Level Sensor Firmware Key Exchange Using a Signed Manifest
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Solution Overview
Problem
Existing firmware update methods for level sensors require replacing the public key due to private key compromise or expiration, necessitating a new firmware version that includes the new public key, which is undesirable for system operators.
Innovation Solution
The public key is stored as an independent binary manifest within the firmware update package, signed with the manufacturer's private key, ensuring its trusted origin, and verified during installation without altering the existing firmware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the public key is stored directly in the program memory of the firmware, then the public key can be exchanged by creating a new firmware, but this requires replacing the entire firmware including measurement application and other device functions
Solution Approach 1:
The patent segments the firmware update into separate components: the measurement application firmware and the manifest containing the public key. This allows the public key to be updated independently without replacing the entire firmware, resolving the contradiction between adaptability and device complexity.
Solution Approach 2:
The public key is extracted from the firmware and placed in a separate manifest file. This extraction allows the public key to be updated independently while keeping the measurement application intact, eliminating the need to replace entire firmware and reducing device complexity.
2Adaptability or versatility
If a new firmware is created to exchange the public key, then the new public key can be implemented, but system operators do not welcome firmware updates that include measurement application changes
Solution Approach 1:
By segmenting the update into a manifest-only update rather than full firmware update, the solution enables public key exchange without changing measurement application, thereby improving operator acceptance while maintaining update capability.
Solution Approach 2:
Extracting the public key into a separate manifest allows updates to be performed without modifying the measurement application, making updates more acceptable to operators while preserving the ability to exchange public keys.
3Reliability
If the public key is replaced in the device, then new firmware signed with a new private key can be confirmed as trustworthy, but the replacement process itself must be secure and verified
Solution Approach 1:
The manifest is pre-signed with the manufacturer's private key before being transferred to the device. This preliminary signing action ensures that the public key replacement process itself is secure and verifiable, maintaining reliability while managing the complexity of key replacement.
Solution Approach 2:
The signed manifest acts as an intermediary that carries the new public key in a secure and verifiable manner. This intermediary structure enables trustworthy key replacement without requiring complex direct key injection processes, balancing reliability and complexity.
Data Source
AI summary
A device for exchanging a public key in the course of a firmware update in a level sensor, the device including signing circuitry that generates a manifest comprising a public key and to sign the public key stored in the manifest, and updating circuitry that replaces a pre-installed public key of a previous manifest in the level-measuring device with the signed public key.