Which of the following is NOT a secure protocol?

• A. Telnet
• B. HTTPS
• C. SSH
• D. SFTP

Answer: (A)

Security for network protocols relies on encryption and proper authentication to protect confidentiality and integrity of data in transit. Telnet transmits all data in plaintext, including usernames and passwords, so anyone monitoring the network can read credentials and session content. There’s no encryption or strong integrity protection, making it highly vulnerable to eavesdropping and tampering. In contrast, HTTPS wraps HTTP in TLS/SSL to encrypt traffic and verify the server, SSH creates an encrypted channel for secure remote access, and SFTP uses that same secure SSH channel for file transfers. Because Telnet fails to encrypt or safeguard the data, it is not a secure protocol.