Date: Fri, 04 Jul 2014 18:11:29 -0700 From: Jesse Gooch <lists@gooch.io> To: freebsd-hackers@freebsd.org Subject: Re: geli+trim support Message-ID: <53B750C1.8070706@gooch.io> In-Reply-To: <60445.1404461976@critter.freebsd.dk> References: <alpine.BSF.2.00.1407020036280.4507@wojtek.tensor.gdynia.pl> <7E2718485A3E405D89E5EAB331E9ED70@multiplay.co.uk> <53B6427D.1010403@gooch.io> <60445.1404461976@critter.freebsd.dk>
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Hi, On 04/07/14 01:19 AM, Poul-Henning Kamp wrote: > In message <53B6427D.1010403@gooch.io>, Jesse Gooch writes: > >> IIRC, TRIM is bad for encryption anyway. You want everything to be >> random noise, even the empty sectors. TRIM defeats this. > > The problem is that there is nothing you can do. > > If you overwrite, your old sector is still unchanged somewhere in flash. > > If you TRIM, your old sector is still unchanged somewhere in flash, but > if you're lucky for slightly less time. Perhaps I misunderstand TRIM, isn't the point of TRIM that it zeroes out the sector ahead of time so it doesn't have to re-do it again when it stores more data in that sector later? > Doing both just means that you have both the original and the overwritten > content lingering in flash. > > GBDEs scheme with per sector PRNG keys is marginally better than > GELIs, in that the chances that both the sector and its key survives > is only 3/4 of the chance that the sector survives. > > Without access to and control over the Flash Adaptation Layer, > encrypting SSDs so they are safe against hardware access is impossible. > > For the paranoid: ... and a hostile FTL can make it much harder. >
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