Securing the Edge: Disk Encryption Challenges Under the EU CRA
The European Union’s Cyber Resilience Act (CRA) is redefining security mandates for all products with digital elements. For IoT device manufacturers, compliance begins with securing the data itself.
Two specific requirements detailed in Annex I of the CRA directly address data security and integrity at rest and in transit:
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必要条件
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Summary
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(e) Protect the confidentiality of stored, transmitted or otherwise processed data...
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Mandates the protection of data confidentiality (personal or otherwise), often requiring encryption at rest or in transit using state-of-the-art mechanisms.
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(f) Protect the integrity of stored, transmitted or otherwise processed data...
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Requires protecting the integrity of all data, commands, programs, and configuration against unauthorized manipulation or modification.
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In short, these mandates mean that data collected and stored on an IoT device must be encrypted and its integrity must be verifiable.
The IoT Challenge: Automated Disk Decryption
Disk encryption is a well-established technology—it is not “space rocket technology.” Many operating systems, including Linux (via utilities like LUKS), include built-in features that allow the entire disk to be encrypted. Enabling this feature is the baseline step for meeting the CRA’s requirements for data confidentiality.
However, encryption requires a key or password to unlock the disk upon startup. While desktop and laptop computers rely on the user to manually enter this key or insert a specific key device (like a smart card), this is not a practical solution for IoT devices.
Unattended IoT devices, which are designed to operate without human intervention (e.g., smart meters, remote sensors, industrial controllers), cannot wait for a human to type a password after every reboot or power outage. This creates a critical challenge: How do you securely store and automatically retrieve the encryption key without human input?
Four Technical Approaches to Key Retrieval
Solving this challenge requires a trusted mechanism for key storage that enables automated, secure boot. There are four common technical solutions being explored for this purpose:
- On-Chip Secure Element (Internal)
Using a dedicated secure element located directly on the main processor chip (e.g., a Trusted Platform Module or TPM). Newer Windows-based computers have made this a mandatory feature for security. - External Secured Element (Physical)
Attaching an external security module via a physical interface (such as USB, NFC, or similar) that is pre-paired with the device’s encrypted disk to deliver the key. - Unique Device Identifier (Hashing Challenge)
Deriving the key using some form of unique, immutable hardware identifier or secure boot measurement, often through cryptographic hashing, as the key itself. - Network-Based Retrieval (Bootstrap Device): Storing the password securely over the network, only transmitting it after the device has authenticated itself, to unlock the disk encryption. This is sometimes referred to as “bootstrapping.”
The following table provides a comparison between the technical solutions
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Approach
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Key Storage Location
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Pros (Advantages)
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Cons (Challenges)
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Best Suited For
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On-Chip Secure Element (TPM/HSM)
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Internal to the main processor/SoC.
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Highest Security: Keys never leave the chip (Root of Trust). Highly resistant to physical tampering. Mandatory standard for many new PCs.
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High Initial Cost: Requires specialized hardware integration and development effort. Lack of flexibility (key cannot be easily moved).
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High-value, mass-produced devices (like industrial gateways) where security is paramount.
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External Secured Element (USB/NFC Key)
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Detachable, physical device (e.g., dedicated USB key).
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Simplified Deployment: Easy plug-and-play installation for the end-user (if integrated well). Allows for multi-factor physical control.
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Physical Risk: Key can be lost, stolen, or duplicated. Requires a technician to be physically present to insert/install the key.
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Field service or maintenance scenarios where physical control is necessary to unlock the device.
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Unique Device Identifier (Hashing Challenge)
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Key is derived from the device's immutable hardware identifiers (serial numbers, fuses) and a challenge.
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No Extra Hardware Cost: Utilizes existing components. Highly effective at binding the OS/disk to a specific device.
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Low Flexibility: Changing a major hardware component (e.g., motherboard) or the initial binding process is difficult or impossible.
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Mass-scale, fixed-function devices that are physically secured (e.g., smart meters, unattended industrial sensors).
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Network-Based Retrieval (Bootstrapping/PKI)
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Key is stored on a centralized, trusted server (e.g., PKI or provisioning server).
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Remote Management: Enables fully automated recovery and remote key rotation. Scalable across large, geographically dispersed fleets.
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Single Point of Failure: Requires a reliable network connection (no good if the network is down). Creates a highly attractive target for external cyberattacks.
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Large fleets with high connectivity reliability (e.g., smart city applications) that require centralized control and key rotation.
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All four encryption methods comply with CRA requirements, subject to a specific risk assessment of the IoT product. The choice of method should align with the product’s unique features and requirements.