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doc: update usage for v1

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King Kévin 2022-06-20 13:01:44 +02:00
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README.md
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@ -23,24 +23,25 @@ usage
You first have to copy the Extended Display Identification Data (EDID) information of the equipment to protect.
This data includes information such as the supported resolutions.
You can read it out using the I²C-based Display Data Channel (DDC) interface.
Then disable the write protect on the HDMI firewall using the switch (the LED will turn off).
Write the EDID data on the EEPROM of the HDMI firewall, and turn back on the write protection (the LED will turn on).
Write the EDID data on the EEPROM of the HDMI firewall, and break the tab using pliers to enable write protection.
This will prevent attackers from injecting any malicious payload.
This only has to be done once (per monitor to protect).
Now connect the monitor to be protected on the corresponding port of the HDMI firewall.
Only allow users to connect on the untrusted device port.
Your equipment is not protected.
Now plug in the HDMI firewall in the monitor to be protected.
Connect the cable going to the untrusted device on the HDMI firewall.
Your equipment is now protected.
To re-write the EEPROM of the HDMI firewall in case you want to protect another monitor, you can re-disable write protection by putting a solder blob across the two pads marked WP.
By default, the 5V supplied by the monitor are forwarded to the device.
To further reduce the attack surface, you can disable this by cutting the trace between the two pads marked 5V.
The risk is that some monitors rely on this signal to detect when a device is plugged in.
limitations
===========
High-bandwidth Digital Content Protection (HDCP) is not supported since the DDC interface is limited to the EDID information.
By default, turn the 5V forwarding off using the second switch on the HDMI firewall.
This reduces further more the attack surface.
If the monitor is not able to detect the connected device, then turn it back on.
mode of operation
=================