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HTOP mention Tags: Mobile edit Mobile web edit |
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A '''rolling code''' (or sometimes called a '''hopping code''') is used in [[keyless entry]] systems to prevent [[replay attack]]s, where an [[Eavesdropping|eavesdropper]] records the transmission and replays it at a later time to cause the receiver to 'unlock'. Such systems are typical in [[garage door opener]]s and keyless car entry systems.
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* Common PRNG ([[pseudorandom number generator]]) — preferably [[Cryptographically secure pseudorandom number generator|cryptographically secure]] — in both transmitter and receiver
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* Receiver compares 'next' to its calculated 'next' code.
* A typical implementation compares within the next 256 codes in case receiver missed some transmitted keypresses.
[[HMAC-based one-time password]] employed widely in [[multi-factor authentication]] uses similar approach, but with pre-shared secret key and [[HMAC]] instead of PRNG and pre-shared [[random seed]].
== Application in RF remote control ==
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