On Fri, Dec 07, 2012 at 08:29:09PM +0100, Javier Juan Martínez Cabezón wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 06/12/12 16:29, Arno Wagner wrote: > > Updates: Added a passphrase strength estimate based on > > http://it.slashdot.org/story/12/12/05/0623215/new-25-gpu-monster-devours-strong-passwords-in-minutes > > > > Executive summary: It may be time to increase passphrase length. > > > > ----- > > > > The FAQ can be found at - > > http://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions > > and - in the sources as FAQ in the top-level directory. > > > > > > This is applicable if the algoritm used to cipher is unknown as happen > in plain dmcrypt? It depends. In plain dm-crypt, determining whether you have guessed the password is tricky anyways. Testing for different ciphers would add some overhead and maybe give you something like 5-6 bits of security in addition. > > Arno, is really useful/secure to get the ciphering algoritm in the > LUKS header? Yes, very much so. For LUKS, you do trial decryption of a keyslot, and that is enough to tell you whether you have a good password. My intuition is that the iterated hashing takes a lot longer than the trial decryption, so trying different ciphers does not add significant overhead. And there are not that many possible ciphers anyways. Now, if you decide to not store the cipher, then normal decryption would also need to try them and the time would need to be taken into account in the maximum delay a user is faced with. Better to increase the hash iteration count instead. Bottom line: An unknown hash or cipher algorithm does not add much, unless it is homebrew. But in that case, it is still accessible via the kernel and glaringly obvious. Besides, homebrew ciphers are often insecure. Arno -- Arno Wagner, Dr. sc. techn., Dipl. Inform., Email: arno@xxxxxxxxxxx GnuPG: ID: CB5D9718 FP: 12D6 C03B 1B30 33BB 13CF B774 E35C 5FA1 CB5D 9718 ---- One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision. -- Bertrand Russell _______________________________________________ dm-crypt mailing list dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
