Clock Roll-Forward Detection in DRM Systems
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Solution Overview
Problem
Current Digital Rights Management (DRM) systems struggle to enforce time restrictions on platforms without network connectivity or secure hardware clocks, as users can manipulate the system clock to bypass content access restrictions.
Innovation Solution
A method that records and compares system file timestamps and digests to detect clock tampering, denying access if any manipulation is detected, using a secure database to store initial and subsequent file system times and digests, and implementing a 'sanity' check to validate file integrity during playback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a secure time server or hardware clock is used to enforce time restrictions, then time enforcement reliability is improved, but device complexity and network connectivity requirements increase
Solution Approach 1:
The patent uses file system timestamps as an intermediary to detect clock tampering. Instead of directly trusting the system clock or requiring network connection to a time server, the system records timestamps of system files and compares them to detect if the clock has been manipulated. This intermediary approach provides time enforcement reliability without requiring network connectivity or secure hardware clocks.
Solution Approach 2:
The system performs self-validation by checking its own file system timestamps against expected time ranges. The DRM software autonomously detects clock tampering by examining file modification times without needing external verification from a time server. This self-service mechanism reduces device complexity while maintaining time enforcement reliability.
2Ease of operation
If the system clock is changed to bypass time protection, then content access flexibility is improved, but security is worsened
Solution Approach 1:
The system implements feedback by continuously monitoring file system timestamps and comparing them against the DRM content time restrictions. When a user attempts to access content, the system checks whether the current file timestamps indicate clock tampering. This feedback mechanism maintains security while allowing legitimate time-based access flexibility.
Solution Approach 2:
The system takes preliminary anti-action by pre-recording file system timestamps before content access is attempted. These baseline timestamps are stored and used to detect any subsequent clock manipulation. By establishing this preliminary reference point, the system prevents clock tampering attacks before they can successfully bypass time protection.
3Reliability
If file system timestamps are monitored to detect clock tampering, then security is improved, but measurement precision requirements increase
Solution Approach 1:
The system applies partial monitoring by selecting specific system files whose timestamps are most indicative of clock tampering. Instead of monitoring every file in the system, the DRM software focuses on a subset of critical system files. This partial approach provides sufficient security detection while reducing the measurement precision burden compared to comprehensive file system analysis.
Data Source
AI summary
Method and apparatus to detect clock roll-forward attacks in a computing device or similar system. This protects against hackers who tamper with the system clock of, for instance, a digital media playback device in order to access a content item which has been rented for a limited time. By detecting clock roll-forward tampering, the present method and system prevent such hackers from accessing the content item outside its authorized rental time period.