Some Low Round Zero Knowledge Protocols

In this paper, we focus on zero-knowledge protocols for NP with low round complexity under the augmented black-box simulation technique, in which the simulator has access to the verifier\u27s secret information, and obtain positive results on 3-round zero-knowledge proofs and 2-round zero-knowledge arguments for NP and 2-round zero-knowledge proofs for QNR. More precisely, our contributions are five-fold: (i) we propose the notion of generalized claw-free function and the notion of trapdoor generalized claw-free function, and then we show a construction of trapdoor generalized claw-free function under the discrete logarithm assumption and the knowledge of exponent assumption, (ii) we propose the notion of completely extractable bit-commitment and give a construction of it from trapdoor generalized claw-free functions, (iii) we present a 3-round zero-knowledge proof for NP based on the completely extractable bit-commitment schemes and Yao\u27s garbling circuit technique, (iv) we show a 2-round zero-knowledge argument for NP based on indistinguishable obfuscator, (v) we transform the basic 2-round honest verifier zero-knowledge proof protocol for quadratic non-residue into a 2-round zero-knowledge proof protocol

k-Round MPC from k-Round OT via Garbled Interactive Circuits

We present new constructions of round-efficient, or even round-optimal, Multi-Party Computation (MPC) protocols from Oblivious Transfer (OT) protocols. Our constructions establish a tight connection between MPC and OT: In the setting of semi-honest security, for any $k \ge 2$, $k$-round semi-honest OT is necessary and complete for $k$-round semi-honest MPC. In the round-optimal case of $k = 2$, we obtain 2-round semi-honest MPC from 2-round semi-honest OT, resolving the round complexity of semi-honest MPC assuming weak and necessary assumption. In comparison, previous 2-round constructions rely on either the heavy machinery of indistinguishability obfuscation or witness encryption, or the algebraic structure of bilinear pairing groups. More generally, for an arbitrary number of rounds $k$, all previous constructions of $k$-round semi-honest MPC require at least OT with $k\u27$ rounds for $k\u27 \le \lfloor k/2 \rfloor$. In the setting of malicious security, we show: For any $k \ge 5$, $k$-round malicious OT is necessary and complete for $k$-round malicious MPC. In fact, OT satisfying a weaker notion of delayed-semi-malicious security suffices. In the common reference string model, for any $k \ge 2$, we obtain $k$-round malicious Universal Composable (UC) protocols from any $k$-round semi-malicious OT and non-interactive zero-knowledge. Previous 5-round protocols in the plain model, and 2-round protocols in the common reference string model all require algebraic assumptions such as DDH or LWE. At the core of our constructions is a new framework for garbling interactive circuits. Roughly speaking, it allows for garbling interactive machines that participates in interactions of a special form. The garbled machine can emulate the original interactions receiving messages sent in the clear (without being encoded using secrets), and reveals only the transcript of the interactions, provided that the transcript is computationally uniquely defined. We show that garbled interactive circuits for the purpose of constructing MPC can be implemented using OT. Along the way, we also propose a new primitive of witness selector that strengthens witness encryption, and a new notion of zero-knowledge functional commitments

Contamination in Cryptographic Protocols

We discuss a foundational issue in multi-prover interactive proofs (MIP) which we call "contamination" by the verifier. We propose a model which accounts for, and controls, verifier contamination, and show that this model does not lose expressive power. A new characterization of zero-knowledge naturally follows. We show the usefulness of this model by constructing a practical MIP for NP where the provers are spatially separated. Finally, we relate our model to the practical problem of e-voting by constructing a functional voter roster based on distributed trust

Supporting Cyber-Physical Systems with Wireless Sensor Networks: An Outlook of Software and Services

Sensing, communication, computation and control technologies are the essential building blocks of a cyber-physical system (CPS). Wireless sensor networks (WSNs) are a way to support CPS as they provide fine-grained spatial-temporal sensing, communication and computation at a low premium of cost and power. In this article, we explore the fundamental concepts guiding the design and implementation of WSNs. We report the latest developments in WSN software and services for meeting existing requirements and newer demands; particularly in the areas of: operating system, simulator and emulator, programming abstraction, virtualization, IP-based communication and security, time and location, and network monitoring and management. We also reflect on the ongoing efforts in providing dependable assurances for WSN-driven CPS. Finally, we report on its applicability with a case-study on smart buildings

A Logic and an Interactive Prover for the Computational Post-Quantum Security of Protocols

International audienceWe provide the first mechanized post-quantum sound security protocol proofs. We achieve this by developing PQ-BC, a computational first-order logic that is sound with respect to quantum attackers, and corresponding mechanization support in the form of the PQ-Squirrel prover. Our work builds on the classical BC logic [7] and its mechanization in the Squirrel [5] prover. Our development of PQ-BC requires making the BC logic sound for a single interactive quantum attacker. We implement the PQ-Squirrel prover by modifying Squirrel, relying on the soundness results of PQ-BC and enforcing a set of syntactic conditions; additionally, we provide new tactics for the logic that extend the tool’s scope. Using PQ-Squirrel, we perform several case studies, thereby giving the first mechanical proofs of their computational post-quantum security. These include two generic constructions of KEM based key exchange, two sub-protocols from IKEv1 and IKEv2, and a proposed post-quantum variant of Signal’s X3DH protocol. Additionally, we use PQ-Squirrel to prove that several classical Squirrel case studies are already post-quantum sound

Boosting Verifiable Computation on Encrypted Data

International audienceWe consider the setting in which an untrusted server stores a collection of data and is asked to compute a function over it. In this scenario, we aim for solutions where the untrusted server does not learn information about the data and is prevented from cheating. This problem is addressed by verifiable and private delegation of computation, proposed by Gennaro, Gentry and Parno (CRYPTO'10), a notion that is close to both the active areas of homomorphic encryption and verifiable computation (VC). However, in spite of the efficiency advances in the respective areas, VC protocols that guarantee privacy of the inputs are still expensive. The only exception is a protocol by Fiore, Gennaro and Pastro (CCS'14) that supports arithmetic circuits of degree at most 2. In this paper we propose new efficient protocols for VC on encrypted data that improve over the state of the art solution of Fiore et al. in multiple aspects. First, we can support computations of degree higher than 2. Second, we achieve public delegatability and public verifiability whereas Fiore et al. need the same secret key to encode inputs and verify outputs. Third, we achieve a new property that guarantees that verifiers can be convinced about the correctness of the outputs without learning information on the inputs. The key tool to obtain our new protocols is a new SNARK that can efficiently handle computations over a quotient polynomial ring, such as the one used by Ring-LWE somewhat homomorphic encryption schemes. This SNARK in turn relies on a new commit-and-prove SNARK for proving evaluations on the same point of several committed polynomials. We propose a construction of this scheme under an extractability assumption over bilinear groups in the random oracle model