Stateful Digital Signatures With Reserved Counter Range Backups
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Solution Overview
Problem
Stateful signature schemes face challenges in securely managing counter values during backup processes, leading to potential security breaches if counter values are reused, and existing solutions like forbidding backups impose operational limitations.
Innovation Solution
A method to manage counter values by obtaining and updating reserved counter values across subsets of backup devices, ensuring unique counter value ranges are used, with R + W > N, to prevent reuse and maintain security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backups of private key are implemented in stateful signature scheme, then availability and security are improved, but counter value management complexity increases and security breaches may occur if counter values are reused
Solution Approach 1:
The patent divides the backup devices into two distinct subsets: a first subset used for reading reserved counter values and a second subset used for writing new reserved counter values. This segmentation ensures that read and write operations are separated across different devices, preventing race conditions and counter value reuse while distributing the management complexity across multiple specialized components rather than requiring all devices to perform all operations.
Solution Approach 2:
The system performs preliminary actions by pre-reserving counter value ranges on backup devices before they are needed for signature generation. The apparatus obtains indications of reserved counter values from the first subset of backup devices, determines a new range of counter values in advance, and provides this new range to the second subset of backup devices for updating. This preliminary reservation and updating process ensures that when signature operations occur, unique counter values are already prepared and available, eliminating the need for complex real-time coordination during critical signing operations.
2Productivity
If stricter availability requirements are imposed, then service continuity is improved, but the risk of counter value reuse and security breaches increases
Solution Approach 1:
The patent introduces an intermediary mechanism where the apparatus acts as a coordinator between backup devices. The apparatus obtains reserved counter value indications from the first subset of backup devices, determines new counter value ranges, and provides these updates to the second subset. This intermediary coordination ensures that even with multiple backup devices available for high availability, the counter value assignment remains centralized and controlled, preventing any device from reusing counter values while maintaining service continuity.
Solution Approach 2:
The system implements feedback by having the apparatus read the current reserved counter values from the first subset of backup devices, determine new ranges based on this feedback information, and then update the second subset accordingly. This feedback loop ensures that each apparatus can independently determine safe counter value ranges by considering what has already been reserved, allowing multiple devices to operate concurrently with high availability while the reserved value information feedback prevents any counter reuse.
3Reliability
If more backup devices are used, then security is improved, but operational complexity and difficulty of management increase
Solution Approach 1:
The patent segments the backup devices into two functional subsets: read-subset devices that provide reserved counter value information and write-subset devices that receive updates. This segmentation allows the system to scale to multiple backup devices for enhanced security while maintaining operational simplicity, as each device has a clearly defined role and the apparatus coordinates between them through standardized read and write operations rather than requiring complex peer-to-peer coordination among all devices.
Data Source
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Figure 2A~2C
Figure 3A
AI summary
An apparatus for implementing a digital signature scheme, wherein the apparatus is configured to perform the steps of: (i) obtaining, from each backup device of a first subset of a set of N backup devices, a corresponding indication of reserved counter values, wherein the first subset comprises R backup devices connected to the apparatus; (ii) determining a new range of counter values which are all different from all the reserved counter values; (iii) providing an indication of the new range of counter values to a second subset of the set of N backup devices, whereby the new range of counter values is added to the reserved counter values by updating an indication of reserved counter values on each backup device of the second subset based on the indication of the new range of counter values, wherein the second subset comprises W backup devices connected to the apparatus, and wherein R + W > N; and (iv) generating digital signatures using the private key and the counter values from the new range of counter values.