RW <[email protected]> wrote: > On Wed, 25 Jul 2012 19:52:39 -0500 (CDT) > Robert Bonomi wrote: > > > > From [email protected] Wed Jul 25 14:00:27 2012 > > > Date: Wed, 25 Jul 2012 20:57:30 +0200 (CEST) > > > From: Wojciech Puchar <[email protected]> > > > To: [email protected] > > > Subject: geli - selecting cipher > > > > > > i need high speed disk encryption (many disks running in parallel, > > > lots of data movement). i have processor with AES-NI. > > > > > > geli give 150MB/s performance (tested from/to md ramdisk) using > > > default and recommended AES-XTS > > > > > > and ca 400MB/s read and 700MB/s write using AES-CBC. > > > > > > I'm not cryptography expert, is CBC somehow "less secure", and if > > > so is it really a problem? > > > > If you "don't know" what strength encryption you need, and/or the > > difference between the methods, you need to hire a data-security > > professional to examine your situation and make recommendations > > appropriate for _your_ needs. > > > > 'CBC' -- [C]ypher [B]lock [C]hainig -- is well-suited for strictly > > -sequential- data access. Try reading the blocks of a large (say > > 10gB) file in *reverse* order and see what kind of performance you > > get. > > Exactly the same, in geli the encryption is done per sector. > > > I asked a similar questions to the OPs in the geom list and didn't get > an answer. Geli doesn't need or isn't using any advantages of XTS. And > CBC in geli is actually equivalent to ESSIV (see the previously linked > wikipedia page). > > In the end I went with 128 bit aes-cbc since it's the fastest setting > and Bruce Schneier recommends 128 over 256 AES as being more secure.
Can you provide the source for the "as being more secure" part? I'm aware of the following recommendation: | And for new applications I suggest that people don't use AES-256. | AES-128 provides more than enough security margin for the forseeable | future. But if you're already using AES-256, there's no reason to change. http://www.schneier.com/blog/archives/2009/07/another_new_aes.html But (the way I interpret it) there's no claim that AES-128 is more secure either in general or in the context of disk encryption. Fabian
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