Security Considerations for Hardware Security Module as a Service

A hardware security module (HSM) is a trusted platform for performing cryptographic operations and protecting keys. A main feature of the HSM architecture is its special co-processor that performs cryptography functions. HSMs also consist of a hardware-based random number generator, RAM, storage, and external interface.

HSM-as-a-Service is a growing market, with many organizations using it for their key management needs. Both cloud service providers and HSM vendors may provide HSMaaS solutions.

Why HSMaaS?

Customers might consider using HSMaaS for the following reasons:

• They may allow for greater interaction with existing cloud infrastructure.
• Some customers may have additional key management needs. For example, they may need greater control of root key establishment or greater control of the full key hierarchy.
• Customers may also need additional control over the HSM configuration itself. This includes management of firmware, HSM applications, cryptographic libraries, algorithms, functions, or primitives.
• In some instances, the cloud service provider may extend its APIs to support unique or specialized cryptographic operations. It may also provide the customer with direct access to native HSM APIs.
• Administrative access for HSMaaS may include HSM-level user management or device configuration.

HSMaaS Security Controls

Regarding security, HSMaaS providers need to provide physical access controls that meet or exceed customer security and compliance requirements. Providers generally have complete security and compliance responsibility for physical security of HSMs and their supporting systems. Cloud providers should provide third-party assurance that their physical security controls comply with relevant standards. This may include ISO 13491-2, Webtrust, PCI PIN, or ISO 11568.

When customers use remote key management devices, they may retain some responsibility for physical security. The customer is responsible for the physical controls for their use and storage.

Cloud providers must also demonstrate logical access controls that meet or exceed customer security and compliance requirements. Customers should expect providers to regularly attest to global access control requirements described by ISO 27001 and PCI DSS. This includes assurances of customer data separation, least privilege access, staff training, and other global principles.

Customers retain all their security and compliance responsibilities for key management access control, HSM administration, and HSM use. Even if providers have keys to manage, customers should expect to have ownership and responsibility for their key hierarchy.

Ensure the following security controls are in place when using Hardware Security Modules (HSMs) as a Service. Explore these considerations further in CSA’s HSM-as-a-Service Use Cases, Considerations, and Best Practices publication.

Device Integrity

• Log, audit, and restrict physical access to the HSM.
• Protect the HSM from unauthorized access with barriers, locks, etc.
• A chain of custody ensures the integrity of the device during all phases of the HSM lifecycle. This includes manufacturing, activation, operation, and de-commissioning.
• The HSM performs an “ab initio” selftest regularly to validate the integrity of its logical configuration, firmware, applications, and cryptographic libraries.

Operating Environment Integrity

• Protect the HSM from high temperatures, humidity, electro-magnetic interference, power outages, and power surges.
• The HSM may contain sensors that can detect and alert for operating environment changes.
• Implement strict access control policies to restrict access to the HSM’s operating environment. Only authorized personnel can access and make changes to the HSM’s configuration.

Key Security

• The HSMaaS solution provides strong keys to ensure data security.
• Comprehensive key lifecycle management is considered. This includes key generation, distribution, rotation, revocation, and deletion.
• The HSM hardware provides a tamper-resistant enclosure.
• Sensors initiate the secure deletion of sensitive keys when they detect physical tampering.
• Never expose keys outside the HSM. Employ remote administration tools and key management best practices.
• Customers have access to user-friendly interfaces or robust APIs.
• If needed, agree on Bring-Your-Own-Key (BYOK) and Customer-Managed Key (CMK) provisions through the provider's SLAs.
• Train, authorize, and record all staff with logical access to the HSM. Use split knowledge and dual control.

Service Availability

• Good disaster recovery practices and regular backup plans are in place.
• Configure, monitor, and manage access to HSM functions.

Governance

• Configure additional security measures according to organizational security policies for physical access, video surveillance, motion sensors, door alarms, and so on.
• Establish, maintain, record, and monitor key management processes.
• Create straightforward guidelines that explain how to use, manage, and maintain the HSM.
• Define and assign specific roles to people responsible for managing the HSM. This includes HSM administrators, security officers, system administrators, and auditors.
• Identify potential risks, evaluate their seriousness, and prioritize actions to reduce or eliminate them.
• Ensure HSM deployments meet the relevant regulations and industry standards.
• Keep proper records of policies, risk assessments, audit reports, incident response plans, and compliance documents.
• HSMs are capable of enforcing separation of duties for audit functions.

Identity and Access Management

• Cloud service providers are responsible for authorizing physical access and the corresponding access controls.
• Authorize, train, and manage the access of key admins and custodians.
• HSMs may provide integrated access control for HSM management applications.
• HSMs are capable of enforcing split knowledge for sensitive key operations.

Network Security

• Cloud service providers may enforce isolation of HSM network access to high-sensitivity networks.
• HSMs may have limited access through network protocols, if configured for serial communication only.
• Where network access is available, HSMs should enforce isolation of sensitive processes when connected to networks.

Get a deep dive into HSMaaS use cases, considerations, and best practices by checking out this CSA research publication.