It's true that for KEYTOCARD command, there is optional argument for ECDH.
My point is that for PKDECRYPT command, it will be needed to add mechanism for getting such a parameter (when we use KEM API in gpg-agent).

We already have the ECDH parameters for OpenPGP in the gpg-agent API. The question is how large the data for PQC will be - likely we need to use an inquire already for this reason.

Considering the design of gpg-agent which focuses on private key operations and data, it would be better to enhance the gpg-agent protocol to inquire public key data of any format defined by the client (including ECDH KDF parameters of OpenPGP). I mean, instead of storing data in the key file (originally designed for private key + some additional data), we will enhance the protocol.

Further investigation showed that this was due to a bogus key creating during I wrote the code.

Will be in GnuPG 2.2.42 and 2.4.4. GPGME 1.23.0 with support has been released.

While trying to replicate your findings I might have found a but in the import code which rejected one of the keys (using gnupg 2.2). I'll take care of this.

@ebo: Du have the Ted Tester key (i.e. the ADSK key) also in you keyring?

Encryption to the ADSK seems to work but I'm not sure if everything is displayed as expected.

works

Bugs goes back to 2002 where we stopped checking trust for keys without any signature. This was really useful but has this strange behaviour.

I am not sure about the initial state of the key. What you are doing is to sign the key with itself (self-signature). Why?
In any case, I can't replicate this. Let's talk about this next week.

Okay, will go into the next revision. Thanks.

Thanks for the reply!

The fix actually does the same as my suggested workaround.

There is an easy workaround: Append an exclamation mark to the adsk key. This way gpg will only search for this subkey.
An example with my test keys:

isn't T3456 the same issue?

OCB mode (i.e. packet 20) is only used if the keys announce it. Thus only after moving a (private) key from GnuPG to a non-GnuPG compatible implementation you will run into this problem. The compatibility options won't override the preference system.

Things for 2.4 are all done.

For 2.2 we will for now only implement the encryption.

Thanks for the description; this is good for documentation.