What document outlines security measures for specific vessels?

The Ship Security Plan (SSP) is the correct answer because it is specifically designed to outline the security measures and protocols that must be followed for a particular vessel. This document serves as a comprehensive guide for ensuring that a ship meets international security regulations and can effectively address potential security threats. It details the security assessments, preventive measures, and response procedures tailored to the vessel's operations and environment.

In contrast, the other documents have different focuses. The Cargo Manifest is primarily concerned with the details of the cargo being transported and does not include security measures for the vessel itself. The Safety Management System focuses on safety and operational procedures rather than security. The Vessel Registration Certificate is a legal document indicating ownership and registration details but does not provide information about security policies. Each of these documents plays a crucial role in maritime operations, but only the Ship Security Plan is directly related to outlining security measures for specific vessels.