http://ssd.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/ps/module/deep-dive-end-end-encryption-how-do-public-key-encryption-systems-work
Public key encryption encrypts a symmetric key, which is then used to decrypt the actual message. Pretty Good Privacy ( PGP ) is rarely used anymore, but remains an example of a protocol that uses both symmetric cryptography and public key cryptography (asymmetric).