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15:17 [Pub][ePrint] Relational Hash, by Avradip Mandal and Arnab Roy

  Traditional cryptographic hash functions allow one to easily check whether the original plain-texts are equal or not, given a pair of hash values. Probabilistic hash functions extend this concept where given a probabilistic hash of a value and the value itself, one can efficiently check whether the hash corresponds to the given value. However, given distinct probabilistic hashes of the same value it is not possible to check whether they correspond to the same value. In this work we introduce a new cryptographic primitive called \\emph{relational hash} using which, given a pair of (relational) hash values, one can determine whether the original plain-texts were related or not. We formalize various natural security notions for the relational hash primitive - one-wayness, unforgeability and oracle simulatibility.

We develop a relational hash scheme for discovering linear relations among bit-vectors (elements of $\\FF_2^n$) and $\\FF_p$-vectors. Using these linear relational hash schemes we develop relational hashes for detecting proximity in terms of hamming distance. These proximity relational hashing scheme can be adapted to a privacy preserving biometric authentication scheme.

We also introduce the notion of \\emph{relational encryption}, which is a regular semantically secure public key encryption for any adversary which only has access to the public key. However, a semi-trusted entity can be given a relational key using which it can discover relations among ciphertexts, but still cannot decrypt and recover the plaintexts.

15:17 [Pub][ePrint] Lightweight and Privacy-Preserving Delegatable Proofs of Storage, by Jia Xu and Anjia Yang and Jianying Zhou and Duncan S. Wong

  Proofs of storage (POR or PDP) is a cryptographic tool, which enables data owner or third party auditor to audit integrity of data stored remotely in a cloud storage server, without keeping a local copy of data or downloading data back during auditing. We observe that all existing publicly verifiable POS schemes suffer from a serious drawback: It is extremely slow to compute authentication tags for all data blocks, due to many expensive group exponentiation operations. Surprisingly, it is even much slower than typical network uploading speed, and becomes the bottleneck of the setup phase of the POS scheme. We propose a new variant formulation called \"Delegatable Proofs of Storage\". In this new relaxed formulation, we are able to construct POS schemes, which on one side is as efficient as private key POS schemes, and on the other side can support third party auditor and can switch auditors at any time, close to the functionalities of publicly verifiable POS schemes. Compared to traditional publicly verifiable POS schemes, we speed up the tag generation process by at least several hundred times, without sacrificing efficiency in any other aspect. Like many existing schemes, we can also speed up our tag generation process by N times using N CPU cores in parallel. We prove that our scheme is sound under Bilinear Strong Diffie-Hellman Assumption, and it is privacy preserving against auditor under Discrete Log Assumption. Both proofs are given in standard model.

15:17 [Pub][ePrint] Almost Optimal Short Adaptive Non-Interactive Zero Knowledge, by Helger Lipmaa

  Several recent short NIZK arguments are constructed in a modular way from a small number of basic arguments like the product argument or the shift argument. The main technical novelty of the current work is a significantly more efficient version of the product argument.

Based on this, we propose an adaptive NIZK range argument with almost optimal complexity: constant communication (in group elements), constant verifier\'s computational complexity (in cryptographic operations), and $\\Theta (n \\log n)$ [resp., $\\Theta (n)$] prover\'s computational complexity (in non-cryptographic [resp., cryptographic] operations). The latter can be compared to $n \\log^{\\omega (1)} n$ in the most efficient \\emph{published} short adaptive non-interactive range argument, or $\\Theta (n \\log^2 n)$ [resp., $\\Theta (n \\log n)$] that is achievable when following QAP-based framework from Eurocrypt 2013. Here, $n$ is the logarithm of the range length.

The new product argument can be used to construct efficient adaptive NIZK arguments for many other languages, including several that are $\\mathsf{NP}$-complete like $\\textsc{SubsetSum}$. Importantly, for all such languages, new adaptive arguments achieve better prover\'s computation than the QAP-based framework.

15:17 [Pub][ePrint] Cofactorization on Graphics Processing Units, by Andrea Miele, Joppe W. Bos, Thorsten Kleinjung, and Arjen K. Lenstra

  We show how the cofactorization step, a compute-intensive part of the relation collection phase of the number field sieve (NFS), can be farmed out to a graphics processing unit. Our implementation on a GTX 580 GPU, which is integrated with a state-of-the-art NFS implementation, can serve as a cryptanalytic co-processor for several Intel i7-3770K quad-core CPUs simultaneously. This allows those processors to focus on the memory-intensive sieving and results in more useful NFS-relations found in less time.

06:23 [Job][New] Lecturer/Senior Lecturer in Cyber Security
(equiv. to Assistant/Associate Professor), Surrey Centre for Cyber Security, Department of Computing, University of Surrey, Guildford, UK

  Department of Computing at University of Surrey is currently seeking to make an appointment at Lecturer (equiv. to Assistant Professor) or Senior Lecturer (equiv. to Associate Professor) level in Cyber Security to support the Department’s continued growth by complementing our existing research strengths and contributing to the research leadership within the Department, to play a leading role in the recently established interdisciplinary Surrey Centre for Cyber Security (SCCS) and to contribute to the new MSc Information Security programme.

Applications are welcome particularly in the areas of Software Security, Web and Network Security, System Security, Applied Cryptography and Protocols, Privacy and Data Protection, Multimedia Security, Digital Forensics, and Human-Centred Security.

The Department is research-led with around 70 RAs and PhD students, and is attracting growing research support from funding bodies such as the UK Research Councils, UK Technology Strategy Board (TSB), the EU-IST, and also private foundations e.g. The Leverhulme Trust. Major IT, telecommunication, defence and security organisations are sponsoring research in the Department.

