Date: Wed, 14 Jan 2015 08:56:50 +0300 From: rozhuk.im@gmail.com To: "'Alexey Ivanov'" <savetherbtz@gmail.com>, "'Gleb Kurtsou'" <gleb@freebsd.org> Cc: freebsd-hackers@freebsd.org, 'Adam Nowacki' <nowakpl@platinum.linux.pl>, freebsd-geom@FreeBSD.org Subject: RE: ChaCha8/12/20 and GEOM ELI tests Message-ID: <54b60525.2d08980a.437b.4760@mx.google.com> In-Reply-To: <29DB9466-3DF9-4191-9476-C46BF350848D@gmail.com> References: <54b33bfa.e31b980a.3e5d.ffffc823@mx.google.com> <54B4AE55.9090205@platinum.linux.pl> <54b5d299.4914980a.61cd.43a6@mx.google.com> <20150114041708.GA3189@reks> <29DB9466-3DF9-4191-9476-C46BF350848D@gmail.com>
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> >>> Maybe faster but a stream cipher is unusable for disk encryption - > >>> iv is derived from sector number and doesn't change. Being able to > >>> write a known plaintext and read resulting ciphertext allows you = to > >>> recover the cipher stream and decrypt any past or future data > stored > >>> on that sector. > >> > >> Depends on the capabilities of the attacker. > >> > >> To be able to continuously read encrypted sectors for data > collection > >> is too much. > > > > I disagree. It's the most basic attack scenario. Assuming attacker > was > > able to get access to encrypted disk once, odds are high it may > happen > > again. > Agreed: > In day to day life if anyone had an ability to read content off > laptop=E2=80=99s hdd when it is hibernated - he would break the = encryption. > In server world if one has access to two HDDs from the same raid1 from > different points in time - he also will have the ability to decrypt > data. While the laptop is sleeping from the dump, you can get any encryption = keys the mounted disk, no matter what they are encrypted. With servers agree, but I specifically focus on the conditions of = application of ChaCha. > > Stream cipher (or similarly functioning block cipher mode) should = not > > be used for disk encryption. IMHO swap encryption hardly justifies > > adding insecure encryption mode to geli. Fast swap is certainly nice > > to have, but rather remains a snake oil, system will remain trashed > > due to swapping no matter how fast swap is. > Agreed again, if one really wants to add stream cipher he should then > securely generate random IV and write it to disk along with the data > (e.g. how g_eli_integrity.c does for HMAC, or even something simpler > since one does not have a requirement of storing IV on the same sector > as data) ChaCha perfectly suitable where speed is needed, but you can go to some = risks. I do not see the possibility of an attacker can decrypt ChaCha if he is = unable to read the encrypted data in a different time and compare them = with the plain text. ChaCha is not a silver bullet when encrypting drives, but its area of = application it has.
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