Talking about Cryptodevices... which one?

[Peter Lebbing]

You know, if you had just said right from the start "I know that a smartcard is
supposed to protect theft of the private key but what is the use of that given
that they can still sign and decrypt", the discussion might have progressed a
/lot/ quicker. Also, it doesn't help that you eloquently refute things people
never said in the first place, and hence didn't need to be refuted.

I think the answer to it is the timespan, by the way. If I'm working on a
compromised computer with a smartcard now, hackers can access my encrypted files
and sign stuff with my key. But let's say in a week I will be using a new
computer, then they will lose the ability to sign and can no longer decrypt any
new documents encrypted to me. If they had compromised my PC with the keys on
disk, they would have copied them, and as long as I use the key, they can access
the data and sign new stuff as well.

And given the many escalate-to-root security bugs that are constantly found and
fixed, I do not think any software measure is going to prevent a determined
attacker from gaining full control of your system once they get a hold of your
user account.

Your scenario of the attacker doing a key rollover, revoking your actual key and
substituting their own, can be prevented by using an offline master key so the
attacker only has access to the subkeys. Also, if I'm concerned this might have
happened, I can check with my correspondents to see if they are under the
impression I recently changed keys. Given a secure channel to them, I can detect
this. It's not nearly as stealthy as simply copying the key material.

The attack form popularized by the BadUSB people is a genuine problem; what if,
by plugging in the card reader I used on a compromised PC into a clean PC, it
immediately compromised that clean PC?

Similarly, if I think I'm cleaning my PC from infection by wiping the hard disk,
but the attacker modified the firmware of the hard disk, I'm still screwed, as
shown by Sprite_TM on OHM2013.

Peter.

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