In symmetric or private-key encryption, both parties to the communication most passes a single secret or private key, as show below.
Private-key encryption is a paradox: 1) to use this encryption, a secure channel has to exist between the two parties to transfer the shared key, but if such a secure channel exists, why are use encryption in the first place?
Asymmetric, or public-key encryption as it is more commonly called, allows parties previously unknown to each other to conduct a transaction. Public key-encryption is fairly recent, and has only been in use since the mid 1980s. Mastering Ethereum
The public key is published and widely disseminated, while the private key is kept secret.
Because communication decryption requires only public keys, which are widely available anyway, secret keys need no longer be exchanged RSA is the de facto standard for public-key cryptosystems.
One-way encryption, as its name implies, is encryption that prevents the resulting cipher from being decrypted. A one-way function is relatively easy to compute in one direction, but very difficult ot computer in the other direction.
Historically these functions have been used for storing items such as passwords on Windows and Unix systems.
