Christian Pernegger <pernegger@xxxxxxxxx> wrote: > Hi all, > > I've recently finished setting up our new file server, whose largest > filesystem is 2.5TB in size; ext3 on dm-crypt (aes-256-xts) on lvm on > md-raid5. The setup seems fine, but googling for an unrelated > performance problem brought to light some disconcerting news: > > 1) xts becomes more insecure the larger the encrypted volume is and is > thus not recommended for volumes >1TB. Great. How bad is this in my > case on a "makes cracking the encryption easier in theory" -- "any > scriptkiddie can do it in 5 seconds" scale? Regarding this you could have a look at a mail from Jonas Meurer to this list with Message-ID: <20080902122833.GF29731@xxxxxxxxxxxxxxx> where he forwards a mail from Micah Anderson to pkg-cryptsetup-devel@: | According to the IETF NIST submission[0] for the tweakable block | cipher xts (and I paraphrase here, as the document prohibits direct | quotation): the proof yields strong security guarantees as long as the | same key is not used to encrypt much more than 1 terabyte of data. Up | until this point, no attack can succeed with probability better than | approximately one in eight quadrillion. However this security | guarantee deteriorates as more data is encrypted with the same | key. With a petabyte the attack success probability rate decreases to | *at most* eight in a trillion, with an exabyte, the success | probability is reduced to *at most* eight in a million. So, I would say that you are not in that big trouble with a 2.5T volume. However, when "scriptkiddies" are in your attack vector, the more important question arises: what do you expect them to be able to do? When they are able to hack into your system, they simply have your key. > 2) Something about *-plain being 32 bit only and thus limited to 2TB. > What happens to data over 2TB? Less secure, not encrypted at all, kiss > it goodbye? the data above 2T is less secure but all data is less secure. It is encrypted, it does not get lost and it does not overwrite other data. regards Mario -- Evidently men are more intelligent than women. Every woman on earth believes that men should be able to read minds. Every man knows this is impossible. Ergo, we are more intelligent. _______________________________________________ dm-crypt mailing list dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
