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argilo / secplus

A software implementation of the Security+ system used by garage door openers
GNU General Public License v3.0
235 stars 31 forks source link

Protocol Question: Rollover #21

Closed Crsarmv7l closed 7 months ago

Crsarmv7l commented 7 months ago

Is the entirety of the rolling piece the count? Its not right? I am trying to get a better understanding of the components in the rolling part to prevent an overflow when incrementing the count.

For instance with Keeloq there are also two pieces; the fixed comprised of 8 hex digits, and the rolling part which is also 8 hex digits; however of the rolling part, only the last 4 hex digits are the count. So ignoring overflow bits, the keeloq count rolls over after FFFF.

argilo commented 7 months ago

As far as I know, the entire rolling code is a single count.

Crsarmv7l commented 7 months ago

As far as I know, the entire rolling code is a single count.

Alright. I figure I might as well test the limits and see if it still works on my garage door, eg with 0xFFFFFFFF and 0x00000002