how to require someone to use a public key

how to require someone to use a public key for my github repositories ?  

I came across various guides that showed me how to setup a public key , but none of them explain how I  require someone to use a public key for my github repositories.

Public keys are used to enable communicating with GitHub via the SSH protocol. I am not aware of any way to disable access to a repository based off of which protocol a client is using to communicate with GitHub.

If you wish to allow only certain people to access your repository (via any protocol), then you need to create a private repository and then choose who can access it in repository settings > collaborators.

theoretically , if someone does not have the matching public key , they should not have access to the repository ?