On Fri, Jan 14, 2011 at 05:28:27PM +0200, Tari Mrkis wrote: > Hi, > > I haven’t understood a very basic point. > > If there is the possibility of backclocking why do we have to build the > rainbow tables to begin with. I understand that if there is a hit in the
It is not possible to clock back keystream. You have to know a A5/1 register assignment to be able to reach neighbouring states through forward/backclocking. You cannot know what the A5/1 register content is from examining keystream (because it is a cryptographic one way function). So with the time memory tradeoff attack you can reverse that function and end up anywhere in the state space of internal A5/1 registers along the path that was taken to generate said keystream; from where it is trivial to clock to a point where the frame number has been removed from the state. > table, either this is the state we are looking for (next to get rid of the > frame number) OR this state can be forward clocked for 100 times and then > backwards to reach some more valid states any of which can be the desired > one. So why don’t simply backclock the 64 bit sequence, find the valid > states and then backclock them all for 100 without the need to build tables. > From what I understand there is not a huge numbers of states, 1.4 states on > average for the 100 forward-back clocking, so for the 64 backwards clocking > this number may increase a little but not too much. > > Also one more question; the total size of the constructed tables is about > 1,7 GB with 40 tables of 42 GB each, is it right? 48 tables of 42GB each. _______________________________________________ A51 mailing list [email protected] http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51
