On Tue, Jan 06, 2009 at 03:18:52PM +0100, Thomas wrote: > Hi, > > I'm new to LUKS and I wonder if it makes sense to cascade LUKS devices > with different ciphers, i.e. a Serpent over an AES over a Twofish > device. The idea is if one of the ciphers is broken in the future, the > data is still secure as long as the other ciphers are good. Does this > work You can to it by mapping the dectrypted device again as encrypted, i.e. if /dev/x is your encrypded device and /dev/mapper/y the decrypted one, use /dev/mapper/y as encrypted device and set-up[ /dev/mapper/z ad decrypted for that. This is possible as LUKS/dm-crypt does not care about filesystems. You can have an arbitraty number of layers that way. (Actually I think the mapper devices are limited to 31 or 255.) > and really increase security? Or does it decrease security in the > end? That is a good question and very hard to answer. It is also not the right way to do it. The right way is to use several ciphers in stream mode and then to combine the streams using XOR. This is at least as secure as the most secure cipher used (as long as the leys are independent) and likely better. Layering encryption can decrease security, however not below the level of a known-plaintext attack. Modern ciphers are expected to be able to resist such an attack and the decrease in security may be insubstantial. Personally I think that if AES gets broken, the world has far bigger problems than looking at your data. If you choose to do this anyways, I would propose that you use the best cipher closest to the date, e.g. encrypt with AES first and then with Twofish. Arno -- Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@xxxxxxxxxxx GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans If it's in the news, don't worry about it. The very definition of "news" is "something that hardly ever happens." -- Bruce Schneier --------------------------------------------------------------------- dm-crypt mailing list - http://www.saout.de/misc/dm-crypt/ To unsubscribe, e-mail: dm-crypt-unsubscribe@xxxxxxxx For additional commands, e-mail: dm-crypt-help@xxxxxxxx
