Abstract
This blog explores the implementation of a air-gaped offline Certificate Authority (CA) on a portable Operating System (OS) residing on a USB stick, with its secret key securely stored on a Hardware Security Module (HSM), here a YubiHSM2. The combination of a portable operating system and HSM offers enhanced security and flexibility for managing off-line Root CAs, making it suitable for various use cases, including remote and air-gaped environments.
Introduction
Certificate Authorities play a crucial role in establishing and maintaining trust in digital communications by issuing and managing digital certificates. However, traditional Root CA implementations often rely on centralized servers, which can be vulnerable to security breaches and require continuous network connectivity. To address these challenges, Link2Trust proposes its novel approach, “CA-on-a-stick”, where the Root CA functionality is encapsulated within a portable OS running on a USB stick, with its private key securely stored on a YubiHSM.
Overview
Portable OS
The CA software stack is bundled within a lightweight OS, which can be booted from a USB stick on any compatible hardware like a disk-less laptop. This provides portability and isolation, ensuring that the Root CA operates independently of the host system’s configuration. Once disconnected the system can be maintained by ICT professional (software update, etc.).
HSM
Root CA key are protected by symmetric key split into quorum of component given to Key Custodians and recombined prior usage. The YubiHSM serves as a hardware security module for storing the Root CA’s private key securely. It provides cryptographic operations and key management functionalities, safeguarding the key from unauthorized access and tampering. More information on the YubiHSM can be found here. Once used for CA operation, the key material is cleared from HSM.
CA Metadata
CA related (meta)data are stored separately (policy configuration, issued certificates/crl, etc…), ensuring the separation of concern having on one hand the Operating System stack and the Certificate Authority stack on the other end.
Security considerations
Isolation
By encapsulating the CA within a portable OS, potential security risks from the host system are mitigated, providing a layer of isolation.
Key protection
Storing the private key on a YubiHSM enhances its protection against theft or compromise, as the key never leaves the hardware device.
Secure device
The portable OS on the USB stick is configured for secure boot to prevent unauthorized modifications or tampering.
Access Control
The operation and storing of the CA-on-a-stick requires strict processes and procedures, involving vaults, dual control and segregation of duties.
Use-cases
Remote Environments
The portable nature of the USB stick allows the Root CA to be deployed in remote or air-gaped environments where network connectivity is limited, unavailable or not allowed.
Field Operations
Organizations conducting field operations or on-site deployments can benefit from the flexibility and security offered by the portable CA solution, under strict controls
Disaster Recovery
In the event of a system failure or disaster, the Root CA instance can be quickly restored from the USB stick, minimizing downtime and ensuring continuity of certificate services.
Summary
The implementation of a Certificate Authority as a portable system with its secret key stored on a HSM offers a secure, flexible and cost effective solution for managing Root CAs. By leveraging hardware-based security and technology abstraction, organizations can enhance the integrity and availability of their certificate authority infrastructure across various use cases and environments.
Interested in learning more? Contact us at ca-on-a-stick@link2trust.be for more information.