InvenSense to add PUF security to sensors

November 25, 2015 // By Peter Clarke
MEMS vendor InvenSense Inc. (San Jose, Calif.) has partnered with Intrinsic-ID BV (Eindhoven, The Netherlands) to develop a system of sensor data security based the use of the physically unclonable function (PUF) implemented in silicon.

The companies are calling the system TrustedSensor and envision it providing the root of trust for protecting sensor data that is generated as part of the Internet of Things.

This week Intrinsic-ID is exhibiting a the authentication system working with InvenSense's 'Firefly' inertial measurement microcontroller – the ICM30630 – at an InvenSense company conference and exhibition. The ICM30630 integrates 3-axis accelerometer with 3-axis gyroscope MEMS sensors together with tri-core CMOS microcontroller, embedded flash and SRAM and software. It does this in a package that measures 3mm by 3mm by 1mm.
 

"Our solution extracts a cryptographic key from the unique silicon properties of the sensor chip," said Pim Tuyls, CEO of Intrinsic-ID, in a statement. The Nasiri process used by InvenSense to build its sensors creates a seal using alumimum-germanium to form a eutectic bond that combines a MEMS sensor made on one wafer with a CMOS wafer die that conventionally includes calibration and signal conditioning circuitry. The PUF is set to be implemented in the CMOS ASIC that includes a Cortex-M0 that will run the algorithms to encrypt data, Boris Kennes, business development manager at Intrinsic-ID told EE Times Europe in email correspondence. 

The classic PUF makes use of the cross-coupling metastability of SRAM cells. An SRAM cell will power up as either a 1 or 0 due to the metastable nature of the circuit, but variations in manufactured silicon create an inherent primary stability. A line of such SRAM bit cells effectively provides a multi-bit word that is repeatable but specific to that silicon implementation and hidden. 

This cryptographic key is only present when the IC is powered up and is not evident at other times. The Intrinsic-ID technology has been licensed to such semiconductor companies as NXP Semiconductor and Dialog Semiconductor in the past.

The TrustedSensor addition to the InvenSense FireFly platform will be available early in 2016 and will become a standard feature in the