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a well-known security primitive for secure key storage
and anti-counterfeiting. For both applications it is imperative
that PUFs provide enough entropy. The aim of this paper
is to propose a new model for binary-output PUFs such as
SRAM, DFF, Latch and Buskeeper PUFs, and a method to
accurately estimate their entropy. In our model the measurable
property of a PUF is its set of cell biases. We determine
an upper bound on the \'extractable entropy\', i.e. the number
of key bits that can be robustly extracted, by calculating the
mutual information between the bias measurements done at
enrollment and reconstruction.
In previously known methods only uniqueness was studied
using information-theoretic measures, while robustness was
typically expressed in terms of error probabilities or distances.
It is not always straightforward to use a combination of these
two metrics in order to make an informed decision about
the performance of different PUF types. Our new approach
has the advantage that it simultaneously captures both of
properties that are vital for key storage: uniqueness and
robustness. Therefore it will be possible to fairly compare
performance of PUF implementations using our new method.
Statistical validation of the new methodology shows that
it clearly captures both of these properties of PUFs. In other
words: if one of these aspects (either uniqueness or robustness)
is less than optimal, the extractable entropy decreases.
Analysis on a large database of PUF measurement data shows
very high entropy for SRAM PUFs, but rather poor results
for all other memory-based PUFs in this database.
In this paper, we describe, characterize, and exploit this surprising structure. It is our thesis that the additional structure available in these curves will give rise to novel cryptographic constructions, and we initiate the study of such constructions. Both the subgroup hiding and SXDH assumptions appear to hold in the new setting; in addition, we introduce custom-tailored assumptions designed to capture the trapdoor nature of the projection maps into $G_1$ and $G_2$. Using the old and new assumptions, we describe an extended variant of the Boneh-Goh-Nissim cryptosystem that allows a user, at the time of encryption, to restrict the homomorphic operations that may be performed. We also present a variant of the Groth-Ostrovsky-Sahai NIZK, and new anonymous IBE, signature, and encryption schemes.
The studentships are only open to UK nationals and the successful candidate will be required to spend in the region of 2 - 4 weeks per year at GCHQ headquarters in Cheltenham. To be considered for this studentship, candidates must therefore be prepared to undergo GCHQ\\\'s security clearance procedures.
The studentships will be funded for a period of 3.5 years. GCHQ will cover the costs of university fees (currently £ 3828 per annum) and will provide an annual stipend to the student corresponding to the National Minimum Stipend (currently £ 13,590 per annum) plus an additional stipend of £ 7,000 per annum. Making a total tax-free stipend of £ 20,590 per annum. A generous travel budget is also provided to enable attendance at international conferences and workshops.
More information on Coding and Crypto Research Group at Nanyang Technological University can be found at http://www1.spms.ntu.edu.sg/~ccrg/index.html
The applications will be considered immediately. The positions are for 1 year, but renewable up to 3 years.