The second
day of CHES 2012 brings us a number of interesting sessions, among them a session
devoted to Physically Unclonable Functions. PUF primitives have become popular in
the research community and each year CHES attendees are able to hear about the state-of-the-art
results. That happens this time as well, with a PUF session containing four
papers, ranging from theoretical analysis of PUFs as basic building blocks for cryptographic
schemes to practical evaluation of PUF implementations in ASICs.
In the
first talk of the PUFs session, Ulrich Ruhrmair presented, firstly, an attack
on two oblivious transfer and bit commitment protocols introduced at CRYPTO
2011 and secondly, as follow up, countermeasures that could be applied to
mitigate those security issues.
The most practical
paper of the PUF session was “PUFs: Myth, Fact or Busted? A Security Evaluation
of Physically Unclonable Functions (PUFs) Poured in Silicon” by Stefan
Katzenbeisser et al. In the paper authors evaluate five different types of
intrinsic Physically Unclonable Functions such as arbiter, ring oscillator,
SRAM, flip-flop, latch PUFs. All aforementioned types were implemented in a TMSC
65 nm CMOS process technology. In total, 96 different AISC chips have been evaluated
at different ambient temperatures and varying chip core voltages. Apart from practical
results, the second contribution of the paper is the introduction of a PUF
evaluation framework. More details, plots and full analysis are in the paper.
The only missing part is an ageing test, where ASIC chips are stressed in different
environmental conditions and thus ageing effect can be achieved. This ageing
test will be carried out by authors in future work.
An interesting
paper that concludes the PUF session has been presented by Anthony Van
Herrewege from KU Leuven. The title of said presentation was “PUFKY: a fully
functional PUF-based cryptographic key generator”. The authors successfully evaluated
a practical and modular design for a key generation which uses PUFs primitive
on FPGAs. In their work, the authors have used ring oscillator PUFs, but the
modular approach easily allows to integrate other types of PUFs with a
microprocessor. This flexibility allows to deploy prepared IP without much
hassle.
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