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Carbon Nanotubes Could Improve Hardware Cryptography

A team of researchers from IBM and academia has devised a new use for carbon nanotubes. These tiny objects can act as semiconductors, which has led to speculation about their potential use in computer chips.

Traditionally, there have been two significant drawbacks to this application. First, the procedure used to create them produces an unpredictable blend of semiconducting tubes and non-conducting ones. Second, it is not easy to precisely position the tubes in the way a processor would need. The team has actually managed to make use of these features to create an inherently random process for producing cryptographic information in hardware.

Cryptography in hardware involves fixing a pre-established key — a sequence of bits — into the hardware itself. This physical nature of storing keys can lead to hardware-based cryptography being subject to certain kinds of vulnerabilities. For one, the security of the process can vary with external conditions. Another is the potential for snooping.

hardware cryptography

Schematics of random bits based on a 2D carbon nanotube array
(Image credits: IBM Research/ Shu-Jen Han)

The authors were able to formulate a method for creating a chip that makes the wiring itself random. They coated a number of nanotubes in a negatively-charged detergent solution, which would attract them to segments of the chip that are positively charged. They also gave neighboring areas a negative charge, causing something like a tug-of-war between the different areas.

The spacing of these segments allowed the researchers to determine the number of areas with nanotubes to a high degree of precision. However, the areas themselves can’t be predicted, making it impossible to tell which are conducting and which aren’t. This is an ideal starting point for a random cryptographic key. Moreover, since carbon nanotubes themselves can be semiconductors or metallic, the total number of possible states for each bit goes up to three.

The reliability of the procedure was confirmed when the authors developed test hardware that produced similar keys under similar environmental conditions, which is a sign that external factors should not be a problem.

Snooping is also deterred with this new process. The only way to effectively do so would be to get down into the wiring of the device itself, since that is where the nanotubes reside. However, the wiring would become damaged beyond repair if it were imaged using current methods.

Due to the process’s overall simplicity, it can be smoothly incorporated into chip-building processes that already exist. More work is undoubtedly needed, but the team’s findings raise the possibility of carbon nanotubes being used widely in future computer chips.

Findings have been published in the journal Nature.

About the author

Warren Simons