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02 January 2024
University of Surrey, UK
Fixed Term Contract until 30th September 2025
Closing Date: Monday 15th January
This post will work on challenges around decentralized identity and personal data, and approaches across distributed platforms such as Distributed Ledgers.
The Computer Science Research Centre at the University of Surrey is seeking to recruit a full-time researcher to the Surrey Centre for Cyber Security (SCCS). The successful candidate will join the DECaDE Next Stage Digital Economy Centre for the Decentralised Digital Economy (http://decade.ac.uk), a multidisciplinary UKRI-funded Centre with the University of Surrey, the University of Edinburgh, and the Digital Catapult.
The Centre is initially focused on three themes: value co-creation in the digital economy, data trusts for identity and data, and the world of work and the gig economy.
Surrey is recognized by the National Cyber Security Centre as an Academic Centre of Excellence in Cyber Security Research, and offers a thriving research environment with world leading researchers. We were also recognised as Cyber University of the Year 2023 in the National Cyber Awards. Our research includes security and privacy, verification, cryptography, distributed systems, and networked systems.
The position offers the platform for the research fellow to develop skills to become an independent researcher and to contribute to the DECaDE vision. The successful candidate will work within a team under the direction of Professor Steve Schneider. Significant interaction with project partners is encouraged, and the dissemination strategy may involve national and international travel, with many personal development opportunities.
Closing date for applications:
Contact: Contact: Professor Steve Schneider: s.schneider@surrey.ac.uk
More information: https://jobs.surrey.ac.uk/Vacancy.aspx?id=13775
31 December 2023
Riddhi Ghosal, Yuval Ishai, Alexis Korb, Eyal Kushilevitz, Paul Lou, Amit Sahai
We give the first evidence for the existence of unstructured hard languages in $\mathsf{NP} \,\cap\,\mathsf{coNP}$ by showing that if $\mathsf{UP} \not \subseteq \mathsf{RP}$, which follows from the existence of injective one-way functions, the answer to Bennett and Gill's question is affirmative: with probability 1 over a random oracle $\cal O$, we have that $\mathsf{P}^{\cal O} \neq \mathsf{NP}^{\cal O} \cap \mathsf{coNP}^{\cal O}$. Our proof gives a constructive non-black-box approach for obtaining candidate hard languages in $\mathsf{NP} \,\cap\,\mathsf{coNP}$ from cryptographic hash functions.
The above conditional separation builds on a new construction of non-interactive zero-knowledge (NIZK) proofs, with a computationally unbounded prover, to convert a hard promise problem into a hard language. We obtain such NIZK proofs for $\mathsf{NP}$, with a uniformly random reference string, from a special kind of hash function which is implied by (an unstructured) random oracle. This should be contrasted with previous constructions of such NIZK proofs that are based on one-way permutations or other structured primitives, as well as with (computationally sound) NIZK arguments in the random oracle model.
Zhengjun Cao, Zhenfu Cao
Anupam Chattopadhyay, Subhamoy Maitra, Bimal Mandal, Manmatha Roy, Deng Tang
Xinle Cao, Yuhan Li, Dmytro Bogatov, Jian Liu, Kui Ren
We present two oblivious FD protocols and prove them secure in the presence of the persistent adversary (monitoring processes on the server). The first protocol leverages Oblivious RAM (ORAM) and is suitable for dynamic databases. The second protocol relies on oblivious sorting and is more practical in static databases due to high parallelism. We also present a thorough experimental evaluation of the proposed methods.
Kelsey A. Jackson, Carl A. Miller, Daochen Wang
Shafik Nassar, Brent Waters, David J. Wu
In this work, we describe a generic approach for constructing monotone policy BARGs from any BARG for $\mathsf{NP}$ together with an additively homomorphic encryption scheme. This yields the first constructions of monotone policy BARGs from the $k$-Lin assumption in prime-order pairing groups as well as the (subexponential) DDH assumption in pairing-free groups. Central to our construction is a notion of a zero-fixing hash function, which is a relaxed version of a predicate-extractable hash function from the work of Brakerski et al. Our relaxation enables a direct realization of zero-fixing hash functions from standard BARGs for $\mathsf{NP}$ and additively homomorphic encryption, whereas the previous notion relied on leveled homomorphic encryption, and by extension, the LWE assumption.
Matteo Campanelli, Chaya Ganesh, Rosario Gennaro
Rational arguments are an interesting primitive because they allow for sublinear verification and a more efficient protocol in general. In this paper we aim at narrowing the gap between literature on rational schemes and real world applications. Our contribution is two-fold.
We provide the first construction of rational arguments for the class of polynomial computations that is practical (i.e., it can be applied to real-world computations on reasonably common hardware) and with logarithmic communication. Techniques-wise, we obtain this result through a compiler from information-theoretic protocols and rational proofs for polynomial evaluation. The latter could be of independent interest.
As a second contribution, we propose a new notion of extractability for rational arguments. Through this notion we can obtain arguments where knowledge of a witness is incentivized (rather than incentivizing mere soundness). We show how our aforementioned compiler can also be applied to obtain efficient extractable rational arguments for $\mathsf{NP}$.