Applicants at the Lecturer level should have a relevant PhD, a developing track record in publication with demonstrable high potential in high-quality research and teaching. Applicants at the Senior Lecturer level will have an international research profile, a significant track record of high-quality publications in leading journals and conference proceedings, and experience in a leadership or development role in high quality teaching. A record in attracting research funding would be an advantage.

Closing date for applications is 30 June 2014. The post is to start in September 2014 or as soon as possible thereafter.

18:17 [Pub][ePrint] Improved Cryptanalysis on Reduced-Round GOST and Whirlpool Hash Function (Full Version), by Bingke Ma and Bao Li and Ronglin Hao and Xiaoqian Li

  The GOST hash function family has served as the new Russian national hash standard (GOST R 34.11-2012) since January 1, 2013, and it has two members, $i.e.$, GOST-256 and GOST-512 which correspond to two different output lengths. Most of the previous analyses of GOST emphasize on the compression function rather than the hash function. In this paper, we focus on security properties of GOST under the hash function setting. First we give two improved preimage attacks on 6-round GOST-512 compared with the previous preimage attack, $i.e.$, a time-reduced attack with the same memory requirements and a memoryless attack with almost identical time. Then we improve the best collision attack on reduced GOST-256 (resp. GOST-512) from 5 rounds to 6.5 (resp. 7.5) rounds. Finally, we construct a limited-birthday distinguisher on 9.5-round GOST using the limited-birthday distinguisher on hash functions proposed at ASIACRYPT 2013. An essential technique used in our distinguisher is the carefully chosen differential trail, which can further exploit freedom degrees in the inbound phase when launching rebound attacks on the GOST compression function. This technique helps us to reduce the time complexity of the distinguisher significantly. We apply this strategy to Whirlpool, an ISO standardized hash function, as well. As a result, we construct a limited-birthday distinguisher on 9-round Whirlpool out of 10 rounds, and reduce the time complexity of the previous 7-round distinguisher. To the best of our knowledge, all of our results are the best cryptanalytic results on GOST and Whirlpool in terms of the number of rounds analyzed under the hash function setting.

18:17 [Pub][ePrint] How Secure is Deterministic Encryption?, by Mihir Bellare and Rafael Dowsley and Sriram Keelveedhi

  This paper presents three curious findings about deterministic public-key encryption (D-PKE) that further our understanding of its security, in particular because of the contrast with standard, randomized public-key encryption (R-PKE):

(1) It would appear to be a triviality, for any primitive, that security in the standard model implies security in the random-oracle model, and it is certainly true, and easily proven, for R-PKE. For D-PKE it is not clear and depends on details of the definition. In particular we can show it in the non-uniform case but not in the uniform case.

(2) The power of selective-opening attacks (SOA) comes from an adversary\'s ability, upon corrupting a sender, to learn not just the message but also the coins used for encryption. For R-PKE, security is achievable. For D-PKE, where there are no coins, one\'s first impression may be that SOAs are vacuous and security should be easily achievable. We show instead that SOA-security is impossible, meaning no D-PKE scheme can achieve it.

(3) For R-PKE, single-user security implies multi-user security, but we show that there are D-PKE schemes secure for a single user and insecure with two users.

18:17 [Pub][ePrint] Logic Synthesis based Public Key Scheme, by Boaz Shahar

  This article proposes a method for the construction of a public key system that is based on VLSI logic synthesis algorithms. First, we discuss the properties of VLSI logic synthesis algorithms. Then we view them in the context of cryptographic primitives. Then we propose a public key encryption system and finally discuss its security properties.

18:17 [Pub][ePrint] Attacks on Lin\'s Mobile Dynamic Identity-based Authenticated Key Agreement Scheme using Chebyshev Chaotic Maps, by SK Hafizul Islam

  In 2014, Lin proposed an authentication system with dynamic identity of the user for low-power mobile devices using Chebyshev chaotic map. The scheme is proposed to provide mutual authentication and session key agreement between a remote server and its legitimate user. The scheme provides user anonymity and untracibility, and resilience from many cryptographic attacks. However, the author of this paper showed that Lin\'s scheme is no longer usable for practical applications as (i) it cannot verify the wrong identity and password at the user side in the login and password change phases, (ii) it cannot protect user impersonation attack, and (ii) it has the problem of session key forward secrecy.

18:17 [Pub][ePrint] Hyper-and-elliptic-curve cryptography, by Daniel J. Bernstein and Tanja Lange

  This paper introduces \"hyper-and-elliptic-curve cryptography\", in which a single high-security group supports fast genus-2-hyperelliptic-curve formulas for variable-base-point single-scalar multiplication (e.g., Diffie--Hellman shared-secret computation) and at the same time supports fast elliptic-curve formulas for fixed-base-point scalar multiplication (e.g., key generation) and multi-scalar multiplication (e.g., signature verification).

18:17 [Pub][ePrint] Efficient Adaptively Secure IBBE from Standard Assumptions, by Somindu C. Ramanna and Palash Sarkar

  This paper describes the first construction of efficient identity-based broadcast encryption (IBBE) schemes which

can be proved secure against adaptive-identity attacks based on standard assumptions. The constructions are

obtained by extending the currently known most efficient identity-based encryption scheme proposed by Jutla

and Roy in 2013. Ciphertext size and user storage compare favourably to previously known constructions. The

new constructions fill both a practical and a theoretical gap in the literature on efficient IBBE schemes.