How to prepare for an ENS compliance audit?

Preparing for a compliance audit of the National Security Framework (ENS) requires proper planning, the real implementation of security controls, and a continuous improvement approach to information security management. An ENS audit not only verifies regulatory compliance, but also assesses the effectiveness of the security measures applied to an organization’s information systems.

Before starting any preparation, it is essential to understand what the ENS requires. Regulated by Royal Decree 311/2022, this regulation establishes a set of security requirements applicable to public administrations, service providers that deliver services to or manage information for them, and, in certain cases, systems that process classified information and operators of essential services when required by the corresponding regulatory framework.

One of the central references is CCN-STIC Guide 808, developed by the National Cryptologic Center, which outlines the audit roadmap for verifying ENS compliance. This guide is key for both auditors and organizations subject to audit, as it details how the different requirements and security measures set out in Annex II of the ENS are assessed.

In addition, during the preparation phase, other CCN-STIC guides are especially relevant. CCN-STIC Guide 803 establishes the methodology for assessing and categorizing information systems, while CCN-STIC Guide 804 provides practical guidance for the effective implementation of ENS measures. Together, these guides form the main technical reference for properly addressing the stages prior to the audit.

Planning the preparation: pre-audit phases

Definition of scope and categorization

The first step in preparation is to clearly define which information systems will be audited and determine their security category (basic, medium, or high). This categorization is based on the criticality of the services and the sensitivity of the information they manage, following the assessment guidelines set out in CCN-STIC Guide 803. Depending on the category, security requirements will be more or less demanding.

A clearly defined scope allows preparation efforts to focus on the processes and controls that will actually be verified, reducing the risk of improvisation and omissions on the day of the audit.

Developing and implementing an adaptation and security plan

Once the scope and categorization have been defined, it is essential to have an ENS Adaptation Plan that includes, among other elements, the information security policy, the risk analysis, and the corresponding compliance documentation.

For MEDIUM and HIGH category systems, a Statement of Applicability (SoA) is required. For BASIC category systems, Royal Decree 311/2022 introduces the compliance profile as a specific simplified mechanism to justify regulatory compliance.

This plan acts as a roadmap for implementing the necessary measures and ensuring that security controls are not only documented, but effectively operational, in line with the practical recommendations set out in CCN-STIC Guide 804.

Security implementation should not be understood as a purely documentary exercise. It involves integrating security controls into the daily operation of information systems and the organization’s management processes, supported by evidence that can be presented during the audit.

Implementing controls and demonstrating effectiveness

Operational and management security measures

An ENS audit does not merely check the existence of policies or manuals. It evaluates whether security measures work in practice. This means that procedures, records, technical controls, and evidence must be up to date and accessible. For example, if a logical access control exists for a system, it is not enough to describe it; there must be records demonstrating its use, periodic reviews, and corrective actions when applicable.

Likewise, incident management, backups, service continuity, and document management must be implemented and aligned with one another. The audit, based on the criteria and methods defined in ENS regulations and guides, will rely on tangible evidence to assess the effectiveness of each security measure.

Preparing consistent evidence

Evidence generation cannot be left until the last minute. Consistent evidence includes configuration records, access logs, security testing reports, minutes of security meetings, risk analysis reports, and any document demonstrating that security measures are applied, reviewed, and updated. In ENS audits, the absence of clear evidence may lead to nonconformities, directly impacting the outcome of the assessment.

Pre-assessments and internal audits

Conducting a pre-assessment under conditions similar to the formal audit helps identify weaknesses and areas for improvement that may go unnoticed in day-to-day operations. These internal reviews, known as internal audits, are especially useful for detecting gaps in documentation, control implementation, or the consistency of security processes.

The type of audit will also depend on the system’s category. According to CCN-STIC Guide 808, BASIC category systems may be evaluated through self-assessment, while MEDIUM and HIGH category systems must be audited by certified entities or auditors with recognized qualifications. Understanding this requirement during the preparation phase allows organizations to adapt their evidence generation and level of formalization to what will be expected during the assessment.

An audit simulation also allows the responsible team to become familiar with the approach of external auditors, the type of evidence typically requested, and the potential questions that may arise during the review.

Integrating continuous improvement into preparation

Preparing for an ENS audit is not a one-time event, but part of an ongoing security improvement process. As systems, the organization, or the threat landscape evolve, security measures must adapt and mature. Integrating continuous improvement into security management demonstrates the organization’s maturity and genuine commitment to information protection.

Preparing for compliance with the ENS requires both a strategic and practical vision of information security. From fully understanding regulatory requirements to implementing effective controls and generating verifiable evidence, each step is essential to successfully achieve certification. Planning ahead, applying effective measures, and maintaining a continuous improvement approach are the foundation not only for regulatory compliance, but also for strengthening the security and resilience of information systems in any organization operating within the Spanish public sector, as well as in the private sector.