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Henk henk.vergonet at gmail.comOn Tue, Mar 8, 2011 at 4:31 PM, Alfonso De Gregorio wrote: > On Tue, Mar 8, 2011 at 3:28 PM, Henk wrote: >> Actually comp128-2 has a 54bit Kc it seems. > > Have you observed a COMP128-2 implementation returning a 54bit long > Kc?, or have you heard about this from somebody else? > Can you please disclose more about the SIM model and the operator > running this A3/A8 implementation? > I found it in a some vendor related 3G spec some while ago, can't remember which one. After some googling I found the reference below, which also confirm a Kc of 54 bits, unfortunately I don't have access to the algorithm. This seems to indicate a completely new algorithm, some others suggest its a "patched" version of comp128. - henk "Quirke (2004). Security in the GSM system." ... Implementations of A3, A8 Although the design of the GSM system allows an operator to choose any algorithm they like for A3 & A8, many decided on the one that was developed in secret by the GSM association, COMP128. COMP128 eventually ended up in public knowledge due to a combination of reverse engineering and leaked documents, and serious flaws were discovered (as discussed below). Some GSM operators have moved to a newer A3/A8 implementation, COMP128-2, a completely new algorithm which was also developed in secret. This algorithm for now seems to have addressed the faults of the COMP128 algorithm, although since it has yet to come under public scrutiny it may potentially be discovered via reverse-engineering and any possible flaws could be learned. Finally, the COMP128-3 algorithm can also be used, it is simply the COMP128-2 algorithm, however all 64-bits of the Kc are generated, allowing maximal possible strength from the A5 ciphering algorithm (COMP128-2 still sets the 10 rightmost bits of the Kc to 0), deliberately weakening the A5 ciphering. …