Philips/NXP/Mifare CRYPTO1 mostly reverse-engineered

Ralf-Philipp Weinmann weinmann at
Sun Dec 30 05:29:32 EST 2007


"MiFare’s CRYPTO1 stream cipher has captured my attention for a while.  
However, hardware reverse-engineering is not a field I actively engage  
in. So I was very happy when Karsten Nohl (University of Virginia),  
Starbug and Henryk Plötz gave a talk at the 24C3 [the 24th Congress of  
the Chaos Computer Club taking place in Berlin at this very moment]  
yesterday evening showing that they have reverse-engineered most parts  
of this cipher. CRYPTO1 uses a 48-bit LFSR-based filter generator to  
generate key stream.

The filter function - if I understood correctly - uses 20 taps (this  
was not mentioned in the talk, I asked Karsten privately about this)  
however the degree of the boolean function implementing the filter,  
thus it remains to be seen whether algebraic attacks can be applied.  
Even if no algebraic attacks are applied, a BSW sampling TMTO will  
break CRYPTO1 completely. This was pretty obvious before they gave  
their talk, but now vendors actually have to worry about this being  
out in the wild once the feedback and the filter function have been  

My colleague Erik took photos of the slides which I put up on Zooomr  
[0]. A video recording of the talk should be available shortly and  
will be linked here."

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