And what about when a notebook is encrypted? [LWN.net]

And what about when a notebook is encrypted?

Posted Sep 17, 2018 22:27 UTC (Mon) by ThinkRob (guest, #64513)
In reply to: And what about when a notebook is encrypted? by pbryan
Parent article: Fedora reawakens the hibernation debate

For the paranoid (properly, or otherwise) among us, the idea of RAM being written out in whole to disk is a scary one even if it is -- in theory -- done safely. You're only one configuration bug or one non-public exploit away from someone getting a complete memory image.

Plus it -- again in theory -- opens you up to known-plaintext attacks. If you know a box is running $OS_VERSION then you know the contents of a ton of stuff that's going to be in memory. Shared libs alone would give you hundreds of megs of known plaintext on your standard Fedora/GNOME install. And while AES-256 in XTS mode isn't vulnerable to known plaintext attacks at the moment (as far as I know), I would venture a guess that some folks might not want to tempt fate.

Personally the security angle doesn't bother me much, provided Fedora implements it right. My only main concern is that it's bloody useless for me, hence I hope it's made (and stays!) configurable. My laptop loses ≤ 1% of battery when left off overnight, and with some 75+Wh of charge available, this is solving a non-issue... at the cost of a rather annoying wait time when I do want to start using my laptop. So here's hoping that it can be turned off!

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And what about when a notebook is encrypted?

Posted Sep 18, 2018 16:01 UTC (Tue) by epa (subscriber, #39769) [Link] (2 responses)

Presumably a known-plaintext attack could be mitigated a bit if you compress the memory dump before writing it to disk. A sliding-window compressor could be seeded with a fairly random initial window, or some small nondeterminism could be added to the construction of frequency tables for Huffman coding. Or do these ideas fall under the category of "please don't roll your own crypto"?

And what about when a notebook is encrypted?

Posted Sep 18, 2018 16:32 UTC (Tue) by hkario (subscriber, #94864) [Link]

CRIME showed that compression is not a workaround for leaky encryption

And what about when a notebook is encrypted?

Posted Sep 21, 2018 16:50 UTC (Fri) by ThinkRob (guest, #64513) [Link]

Or do these ideas fall under the category of "please don't roll your own crypto"?

I'd say so.

There probably are ways to defend against this though. Plus, AFAIK there aren't any significant known plaintext attacks against AES256 in XTS mode. And since this isn't a long-term storage situation but rather a short term one it's not like we have to worry about an exploit twenty years from now putting our data at risk.