What is the short description of Public-Key-Algorithm?

Answer 1

Public key algorithms (PKA) use two keys: one for encryption and the other for decryption. A "secret" or "symmetric" algorithm uses the same key to do both. In PKA, the owner of a secret key publishes the matching private key. Anything sent using the secret key can only be read using the public key assigned to that owner and anything sent to the owner using the public key can only be read using the secret key. Historically, PKA is very complicated and time-consuming, so most systems would use it only for highly secure transactions, such as sending a new (and much faster) symmetric key, or for user authentication (often done at human speeds).