, though mp_init is a bit different I
think (it allocates whereas the straight libtommath version
doesn't?). Take a look at
https://secure.ucc.asn.au/hg/dropbear/file/75509065db53/ecdsa.c#l169
- the ltc_mp variable is set up at
https://secure.ucc.asn.au/hg/dropbear/file/75509065db53/crypto_desc.c#l71
so it could be set to tfm_desc instead.
Tomsfastmath 0.12 would be best from libtom.org
Cheers,
Matt
On Sat, May 25, 2013 at 10:01:16AM -0500, William Welch wrote:
Thank you for your reply.
If I were to attempt to add support for tomsfastmath, using ltc_mp as
you
described, which version of dropbear should I start from? And where
should
I obtain the tomsfastmath library?
Thank you,
William
On Sat, May 25, 2013 at 3:41 AM, Matt Johnston m...@ucc.asn.au
wrote:
Hi,
I think the solution is to use tomsfastmath instead. There was a
patched
version posted a while ago on this list. Eventually I'd like to have
Dropbear able to build against either tomsfastmath (for speed) or
libtommath (for portability) using the ltc_mp mechanism in
libtomcrypt.
There's also ECC support nearly complete in the 'ecc' mercurial
branch.
That's a few times faster than normal kexdh. It adds around 30kB to
binary
size on x86. That should make it into the next Dropbear release,
though
only will help for recent OpenSSH peers.
Matt
William Welch bvwe...@gmail.com wrote:
Greetings,
First -- thank you for dropbear! I have enjoyed using dropbear on
various smallish systems for years now!
But I have a problem with a specific system -- admittedly it is
rather
slow -- only 50 BogoMips according to the linux kernel. It is a
Microblaze.
I use the Buildroot system for many different routers and other
small
systems here. I have compared different versions of dropbear,
against
openssh.
My issue is with the server mode -- sshd -- I note that on
dropbear 0.52
(which I happen to run on other routers here), I can connect from
my ubuntu
or mac, to
