Puzzling
23 February 2000, 07:10 AM
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Just a thought,
If (as most modern alarms do) the code between alarm and remote changes everytime its used, how come when you come along a week later with your spare remote, it still works?
Surely the spare remote still has the code from a the last time IT was used?
Am I missing something?
Paul L
If (as most modern alarms do) the code between alarm and remote changes everytime its used, how come when you come along a week later with your spare remote, it still works?
Surely the spare remote still has the code from a the last time IT was used?
Am I missing something?
Paul L
23 February 2000, 08:13 AM
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I wondered about this also...
The only thing I could think of was..
Maybe the Alarm stores which codes have been used. Once it has been used once to unlock the car, it can't be used again???
This would have the desired effect...
The only problem would be if you ran out of codes or something???
There is an encryption algorythm called factoring (if anyone truly understands this could they please explain it to me!!) where you take a number and perform all sorts of calculations to produce a really long prime number (maybe 16 digits or something). I read somewhere that it would take the smartest computer on the planet 100 years to crack one which was 12 digits long or something.
Oh yeah... also, there are millions of pissible 16 digit codes which will work back to the original code.
If you have the orriginal code stored in the alarm it would be possible for it to varify the 16 digit unlock code even if it had been generated independantly, as long as both are working from the orriginal code. This code would be kept private to both the alarm and the fob.
It would be nice to know though... I'm the kind of sad git who finds this stuff really interesting!!
Cheers
Simon
The only thing I could think of was..
Maybe the Alarm stores which codes have been used. Once it has been used once to unlock the car, it can't be used again???
This would have the desired effect...
The only problem would be if you ran out of codes or something???
There is an encryption algorythm called factoring (if anyone truly understands this could they please explain it to me!!) where you take a number and perform all sorts of calculations to produce a really long prime number (maybe 16 digits or something). I read somewhere that it would take the smartest computer on the planet 100 years to crack one which was 12 digits long or something.
Oh yeah... also, there are millions of pissible 16 digit codes which will work back to the original code.
If you have the orriginal code stored in the alarm it would be possible for it to varify the 16 digit unlock code even if it had been generated independantly, as long as both are working from the orriginal code. This code would be kept private to both the alarm and the fob.
It would be nice to know though... I'm the kind of sad git who finds this stuff really interesting!!
Cheers
Simon
23 February 2000, 10:22 AM
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Just a guess - I've no idea if this is how the alarms actually work.
From what I understand, the alarms maintain a sequence of changing codes that will match the transmitter (and presumably this is why continuous pressing of the remote out of range can cause the sequence in alarm and remote to diverge to the point they don't work)
Anyway, for multiple transmitters I assume it would be simple to maintain multiple sequences - one for each transmitter. So when you use your spare remote, it's being matched against a different sequence in the alarm from the main one.
I assume this might also be how alarms like the Cliffords etc allow lost remotes to be blocked or new ones added - just remove or add a new sequence for that remote as required?
As I said tho, that's just a guess and it may in fact be totally different!
Cheers
Alastair
From what I understand, the alarms maintain a sequence of changing codes that will match the transmitter (and presumably this is why continuous pressing of the remote out of range can cause the sequence in alarm and remote to diverge to the point they don't work)
Anyway, for multiple transmitters I assume it would be simple to maintain multiple sequences - one for each transmitter. So when you use your spare remote, it's being matched against a different sequence in the alarm from the main one.
I assume this might also be how alarms like the Cliffords etc allow lost remotes to be blocked or new ones added - just remove or add a new sequence for that remote as required?
As I said tho, that's just a guess and it may in fact be totally different!
Cheers
Alastair
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06 December 2001 01:42 AM