cryptofreak.org cryptofreak home projects
contact about
Contact:


projects
News Agenda
Antera Antera
News Commentator
News fcreate
Linux Porting Linux Porting
mod-chal mod-chal
Quake III Quake III
News Zope
Contact: webmaster

From: Michael Dwyer (mdwyer, timestreamtech dot com)
Date: 2001.03.08 - 16.38 MST


Damnit, man, I'm at WORK right now!  Why couldn't you send me this one
on a weekend or something... well, not this weekend...  Anyway...

--- Jay Miller <jnmiller, cryptofreak dot org> wrote:
> Okay, so my original "this is gonna be a piece of cake" idea didn't
> pan
> out.  The parity bit business isn't working out.  Consider the first
> 20
> bits in the thing:
> 
> 1 1 1 1  0 0 1 1  0 0 1 1  0 1 1 1  0 0 0 1

Are we sure we've got the keying correct?  The bits come out
significantly different if you consider it to be phase-shift or
manchester encoding.  I need to sit down and stare at it a while, and
can't do that right now. :(

> Parity just doesn't seem to work on that sucker.  And the 'inserting
> one or zero to break up a BRK' doesn't apply, either..

Parity is limited to none, even, or odd.  That should be relatively
easy to eyeball... Should be.  Do we know that this is a consumer
modem?  Is this assured to be on a phone?  With more info, we could
make assumptions...

For instance, since the frequency doesn't change, it isn't FSK, so it
isn't a 300-baud modem.  PSK looks a bit more reasonable, but it should
be noted that PSK encodes 2 bits per transition, so we could be reading
it all wrong.  They could be using Manchester encoding, but I've never
heard of that being used in modem technology, so I would doubt it.

Consumer modems generally run [n|o|e][8|7][1|1.5|2], and that should be
easy to clock out, right?  <sigh>  Modems are asynchronous, so there
should be some form of clocking in the signal, too -- if not the stop
bits. 

I really have to look at my notes, so I'm mostly just spewing ideas for
the rest of you.  Good luck.

> I was also thinking that any encryption would, it seems to me, have
> to be applied to letters rather than bits.. so we shouldn't have to
> worry about that.  Right?

Our first step need to be finding a reasonably bitstream.  The
encryption is an entirely different problem.  That said, I cannot
imagine the prof being THAT evil -- I'm looking forward to PigLatin or
ROT13. :)

More later...


__________________________________________________
Do You Yahoo!?
Get email at your own domain with Yahoo! Mail. 
http://personal.mail.yahoo.com/
--
This is the mod-chal mailing list.  To unsubscribe, email
majordomo, cryptofreak dot org with message body 'unsubscribe mod-chal'.
Or, for more information, visit http://www.cryptofreak.org/.



This archive was generated by hypermail 2b30 : 2001.09.26 - 14.03 MDT