Which of the following is considered secure for system operation?

• A. Telnet
• B. FTP
• C. Rlogin
• D. SSH

Answer: (D)

When you’re managing systems, you want the communication channel to protect both the credentials you enter and the data you exchange. The secure choice is SSH because it creates an encrypted channel between the client and the server, authenticates both ends, and protects against eavesdropping, tampering, and impersonation. SSH also supports strong authentication methods, like public-key authentication, and host key verification, which helps prevent man-in-the-middle attacks.

In contrast, protocols like Telnet and Rlogin transmit login information and session data in plaintext, so anyone sniffing the network can read usernames, passwords, and commands. FTP also sends credentials in plaintext by default, making it insecure for remote administration. Because these options expose sensitive information, they’re not suitable for secure system operation. SSH combines confidentiality, integrity, and authentication, making it the secure choice.