RTC Check Register for Unauthorized Time Write Detection
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Solution Overview
Problem
Real-time clocks (RTC) cannot differentiate between authorized and unauthorized write operations, making them vulnerable to malicious modifications, both through hardware and software access.
Innovation Solution
A secure RTC implementation that includes a counter for storing a time signal and a check register to determine the authenticity of write operations, where the check register is updated upon each write operation and can only be altered securely, allowing legitimate sources to verify authorized access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the RTC is made programmable to allow easy setting of time, alarms, and calendar events, then ease of operation is improved, but vulnerability to unauthorized modifications increases
Solution Approach 1:
The patent implements a check register that is preliminarily configured to store expected check values before write operations occur. This preliminary setup enables the system to automatically verify whether subsequent write operations are authorized by comparing them against the pre-stored check values, thus preventing unauthorized modifications while maintaining programming capability
Solution Approach 2:
The patent employs a feedback mechanism where the check register continuously monitors and compares write operations against authorized check values. This feedback loop provides real-time detection of unauthorized modifications, allowing the system to identify and respond to security violations while maintaining normal programming operations
2Adaptability or versatility
If the RTC is accessed via serial interface to allow hardware modification, then adaptability is improved, but security against malicious access deteriorates
Solution Approach 1:
The patent introduces the check register as an intermediary security layer between the serial interface and the RTC counter. This intermediary component intercepts and validates all write operations passing through the serial interface, ensuring that even if hardware access is obtained, unauthorized modifications cannot successfully alter the RTC state without detection
3Adaptability or versatility
If software can access RTC without knowledge of legitimate system software, then versatility is improved, but reliability deteriorates
Solution Approach 1:
The check register provides continuous feedback monitoring of all software-initiated write operations to the RTC. By comparing each write operation against authorized check values, the system can reliably detect any unauthorized software access, thus maintaining reliability even while allowing versatile software accessibility
Data Source
AI summary
A real time clock comprises a counter which stores a count value, the count value representing a time signal. The counter may be written, for example by a host processor (not shown), such that the time signal can be set to any desired value. The real time clock comprises a check register that stores a check value. The content of the check register (i.e. the check value) is modified each time a write operation is performed on the counter. For example, the content of the check register can be updated by a control signal each time a write operation is performed on the counter. The check value stored in the check register is used for determining whether a write operation performed on the counter is an authorized write operation or an unauthorized write operation. The check value may be incremented each time a write operation is performed, replaced with a new random number each time a write operation is performed, or a combination of both.