The PGP plugin of claws displays key ids in some situations, e.g. when one tries to verify a signature where the key is not on the system it'll display: "Key 0xFFFFFFFF not available to verify this signature" The short 8 digit key ids are problematic and should be deprecated. The reason is that it's easy to create collision keys with an identical key id. There are already a bunch of duplicate key ids on the public key servers (however mostly revoked ones, they come from an experiment from the evil32 project [1]). This can cause confusion and in the worst case can cause people to get a wrong key. Later versions of GnuPG have moved to use the full fingerprint as a long key id instead, which is unique. E.g. my key id looks like: FE73757FA60E4E21B937579FA5880072BBB51E42 I think it would be good to use this long key id form everywhere where a key id is displayed. [1] https://evil32.com/
In the particular situation you are describing (trying to verify a signature without having the public key), it seems to be impossible to display the full key ID - the GpgME library only exposes the "long", 20-char ID for signatures (the "fpr" member of gpgme_signature_t). At least the version I have installed does (1.9.0). But you are right that displaying the short ID is not enough, we should display what we get from the library instead of trimming it down.
Changes related to this bug have been committed. Please check latest Git and update the bug accordingly. You can also get the patch from: http://git.claws-mail.org/ ++ ChangeLog 2017-11-09 00:33:02.728230601 +0100 http://git.claws-mail.org/?p=claws.git;a=commitdiff;h=35280cf63869f0be36e049330fafc6add1af79a3 Merge: f8459b7 9f1c5fe Author: Colin Leroy <colin@colino.net> Date: Thu Nov 9 00:33:02 2017 +0100 Merge branch 'master' of file:///home/git/claws http://git.claws-mail.org/?p=claws.git;a=commitdiff;h=9f1c5fef1adcdfe9fcda6ee42123123242ab3efd Author: Andrej Kacian <ticho@claws-mail.org> Date: Thu Nov 9 00:31:27 2017 +0100 Show full key/signature fingerprints. Closes bug 3910 - Displaying of problematic short key IDs for GPG messages