1.9 KiB
ID48LIB
Purpose
Enable reliable and repeatable key-writing and verification on ID48 RFID tags. Improve key recovery when the tag is present and writable.
Why this is needed.
Have you ever lost data when a computer shutdown unexpectedly? This occurs when the program believes the data was written, but the device did not actually store the data before power was lost.
With RFID tags, the same problem exists, except the power is wirelessly provided, and may be only enough to read data (writing takes more power). Thus, it's even more critical for RFID tags to validate what was written.
If you are bothered by unreliable processes, and enjoy a measure of certainty, and need to write a new key to an ID48 tag, then read on.
Problem background
The ProxMark3 RFID research tool has had basic support for reading and writing ID48-based RFID tags (aka em4x70). However, although the code existed to write new 96-bit keys, there was no way to verify that the keys were actually written to the tag.
This is because the keys are not directly readable from the tag (by design). The only way to verify that the key was successfully stored on the tag is to perform an authentication against the tag, using the new key that you had attempted to write, and verify that the tag's response to the nonce and challenge matches.
Obviously, this requires the ability to calculate, given a known key and nonce, the challenge to send to the tag, and the expected response from the tag. Without this, folks simply could not know if the key was safely stored on the tag or not.
Capabilities
This library provides the ability to calculate the challenge and expected response for a known key and nonce. In addition, if provided the first half of the key, and at least one successful authentication trio of nonce, challenge, and response, then the library can recover all potentially valid values for the second half of the key.