Which protocol transmits individual messages or pages securely between a web client and server?

The Secure Hypertext Transfer Protocol (S/HTTP) is specifically designed to securely transmit individual messages or pages between a web client and server. It provides a layer of security by encrypting the data exchanged, which helps protect against eavesdropping and man-in-the-middle attacks. S/HTTP operates at the application layer of the Internet Protocol Suite, ensuring that the communication between the client and the server is private and secure.

This makes S/HTTP distinct from other protocols such as Hypertext Transfer Protocol (HTTP), which transmits data in plain text and does not offer security measures. File Transfer Protocol (FTP) focuses on transferring files and lacks built-in security features in its standard form. Simple Mail Transfer Protocol (SMTP) is used for sending emails and, while it can support secure transmission, it does not facilitate the secure exchange of web pages or messages like S/HTTP does. Thus, the focus of S/HTTP on secure, message-based transmission between web clients and servers makes it the appropriate choice for this question.