Which protocol uses port 443?

HTTPS (Hypertext Transfer Protocol Secure) is the protocol designated to use TCP port 443. It is the secure version of HTTP, where communications are encrypted using Transport Layer Security (TLS) or its predecessor, Secure Sockets Layer (SSL). The Internet Assigned Numbers Authority (IANA), which governs global IP address allocation and other Internet protocol standards, has officially assigned port 443 for HTTPS traffic. This ensures that data exchanged between a user's web browser and a website is encrypted, protecting its confidentiality and integrity from eavesdropping or tampering.

A. HTTP: This protocol is used for unencrypted web communication and is assigned the well-known TCP port 80.

C. FTP: The File Transfer Protocol uses TCP port 21 for the control connection and typically port 20 for the data connection.

D. SMTP: The Simple Mail Transfer Protocol, used for sending email, operates on the well-known TCP port 25.

1. Internet Assigned Numbers Authority (IANA). (2023). Service Name and Transport Protocol Port Number Registry. IANA. Retrieved from https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml. The registry explicitly lists https with port number 443 for TCP.

2. Cisco Systems, Inc. (2018). TCP and UDP Ports Used by Cisco Software. In this document, under the "Commonly Used Ports" section, HTTPS is listed with TCP port 443. This is fundamental knowledge for configuring security features like Access Control Lists (ACLs) on Cisco devices. (Reference: Document ID 13790).

3. Kurose, J. F., & Ross, K. W. (2021). Computer Networking: A Top-Down Approach (8th ed.). Pearson. In Chapter 2, "Application Layer," the text specifies that "An HTTP server uses port 80, and an HTTPS server uses port 443." This is standard university-level courseware.

4. Postel, J. (1981). RFC 793: Transmission Control Protocol. Internet Engineering Task Force (IETF). Section 3.1, "Header Format," discusses the concept of source and destination ports, which are standardized by IANA for well-known services like HTTPS.