Which of the following protocols is most secure for transferring files?

A. FTP
B. FTPS
C. SFTP
D. TFTP

Answer: C. SFTP

Explanation:

A. FTP (File Transfer Protocol)

FTP is an ancient protocol that operates at the Application Layer (Layer 7).  

• The Vulnerability: It transmits both credentials (username/password) and data in cleartext.  Anyone with a simple packet sniffer on the same network can capture your password. 

•  The Mechanism: It uses two separate ports: Port 21 for commands and Port 20 for data.  

B. FTPS (FTP over SSL/TLS)

FTPS is essentially standard FTP that has been wrapped in an SSL/TLS tunnel.

• The Complexity: While it is secure, it is notoriously difficult to configure through firewalls because it still uses multiple ports (commands vs. data) and can require a wide range of ports to be opened for "Passive" mode.

• Comparison: It provides confidentiality, but it is considered less "elegant" and slightly more prone to implementation errors than SFTP.

C. SFTP (SSH File Transfer Protocol)

SFTP is not "FTP" at all; it is an entirely different protocol based on SSH (Secure Shell).  

• Why it's the Answer: It provides a single, secure, encrypted tunnel for both commands and data over a single port (Port 22).  

• The Security: Because it uses SSH, it provides strong authentication (including public-key authentication) and ensures that everything—including the login credentials—is encrypted from the start. It is the industry standard for secure transfers.

D. TFTP (Trivial File Transfer Protocol)

TFTP is a stripped-down version of FTP.  

• The Vulnerability: It has no authentication and no encryption.

• The Use Case: It is primarily used for transferring firmware updates or configuration files to network devices (like routers or VOIP phones) within a trusted local network. It should never be used over the internet.

• The Mechanism: It uses UDP Port 69, making it "best effort" rather than reliable.