Which of the following is most likely used to control door access?

Radio-Frequency Identification (RFID) is a technology that uses electromagnetic fields to automatically identify and track tags attached to objects. In physical security, RFID is commonly embedded in key cards or fobs. When an individual presents the card to a reader installed near a door, the reader wirelessly interrogates the tag, verifies the credentials against an access control list, and unlocks the door if authorized. This makes it a primary technology for modern door access control systems.

A. DMCA: The Digital Millennium Copyright Act is a United States copyright law, not a technology for physical access control.
B. DRM: Digital Rights Management is a set of technologies used to control access to digital content and devices, not physical locations.
D. VPN: A Virtual Private Network is a technology that creates a secure, encrypted connection over a public network for data access, not physical entry.

1. Vendor Documentation: HID Global, a leading manufacturer of access control systems, details the use of RFID technology in their solutions. "What is RFID? How RFID Works" document explains its application in "access control, where RFID cards or key fobs grant authorized individuals access to buildings or restricted areas." (HID Global, "What is RFID?", Section: "RFID Applications").

2. Peer-Reviewed Academic Publication: A study on access control systems states, "RFID technology is widely used in many applications such as access control systems... The system allows only the authorized person to access a restricted area." (P. H. V. R. Kumar, et al., "RFID Based Security and Access Control System," International Journal of Engineering Research & Technology, Vol. 3, Issue 4, April 2014, p. 1135, Section I. Introduction).

3. University Courseware: The University of California, Berkeley, in its course materials for "CS 161: Computer Security," discusses physical security mechanisms. Lecture notes describe how RFID-based systems, such as key cards, are used to implement access control policies for physical spaces like buildings and labs. (UC Berkeley, EECS Department, CS 161 Lecture Notes on Physical Security).