[SOLVED] Why does signing commit with SSH key fail with "invalid format?" and "failed to write commit object"?

Why does signing commit with SSH key fail with "invalid format?" and "failed to write commit object"?

I followed GitHub's instructions for telling git about my SSH key, but when I tried to sign a commit

git commit -S

I got this error:

error: Load key 
"C:\\Users\\MyName\\AppData\\Local\\Temp/.git_signing_key_tmpC5KwFc": invalid format?

fatal: failed to write commit object

What might I be doing wrong?

Solution

Setup

For Git to successfully sign the commit,

Git (v2.34 or later) needs to know about your SSH key
The ssh-agent needs to be running
- eval "$(ssh-agent -s)" to start it
- (Windows can be told to auto-start it; Mac and Linux already do.)
The ssh-agent needs to have your key
- ssh-add -L to list existing keys
- ssh-add ~/.ssh/id_ed25519 to add your key

Then you should be able to sign the commit!

git commit -S

To automatically sign all commits, flip the switch in your settings with git config --global commit.gpgsign true