Position-Verification in Multi-Channel Models

We propose an collusion-attack-resistant position-verification protocol in a new model called multi-channel model. In the multi-channel model, there are lots of communication channels. When a player picks a random channel and sends a short message over it, the message might slip by an adversary with high probability if the adversary does not know the channel beforehand. This idea is motivated from the spread spectrum communication techniques. We adopt it to solve the position-verification task. Adding different constraints into the multi-channel model, we make three sub-models: receiving-constrained multi-channel model, sending-constrained multi-channel model and cover-constrained multi-channel model. Our position-verification protocol is secure under all of these sub-models with appropriate parameters

Adaptive Security of Concurrent Non-Malleable Zero-Knowledge

A zero-knowledge protocol allows a prover to convince a verifier the correctness of a statement without disclosing any other information to the verifier. It is a basic tool and widely used in many other cryptographic applications. However, when stand-alone zero-knowledge protocols are used in complex environments, e.g., the Internet, the basic properties may not be sufficient. This is why researchers considered security of zero-knowledge protocols under concurrent composition and man-in-the-middle attacks. Moreover, it is more likely that an adversary might break computers that run the protocol and get internal information of the parties. It is thus very necessary to take account of the security of zero-knowledge protocols when adaptive corruptions are allowed. Previous adaptively secure zero-knowledge protocols work either in a stand-alone setting, or in a concurrent setting with trusted setup assumptions. In this paper, we study adaptive security of zero-knowledge protocols under both concurrent self composition and man-in-the-middle attacks in the plain model (i.e., without any set-up assumptions). We provide a construction of adaptively secure concurrent non-malleable zero-knowledge proof/argument for every language in NP

Single-Molecule Spectroscopy of Disordered States and Dynamics in Proteins

Single-molecule fluorescence techniques, such as Fรถrster resonance energy transfer (FRET) and fluorescence correlation spectroscopy (FCS), were applied to investigate the conformations, dynamics and interactions of disordered protein systems using custom-built confocal and total internal reflection microscopes. Conformational states of the N-terminal Src-homology-3 domain of downstream of receptor kinases (drkN SH3) were characterized. Both folded and unfolded states of drkN SH3 were detected under non-denaturing conditions. When exposed to high concentrations of urea and GdmCl denaturants, the protein still exhibits two distinct smFRET populations. We propose that the high-FRET population corresponds to denaturation-induced looped conformations. FRET experiments in formamide and DMSO suggest that interactions between hydrophobic amino-acid groups in the distal regions are involved in the formation of the looped state. To gain more insight into the determinants of unfolded protein structures, we studied an intrinsically disordered protein (IDP), the eukaryotic initiation factor 4E (eIF4E) binding protein 2 (4E-BP2). Nanosecond-scale dynamics was observed by FCS and was tentatively assigned to local peptide chain contact formation. Our data suggest that multi-site phosphorylation of the protein slows down the proximal chain motions and modulates the kinetics of distal regions. Segmental rotational correlation times and wobbling cone angles provided a rigidity map of the protein at different sites and were used to evaluate the binding mode to eIF4E. smFRET analysis reveals changes in the conformational ensemble responding to phosphorylation, denaturation, salt and pH. It is shown that both hydrophobic and electrostatic interactions play vital roles in determining the conformations of 4E-BP2. Encapsulating proteins into lipid vesicles has been widely used in studying their structural properties and the kinetics of protein-protein interactions. False signals will be introduced in these studies if the fluorescent probe itself interacts with the lipid wall. We employed the FCS method to systematically quantify the interaction between commonly used fluorophores and lipids and proposed mechanisms for the underlying interactions. This study offers a baseline correction for non-specific interactions and can be used to guide the pairing of dyes and lipids in the single-molecule fluorescence studies.Ph.D

Generalized (Identity-Based) Hash Proof System and Its Applications

Abstract. In this work, we generalize the paradigm of hash proof system (HPS) proposed by Cramer and Shoup [CS02]. In the central of our generalization, we lift subset membership problem to distribution distinguish problem. Our generalized HPS clarifies and encompass all the known publickey encryption (PKE) schemes that essentially implement the idea of hash proof system. Moreover, besides existing smoothness property, we introduce an additional property named anonymity for HPS. As a natural application, we consider anonymity for PKE in the presence of key-leakage, and provide a generic construction of leakage-resilient anonymous PKE from anonymous HPS. We then extend our generalization to the identity-based setting. Concretely, we generalize the paradigm of identity-based hash proof system (IB-HPS) proposed by Boneh et al. [BGH07] and Alwen et al. [ADN + 10], and introduce anonymity for it. As an interesting application of anonymous IB-HPS, we consider security for public-key encryption with keyword search (PEKS) in the presence of token-leakage, and provide a generic construction of leakage-resilient secure PEKS from leakageresilient anonymous IBE, which in turn is based on anonymous IB-HPS. Key words: (identity-based) hash proof system, leakage-resilience, anonymity, public-key encryptio