Building Lossy Trapdoor Functions from Lossy Encryption, by Brett Hemenway and Rafail Ostrovsky
Injective one-way trapdoor functions are one of the most fundamental cryptographic primitives. In this work we show how to derandomize lossy encryption (with long messages) to obtain lossy trapdoor functions, and hence injective one-way trapdoor functions.
Bellare, Halevi, Sahai and Vadhan (CRYPTO \'98) showed that if E is an IND-CPA secure cryptosystem, and $H$ is a random oracle, then $x \\mapsto E(x,H(x))$ is an injective trapdoor function. In this work, we show that if E is a lossy encryption with messages at least 1-bit longer than randomness, and $h$ is a pairwise independent hash function, then $x \\mapsto E(x,h(x))$ is a lossy trapdoor function,
and hence also an injective trapdoor function.
The works of Peikert, Vaikuntanathan and Waters and Hemenway, Libert, Ostrovsky and Vergnaud showed that statistically-hiding 2-round Oblivious Transfer (OT) is equivalent to Lossy Encryption.
In their construction, if the sender randomness is shorter than the message in the OT, it will also be shorter than the message in the lossy encryption.
This gives an alternate interpretation of our main result. In this language, we show that any 2-message statistically sender-private semi-honest oblivious transfer (OT) for strings
longer than the sender randomness implies the existence of injective one-way trapdoor functions. This is in contrast to the black box separation of
injective trapdoor functions from many common cryptographic protocols, e.g. IND-CCA encryption.
Duality in ABE: Converting Attribute Based Encryption for Dual Predicate and Dual Policy via Computational Encodings, by Nuttapong Attrapadung and Shota Yamada
We show a generic conversion that converts an attribute based encryption (ABE) scheme for arbitrary predicate into an ABE scheme for its dual predicate. In particular, it can convert key-policy ABE (KP-ABE) into ciphertext-policy ABE (CP-ABE), and vice versa, for dually related predicates. It is generic in the sense that it can be applied to arbitrary predicates. On the other hand, it works only within the generic ABE framework recently proposed by Attrapadung (Eurocrypt\'14), which provides a generic compiler that compiles a simple primitive called pair encodings into fully secure ABE. Inside this framework, Attrapadung proposed the first generic dual conversion that works only for subclass of encodings, namely, perfectly secure encodings. However, there are many predicates for which realizations of such encodings are not known, and hence the problems of constructing fully secure ABE for their dual predicates were left unsolved.
In this paper, we revisit the dual conversion of Attrapadung, and show that, somewhat surprisingly, the very same conversion indeed also works for broader classes of encodings, namely, computationally secure encodings. Consequently, we thus solve the above open problems as we obtain the first fully secure realizations of completely-unbounded CP-ABE and CP-ABE with short keys for Boolean formulae, via applying the conversion to previously proposed KP-ABE.
Moreover, we provide a generic conversion that converts ABE into its dual-policy variant. Dual-policy ABE (DP-ABE) conjunctively combines both KP-ABE and CP-ABE into one primitive, and hence can be useful in general-purpose applications. As for instantiations, we obtain the first realizations of fully secure DP-ABE for formulae, unbounded DP-ABE for formulae, and DP-ABE for regular languages. The latter two systems are the first to realize such functionalities, let alone are fully secure.
From Single-Input to Multi-Input Functional Encryption in the Private-Key Setting, by Zvika Brakerski and Ilan Komargodski and Gil Segev
We construct a general-purpose multi-input functional encryption scheme in the private-key setting. Namely, we construct a scheme where a functional key corresponding to a function $f$ enables a user holding encryptions of $x_1, \\ldots, x_t$ to compute $f(x_1, \\ldots, x_t)$ but nothing else. Our construction assumes any general-purpose private-key single-input scheme (without any additional assumptions), and is proven to be adaptively-secure for any constant number of inputs $t$. Moreover, it can be extended to a super-constant number of inputs assuming that the underlying single-input scheme is sub-exponentially secure.
Instantiating our construction with existing single-input schemes, we obtain multi-input schemes that are based on a variety of assumptions (such as indistinguishability obfuscation, multilinear maps, learning with errors, and even one-way functions), offering various trade-offs between security and efficiency.
Previous constructions of multi-input functional encryption schemes either relied on somewhat stronger assumptions and provided weaker security guarantees (Goldwasser et al., EUROCRYPT \'14), or relied on multilinear maps and could be proven secure only in an idealized generic model (Boneh et al., EUROCRYPT \'15).
A Practical Key Exchange for the Internet using Lattice Cryptography, by Vikram Singh
In , Peikert presents an efficient and provably secure set of lower level primitives for practical post-quantum cryptography. These primitives also give the first lattice-based scheme to provide perfect forward secrecy, and thus represent a major advancement in providing the same sort of security guarantees that are now expected for modern internet traffc protection. However, the presentation in  might prove a bit daunting for the slightly less mathematical reader. Here we provide what we hope will be a clear and self-contained exposition of how the algorithm can be implemented, along with sample code and some initial analysis for potential parameter sizes.
We focus on the simpler case, as chosen by Bos et al in , of cyclotomic rings whose degree is a power of two. We describe the necessary arithmetic setup and choices regarding error sampling, and give a possibly cleaner mechanism for reconciliation of the shared secrets. Then we present Peikert\'s Diffe-Hellman-like key exchange algorithms along with security, correctness and implementation analysis.
Post-Doc, Ph.D., High Assurance Software Lab --- INESC TEC & Minho University
The High Assurance Software Lab (HASLab) is an R&D unit at INESC TEC, a leading research institution in Portugal. The HASLab specialises in the rigorous development of software applications for critical systems and infrastructures, drawing on expertise in software engineering, dependable distributed systems, and cryptography and information security.
The HASLab has recently opened 10 positions for Post Doctoral researchers and 6 positions for Ph.D. students.
We are looking for Post Doctoral researchers that can be integrated into the activities of HASLab — in EU and national projects — and also lead their own research projects within the group, preferably in the following areas: source code analysis, testing and verification, formal methods, large scale data management, theory of cryptography or computer and network security.
A successful Post Doctoral candidate will be offered a package that may include up to 25K EUR/Year salary, health insurance, one Ph.D. grant and one internship grant for recruitment, as well as access to the HASLab travel and equipment funding schemes. Post-doc positions may be extended until up to 5 years.
Research Fellow / Post-doc, Nanyang Technological University (NTU), Singapore
SYmmetric and Lightweight cryptography Lab (SYLLAB) at Nanyang Technological University (NTU), Singapore, is seeking candidates for 2 research fellow positions (from fresh post-docs to senior research fellows) in the areas of:
- symmetric key cryptography
- lightweight cryptography
- side-channel attacks
Salaries are competitive and are determined according to the successful applicants accomplishments, experience and qualifications. Interested applicants should send their detailed CVs, cover letter and references to Thomas Peyrin (thomas.peyrin [at] ntu.edu.sg).
Review of applications starts immediately and will continue until positions are filled.