I have got an issue that seems about the format of SSH key used by GitHub. I used Git Bash to generate a new SSH key
$ ssh-keygen -t rsa -C "firstname.lastname@example.org"
Key is invalid. It must begin with 'ssh-ed25519', 'ssh-rsa', 'ssh-dss', 'ecdsa-sha2-nistp256', 'ecdsa-sha2-nistp384', or 'ecdsa-sha2-nistp521'. Check that you're copying the public half of the key
Simply follow those steps and you will set up your ssh key in no time:
Generate a new ssh key (or skip this step if you already have a key)
ssh-keygen -t rsa -C "your@email"
Once you have your key set in
home/.ssh directory (or
Users/<your user>.ssh under windows), open it and copy the content
Add ssh key
And you all set to go :-)