Stateful Signature Timing Intervals to Prevent OTS Key Reuse
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Solution Overview
Problem
Existing stateful signature schemes face security risks due to the potential reuse of OTS private keys, which compromises the integrity of the signing ecosystem, especially when a signer fails and recovers from a backup with an outdated state.
Innovation Solution
Implement a mechanism that uses time intervals to ensure each OTS private key is generated only once within a specific time frame, preventing reuse by associating states with non-overlapping time intervals, and allowing backup signers to continue the signing process without risking state reuse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a signer recovers from a backup with an outdated state, then the signer can continue signing operations, but the OTS private key may be reused which compromises security
Solution Approach 1:
The system performs preliminary actions by establishing non-overlapping time intervals and associating each state with a specific time interval before signing operations begin. This preliminary time-based association prevents state reuse by ensuring that a state can only be used within its designated time window, resolving the contradiction between signer continuity and security.
Solution Approach 2:
Time intervals serve as an intermediary mechanism between the signer's state and the OTS private key generation process. By introducing this time-based mediator, the system ensures that even if a signer recovers from backup with an outdated state, the state cannot be reused because it is bound to a specific time interval that has already passed, thus maintaining security while allowing operational continuity.
2Object-affected harmful factors
If time intervals are enforced to prevent state reuse, then security is maintained, but the complexity of the signing mechanism increases
Solution Approach 1:
The system changes the parameter of state identification from purely sequential (state counters) to time-based (time intervals). This parameter change simplifies the overall mechanism by using the naturally progressing time parameter to automatically prevent state reuse, rather than requiring complex tracking and validation of state sequences across multiple signers.
3Reliability
If backup signers are allowed to continue signing, then resilience against signer failure is improved, but the risk of state reuse increases
Solution Approach 1:
The system performs preliminary action by pre-associating each state with a unique, non-overlapping time interval before any signing operations occur. This preliminary time-based binding ensures that when backup signers continue signing operations, they are automatically constrained to use only states within valid future time intervals, preventing any possibility of state reuse while maintaining full resilience against signer failures.
Data Source
AI summary
In an example, a computing device is described. The computing device comprises a memory to store a set of states and a corresponding set of non-overlapping time intervals. The computing device further comprises a timing unit to indicate a time at which a signature is to be produced. The computing device further comprises a processor to: identify which time interval of the set of non-overlapping time intervals includes the indicated time; generate a signing key based on a state associated with the identified time interval; and produce a signature, under a stateful signature scheme, with the signing key.