University of Massachusetts researchers have found a way to make hardware backdoors virtually undetectable.
What are hardware backdoors?
Hardware backdoors aren't exactly new. We've known for a while that they are possible, and we have examples of them in the wild. They are rare, and require a very precise set of circumstances to implement, which is probably why they aren't talked about as often as software or network code. Even though hardware backdoors are rare and notoriously difficult to pull off, they are a cause of concern because the damage they could cause could be much greater than software-based threats. Stated simply, a hardware backdoor is a malicious piece of code placed in hardware so that it cannot be removed and is very hard to detect. This usually means the non-volatile memory in chips like the BIOS on a PC, or in the firmware of a router or other network device.
A hardware backdoor is very dangerous because it's so hard to detect, and because it typically has full access to the device it runs on, regardless of any password or access control system. But how realistic are these threats? Last year, a security consultant showcased a fully-functioning hardware backdoor. All that's required to implement that particular backdoor is flashing a BIOS with a malicious piece of code. This type of modification is one reason why Microsoft implemented Secure Boot in Windows 8, to ensure the booting process in a PC is trusted from the firmware all the way to the OS. Of course, that doesn't protect you from other chips on the motherboard being modified, or the firmware in your router, printer, smartphone, and so on.
The University of Massachusetts researchers found an even more clever way to implement a hardware backdoor. Companies have taken various measures for years now to ensure their chips aren't modified without their knowledge. After all, most of our modern electronics are manufactured in a number of foreign factories. Visual inspections are commonly done, along with tests of the firmware code, to ensure nothing was changed. But in this latest hack, even those measures may not be enough. The way to do that is ingenious and quite complex.
The researchers used a technique called doping transistors. Basically, a transistor is made of a crystalline structure which provides the needed functionality to amplify or switch a current that goes through it. Doping a transistor means changing that crystalline structure to add impurities, and change the way it behaves. The Intel Random Number Generator (RNG) is the basic building block of any encryption system since it provides those important starting numbers with which to create encryption keys. By doping the RNG, the researchers can make the chip behave in a slightly different way. In this case, they simply changed the transistors so that one particular number became a constant instead of a variable. That means a number that was supposed to be random and impossible to predict, is now always the same.
By introducing these changes at the hardware level, it weakens the RNG, and in turn weakens any encryption that comes from keys created by that system, such as SSL connections, encrypted files, and so on. Intel chips contain self tests that are supposed to catch hardware modifications, but the researchers claim that this change is at such a low level in the hardware, that it doesn't get detected. Fixing this flaw isn't easy either, even if you could detect it. The RNG is part of the security process in a CPU, and for safety, it is isolated from the rest of the system. That means there is nothing a user or even administrator can do to correct the problem.
There's no sign that this particular hardware backdoor is being used in the wild, but if this type of change is possible, then it's likely that groups with a lot of technical expertise could find similar methods. This may lend more credence to moves from various countries to ban certain parts from some regions of the world. This summer Lenovo saw its systems being banned from defense networks in many countries after allegations that China may have added vulnerabilities in the hardware of some of its systems. Of course, with almost every major manufacturer having their electronics part made in China, that isn't much of a relief. It's quite likely that as hardware hacking becomes more cost effective and popular, we may see more of these types of low level hacks being performed, which could lead to new types of attacks, and new types of defense systems.