Rolling code: Difference between revisions

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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]].

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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]]