The University of Massachusetts Amherst
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UMass Engineers Create More Secure and Efficient Memristive Hardware Systems

Microchip imprinted with a glowing padlock

A new paper by a research team led by Qiangfei Xia, Daniel Holcomb, and Joshua Yang of the Electrical and Computer Engineering Department at the University of Massachusetts Amherst describes a pioneering new technique to support the safe use of all-important “digital keys” in protecting hardware security systems and producing more secure, compact, and efficient memristive hardware. The paper, titled "A provable key destruction scheme based on memristive crossbar arrays," has just been published in the prestigious peer-reviewed journal Nature Electronics.

The researchers have achieved their breakthrough by leveraging another unique property of memristors that has been rarely exploited so far; i.e., a hidden, intrinsic fingerprint of memristors that can only be revealed by erasing the stored information with a certain electrical operation.

The Nature Electronics paper explains that stored digital keys are frequently used in today’s security systems to encrypt and decrypt data and to unlock certain functionalities on a variety of electronic circuits and chips. However, once the user’s key-based permissions are revoked or forfeited, the digital key should be erased. But a challenging problem still remains: proving that the key has really been erased – that is, achieving verifiable key destruction – and whether such erasure is done in the desired chip or device.

“Take pay television for instance,” explains Xia. “If a user decides to cancel service, a deactivation signal will be sent out from the cable company to wipe out the key. However, if the user is dishonest, he or she can block the signal physically and still retains the key without the awareness from the cable company. With our new technology, the cable company will be able to find out if the key has been erased, because only after it is erased, the fingerprint of the device becomes visible.”

In this Nature Electronics article, the authors report a provable key destruction scheme based on memristive devices. Most digital security systems that use traditional, complementary, metal–oxide–semiconductor transistors are not well suited to address this issue because of their volatility and unreliability at small scales. 

“Here we show that the unique physical fingerprint of a 128 × 64 hafnium oxide memristor crossbar array integrated with transistors is capable of provable key destruction,” say the authors of the Nature Electronics paper. “The fingerprint is extracted by comparing the conductance of neighboring memristors, and it can only be revealed if a digital key stored on the same array is erased.”

Xia adds that the new key-erasing technique developed by his team can have a far-reaching impact on memristor hardware. “From a technology advancement perspective, our chip integrates security, memory, and computing functionalities into the same circuits, leading to much more compact and efficient hardware systems.”

As the Nature Electronics paper puts it: “Based on this provable key destruction technique, we propose a protocol for logic locking or unlocking that can support secure outsourcing of integrated circuits manufacturing. By leveraging the unique properties of memristor, including reconfigurability and variability, our security chip demonstrates the integration of security, memory, and computing functionalities into the same circuits and could be used to develop more secure, compact, and efficient memristive hardware systems.”

According to the authors, in the semiconductor industry logic locking is a common technique to lessen threats, including intellectual property theft, counterfeiting, and unauthorized overproduction during the outsourcing of chip fabrication to foundries around the world. “This is currently achieved,” they say, “by adding extra logic gates (key gates), which enable the chip to function correctly only after the designer unlocks these gates with a universal unlocking key.”

However, as the authors observe, the universal unlocking key may be permanently stored in each device, which means that once a device has the key it can forever unlock the logic, voiding the controlling capability of the service provider or chip designer.

“To address these challenges, there is growing interest in developing security primitives based on emerging electronic devices, such as memristive devices, which are two-terminal resistance switches,” the authors write. “These devices offer great scalability, CMOS compatibility, fast switching speed, high endurance, and low power consumption. In addition to memory, data storage, and unconventional computing applications, memristors have also been used to build security primitives such as physical un-clonable functions and true random number generators.”

In addition to Xia, Holcomb, and Yang, the other co-authors of the Nature Electronics paper are Hao Jiang, Can Li, Rui Zhang, Peng Yan, Peng Lin, and Yunning Li, all of the ECE department. This work involves ECE faculty members and graduate students from differing fields in two buildings. As ECE Department Head Christopher Hollot says about this interdisciplinary cooperation: “The department is very happy to see a Knowles Engineering Building /Marcus Hall collaboration.” (October 2018)