private key protection

Peter Lebbing peter at
Tue Oct 18 15:37:38 CEST 2011

On 18/10/11 15:23, Jerome Baum wrote:
> It doesn't prevent a trojan from signing something other than what you
> intended (if it's your master key on card, even another key or a new
> sub-key) but whether this is a problem depends on your threat model.

The signature problem can still be solved by manual labour: you made *one*
signature. If you have a signature on your file that checks out, that's
apparently the one signature you made. This is thanks to the "Signature PIN:
forced" setting of OpenPGP smartcards.

However, there's another scenario involving encrypted files.

Once you've entered your PIN, your smartcard will decrypt files and stuff
without asking for the PIN again. So if you enter the PIN on your secure
smartcard reader, and someone has trojaned your PC, the trojan or attacker can
then decrypt further files until the smartcard is "reset".

Still, it is all restricted to the timeframe the smartcard is active "inside"
the hacked computer. At no point is the key fully compromised: the attacker
can't copy the key to his own system, and he can't sign or decrypt anything
without the smartcard being in a hacked computer at the time he wants to decrypt
or sign.


I use the GNU Privacy Guard (GnuPG) in combination with Enigmail.
You can send me encrypted mail if you want some privacy.
My key is available at

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