GPG TLDR; commands

README.md

Expire and update keys

$> gpg --edit-key <key-id>
gpg> key 1
(for subkey, ssb, just expire for key 0, sec)
gpg> expire
(follow prompts)
gpg> save

You can list keys via:

gpg --list-secret-keys --keyid-format=long --list-options show-unusable-subkeys
# or get your .gitconfig configured key via
grep "signingkey" ~/.gitconfig