gitui commit fails with "cryptographic error" when using GitHub SSH Signing Keys

[GustafXTT]

Hello, I’m using GitHub’s SSH Signing Key feature to sign my commits with an SSH key.

My Git configuration is as follows:

git config --global gpg.format ssh
git config --global user.signingkey ~/.ssh/id_rsa.pub
git config --global commit.gpgsign true

This works fine when I commit via the Git command line or other GUI tools that invoke Git.

However, when I try to commit using gitui, I get the following error:

Error
commit error:
sign error: Failed to spawn signing process: cryptographic error

Has anyone else encountered this issue, and is there a known fix or workaround for SSH commit signing in gitui?