slow logins -- some data for comparison

Peter Turczak peter at turczak.de
Sun May 26 02:14:48 WST 2013


Hi William,

a few years ago I did the port of dropbear to use TFM. It was more a proof of concept port, but it worked a treat. 
There were some functions missing in TFM, which I had to port forward from libtommath. 
You can find my old tarball here http://peter.turczak.de/dropbear-tfm.tgz .

Best regards,
  Peter

On 25.05.2013, at 19:52, William Welch <bvwelch at gmail.com> wrote:

> OK, thanks for the pointers.  I realize that you are in no way obligated to incorporate such changes into your official version, but I will try to make these changes in such a way that they may be useful to you...
> 
> Right now, after a brief review, my thinking is to add tomsfastmath (TFM) to your BUNDLED_LIBTOM list, and enable it in your options.h, with USE_TFM as per the libtomcrypt document.  In places where the changes are more involved than just cut & paste, I will if-def with USE_TFM.
> 
> thanks for any suggestions!
> 
> 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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