[nycbug-talk] Roland Dowdeswell interview on CGD

Roland Dowdeswell elric
Tue Jan 3 14:47:44 EST 2006

On 1135398666 seconds since the Beginning of the UNIX epoch
Okan Demirmen wrote:

>On Fri 2005.12.23 at 11:18 -0500, Ray Lai wrote:
>> On Fri, Dec 23, 2005 at 09:05:54AM -0500, michael wrote:
>> > If you haven't seen it:
>> > http://www.onlamp.com/pub/a/bsd/2005/12/21/netbsd_cgd.html
>> > 
>> > He has been a repeat speaker at NYCBUG meetings.
>> I've always wondered how gracefully encrypted disks handled crashes.
>> Does anyone have any experience?  I've used the encrypted disk image
>> for qemu before, but a crash rendered the whole image useless.
>doh, that sucks. i haven't had many issues with svnd(4) before. i have
>all my home data that i care about in a svnd(4). before i got my new
>laptop, i had this old laptop which had zero battery life. i can't count
>the number of times i accidentally pulled the power cord, but the device
>came up successfully each time. now that i've got a working battery, i
>can't recall the last time this thing actually crashed completely, but
>what i can say is that i've yet to lose the data in that svnd(4).
>now, my use of the device is for files, created/modified by me, a
>human. milage varies....
>now, i do backups all the time though ;) which i'm sure you do as well.

All of CGD, svnd, GBDE and GELI are block level encryption schemes.
Of them, only GBDE has atomicity issues which can result in corruption
upon a crash, so if you are using svnd then you should be safe.
If you are using FreeBSD, I would suggest that you evaluate GELI
as it does not appear to have these atomicity issues---and it does
use PKCS#5 PBKDF2 to counter dictionary attacks, etc.

Of course, with svnd you need to be extremely careful when selecting
a passphrase as it is vulnerable to offline dictionary attacks.
I would suggest generating passphrases via something like:

	$ openssl rand -base64 12

to counter this issue.

    Roland Dowdeswell                      http://www.Imrryr.ORG/~elric/

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