Rolling code: Difference between revisions

Revision as of 03:56, 24 November 2023

Latest revision as of 23:34, 5 July 2024

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== Application in RF remote control ==

A rolling code transmitter is useful in a security system for improving the security of [[radio frequency]] (RF) transmission, comprising an interleaved trinary bit fixed code and rolling code. A receiver demodulates the encrypted RF transmission and recovers the fixed code and rolling code. Upon comparison of the fixed and rolling codes with stored codes and seeing that they pass a set of algorithmic checks, a signal is generated to actuate an electric motor to open or close a movable component.{{citation-needed|date=November 2023}}

== Rolling code vs. fixed code RF remote control ==

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{{main|KeeLoq}}

The Microchip HCS301 was once the most widely used system on garage and gate remote control and receivers. The chip uses the KeeLoq algorithm. The HCS301 KeeLoq system transmits 66 data bits.:

* 34 bits are not encrypted : a 28-bit serial number, 4 bits of button information, and 2 status bits (repeat and low battery indicators).

* 32 bits are encrypted (the rolling code) : 4 bits of button information, 2 bits of OVR (used to extend counter value), 10 bits of DISC (discrimination value; often the low 10 bits of the serial number), and a 16-bit counter.<ref>{{Citation |last=Microchip |title=HC301 KeeLoq Code Hopping Encoder |year=2001 |id=DS21143B |publisher=Microchip Technology Inc. |url=http://ww1.microchip.com/downloads/en/devicedoc/21143b.pdf}}</ref><ref>{{cite web|url=https://garagedoorpitt.com/garage-door-remote-not-working-reasons/|title=Garage Door Remote Not Working Reasons| date=4 November 2021 }}</ref> In a resyncing situation, the encrypted 32 bits are replaced with a 32-bit seed value.

As detailed at [[KeeLoq]], the algorithm has been shown to be vulnerable to a variety of attacks, and has been completely [[Broken (cryptography)|broken]].

== Rolljam vulnerability ==

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==External links==

* [http://auto.howstuffworks.com/remote-entry1.htm How Remote Entry Works]; cites successful attack on KeeLoq.

* Atmel Inc.'s application note [httphttps://wwwww1.atmelmicrochip.com/Imagesdownloads/aemDocuments/documents/OTH/ApplicationNotes/ApplicationNotes/Atmel-2600-AVR411-Secure-Rolling-Code-Algorithm-for-Wireless-Link_Application-Note.pdf AVR411][[Category:Automotive technologies]]

[[Category:Radio electronics]]