"Ted Mittelstaedt" <tedm@[EMAIL PROTECTED]
> wrote in message
news:newscache$l6imuj$ume$1@[EMAIL PROTECTED]
>
> "maxpower" <damnnickname@[EMAIL PROTECTED]
> wrote in message
> news:zNmdnYmJIMnPnBfanZ2dnUVZ_t2inZ2d@[EMAIL PROTECTED]
> >
> > "MoPar Man" <MoPar@[EMAIL PROTECTED]
> wrote in message
> > news:4789AA15.A54FE2BB@[EMAIL PROTECTED]
> > > maxpower wrote:
> > >
> > > > The RKE system and transmitter use a rolling code method ...
> > > > The transmitter sends a randomly selected sequence code each time
> > > > The code increments vary depending on a unique algorithm that
> > > > is preprogrammed to each transmitter at the time it was built.
> > > > The sequence changes each time the transmitter is used.
> > >
> > > > the sequence code cannot be calculated from the encoded
> > > > transmission. The receiver module also learns the transmitter
> > > > id code
> > >
> > > So far, what you're saying is that the FOB sends out a different
> > > sequence each time it's pressed, and that the ID code of the fob can
> > > be uniquely calculated from the transmitted data stream based on an
> > > algorythm.
> > >
> > > I doubt that the fob actually does generate a completely different
> > > stream each and every time it's pressed, as I doubt that the
designers
> > > would ever anticipate someone with enough electronic gear would be
> > > close enough to the car to (a) want to open/unlock the car without
> > > possessing the real fob or key, (b) be close enough to evesdrop and
> > > capture the transmission, and (c) possess the electronics required
to
> > > replicate the transmission. Just consider a use-case situation.
> > >
> > > But even if the fob does generate a different stream each time it's
> > > pressed, then I guess the receiver in the car would have to never
> > > respond to the same stream twice.
> > >
> > > > and initial sequence code at the time of transmitter programming.
> > > > The receiver then expects the next transmitted sequence code to
> > > > increment within a predetermined range of numbers
> > >
> > > Now that has got to be total bull****.
> >
> > Your right it has to be total bull****, But it isnt, google rolling
code!!
> > No wait, I will do it for you.
http://en.wikipedia.org/wiki/Rolling_code
>
> maxpower, there is nothing in this description that would preclude
> the original poster from programming the same keyfob to open multiple
> cars - as long as the keyfobs were the same part number AND as
> long as the system didn't have a different set of pseudo random number
> generators. (PRNGs)
>
> If for example the transmitter had a table of, lets say 200 different
> PRNGs, and during keyfob programming the transmitter uploaded
> a selected PRNG to the keyfob, then you would have a problem
> doing it. What would happen is both vehicles would likely use a
> different PRNG.
>
> But, if the PRNG's are only different between vehicle models, and
> or years, and the PRNG was burned into the keyfob, then as long
> as both cars used the same PRNG you could do it.
>
Keep in mind that when you program one remote on this system you have to
program all at the same time. Or it wipes out the ones that you didnt
program.
> I can guarentee to you that at least up to 1995 Chrysler did in fact
> use fixed PRNGs in the RKE system. In fact the sequence generator
> was the same algorithim for multiple YEARS. That is why I was
> able to program both my '94 and '95 van to use the same keyfobs.
You were able to do your older vehicles because it was not using the
rolling
code system I would think. when program a key fob into that year you
didnt
have to have all of them to reprogram. You were able to add one
>
> They changed the remotes in 96, and I would assume the system
> as well. But, if the new keyfobs are transmit-only, then it would be
> very likely that keyfobs of the same part number would use the
> same PRNG and would work.
>
> Frankly the entire system is way overengineered. A thief simply
> walks up to the car and smashes the window with a rock, he does
> not bother fiddling around with sniffing RKE signals.
I beleive the key fobs were designed more to lock and unlock doors
easier.... not to deter thiefs. The skim key is to deter thiefs from
stealing the vehicle. and the vehicle theft alarm was to deter them
>
> Ted
>
>
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