Hash mismatch when SSHing to dropbear server

Hans-Christian Egtvedt hcegtvedt at atmel.com
Fri Aug 11 14:18:51 WST 2006


Matt Johnston wrote:
> On Tue, Aug 08, 2006 at 10:59:15AM +0200, Hans-Christian Egtvedt wrote:
>> I put the logs here:
>> http://www.egtvedt.no/dropbear/
>>
>>> Hopefully that might be of use.
>> I'm not quite seeing what I should be looking for, if anybody have a
>> pointer to what I should see (correct calculations etc) then I can start
>> my debugging :)
> 
> I've taken another look, turns out that my rigged random
> number generator had endian-specific output :( Could you
> give it another go with the new version at 
> http://matt.ucc.asn.au/dropbear/testing/db-unrandom2.tar.gz
> , sorry about that.

Thanks again for making this test :)

> I've put what I see as dump2.gz, it should be the same as
> you see on the workstation (at least for the calculations).
> 
> For debugging, I'd compare the two traces (avr versus x86)
> using vimdiff or something similar. Find the first point
> where they begin to differ in their numeric output (the
> big-numbers printed etc), and then add more debugging
> statements before and after that to narrow down the point
> where they start to differ. (Note that some of the
> hexadecimal output will differ with endianness, those should
> be marked).

I looked in your dump2-ppc vs. dump2, and found that in my x86 vs avr32
I have something faulty with the lines below:

X86
mp_int mp_exptmod_fast X:
57177274837176085710416002504255433114092271661685833986820045309615224297446777341551735779854568082929739086299104916069027366371956577873538725199184070295968371188748133537718214011550432576681564852689543774176794595038388421094953024485861852872341010938808415634567578860387138830446329229275810102561

AVR32
mp_int mp_exptmod_fast X:
26144629297143774191971619660891134373249478019090098695819374263386738314451768455401121680453697629379694697503955208976597983567979834942305834318644583895981375065787344042040457278746854017585464708420108154208341890971865764261601653839167444443692604372044120220262714803272834772806762057598126328370

> Have a look at libtommath/bn_mp_exptmod_fast.c for how I've
> added the debugging output there - it requires the extra
> #include up the top, and order of includes does matter.

I'll have a look inside here to see what I find :)

> I'd be interested to see the logs, let me know how you go.

http://www.egtvedt.no/dropbear/

v2 is the new logs.

-- 
With kind regards,
Med vennlig hilsen,

Hans-Christian Egtvedt
Applications Engineer - AVR Applications Lab
Atmel Norway




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