Hi Junk ;-) junk <junk@...> writes: > > Roscoe wrote: > > My two cents: > > > > > > I personally think that page should be reworded. > > "This makes breaking the passphrase so much harder" Says who? > > > > > > Overwriting the previous contents of the HD does have some value > > regarding secure deletion IMHO, just not very much - someone can't > > just run `strings /dev/sda` after you've zeroed out a hard drive, > > rather they need some specialized hardware and skills. > > > > > > As for writing random data to the disk for the purposes of obscuring > > the ciphertext location: > > > > So what if they do know the exact boundaries of the ciphertext? The > > ciphertext doesn't need to be kept secret. That's the whole idea of > > ciphertext. > > > That's true only if the plaintext is genuinely unknown. This is not the > case for filesystem data - it contains many elements that are pretty > predicatable. Not overwriting the disk with random data before creating > an encrypted file system on it might give an attacker useful information > about the boundaries between unused portions of the disk and files > system structures and the files themselves. This in turn could be used > to mount a known plaintext attack, particularly if the attacker knows > your operating system/distribution/file system type This is a good point. Although I'm not really able to quantify the loss of security here, I understand that knowing the BOUNDARIES between encrypted and unencrypted data yields some info on the allocation of the file system, hence makes it easier to do educated guesses on certain sectors that contain FS administration data only. So it increases the attack vector for known plaintext attacks. I didn't think of this in the first place. Is anyone able to pursue this train of thoughts any further, how these known plaintext attacks help breaking confidentiality of the ciphertext? --------------------------------------------------------------------- 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
