There is currently no way to encorce signing/encryption to a subkey in GPGME in the same way we allow
it with the '!' suffix on the CLI.
This can be implemented by allowing to set a selected flag in the gpgme_subkey_t. engine-gpg.c could then scan the subkeys for such a flag and use that fingerprint with the '!' suffix.
| rM GPGME | |||
| rMbfd320abfeaf Allow signing using an exactly specified subkey. | |||
| rM87d6da1188db Mark the subkey used to find a key. | |||
With the recpstring feature in 1.11 this is now possible because the args are passed verbatim to gpg.
@werner Looks like recpstring is only supported for encrypt and encrypt+sign, but not just for signing. Is there a way to specify the subkey to use when signing?
@werner This one? https://www.gnupg.org/documentation/manuals/gpgme/Selecting-Signers.html
It doesn't mention subkeys. Signing just seems to use a "default" subkey.
Attached is a patch which adds gpgme_subkey_set_flag() to handle both encryption and signing keys. Or maybe it would be better to add another signing function that does recpstring?