Abstract
The recent flurry of security breaches have raised serious concerns about the security of data
communication and storage. A promising way to enhance the security of the system is based
on physical root of trust. The use of physical unclonable function (PUF) to provide device
specific authentication and encryption is presented in this thesis. First the design of the highly
reliable RRAM PUF which is the key requirement for such a system is discussed. A new design
is presented where the sum of the read-out currents of multiple RRAM cells is used for
generating one response bit. This method statistically minimizes any early-lifetime failure due
to RRAM retention degradation at high temperature or under voltage stress. The RRAM device
model was calibrated using IMEC HfOx RRAM experimental data and it was shown that with
8 cells per bit, 99.9999% reliability for a lifetime >10 years at 125℃ can be achieved.
Furthermore, the hardware area overhead of the proposed RRAM PUF architecture was
analysed against a traditional RRAM PUF with error correction coding unit.
Next a basic security primitive is presented where RRAM PUF is embedded in cryptographic
module: SHA-256. This architecture is referred as Embedded PUF or EPUF. The EPUF has
security advantage as it never exposes the PUF response to the outside world. Instead in each
round the PUF response is used to change a few bits of the message word to produce a unique
message digest for each IC. Also in cryptography, key generation for encryption is another
major challenge. The use of EPUF as a key generation module for AES is shown, utilizing the
property of SHA-256 that even with a small change in its input it produces a large variation in
its output. The hardware area requirement for SHA256 and AES 128 is then analysed using
ASIC synthesis results based on TSMC 65nm library and it is shown that the area overhead of
multi cell per bit RRAM PUF is significantly less than these existing modules in the system.
Finally the security analysis of the complete system is presented.