Re: GnuPG Smartcard and Authentication Key

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GnuPG Smartcard and Authentication Key
\ Volker Dormeyer (28 May 2006)
. \ David Shaw (28 May 2006)
. . \ Volker Dormeyer (28 May 2006)
. . . \ Volker Dormeyer (2 Jun 2006)

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Subject:	Re: GnuPG Smartcard and Authentication Key
Group:	Gnupg-users
From:	Volker Dormeyer
Date:	28 May 2006

Hi David,

thanks for the reply.

* On Sun, 28 May 2006 16:30:55 -0400,
* David Shaw <dshaw> wrote:

> On Sun, May 28, 2006 at 08:24:14PM +0200, Volker Dormeyer wrote:
>> Hello all,
>>
>> recently I received a message which is encrypted with my public
>> authentication key instead of my encryption key.
>>
>> I wonder how this can happen, because I thought GnuPG does not use the
>> authentication key as encryption key. Am I wrong?
>>
>> Further, I am not able to decrypt the message. I tried it manually with
>> "--try-all-secrets", but it doesn't seem to work. Basically it should
>> work. I mean, I have the authentication private key.

> This is unfortunately turning into a FAQ. Basically, you've run into
> an old PGP bug. It was recently fixed (I don't recall exactly in what
> version), but there are countless installations of PGP that predate
> the fix.

This is what I read in the gnupg-users archive before I send the
question. I have to admit, I do not understand exactly, because I know
that the user who sent me the message is using GnuPG. It shows

-----BEGIN PGP MESSAGE-----
Version: GnuPG v1.2.5 (GNU/Linux)

in the ASCII armored cipher text.

> OpenPGP keys have "key flags" that indicate what a key is to be used
> for (encryption, signing, or authentication). GnuPG honors these
> flags and will not encrypt to any key that isn't marked for
> encryption. The bug is that PGP is not properly looking at the key
> and will happily encrypt to a signing or authentication key.

I am aware of the different "key flags". This was the reason why I
wondered how this could be happen.

> As to what you can do about it, your best bet is to contact the sender
> and ask for a retransmission encrypted to the proper key. It might be
> possible to write a program that can essentially trick the smartcard
> into decrypting the message by pretending it is a signature that needs
> to be verified but it depends on how exactly the card handles
> signatures. In any event, no such program exists today.

Thanks,
Volker

--
Volker Dormeyer <volker>
Join the Fellowship and protect your Freedom! (http://www.fsfe.org)

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