International Association for Cryptologic Research

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16:17 [Pub][ePrint] A Robust and Plaintext-Aware Variant of Signed ElGamal Encryption , by Yannick Seurin and Joana Treger

  Adding a Schnorr signature to ElGamal encryption is a popular proposal aiming at thwarting chosen-ciphertext attacks by rendering the scheme plaintext-aware. However, there is no known security proof for the resulting scheme, at least not in a weaker model than the one obtained by combining the Random Oracle Model (ROM) and the Generic Group Model (Schnorr and Jakobsson, ASIACRYPT 2000). In this paper, we propose a very simple modification to Schnorr-Signed ElGamal encryption that leaves keys and ciphertexts size unchanged, for which the resulting scheme is semantically secure under adaptive chosen-ciphertext attacks (IND-CCA2-secure) in the ROM under the Decisional Diffie-Hellman assumption. In fact, we even prove that our new scheme is plaintext-aware in the ROM as defined by Bellare et al. (CRYPTO\'98). Interestingly, we also observe that Schnorr-Signed ElGamal is not plaintext-aware (again, for the definition of Bellare et al.) under the Computational Diffie-Hellman assumption. We show that our new scheme additionally achieves anonymity as well as robustness, a notion formalized by Abdalla et al. (TCC 2010) which captures the fact that it is hard to create a ciphertext that is valid under two different public keys. Finally, we study the hybrid variant of our new proposal, and show that it is IND-CCA2-secure in the ROM under the Computational Diffie-Hellman assumption when used with a symmetric encryption scheme satisfying the weakest security notion, namely ciphertext indistinguishability under one-time attacks (IND-OT-security).

15:41 [Event][New] RCD-2013: Romanian Cryptology Days, RCD-2013

  Submission: 1 May 2013
Notification: 1 July 2013
From September 16 to September 17
Location: Bucharest, Romania
More Information:

10:28 [Event][New] DBSec: 27th IFIP WG 11.3 Working Conference on Data and Application and Privacy

  Submission: 15 February 2013
Notification: 19 April 2013
From July 15 to July 17
Location: Newark, NJ, USA
More Information:

14:47 [Job][New] Post Doc, DFG Research Training Group UbiCrypt, Horst Görtz Institute for IT-Security, Ruhr-University Bochum, Germany

  The Horst Görtz Institute for IT-Security (HGI) at Ruhr-University Bochum is one of Europe’s leading research centers in IT security. The DFG, or German Research Foundation, awarded more than €4 million to the HGI for the establishment of the interdisciplinary research training group “New Challenges for Cryptography in Ubiquitous Computing”. We are looking for candidates with an outstanding Ph.D. in the fields of computer science, electrical engineering, mathematics or related areas.

The research training group will study problems which are fundamental for securing the Internet of Things. The research is structured in three levels: cryptographic primitives, device and system level. The research topics range from cryptographic foundations such as fully homomorphic encryption for privacy in cloud computing, over security for medical implants to internet security solutions involving new national ID cards.

Beside the own research, the main task of the Post-Doc is to work with the UbiCrypt Ph.D. students, and to encourage collaboration between them. Thus, an interest in working with doctoral students and a broad interest in current research are required.

- Start: 01.04.2013

- Competitive salary

- Application: Send your documents by January 15, 2013, to grako (at)

- Required documents: CV, certificates (Bachelor, Master/Diplom, Ph.D.), transcripts , motivation for applying (1 page), names of at least two people who can provide reference letters (email addresses are sufficient)

A group of internationally renowned researchers together with excellent funding provides an extremely interesting scientific environment. The HGI is known for its good working atmosphere.

13:17 [Pub][ePrint] Protocols for Multiparty Coin Toss With Dishonest Majority, by Amos Beimel and Eran Omri and Ilan Orlov

  Coin-tossing protocols are protocols that generate a random bit with uniform distribution. These protocols are used as a building block in many cryptographic protocols. Cleve [STOC 1986] has shown that if at least half of the parties can be malicious, then, in any r-round coin-tossing protocol, the malicious parties can cause a bias of Omega(1/r) to the bit that the honest parties output. However, for more than two decades the best known protocols had bias t/\\sqrt{r}, where t is the number of corrupted parties. Recently, in a surprising result, Moran, Naor, and Segev [TCC 2009] have shown that there is an r-round two-party coin-tossing protocol with the optimal bias of O(1/r). We extend Moran et al. results to the multiparty model when less than 2/3 of the parties are malicious. The bias of our protocol is proportional to 1/r and depends on the gap between the number of malicious parties and the number of honest parties in the protocol. Specifically, for a constant number of parties or when the number of malicious parties is somewhat larger than half, we present an r-round m-party coin-tossing protocol with optimal bias of O(1/r).

