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List:       gnupg-users
Subject:    Smartcard operation
From:       Peter Lebbing <peter () digitalbrains ! com>
Date:       2019-09-17 17:16:06
Message-ID: b7cacd20-8095-342d-3d8c-34e578046d76 () digitalbrains ! com
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On 17/09/2019 18:59, Stefan Claas via Gnupg-users wrote:
> I assume that in order to decrypt a message the secret key data must be
> unlocked and loaded for a very short time into the computers RAM, in order
> to perform the decryption, or am I wrong with my assumption?

OpenPGP messages encrypted to a public key are hybrid encryption: the
asymmetric (public/private) crypto is used to establish a per-message
shared secret. This shared secret is used by a symmetric encryption
algorithm to encrypt the actual data.

The smartcard does the asymmetric part of it all by itself, the computer
just asks it to decrypt something and gets the per-message shared secret
back from the card.

Then the PC will do the symmetric decryption of the actual data.

During regular use, knowledge about the private key contents never
leaves the smartcard, not for the briefest period.

HTH,

Peter.

-- 
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 <http://digitalbrains.com/2012/openpgp-key-peter>


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