Abstract. The notion of smooth projective hash functions was proposed by Cramer and Shoup and can be seen as special type of zero-knowledge proof system for a language. Though originally used as a means to build efficient chosen-ciphertext secure public-key encryption schemes, some variations of the Cramer-Shoup smooth projective hash functions also found applications in several other contexts, such as password-based authenticated key exchange and oblivious transfer. In this paper, we first address the problem of building smooth projective hash functions for more complex languages. More precisely, we show how to build such functions for languages that can be described in terms of disjunctions and conjunctions of simpler languages for which smooth projective hash functions are known to exist. Next, we illustrate how the use of smooth projective hash functions with more complex languages can be efficiently associated to extractable commitment schemes and avoid the need for zero-knowledge proofs. Finally, we explain how to apply these results to provide more efficient solutions to two well-known cryptographic problems: a public-key certification which guarantees the knowledge of the private key by the user without random oracles or zero-knowledge proofs and adaptive security for password-based authenticated key exchange protocols in the universal composability framework with erasures.
Abstract. Password-authenticated key exchange (PAKE) protocols allow two players to agree on a shared high entropy secret key, that depends on their own passwords only. Following the Gennaro and Lindell's approach, with a new kind of smooth-projective hash functions (SPHFs), Katz and Vaikuntanathan recently came up with the first concrete one-round PAKE protocols, where the two players just have to send simultaneous flows to each other. The first one is secure in the BellarePointcheval-Rogaway (BPR) model and the second one in the Canetti's UC framework, but at the cost of simulation-sound non-interactive zeroknowledge (SS-NIZK) proofs (one for the BPR-secure protocol and two for the UC-secure one), which make the overall constructions not really efficient.This paper follows their path with, first, a new efficient instantiation of SPHF on Cramer-Shoup ciphertexts, which allows to get rid of the SS-NIZK proof and leads to the design of the most efficient one-round PAKE known so far, in the BPR model, and in addition without pairings.In the UC framework, the security proof required the simulator to be able to extract the hashing key of the SPHF, hence the additional SS-NIZK proof. We improve the way the latter extractability is obtained by introducing the notion of trapdoor smooth projective hash functions (TSPHFs). Our concrete instantiation leads to the most efficient oneround PAKE UC-secure against static corruptions to date.We additionally show how these SPHFs and TSPHFs can be used for blind signatures and zero-knowledge proofs with straight-line extractability.
We propose and demonstrate a hybrid photonic-plasmonic nanolaser that combines the light harvesting features of a dielectric photonic crystal cavity with the extraordinary confining properties of an optical nano-antenna. For this purpose, we developed a novel fabrication method based on multi-step electron-beam lithography. We show that it enables the robust and reproducible production of hybrid structures, using a fully top-down approach to accurately position the antenna. Coherent coupling of the photonic and plasmonic modes is highlighted and opens up a broad range of new hybrid nanophotonic devices.
Most of the existing password-based authenticated key exchange protocols have proofs either in the indistinguishability-based security model of Bellare, Pointcheval, and Rogaway (BPR) or in the simulation-based of Boyko, MacKenzie, and Patel (BMP). Though these models provide a security level that is sufficient for most applications, they fail to consider some realistic scenarios such as participants running the protocol with different but possibly related passwords. To overcome these deficiencies, Canetti et al. proposed a new security model in the universal composability (UC) framework which makes no assumption on the distribution on passwords used by the protocol participants. They also proposed a new protocol, but, unfortunately, the latter is not as efficient as some of the existing protocols in BPR and BMP models. In this paper, we investigate whether some of the existing protocols that were proven secure in BPR and BMP models can also be proven secure in the new UC model and we answer this question in the affirmative. More precisely, we show that the protocol by Bresson, Chevassut, and Pointcheval (BCP) in CCS 2003 is also secure in the new UC model. The proof of security relies in the random-oracle and ideal-cipher models and works even in the presence of adaptive adversaries, capable of corrupting players at any time and learning their internal states.
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