Distributed Stateful Hash-Based Signatures Beyond HSM Lifetime
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Solution Overview
Problem
Stateful hash-based signatures require maintaining a state with the private signing key, which is vulnerable to hardware failures or end of life of the hardware security module (HSM), compromising long-term signing capability.
Innovation Solution
A hybrid key pair generation method is implemented across multiple HSMs with disjoint state spaces, using Shamir's secret sharing to distribute key seeds to custodians, allowing for flexible maintenance and instantiation of additional HSMs, minimizing state collisions and ensuring signing capability beyond the typical HSM lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stateful hash-based signatures are implemented using a single HSM, then signing capability is provided, but the system is vulnerable to hardware failures and end of life of the HSM, compromising long-term signing capability
Solution Approach 1:
The patent segments the signing capability across multiple HSMs, each holding a portion of the private key material. This segmentation ensures that no single HSM failure compromises the entire signing capability, thereby improving reliability while managing complexity through modular architecture
Solution Approach 2:
The patent implements a hierarchical key structure where a root HSM generates master key material that is then distributed to multiple child HSMs. This nested structure allows centralized key generation and management while distributing the actual signing capability across multiple independent HSMs, resolving the contradiction between reliability and complexity
2Adaptability or versatility
If multiple HSMs are used to maintain signing keys, then long-term signing capability and availability are improved, but key management and distribution complexity increases
Solution Approach 1:
The root HSM performs preliminary key generation and distributes key material to child HSMs before they are needed for signing operations. This preliminary action simplifies subsequent key management, as the child HSMs already possess their key material and can operate independently, improving adaptability while reducing ongoing management complexity
Solution Approach 2:
The root HSM acts as an intermediary that generates and distributes key material to multiple child HSMs. This intermediary role centralizes the complex key generation process while allowing child HSMs to operate independently with simplified key management, thereby improving versatility without proportionally increasing overall system complexity
3Reliability
If signing keys are maintained in a single HSM, then key management is simple, but the system cannot withstand hardware failures or HSM end of life
Solution Approach 1:
Each child HSM is configured with specific local key material that enables it to perform signing operations independently. This local quality ensures that the failure or end of life of any single HSM does not compromise the overall signing capability, improving reliability while maintaining ease of operation through decentralized, independent HSM operation
Solution Approach 2:
Each child HSM is self-sufficient with its own key material and can perform signing operations independently without requiring coordination with other HSMs. This self-service capability improves reliability against hardware failures while simplifying key management, as each HSM manages its own keys autonomously
4Duration of action of stationary object
If stateful hash-based signatures use distributed HSMs with disjoint state spaces, then state collisions are minimized and long-term capability is ensured, but system complexity and setup requirements increase
Solution Approach 1:
The patent segments the cryptographic state space across multiple HSMs, with each HSM maintaining a disjoint portion of the state. This segmentation ensures that state collisions cannot occur between different HSMs, extending the duration of signing capability beyond what a single HSM could provide, while managing complexity through clear state separation
Solution Approach 2:
The patent creates a nested hierarchical structure where a root HSM generates master state that is distributed to multiple child HSMs as disjoint state spaces. This nested architecture ensures long-term signing capability by distributing state across multiple HSMs while managing complexity through the hierarchical organization of state spaces
Data Source
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AI summary
A system and method of producing a key for a digital signature method, including: providing a plurality of initial hardware security modules (HSM) with global public key parameters; running key generation to produce sub-public keys for respective sub-trees associated with the plurality of initial HSMs based upon the global public key parameters; picking a random seed and generating a sub-public key and a sub-tree based upon the random seed for a plurality of virtual HSMs; sending the sub-public keys of the plurality of initial HSMs to a root HSM; computing an overall public key of a tree structure associated with the root HSM; distributing the sub-public keys for the initial HSMs to the plurality of initial HSMs; splitting the random seed of the virtual HSMs into a plurality of key shares; and providing custodians associated with the plurality of virtual HSMs a key share from the plurality of key shares.