Question

Logic circuits built with standard ICs are easy to duplicate. Write a 500 word paper that discusses how designers can secure the circuits such that they cannot be reversed engineered.

Answer 1

Solution:

A number of techniques exist to protect against counterfeiting and copying. The simplest is to employ a fully trusted foundry for production that is able to guarantee the use of procedures that combat tampering. However, such foundries are expensive and may lack the advanced processes needed to produce competitive commercial devices.

One option to reduce cost is to use split manufacturing, in which different foundries are used to produce different layers of the IC. A single foundry cannot tamper with the design and be assured that it will work. But split manufacturing is at odds with the most efficient interfaces used for fabless production and entail finding foundries with front-end and back-end processes that are compatible with each other.

The move to 3DIC production may provide one answer. At the 22nd Usenix Security Symposium in August 2013, Frank Imeson and colleagues from the University of Waterloo received the best student paper award for their proposal to
use 3DIC technology to prevent an attacker based at a foundry from successfully inserting a Trojan. Their idea was to 'lift' selected circuitry to a separate IC that would be fabricate at a trusted location while the remainder of the chips in the stack would use the conventional foundry supply chain. The method developed by Imeson and colleagues allows the 'trusted' layer to be no more complex than a passive interposer.

A method that involves less supply-chain overhead is to alter the circuit design to make it less amenable to overbuilding, counterfeiting or copying. Logic encryption, for example, inserts logic gates at key points in the design that are wired to a register. Unless this register is loaded with the correct key, the IC will not function correctly.

Layout analysis could be used on a decapped chip to determine register values that will work, so encryption may need to be used in combination with camouflaging or circuit obfuscation, which is normally employed to prevent reverse engineering of the circuit IP.

You may not have given much thought to how easy it is to copy your design, but engineers who have experienced design theft will tell you that once it has happened, you never want it to happen again! For example, if the on-chip code for your MCU design can be read out by a competitor, or even by an unscrupulous contract manufacturer, your entire design can be easily copied and resold — either under a different brand or perhaps even using your brand on the black market. Popular designs that outstrip product capacity are ripe for this type of treatment, and if sellers cannot get product from you they may dip into the black market to satisfy their customer demand.

Just as vulnerable is the actual design or algorithm hidden in the heart of your MCU code. Perhaps you have an innovative approach to analyzing sensor data that dramatically reduces the power or processing time required. Do you want a competitor to be able to just copy your code and reverse engineer your algorithm? There are even software tools that can take binary and regenerate reasonable “C” code so that the algorithmic details are even easier to decipher. Even something as mundane as an on-board test routine may have taken many months to get just right — do you want a competitor to get short-cut access to your infrastructure related code, dramatically reducing their development cost so they can unfairly cut their market price to win your business?

Another aspect of protection is related to hardware authentication. Often a design will allow for peripherals or add-on cards so a base design can be upgraded or enhanced. If the design does not include some capabilities to detect that the add-on module hardware is authorized, it’s possible for other vendors to create lower-cost modules to compete for the add-on business. Printer cartridges are perhaps the most familiar application for hardware authentication, to ensure that you buy a manufacturer’s branded cartridge. Often the printer is sold at a discount and the cartridge price is inflated to cover the discount over the lifetime of the printer. A competitor could sell a cartridge at a lower price, since it need not recoup the printer discount, and still make a healthy profit.