j2497-keyhole: A mitigation against injection of J2497 commands while permitting regulation-required LAMP messages.

The code here accompanies mitigations designed and developed by the National Motor Freight Traffic Association Inc. (NMFTA) to mitigate the issues disclosed in CISA ICS Advisory ICSA-22-063-01 Trailer Power Line Communications (PLC) J2497. The many other mitigations are published into the public domain and available in a paper hosted by the NMFTA.

The mitigation here takes the form of a signal which can be transmitted on a J2497 segment for protection against injection of J2497 commands while permitting regulation-required LAMP messages.. The transmit can be by a DAC or also by bit-banging. From the j2497_keyhole.generate docstring:

Use this function to get a complete set of keyhole mitigation signals. Play them on a loop to prevent all but the
allowed messages from being received by any J2497 receiver on the powerline segment.

The signals will probably need to be prepared for playback on your DAC. They will work even when played on a
bit-banged DAC (1-bit / PWM etc.). Here's an example of preparing the signals for playback @ 1Msps on a signed
8bit output:

dac_ready = [(x * 127).astype('int8').tobytes() for x in j2497_keyhole.generate(1E6)]

And these can be played back-to-back on a loop e.g.

while True:
    for s in dac_ready:
        dac_device_driver_api.write(s)

If you want to bit-bang the output, we have found that even the simplest PWM rule will work:

bangs = [(x >= 0) for x in j2497_keyhole.generate(10E6)]

Note that there is no dynamic generation required. The signals can be pre-computed and played back from non-volatile
storage as well.
[...]

The main.py file contains an example of transmitting the keyhole mitigation signal using cheap FL2K VGA adapters as transmitters (SDRs) by running and writing-to the fl2k_file executable from the osmo-fl2k project.

Installation

1. compile and install osmo-fl2k following the project instructions
2. install this project's python dependencies with pip3 install -r requirements.txt
3. run main.py to transmit the keyhole mitigation on a connected FL2K adapter

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