Information Terminal PCR Reference Value Management for Secure Data Access
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Solution Overview
Problem
The existing Trusted Computing Group (TCG) technology faces issues with decrypting sealed data and providing information services when program data is updated, as the Trusted Platform Module (TPM) cannot decrypt data sealed with a previous PCR value, and updating the PCR reference value on the service provider's server is not synchronized with the program data updates, leading to safety concerns and service disruptions.
Innovation Solution
An information terminal with an update certificate system that includes old and new characteristic values, allowing the terminal to judge whether the current program matches the new program and use the old characteristic value to remove data use restrictions, ensuring the new program can access data as before the update without returning to a vulnerable state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the program data is updated to improve security and functionality, then the reliability is improved, but the sealed data cannot be decrypted and service continuity is lost
Solution Approach 1:
The patent applies preliminary action by storing multiple PCR reference values (first and second reference values) in advance in the storage unit. When a program update occurs, the system can switch to using the second reference value that was pre-prepared for the updated program, allowing seamless decryption without requiring real-time PCR value generation or service interruption.
Solution Approach 2:
The patent implements parameter changes by allowing the PCR reference value to change from the first reference value (for old program) to the second reference value (for new program). The judgment unit dynamically selects which reference value to use based on whether the current program matches the old or new program, enabling the system to adapt to different program versions while maintaining decryption capability.
2Reliability
If the PCR reference value is updated on the service provider's server to match the new program, then the service authentication is improved, but the synchronization timing creates security gaps
Solution Approach 1:
The patent eliminates synchronization delays by performing preliminary action - the second PCR reference value is stored in advance in the terminal's storage unit before the program update occurs. This pre-stored reference value is immediately available when the updated program needs to access sealed data, removing any waiting time for server synchronization and eliminating the security gap that would exist during update transitions.
3Reliability
If the system requires exact match between PCR value and reference value for decryption, then the security is improved, but the system cannot adapt to program updates
Solution Approach 1:
The patent applies dynamics by making the PCR reference value dynamic rather than static. The judgment unit dynamically selects between the first reference value (for old program) and the second reference value (for new program) based on program identification. This dynamic adaptation allows the system to maintain strict security verification (exact match required) while accommodating different program versions through appropriate reference value selection.
Solution Approach 2:
The patent implements parameter changes by allowing the PCR reference value parameter to change based on the program version. When the program is updated, the system transitions from using the first reference value to the second reference value. This parameter change enables the system to maintain security through exact matching while adapting to different program versions by using the appropriate reference value for each version.
4Adaptability or versatility
If the system stores multiple PCR reference values for different program versions, then the adaptability is improved, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the reference value management into distinct segments - the first PCR reference value for the old program and the second PCR reference value for the new program. The judgment unit segments the decryption process by first determining which program version is running, then selecting the corresponding reference value segment. This segmentation approach manages complexity by organizing multiple reference values into clearly defined, separately managed groups rather than requiring a complex unified management system.
Data Source
AI summary
An information terminal that decrypts sealed data without returning program data after update to the state before update. The information terminal includes update certificate storage unit storing an update certificate for certifying update of the program data to be executed by CPU, and a selection unit which, when the CPU is to execute program data, judges whether or not digest of the post-update program data in the update certificate matches digest of the program data to be executed, and selects digest of the pre-update program data in the update certificate when it judges that they match. The CPU executes the post-update program data. The information terminal further includes a security device that stores an extend value of a program data digest when the pre-update program data is executed by the CPU according to a request from the selection unit.