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