On Fri, 2010-05-14 at 00:56 +0200, Sascha Krissler wrote: > The size of an LAPDm frame is always 23 bytes, but most messages are > shorter. A good candidate is the CIPHER MODE ENABLED message which is > the first encrypted message sent in a connection and only uses 3 bytes. > So 20 unused bytes are padded with a constant (0x2b).
In fact, the padding matters little for where we get known key stream samples. We leverage packets that have completely known contents such as 'cipher mode complete' and 'system information 5/6'. If the known contents is shorter than 23 bytes, it will be padded with a known pattern. This cryptographic mistake has been patched in more recent standard version (changing the padding to random after the first byte that is still 2B). The newer standard is not rolled out in many palces yet, even though it seems like a tiny change. > Another source of known plaintext are messages with predictable content, > for example SYSTEM INFORMATION messages, which are > the same for all subscribers of a cell and are periodically sent to each > connected MS. Among those known bits of information are frequency > allocation of neighbouring cells, "location area identification" or > "cell identity". > In theory from analysis of the voice codec and the forward error correction > there may be sources of known plaintext bits found in the bursts transmitting > voice data. AFAIK nobody from the project looked into this by now. > --------------------- > Von: MIHAITA ADELA <[email protected]> > Gesendet: 13.05.2010 19:08:29 > An: [email protected] > Betreff: [A51] rainbow table > > > > > Hello, > > I'm interested to learn more about the project you're working on and I would > kindly ask you to help me with an answer to a simple question. > As far as I understood, the rainbow tables provide, for 64 bits known of > keystream, the initial internal state that generated those bits. Once you > have the initial internal state, you can find the secret key used. My > question is how do you have access to few samples of 64 bits of keystream, > how do you get to find them out? Is it because of that padding with known > plaintext? but then, I don't get it with that known plaintext, who add is > there? > > I tried to follow the explanations given in the "GSM Basic" section but it's > not clear for me. > > Thank you very much, > ___________________________________________________________ > NEU: WEB.DE DSL für 19,99 EUR/mtl. und ohne Mindest-Laufzeit! > http://produkte.web.de/go/02/ > _______________________________________________ > A51 mailing list > [email protected] > http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51 > _______________________________________________ > A51 mailing list > [email protected] > http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51 _______________________________________________ A51 mailing list [email protected] http://lists.lists.reflextor.com/cgi-bin/mailman/listinfo/a51
