[Enigmail] Using a subkey for signing a public key

[Tobias Rapp]

Hello!

I am using enigmail with my private subkeys stored on an OpenPGP
smartcard. Now I wanted to sign somebody's public key and noticed that I
can't select my signing subkey for that in the dialog - only the main
key is available in the drop-down list. Key signing fails then with some
"general error" - most likely because the secret part of the main key is
not available (it is guarded by Orks as I have followed the HOWTO in [1]
:-).

Is my thinking going into the wrong direction or is there a problem with
enigmail/gnupg? How can I choose my signing subkey in the drop-down
list? Do I really need the secret main key for signing other keys? I can
sign my mails using the subkeys pretty fine.

My first assumption was that it is not working because the subkey
cross-certification is missing. Then I added the cross-certification as
described in [2] but the problem remains.

Does anybody have an idea?

/Tobias


[1] https://www.fsfe.org/en/card/howto/subkey_howto
[2] https://www.gnupg.org/faq/subkey-cross-certify.html