A VPN may use both an asymmetric key and a symmetric encryption algorithm. The key is pre-configured by the network administrator. The router authentication with CHAP uses a symmetric key algorithm. Encrypting files before saving them to a storage device uses a symmetric key algorithm because the same key is used to encrypt and decrypt files. The SSH server generates a pair of public/private keys for the connections. The SSH protocol uses an asymmetric key algorithm to authenticate users and encrypt data transmitted.
