PhD studentship, University College London, United Kingdom, European Union
We are looking for outstanding candidates for a fully funded PhD studentship in cryptography. The PhD studentship is funded by an ERC Starting Grant on Efficient Cryptographic Arguments and Proofs. The studentship will provide a tax-free annual stipend of £21,000, however, ERC funding does not cover student fees (currently £4,400 for UK/EU students and £20,250 for Overseas students).
The goal of the PhD studentship under the supervision of Dr Jens Groth is to develop new and efficient zero-knowledge techniques. Zero-knowledge proofs enable a prover to convince a verifier that a statement is true without revealing any other information and are widely used in cryptographic protocols.
University College London has been recognized by the EPSRC and GCHQ as an Academic Centre of Excellence in Cyber Security Research and is one of the highest ranked universities in Europe. The Computer Science Department is one of the largest in the UK and is located at UCL\\\'s main campus in the centre of London.
Plug-and-Play IP Security: Anonymity Infrastructure Instead of PKI, by Yossi Gilad and Amir Herzberg
We present the Plug-and-Play IP Security (PnP-IPsec) protocol. PnP-IPsec automatically establishes IPsec security associations between gateways, avoiding the need for manual administration and coordination between gateways, and the dependency on IPsec public key certificates - the two problems which are widely believed to have limited the use of IPsec mostly to intra-organization communication.
PnP-IPsec builds on Self-validated Public Data Distribution (SvPDD), a protocol that we present to establish secure connections between remote peers/networks, without depending on pre-distributed keys or certification infrastructure. Instead, SvPDD uses available anonymous communication infrastructures such as Tor, which we show to allow detection of MitM attacker interfering with communication. SvPDD may also be used in other scenarios lacking secure public key distribution, such as the initial connection to an SSH server.
We provide an open-source implementation of PnP-IPsec and SvPDD, and show that the resulting system is practical and secure.
Short collision search in arbitrary SL2 homomorphic hash functions, by Ciaran Mullan and Boaz Tsaban
We study homomorphic hash functions into SL2(q), the 2x2 matrices with determinant 1 over the
field with q elements.
Modulo a well supported number theoretic hypothesis, which holds in particular for all concrete
homomorphisms proposed thus far, we prove that
a random homomorphism is at least as secure as any concrete homomorphism.
For a family of homomorphisms containing several concrete proposals in the literature,
we prove that collisions of length O(log q) can be found in running time O(sqrt q).
For general homomorphisms we offer an algorithm that, heuristically and according to experiments,
in running time O(sqrt q) finds collisions of length O(log q) for q even, and length O(log^2 q/loglog q) for arbitrary q.
For any conceivable practical scenario, our algorithms are substantially faster than all earlier algorithms
and produce much shorter collisions.
Computational Fuzzy Extractors, by Benjamin Fuller and Xianrui Meng and Leonid Reyzin
Fuzzy extractors derive strong keys from noisy sources. Their security is defined information- theoretically, which limits the length of the derived key, sometimes making it too short to be useful. We ask whether it is possible to obtain longer keys by considering computational security, and show the following.
-Negative Result: Noise tolerance in fuzzy extractors is usually achieved using an information reconciliation component called a \"secure sketch.\" The security of this component, which directly affects the length of the resulting key, is subject to lower bounds from coding theory. We show that, even when defined computationally, secure sketches are still subject to lower bounds from coding theory. Specifically, we consider two computational relaxations of the information-theoretic security requirement of secure sketches, using conditional HILL entropy and unpredictability entropy. For both cases we show that computational secure sketches cannot outperform the best information-theoretic secure sketches in the case of high-entropy Hamming metric sources.
-Positive Result: We show that the negative result can be overcome by analyzing computational fuzzy extractors directly. Namely, we show how to build a computational fuzzy extractor whose output key length equals the entropy of the source (this is impossible in the information-theoretic setting). Our construction is based on the hardness of the Learning with Errors (LWE) problem, and is secure when the noisy source is uniform or symbol-fixing (that is, each dimension is either uniform or fixed). As part of the security proof, we show a result of independent interest, namely that the decision version of LWE is secure even when a small number of dimensions has no error.