Ephemeral key lifetime & system sleep

Daniel Kahn Gillmor dkg at fifthhorseman.net
Wed Dec 7 23:04:45 CET 2016

On Wed 2016-12-07 16:20:43 -0500, Jason A. Donenfeld wrote:
> But I was thinking that instead of this, maybe it'd be simpler and
> even more desirable to simply *always wipe all keys immediately
> /before/ system suspend*. This would have the desirable property of
> preventing ephemeral key recovery from physical access to the ram or
> CPU of a suspended system, or attacks against modified SMM handlers
> pilfering data during resume just before handing control back to the
> kernel. Is this desirable? Is it absurd?
> The downside is that if you put your computer to sleep for just a
> couple of seconds, when it comes back up, the [mostly invisible
> anyway] 1-RTT handshake must occur again, and you won't be able to
> decrypt any packets that were sent to you before going to sleep and
> arrived after resuming.
> The upside is the tinfoil hat security properties outlined above.

I think scrubbing the ephemeral keys prior to suspend is the right thing
to do.  It's simpler to reason about, sounds straightforward to
implement, the usability cost isn't that great, and it's likely to be
the right thing in almost all long-term suspend cases.

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