slow logins -- some data for comparison

[William Welch]

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 <matt at 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 <matt at 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 <bvwelch at 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 dropbear sshd, in about 45 seconds.  This is having
> disabled the
> > >> RSA host key, and already generated the DSS host key.   But on more
> recent
> > >> versions of dropbear, e.g. 2013.58, several minutes elapse without a
> > >> connection.
> > >>
> > >> In contrast, switching to openssh in buildroot, and also disabling the
> > >> RSA host key, connection time is 5 to 10 seconds!  Unfortunately, the
> > >> openssh has a huge 'footprint' in the flash filesystem that I would
> rather
> > >> avoid.
> > >>
> > >> The issue seems to be in the key exchange ( I can watch this by doing
> > >> 'ssh -v ' from my client connection).  Meanwhile, running 'top' on my
> > >> Microblaze shows near 100% cpu used.  the debug message is: expecting
> > >> SSH2_MSG_KEXDH_REPLY
> > >>
> > >> Buildroot has the gnu cross tool chain set to 'optimize for size' in
> all
> > >> cases.
> > >>
> > >> Suggestions welcome!
> > >>
> > >> thank you,
> > >>
> > >> William
> > >>
> > >>
>
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