Galindo-Garcia Identity-Based Signature Revisited, by Sanjit Chatterjee and Chethan Kamath and Vikas Kumar
In Africacrypt 2009, Galindo-Garcia  proposed a lightweight identity-based signature (IBS) scheme based on the Schnorr signature. The construction is simple and claimed to be the most efficient IBS till date. The security is based on the discrete-log assumption and the security argument consists of two reductions: B1 and B2, both of which use the multiple-forking lemma  to solve the discrete-log problem (DLP).
In this work, we revisit the security argument given in . Our contributions are two fold: (i) we identify several problems in the original argument and (ii) we provide a detailed new security argument which allows significantly tighter reductions. In particular, we show that the reduction B1 in  fails in the standard security model for IBS , while the reduction B2 is incomplete. To remedy these problems, we adopt a two-pronged approach. First, we sketch ways to fill the gaps by making minimal changes to the structure of the original security argument; then, we provide a new security argument. The new argument consists of three reductions: R1, R2 and R3 and in each of them, solving the DLP is reduced to breaking the IBS. R1 uses the general forking lemma  together with the programming of the random oracles and Coron\'s technique . Reductions R2 and R3, on the other hand, use the multiple-forking lemma along with the programming of the random oracles. We show that the reductions R1 and R2 are significantly tighter than their original counterparts.
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) hgi.rub.de
- 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.
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.
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