Holden BCM and Key Fobs

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Re: Holden BCM and Key Fobs

Postby j_ds_au » Mon Jan 28, 2019 10:51 pm

The1 wrote:i would think it would be so if you lost your key then it would stop someone eventually finding it and being able to open your car, though it will work and update itself once used in the ignition, so BCM must have some kind of timer or last X number of rolling codes only stored, key may still retain a master value that works in the barrel so it can disarm to get a new rolling code, perhaps that's what these people have worked out via the BCM serial number.

Yeah, maybe this scheme is to "deactivate" a lost key. Unless the lost key has a tag which can identify its vehicle, if you found this key, you'd need to walk past potential vehicles and press the open button to see if that's indeed the vehicle. This scheme would (eventually) prevent that. If you found the key, you could of course always try that on the doors of potential vehicles, but that would look very suspicious.

I don't think that the rolling key code is checked when the key is inserted into the reader, as that wouldn't serve any practical purpose (a bad rolling key code has no effect here). Only the respective ID(s) would need to be checked, most likely via an encryted data exchange via the reader (although I do wonder if the key reader interface is actually bi-directional, or if it's uni-directional, from the BCM to the key fob, with the key fob's RF transmitter being used for the other data direction).

Joe.

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Re: Holden BCM and Key Fobs

Postby j_ds_au » Mon Jan 28, 2019 11:09 pm

delcowizzid wrote:I can see it transmit on my sdr at 304mhz wonder if I can decode the data hmm

...1010101

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Re: Holden BCM and Key Fobs

Postby delcowizzid » Tue Jan 29, 2019 2:36 pm

Haha yeah I saved an audio file need to open it in audacity or similar and look at the wave form to find the 1s and 0s and the sample rate .I might see if I can transmit the audio file back and open the car lol
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Re: Holden BCM and Key Fobs

Postby j_ds_au » Fri Feb 01, 2019 12:10 am

delcowizzid wrote:Haha yeah I saved an audio file need to open it in audacity or similar and look at the wave form to find the 1s and 0s and the sample rate .I might see if I can transmit the audio file back and open the car lol

Yeah, if the key hasn't been back in the lock-reader (ie. a new rolling code issued) since the recording was made, it should work, particularly if the BCM hasn't heard it already.

Joe.

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Re: Holden BCM and Key Fobs

Postby j_ds_au » Fri Feb 01, 2019 12:26 am

The1 wrote:i went and found the keys i used to check, the keys i used had atmel 93C46C from factory

That's odd. The ones I've seen have used a Fairchild 93CS46 or ST 93S46, which is a 93C46 derivative with an added security feature, whereby the upper portion of memory can be either temporarily or permanently write protected. No doubt this feature is used in BCM pairing and would be why only a new key fob can be paired.

Joe.

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