13:17 [Pub][ePrint] Impossibility Results for Indifferentiability with Resets, by Atul Luykx and Elena Andreeva and Bart Mennink and Bart Preneel

  The indifferentiability framework of Maurer, Renner, and Holenstein (MRH) has gained immense popularity in recent years and has proved to be a powerful way to argue security of cryptosystems that enjoy proofs in the random oracle model. Recently, however, Ristenpart, Shacham, and Shrimpton (RSS) showed that the composition theorem of MRH has a more limited scope than originally thought, and that extending its scope required the introduction of reset-indifferentiability, a notion which no practical domain extenders satisfy with respect to random oracles.

In light of the results of RSS, we set out to rigorously tackle the specifics of indifferentiability and reset-indifferentiability by viewing the notions as special cases of a more general definition. Our contributions are twofold. Firstly, we provide the necessary formalism to refine the notion of indifferentiability regarding composition. By formalizing the definition of stage minimal games we expose new notions lying in between regular indifferentiability (MRH) and reset-indifferentiability (RSS).

Secondly, we answer the open problem of RSS by showing that it is impossible to build any domain extender which is reset-indifferentiable from a random oracle. This result formally confirms the intuition that reset-indifferentiability is too strong of a notion to be satisfied by any hash function. As a consequence we look at the weaker notion of single-reset-indifferentiability, yet there as well we demonstrate that there are no ``meaningful\'\' domain extenders which satisfy this notion. Not all is lost though, as we also view indifferentiability in a more general setting and point out the possibility for different variants of indifferentiability.

13:17 [Pub][ePrint] Simple, Efficient and Strongly KI-Secure Hierarchical Key Assignment Schemes, by Eduarda S. V. Freire, Kenneth G. Paterson, Bertram Poettering

  Hierarchical Key Assignment Schemes can be used to enforce access control policies by cryptographic means. In this paper, we present a new, enhanced security model for such schemes. We also give simple, efficient, and strongly-secure constructions for Hierarchical Key Assignment Schemes for arbitrary hierarchies using pseudorandom functions and forward-secure pseudorandom generators. We compare instantiations of our constructions with state-of-the-art Hierarchical Key Assignment Schemes, demonstrating that our new schemes possess an attractive trade-off between storage requirements and efficiency of key derivation.

13:41 [Job][New] PHD Studentship, University of Bristol, United Kingdom of Great Britain and Northern Ireland

  The Government Communications Headquarters (GCHQ) in Cheltenham has agreed in principle to sponsor two PhD/Doctoral Studentships at Bristol University in the area of Cryptography.

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 two studentships will be in the following areas:

Title: Authentication, Ciphers, and Encryption

Supervisors: Dan Page and Martijn Stam

Title: Information Leakage aware Verification

Supervisors: Elisabeth Oswald and Kerstin Eder

13:32 [Event][New] AsiaARES 2013: The 2013 Asian Conference on Availability, Reliability and Security

  Submission: 27 November 2012
Notification: 15 December 2012
From March 25 to March 29
Location: Yogyakarta, Indonesia
More Information:

13:32 [Event][New] SECRYPT: 10th International Conference on Security and Cryptography (SECRYPT 2013)

  Submission: 22 February 2013
Notification: 6 May 2013
From July 29 to July 31
Location: Reykjavk, Iceland
More Information:

09:55 [Job][New] PhD , University of Luxembourg

  The University of Luxembourg seeks to hire an outstanding researcher for the Applied Security and Information Assurance (APSIA) group at its Interdisciplinary Centre for Security, Reliability and Trust (SnT). SnT is a recently formed centre carrying out interdisciplinary research in secure, reliable and trustworthy ICT systems and services, often in collaboration with industrial, governmental or international partners. The APSIA group is also associated with Laboratory of Algorithmics, Cryptology and Security (LACS) of the Computer Science and Communications Research Unit (CSC), which is part of the international and multidisciplinary Faculty of Science, Technology and Communication (FSTC) in University of Luxembourg.

REF : F1-070079

Fixed-term contract 3 years, full-time (40 hrs/week)

Number of Positions : 1

Your Role

The PhD topic is to design and analyse lattice-based cryptosystems. The research focus will mainly be on (but not limited to) investigating lattice-related hardness assumptions, both in terms of classical and quantum models of computation, and then designing novel, practical lattice-based public-key cryptosystems. Other classes of “hard” problems, for example based on coding theory and braid groups, will also be investigated.

The student will work closely with Prof. Peter Y. A. Ryan and Dr. Qiang Tang. Moreover, the student will be encouraged to work with other members in the APSIA group and collaborate with researchers from other related research units, such as LACS.