Gallagher Desfire default site key

Aoxhwjfoavdlhsvfpzha · December 17, 2022, 5:58am

This link:

megabug/gallagher-research/blob/master/formats/card-specific/mifare-desfire.md

# MIFARE DESFire

## About

The [MIFARE DESfire](https://www.nxp.com/products/rfid-nfc/mifare-hf/mifare-desfire:MC_53450) card is the latest MIFARE version supported by the Gallagher system. When a site has been configured with a non-default *MIFARE Site Key*, the use of such cards is considered secure by Gallagher (and by this research!)

These cards hold data in a different structure than the MIFARE Classic and MIFARE Plus cards; instead of a sector/block-based memory layout, they hold individual files and keys in application (i.e. card use-case) specific structures.


## Keys

The keys used in the applications are either fixed or generated by diversifying the MIFARE Site Key using application- and key-specific data, as outlined below.

The algorithm appears to have meant to be the NXP-defined [AN10922](https://www.nxp.com/docs/en/application-note/AN10922.pdf) algorithm, but it has a slight difference: the last output block of diversification input is re-ciphered before XORing with K<sub>2</sub> (using the notation in the document linked above). Whether this is intentional or a mistake is hard to tell.

For most keys, the input to the diversification algorithm can take one of two forms:

* Card serial number (CSN) included: in which case, the input is the 4 byte CSN, followed by the 1 byte key number, followed by the 3 byte AID.

* Card serial number excluded: in which case, the input is the 1 byte key number, followed by the 3 byte AID.

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Says:
“Finally, the default application key is the result of diversifiying the bytes 0x03 0x00 0x00 0x00.”

Not sure if that’s helpful, or what it means