Sorry for the confusion about "encryption". I meant "signing" which is encrypting a hash of the commit with your private key, so that others can verify that your the author of the commit using your public key and the hash.
I think, the only confusion here was the original comment that referenced the public key for signing, but this was resolved, as it is just telling git which key pair to use. Probably, all people here understand the basics of asymmetrical encryption and signing and it was merely misunderstanding of how the command for signing git commits can be used.
And a lot of time spent in Bunkers