On Mon, May 17, 2010 at 02:01:34AM -0700, MIHAITA ADELA wrote: > Hello, > > I'm not sure I understood the whole process of the A5/1 attack and I have > two more questions: > > 1) the tables and the lookup provides an A5/1 state that generates those 64 > bits of keystream.; which state is this? is it the state after the 100 steps > with majority clocking and that's why you need to backclock the state > provided by the tables?
The immediate result from the table lookup process gives you the state before 100 clockings. With a little forward-then-backward clocking on this result you can find a few more valid states (i think it was 3%). Still you have to backclock the result to get rid of the frame number forward clocking step to arrive at Kc. So apart from the above optimization, all the backclocking you have to do is in no-majority-clocking mode. > > 2) how do the 32 round functions look like, or what is the difference among > them, how do they change from one to another? A round function is a 64bit xor with a value that is generated by a 64bit wide maximum length Xilinx LFSR. Round function N + 1 is the content of the LFSR 64 clockings after N, or in other words, starting the LFSR at 0, clock N * 64 times and take the LFSR content to get the value for round N. _______________________________________________ A51 mailing list [email protected] http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51
