*15:17* [Pub][ePrint]
Authenticated Encryption without Tag Expansion (or, How to Accelerate AERO), by Kazuhiko Minematsu
Standard form of authenticated encryption (AE) requires the ciphertext to be expanded by the nonce and the authentication tag. These expansions can be problematic

when messages are relatively short and communication cost is high.

This paper studies a form of AE scheme whose ciphertext is only expanded by

nonce, with the help of stateful receiver which also enables detection of replays.

While there is a scheme having this feature, called AERO, proposed by McGrew and Foley,

there is no formal treatment based on the provable security framework.

We propose a provable security framework for such AE schemes, which we call MiniAE, and

show several secure schemes using standard symmetric crypto primitives.

Most notably, one of our schemes

has a similar structure as OCB mode of operation and uses only one blockcipher call

to process one input block, thus the computation cost is comparable to the

nonce-based encryption-only schemes.

*15:17* [Pub][ePrint]
Predictable Arguments of Knowledge, by Antonio Faonio and Jesper Buus Nielsen and Daniele Venturi
We initiate a formal investigation on the power of predictability for argument of knowledge systems for NP.Specifically, we consider private-coin argument systems where the answers of the prover can be predicted, given the private randomness of the verifier.

We show that predictable arguments of knowledge (PAoK) can be made extremely laconic, with the prover sending a single bit, and assumed to have only one round (two messages) without loss of generality. We then explore constructs of PAoK. For specific relations we obtain PAoK from Extractable Hash Proof systems (Wee, Crypto \'10); we also show that PAoK are equivalent to Extractable Witness Encryption. Unfortunately, the latter poses serious doubts on the existence of PAoK for all NP. However, we show that for the class of random self-reducible problems in NP we can avoid the problem relying on the assumption of public-coin differing-inputs obfuscation (Ishai et al., TCC \'15).

Finally, we apply PAoK in the context of leakage-tolerant PKE protocols.

At PKC \'13 Nielsen et al. have shown that any leakage-tolerant PKE protocol requires long keys already when it tolerates super-logarithmic leakage.

We strengthen their result proving a more fine-grained lower bound for any constant numbers bits of leakage.

*15:17* [Pub][ePrint]
On Generic Constructions of Circularly-Secure, Leakage-Resilient Public-Key Encryption Schemes, by Mohammad Hajiabadi, Bruce M. Kapron, Venkatesh Srinivasan
Abstract. We propose generic constructions of public-key encryption schemes, satisfying key- dependent message (KDM) security for projections and different forms of key-leakage resilience, from CPA-secure private key encryption schemes with two main abstract properties: (1) additive homomorphism with respect to both messages and randomness, and (2) reproducibility, providing a means for reusing encryption randomness across independent secret keys. More precisely, our construction transforms a private-key scheme with the stated properties (and one more mild condition) into a public-key one, providing:- n-KDM-projection security, an extension of circular security, where the adversary may also ask for encryptions of negated secret key bits;

- a (1-o(1)) resilience rate in the bounded-memory leakage model of Akavia et al. (TCC 2009); and

- Auxiliary-input security against subexponentially-hard functions.

We introduce homomorphic weak pseudorandom functions, a homomorphic version of the weak PRFs proposed by Naor and Reingold (FOCS \'95) and use them to realize our base encryption scheme. We obtain homomorphic weak PRFs under assumptions including subgroup indistinguishability (implied, in particular, by QR and DCR) and homomorphic hash-proof systems (HHPS). As corollaries of our results, we obtain (1) a projection-secure encryption scheme (as well as a scheme with a (1-o(1)) resilience rate) based solely on the HHPS assumption, and (2) a unifying approach explaining the results of Boneh et al (CRYPTO \'08) and Brakerski and Goldwasser (CRYPTO \'10). Finally, by observing that Applebaum\'s KDM amplification method (EUROCRYPT \'11) preserves both types of leakage resilience, we obtain schemes providing at the same time high leakage resilience and KDM security against any fixed polynomial-sized circuit family.

*15:17* [Pub][ePrint]
A Matrix Decomposition Method for Optimal Normal Basis Multiplication, by Can K{\\i}z{\\i}lkale and \\\"{O}mer E\\v{g}ecio\\v{g}lu and \\c{C}etin Kaya Ko\\c{c}
We introduce a matrix decomposition method and prove that multiplication in GF$(2^k)$ with a Type 1 optimal normal

basis for can be performed using $k^2-1$ XOR gates irrespective

of the choice of the irreducible polynomial generating the field.

