The Shared Responsibility Model

The Shared Responsibility Model defines how security responsibilities divide between cloud service providers and their customers. Understanding this division is fundamental to secure cloud operations because assumptions about who handles what frequently lead to security gaps.

Fundamental Principle

Cloud providers take responsibility for security of the cloud, meaning the underlying infrastructure, facilities, hardware, and the platform services they offer. Customers bear responsibility for security in the cloud, meaning their data, applications, access management, and configurations within the cloud environment.

Responsibility by Service Model

Infrastructure as a Service (IaaS) places the most responsibility on customers. Providers handle physical security, hypervisor management, and underlying network infrastructure. Customers must secure operating systems, middleware, applications, data, identity management, and network configuration within their virtual environments.

Platform as a Service (PaaS) shifts more responsibility to providers who additionally manage operating systems, runtime environments, and middleware. Customers remain responsible for applications, data, and identity management.

Software as a Service (SaaS) places maximum responsibility on providers who manage everything except customer data and access credentials. Customers must still manage data classification, user access, and application configuration within provider constraints.

Practical Customer Responsibilities

Certain responsibilities always remain with customers regardless of service model. Data classification determines what data requires what protections. Access authorization defines who can access what resources. Regulatory compliance with organization-specific requirements cannot be delegated. Backup strategy must ensure data recoverability. Data encryption protects confidentiality from unauthorized access. Security monitoring detects threats and anomalies. Incident response addresses security events when they occur.

Gray areas require explicit clarification through provider documentation, service level agreements, and formal contracts. Organizations should request cloud certifications and examine penetration testing policies.

Common Misconceptions

Many organizations wrongly assume providers automatically back up their data. In practice, provider backups often cover infrastructure only, not customer data. Organizations incorrectly believe provider compliance automatically makes them compliant. In reality, provider compliance supports but does not replace customer compliance obligations. Encryption assumptions frequently prove false and require explicit verification and documentation.

Creating RACI matrices for all cloud services clarifies security responsibility assignments and prevents dangerous assumptions.