Writeup by Yxene for I've lost my comment

We’re provided with an OpenSSH private key and a corrupted public key. Since an OpenSSH public key is determined by its private key, regenerating it shouldn’t be a problem.

And indeed, we find the -y option of ssh-keygen for this purpose:

-y      This option will read a private OpenSSH format file
        and print an OpenSSH public key to stdout.

So we use the following command:

ssh-keygen -f i-ve-lost-my-comment -y

And we get the complete public key:

ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIEhnlalzNKqkJshHrAqwmaphUt4Fg652Bei6Kb7hJp/G https://fcsc.fr/PsIg0VBu7n