For sharing highly classified data safely on a network, which protocol would be BEST to use?

The best protocol for safely sharing highly classified data on a network among the given options is Secure Copy Protocol (SCP).

SCP is designed specifically for securely transferring files between hosts on a network. It uses Secure Shell (SSH) for data transfer and provides the authentication and encryption necessary to safeguard the data being transmitted. This enhances security by ensuring that any data shared over the network is protected against eavesdropping and unauthorized access, making it ideal for highly classified data.

In contrast, while Secure Shell (SSH) is fundamental for secure logins and command execution, it doesn't inherently provide a file transfer mechanism on its own without SCP. Network Time Protocol (NTP) is primarily used for synchronizing clocks across networked devices, not for file transfer. File Transfer Protocol (FTP) is an older protocol that lacks encryption, leaving data vulnerable to interception during transmission. Therefore, given the need for security when sharing sensitive information, SCP stands out as the most appropriate choice.