On Fri, Jun 16, 2017 at 14:55:11 CEST, Michael Kjörling wrote: > On 15 Jun 2017 10:24 -0700, from mhalcrow@xxxxxxxxxx (Michael Halcrow): > >> If this is accepted, we basically allow attacker to trick system to > >> write plaintext to media just by setting this flag. This must never > >> ever happen with FDE - BY DESIGN. > > > > That's an important point. This expands the attack surface to include > > the file system, so if an adversary can provide a bad encryption key > > or policy at the file system layer or if there's a bug in the file > > system that an adversary can exploit, then users setting the > > allow_encrypt_override option on dmcrypt would be vulnerable. > > No; it would seem to expand the attack surface to _anything_ that can > set this flag on write. That implies that at the very least _anything_ > that runs as root can now plant _plain text_ on storage media which is > intended to be fully encrypted. On the surfacte, root can do that anyways. But this would allow to do that without a kernel compromise or direct write to disk. And it would make detection of a related attack much harder, hence violating KISS rather badly. [...] > If double encryption is too expensive, particularly in the product > space where one device is typically controlled by a single individual > or entity, why do file system layer encryption at all? Just offload > that to the device layer; in this case, LUKS and dm-crypt. File system > layer encryption makes more sense where a large number of users all > have deep level access to a system, possibly being able to read disks > directly, and want to keep data secure from other users of the same > system. I fail to see how that threat model is particularly relevant > in the mobile space. Same here. And I do not see why there would be significant performance or energy impact either. AES hardware is fast and does not consume a lot of energy. Regards, 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 ---- A good decision is based on knowledge and not on numbers. -- Plato 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 dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
