An Access Control List (ACL) is the direct reference for determining who has access to a specific data object or document. An ACL is a table or list of permissions attached to an object, specifying which users or groups are granted access and what operations (e.g., read, write, execute) are allowed. It explicitly defines the "who" and "what" of access rights for a resource, directly aligning with the requirements of ISO 27001's control A.9.4.1 (Information access restriction). While other options are related to access control, the ACL is the fundamental implementation that lists the authorized entities.

A. Data Classification Label: This label indicates the data's sensitivity level (e.g., Confidential), which informs the access policy, but it does not list the specific individuals or groups who are granted access.

C. Masterlist of Project Records (MLPR): This is a records management or project management document used for inventory and tracking of documents, not for defining or enforcing granular user access rights.

D. Information Rights Management (IRM): IRM is a technology that enforces access policies on data (e.g., preventing printing/forwarding). The policy it enforces is typically defined by an underlying mechanism like an ACL.

1. Saltzer, J. H., & Schroeder, M. D. (1975). The Protection of Information in Computer Systems. Proceedings of the IEEE, 63(9), 1278–1308. (A foundational academic paper in computer security). In Section I.A.3, it defines an access control list as a list for each object "which enumerates all the subjects that have access to it and the kinds of access they have." This directly supports the ACL as the reference for "who" has access.

DOI: https://doi.org/10.1109/PROC.1975.9939

2. Massachusetts Institute of Technology (MIT) OpenCourseWare. (2014). 6.858 Computer Systems Security, Lecture 2: Control Hijacking. In the section on "Access control," an ACL is defined as: "For each object, keep a list of subjects and their permissions." This university courseware explicitly identifies the ACL as the list defining subject (who) access to objects (data/document).

Source: MIT OCW, 6.858 Computer Systems Security, Fall 2014, Lecture 2 Notes

3. Humphreys, E. (2016). Implementing the ISO/IEC 27001:2013 ISMS Standard. Artech House. While a commercial book, its principles are widely cited in academic contexts for ISMS implementation. It explains that control A.9.4.1 is implemented by defining and applying rules, which in technical systems are commonly realized through Access Control Lists (ACLs) that associate users with permissions on information assets.