answer:As I understand it (general disclaimer) The public key serves two purposes 1) “Hey, I’m using <blank> encryption, so we’ll have to converse using that, ok?” 2) “Here’s the decoder ring I’m going to use on your private key, make sure it matches” So the public key has to be public because there’s nothing that comes before it but it’s also under the control of the side that is theoretically holding the valuable information, so can be changed at any time. It’s the lock, there for anyone to try their key in, the private key is the key brought by the person trying to enter. If I don’t want your key to work anymore, I just change the lock, since I can’t necessarily take your key.