The previous results achieved this bound only with special

irreducible polynomials. Furthermore, the decomposition method

performs the multiplication operation using $1.5k(k-1)$ XOR gates

for Type 2a and 2b optimal normal bases, which matches previous

bounds.

*15:17* [Pub][ePrint]
Short Group Signatures via Structure-Preserving Signatures: Standard Model Security from Simple Assumptions, by Benoit Libert and Thomas Peters and Moti Yung
Group signatures are a central cryptographic primitive which allows users to sign messages while hiding their identity within a crowd of group members. In the standard model (without the random oracle idealization), the most efficient constructions rely on the Groth-Sahai proof systems (Eurocrypt\'08). The structure-preserving signatures of Abe et al. (Asiacrypt\'12) make it possible to design group signatures based on well-established, constant-size number theoretic assumptions (a.k.a. ``simple assumptions\'\') like the Symmetric eXternal Diffie-Hellman or Decision Linear assumptions. While much more efficient than group signatures built on general assumptions, these constructions incur a significant overhead w.r.t. constructions secure in the idealized random oracle model. Indeed, the best known solution based on simple assumptions requires 2.8 kB per signature for currently recommended parameters. Reducing this size and presenting techniques for shorter signatures are thus natural questions. In this paper, our first contribution is to significantly reduce this overhead. Namely, we obtain the first fully anonymous group signatures based on simple assumptions with signatures shorter than 2 kB at the 128-bit security level. In dynamic (resp. static) groups, our signature length drops to 1.8 kB (resp. 1 kB). This improvement is enabled by two technical tools. As a result of independent interest, we first construct a new structure-preserving signature based on simple assumptions which shortens the best previous scheme by 25%. Our second tool is a new method for attaining anonymity in the strongest sense using a new CCA2-secure encryption scheme which is simultaneously a Groth-Sahai commitment.

*15:03* [Job][New]
Marie Sklodowska-Curie Research Fellows in Cryptography (Early Stage Researchers - 1 post), *Ruhr-University Bochum*
The Cryptology Group at Ruhr-University Bochum (Horst-Goertz Institute) is seeking to recruit one Marie Sklodowska-Curie Research Fellows in Cryptography to start in October 2015, as part of the ECRYPT-NET project.ECRYPT-NET is a research network of six universities and two companies that intends to develop advanced cryptographic techniques for the Internet of Things and the Cloud, and to create efficient and secure implementations of those techniques on a broad range of platforms. ECRYPT-NET is funded by a prestigious Marie Sklodowska-Curie ITN (Integrated Training Network) grant. The network will educate a group of 15 PhD students with a set of interdisciplinary skills in the areas of mathematics, computer science and electrical engineering. The training will be provided in an international context that includes Summer Schools, workshops and internships. Participants are expected to spend at least six months abroad with a network partner, or in one of the seven associated companies. We are looking for highly motivated candidates, ideally with background on cryptology and with proven research abilities.

One of the ECRYPT-NET ESR (Early Stage Researcher) positions will be based at Ruhr-University Bochum, to work on the project Fully Homomorphic Encryption - Design and Analysis.

We are looking for a candidate with a **strong background in algorithmics** and with a passion for **cryptanalysis**.

Marie Curie ITN eligibility criteria apply to this position.

Founded in 2001, the Horst-Görtz Institute at Ruhr-University Bochum is a world-leading interdisciplinary research center dedicated to research and education covering all aspects of IT security, with an excellent record of research in cryptography. The Horst-Görtz Institute has 15 professors and over 80 PhD students. It hosts the only German Research Training Group for Doctoral students in Cryptology.

*16:49* [Job][New]
Assistant/Associate Professor, *Hangzhou Normal University, China*
The group for Cryptography and Network Security at Hangzhou Normal University, China chaired by Prof. Dr. Qi Xie is looking for two faculty members with strong crypto/security background. Candidates should have a PhD degree in mathematics, computer science, or related disciplines, be highly motivated with strong R&D capability and also a good team player, have good presentation and communication skills, be able to perform deep system-level investigations of security mechanisms. The candidates are expected to publish high-quality papers OR develop security-related projects. Any prior experience in cloud computing, e-health or WSN/VANETs security is certainly an asset..Interested candidates please send CV to Qi Xie {qixie68 (at) 126.com}. The positions offer a competitive salary. All candidates will be contacted for further infomation.