are you looking for the algorithm as used in a car key fob (keyless entry)
or garage door opener? this is just simple PRBS and can be implemented
as a shift register with XOR taps, pretty easy.
there are several open source implementation based on linux ... look for one time password or similar solution as far as i understood your qeustion ...
you need to reset the transmitter and receiver before putting them in use.
then, whenever the transmitter sends a code and the receiver gets it,
the code changes to the next one, it's that easy. transmitter and receiver
are running the same algorithm and a comparison is done at the receiver.
the only trick is you need to allow a code range at the receiver in case
that the transmitter sends a signal while the receiver does not get it.
most car keyfobs allow a 256 forward search range. (it's not a problem to
do this in a keyless entry or garage door opener situation, but it will be
if you are using this algorithm in a high-speed application)
I am looking for any possible vulnerabilities in Microchip HCS200 KEELOQ® Code Hopping Encoder. More specifically I am analyzing this security protocol to find flaws in it. Could any of you help me out? Thanks!
HCS200 KEELOQ has been broken already some years ago. Microchip has introduced a new chip with a better code this time . HCS200 is being used in about 80% of the remote car fobs and lots and lots of cars are now stolen and broken into.