Which protocol uses public-key cryptography to authenticate the remote computer?

A.

The correct answer is A. SSH (Secure Shell).

Secure Shell (SSH) is a protocol used for secure remote login and other secure network services. SSH is designed to provide secure encrypted communication between two untrusted hosts over an insecure network.

SSH uses public-key cryptography to authenticate the remote computer. The remote computer generates a public-private key pair, and the public key is placed on the server. When the client connects to the server, the server sends its public key to the client, which is used to encrypt a message that is sent back to the server. If the server can decrypt the message using its private key, it knows that the client has the correct public key and that the client is who it claims to be.

Telnet is a protocol used for remote login that does not use encryption and is therefore not considered secure.

SCP (Secure Copy) is a protocol used for secure file transfer between hosts. SCP uses SSH for authentication and encryption.

SSL (Secure Sockets Layer) is a protocol used for secure communication over the internet. SSL uses public-key cryptography to authenticate servers and clients, but it does not use public-key cryptography to authenticate remote computers.