The primary function of a Data Loss Prevention (DLP) system is to enforce policies regarding the handling of sensitive data. It operates by identifying, monitoring, and protecting data in use, in motion, and at rest. The core purpose is to prevent the unauthorized exfiltration or leakage of confidential information from an organization's network. DLP systems use deep content inspection and contextual analysis to detect sensitive data within network traffic or on endpoints and can block the transmission if it violates a predefined security policy.

A. This describes the function of a network firewall or an Intrusion Prevention System (IPS), which focuses on filtering incoming threats.

B. This is the primary role of a User and Entity Behavior Analytics (UEBA) system, often integrated with a SIEM.

D. This describes encryption, a distinct data protection control. While DLP can work with encrypted data, its main function is policy enforcement, not encryption itself.

1. Microsoft Corporation. (2023). Overview of data loss prevention. Microsoft Purview documentation. In the "What is data loss prevention" section, it states, "Data loss prevention (DLP) is a system that is designed to detect and prevent the potential exfiltration or leakage of sensitive information from a system."

2. Saltzer, J. H., & Kaashoek, M. F. (2014). 6.858 Computer Systems Security, Fall 2014 - Lecture 21: Data Loss Prevention. MIT OpenCourseWare. The lecture notes state that the goal of DLP is to "scan data leaving the organization for sensitive information" and "block it if found."

3. Kanth, P. A. K. V. L. K. S. N. S., & Sastry, V. L. N. (2014). Data Leakage/Loss Prevention Systems (DLP). International Journal of Computer Applications, 97(1), 1-4. The abstract defines DLP as a system used "to detect and prevent the unauthorized use and transmission of the confidential information." (DOI: 10.5120/16931-6811)