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 ? >> > _______________________________________________ A51 mailing list [email protected] http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51