Shuai Han, Shengli Liu, Dawu Gu
Firstly, we formalize the strong leakage and tamper-resilient (sLTR) security model for signature, which provides strong existential unforgeability, and deals with bounded leakage and restricted tampering attacks, as a counterpart to the sLTR security introduced by Sun et al. (ACNS 2019) for PKE.
Then, we present direct constructions of signature and chosen-ciphertext attack (CCA) secure PKE schemes in the sLTR model, based on the matrix decisional Diffie-Hellman (MDDH) assumptions (which covers the standard symmetric external DH (SXDH) and k-Linear assumptions) over asymmetric pairing groups. Our schemes avoid the use of heavy building blocks such as the true-simulation extractable non-interactive zero-knowledge proofs (tSE-NIZK) proposed by Dodis et al. (ASIACRYPT 2010), which are usually needed in constructing schemes with leakage and tamper-resilience. Especially, our SXDH-based signature and PKE schemes are more efficient than the existing schemes in the leakage and tamper-resilient setting: our signature scheme has only 4 group elements in the signature, which is about 5×~8× shorter, and our PKE scheme has only 6 group elements in the ciphertext, which is about 1.3×~3.3× shorter.
Finally, we note that our signature scheme is the {\it first} one achieving strong existential unforgeability in the leakage and tamper-resilient setting, where strong existential unforgeability has important applications in building more complex primitives such as signcryption and authenticated key exchange.
Clara Shikhelman
Andrew Mendelsohn, Edmund Dable-Heath, Cong Ling
Vincent Hwang
There are three emphases in this paper: (i) modular arithmetic, (ii) homomorphisms, and (iii) vectorization. For modular arithmetic, we survey Montgomery, Barrett, and Plantard multiplications. For homomorphisms, we survey (a) various homomorphisms such as Cooley–Tukey FFT, Bruun’s FFT, Rader’s FFT, Karatsuba, and Toom– Cook; (b) various algebraic techniques for adjoining nice properties to the coefficient rings, including injections, Schönhage’s FFT, Nussbaumer’s FFT, and localization; and (c) various algebraic techniques related to the polynomial moduli, including twisting, composed multiplication, evaluation at ∞, Good–Thomas FFT, truncation, incomplete transformation, and Toeplitz matrix-vector product. For vectorization, we survey the relations between homomorphisms and the support of vector arithmetic. We then go through several case studies: We compare the implementations of modular multiplications used in Dilithium and Kyber, explain how the matrix-to-vector structure was exploited in Saber, and review the design choices of transformations for NTRU and NTRU Prime with vectorization. Finally, we outline several interesting implementation projects.
David Naccache, Ofer Yifrach-Stav
In essence, the idea underlying this transform is that deriving the challenge from the digest of the commitment suppresses simulatability and hence provides non-interactive proofs of interaction.
It follows from that observation that if one wishes to preserve deniability the challenge size (per round) must be kept low. For instance in the original Fiat-Shamir protocol the authors recommend 18 bits but suggest that the challenge size can be made larger to reduce communication overhead, e.g. the value of 20 is proposed in \cite{micali}.
We show that even with relatively small challenge sizes \textsl{practical} deniability can be destroyed by having the verifier artificially impose upon himself the use of slowed-down hash function or by resorting to a trusted agency proposing an on-line deniability enforcement service against the provers community's will.
David Anthony Stainton
Theophilus Agama
25 December 2023
Yu Dai, Debiao He, Cong Peng, Zhijian Yang, Chang-an Zhao
Takahiro Matsuda
Abdelhaliem Babiker
Vincent Hwang, YoungBeom Kim, Seog Chung Seo
Compared to the state-of-the-art assembly-optimized implementations on Cortex-M3, our constant-time NTT/iNTT are 1.38−1.51 times faster and our variable-time NTT/iNTT are 1.10−1.21 times faster. On our 8-bit AVR, we outperform Montgomery-based C implementations of NTT/iNTT by 6.37−7.27 times by simply switching to the proposed Barrett-based implementation. We additionally implement Barrett-based NTT/iNTT in assembly and obtain 14.10− 14.42 times faster code.
For the overall scheme, we provide speed-optimized implementations for Dilithium parameter sets dilithium2 and dilithium3 on Cortex-M3, and stack-optimized implementations for all parameter sets on Cortex-M3 and 8-bit AVR. We briefly compare the performance of speed-optimized dilithium3. Compared to the state-of-the-art assembly implementation on Cortex-M3, our assembly implementation reduces the key generation, signature generation, and signature verification cycles by 2.30%, 23.29%, and 0.69%. In the 8-bit AVR environment, our Barrett-based C implementation reduces the key generation, signature generation, and signature verification cycles by 45.09%, 56.80%, and 50.40%, respectively, and our assembly-optimized implementation reduces the cycles of each operation by 48.85%, 61.70%, and 55.08%, respectively.