Which protocol is commonly used for secure communication over a computer network?

The protocol commonly used for secure communication over a computer network is HTTPS. HTTPS, which stands for Hypertext Transfer Protocol Secure, is an extension of HTTP that incorporates encryption through SSL/TLS (Secure Sockets Layer/Transport Layer Security). This encryption ensures that the data transmitted between a user's web browser and the web server remains confidential and secure from eavesdroppers or man-in-the-middle attacks.

When a user accesses a website through HTTPS, the connection is established with a secure certificate that validates the authenticity of the site. This process not only protects sensitive information, such as passwords and credit card numbers, but also ensures data integrity, preventing it from being altered during transmission.

In contrast, other protocols like HTTP do not provide any encryption, making it risky for transmitting personal or financial data. SMTP, which stands for Simple Mail Transfer Protocol, is primarily used for sending email and also lacks inherent security features. FTP, or File Transfer Protocol, is used for transferring files over a network but similarly does not include built-in security and should be secured with additional protocols like FTPS or SFTP to protect data during transmission. Thus, HTTPS is clearly the protocol of choice for secure communication over the Web.