Hybrid Clock Architecture for Reliable Event Ordering
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Solution Overview
Problem
Electronic devices often lack a reliable means to maintain accurate time information without constant power, making it difficult to log events precisely and securely, especially in forensic contexts where event ordering is crucial.
Innovation Solution
A hybrid clock architecture that provides both clock time and monotonic time, distinguishing between high and low trust sources, and accounting for lag time, allowing for reliable event ordering even without constant power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a real time clock is included to maintain accurate time without power, then timekeeping reliability is improved, but device cost and complexity increase
Solution Approach 1:
The clock system is segmented into two distinct components: a real-time clock (RTC) for maintaining wall-clock time when powered, and a monotonic counter for tracking elapsed time intervals. Each component has specialized functionality, allowing the system to achieve reliable timekeeping without requiring a single complex clock mechanism that must function under all power conditions.
Solution Approach 2:
The system dynamically switches between different time sources and modes based on power availability. When power is present, the RTC maintains accurate wall-clock time. When power is lost, the system transitions to using the monotonic counter with stored offset values, allowing the clock to adapt its behavior to current power conditions rather than requiring a static, always-on RTC.
2Measurement precision
If a real time clock with battery is used to keep time after power down, then event logging accuracy is improved, but power consumption and cost increase
Solution Approach 1:
Instead of continuously powering the RTC, the system periodically updates and stores the RTC time value in non-volatile memory before power loss. The monotonic counter continues tracking intervals without power, and the stored RTC value is retrieved after power restoration to reconstruct accurate timestamps, converting continuous power consumption into periodic operations.
Solution Approach 2:
The system performs preliminary actions by continuously updating the monotonic counter even when powered off, and pre-storing RTC offset values in non-volatile memory before power loss occurs. This preliminary preparation ensures that when power is restored, the system can immediately reconstruct accurate timestamps without requiring the RTC to have remained powered throughout the entire interval.
3Device complexity
If clock time is used without trust indicators, then system simplicity is maintained, but security and forensic reliability deteriorate
Solution Approach 1:
The trust indicator acts as an intermediary between the clock time data and the forensic analysis process. It provides metadata about the reliability and source of timestamp data without fundamentally changing the clock mechanism itself, allowing forensic systems to make informed decisions about evidence quality while maintaining relative system simplicity.
Data Source
AI summary
A clock object is provides, which includes a clock time and a monotonic time that are readable by the electronic device. The monotonic time is incremented every read of the monotonic time from the clock object. The clock object can also include an indication of a level of trust of the clock time.