In many applications, the high cost of encrypting long messages in a public-key cryptosystem can be prohibitive. So we use asymmetric crypto to establish a secret session key (as well as to authenticate the communicating party), and use that session key to encrypt the session using symmetric key crypto.

The simple symmetric encryption algorithm, AES, is used to handle large volumes of data, and the asymmetric encryption algorithm, RSA, is used to handle small volumes of data.

#### Real world application practice

- Long-term (static) keys are bound to an identity for Digital Signature

- Short-term (ephemeral) keys are bound to a session.