On January 29, 2015, the U.S. Patent & Trademark Office published a patent application from Apple that reveals a solution to counter a common hacking method involving clock overdriving.

Apple notes in their patent filing that some system-on-a-chip (SoC) designs may be used in applications which may be targeted by a subset of users who attempt to gain unauthorized access into the system (commonly referred to as "hacking a system" or "hacking"). Some typical applications targeted for hacking include mobile phones, tablet computers, and video game systems.

A common method used to attack systems is to overdrive the clock input into one of the processing chips in the system. The intent is to force the chip into a logic error which may result in the chip entering a state from which the attacker may gain control over the execution of the processor. Once the attacker has whole or partial control of the chip, the attacker may be able to access information within the system, such as, e.g., security keys for accessing a cellular network, encryption key for data stored in the system, and the like.

A clock signal monitoring circuit may be used within a system for the purpose of detecting if the frequency of a clock signal is operating at a frequency higher than for which the system is designed. A clock signal monitoring circuit may sample an input clock signal to determine if the input clock is running above or below a predetermined frequency.

Apple notes that in order to help defend a system from being affected by clock attacks, some SoCs may include a clock monitoring circuit. A clock monitoring circuit, or clock monitor, is a means for determining if a clock signal is running at a frequency above or below a designated frequency.

Various embodiments of a clock monitoring circuit are described in Apple's invention/patent application. Some clock monitor embodiments may be limited to a certain range of frequencies they are capable of detecting. The embodiments illustrated in the drawings and described below may provide techniques for monitoring clock signals within a computing system over a wider range of frequencies.





Apple's patent FIG. 6 noted above illustrates a block diagram of a clock monitoring system. This is the key patent figure that Apple highlights in their application as being the heart of their invention.

Once again, this is a highly technical invention that only engineers and programmers could truly appreciate. Yet if you're a glutton for punishment, you can check out the nitty-gritty details of Apple's invention titled "Harmonic Detector of Critical Path Monitors," here.

Patent Credits

Apple credits Shu-Yi Yu and Timothy Paaske as the inventors of patent application 20150033061 which was originally filed in Q3 2013. Considering that this is a patent application, the timing of such a product to market is unknown at this time.

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