is this attack based on a publicly available paper that we can read ? where to obtain LAPDm frame ? uplink or downlink ? why did you say we have got 4*114 bits of known plain text ? how much more data we should generate comparing to 2TB to achieve 80% success ? you said people will not continue generating the tables after 50% , its just because of the lookup time or storing data being expensive or what ? and finally how much tables have been produced until now ? i have a free computer with two CUDA enabled cards and i will contribute with them now its good to have some ideas how much time does it need to be working ? thank you
> > > post your questions. > > > thanks . sorry this is probably my fault but i couldn't clearly > > understand what would be the success chance of this attack , roughly > > and why . is there any detailed paper on this so i can put some time > > and read to finally understand it or maybe you can elaborate more ? > > > > thank you in advance > > > > > > > > the keyspace of A5/1 is 2^64. When you record a conversation you can > guess > > > a > > > whole LAPDm frame, > > > so you get enough plaintext and thus A5/1 keystream that you can do 204 > > > lookups in the database. > > > That is because, suppose you have 114 bits of known keystream, then you > can > > > try to reverse the > > > A5/1 register state that produced keystream 0..63 or you can try to > reverse > > > the state that produced > > > keystream bits 1..64 and so on. with 114 bits you would get 51 values > to > > > lookup in the table that > > > gives you a register state for a keystream. we get 4x114 bits of known > > > plaintext. > > > So a table with 2^57 values stored in it, would give you a success > > > probability of 1/(2^7) (because > > > 57 + 7 = 64). The probability of a failed lookup is thus 1-1/(2^7). > > > calculate (1-1/2^7)^204 and you get the probability that 204 lookups > fail. > > > that would be 20%, > > > so the tables at this point of completion can decrypt 80% of the > > > conversations. > > > 50%, 80% ... actually there is no definitive point to say we are done > it is > > > more like > > > the chances of success are continually rising. > > > > > > i'm not advanced on cryptography . would you tell me why 50% ? > > >> > > >> From: *Sascha Krissler*<[email protected]> > > >> Date: Fri, Sep 11, 2009 at 8:16 PM > > >> Subject: Re: [A51] sucess? > > >> To: [email protected] > > >> > > >> When reach our initial goal of 2^8.5 tables with 2^28.5 unique chains > > >> each, we would get a probability > > >> of around 50%, so at some point this would be the actual probability. > > >> It is not unlikely that people will carry > > >> on generating, increasing this probability and also increasing the > > >> lookup speed. > > >> > > >> > suppose the community build all the tables then how much is our > > >> success chance to crack a given recorded conversation ? > > >> > >
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