Efficient Synchronous Byzantine Consensus

We present new protocols for Byzantine state machine replication and Byzantine agreement in the synchronous and authenticated setting. The celebrated PBFT state machine replication protocol tolerates $f$ Byzantine faults in an asynchronous setting using $3f+1$ replicas, and has since been studied or deployed by numerous works. In this work, we improve the Byzantine fault tolerance threshold to $n=2f+1$ by utilizing a relaxed synchrony assumption. We present a synchronous state machine replication protocol that commits a decision every 3 rounds in the common case. The key challenge is to ensure quorum intersection at one honest replica. Our solution is to rely on the synchrony assumption to form a post-commit quorum of size $2f+1$, which intersects at $f+1$ replicas with any pre-commit quorums of size $f+1$. Our protocol also solves synchronous authenticated Byzantine agreement in expected 8 rounds. The best previous solution (Katz and Koo, 2006) requires expected 24 rounds. Our protocols may be applied to build Byzantine fault tolerant systems or improve cryptographic protocols such as cryptocurrencies when synchrony can be assumed

Optimal Good-Case Latency for Rotating Leader Synchronous BFT

This paper explores the good-case latency of synchronous Byzantine Fault Tolerant (BFT) consensus protocols in the rotating leader setting. We first present a lower bound that relates the latency of a broadcast when the sender is honest and the latency of switching to the next sender. We then present a matching upper bound with a latency of 2? (? is the pessimistic synchronous delay) with an optimistically responsive change to the next sender. The results imply that both our lower and upper bounds are tight. We implement and evaluate our protocol and show that our protocol obtains similar latency compared to state-of-the-art stable-leader protocol Sync HotStuff while allowing optimistically responsive leader rotation

A comparison of efficacy and safety with add on therapy of pioglitazone in adult patients of psoriasis with and without metabolic syndrome

Background: Psoriasis is a chronic disease involving skin with systemic manifestations whose etiology remains unknown. In recent times, an increased occurrence of metabolic syndrome has been seen in psoriatic patients and potential role of antihyperglycemic in such conditions is being evaluated.Methods: This was a prospective, controlled, randomized, open label comparative clinical study conducted on 51 psoriatic patients. The patients were divided into two groups with and without MS and both these groups were further randomised to receive either standard therapy alone (topical 0.05% betamethasone dipropionate applied twice daily) or therapy with pioglitazone 15 mg orally once daily as add on to standard treatment. The study was conducted over a period of 12 weeks and the primary efficacy outcome was assessed by a change in psoriasis area severity index (PASI). The secondary outcomes were achievement PASI 50/75 and change in parameters of metabolic syndrome (MS). Change in quality of life assessed using dermatological life quality index (DLQI). Results: Both the treatments significantly reduced the PASI score in psoriatic patients with and without MS, maximum being at 12 weeks. In patients with and without MS, pioglitazone caused a greater reduction in PASI score and DLQI score though it was found comparable to ST alone. Significant improvement in parameters of metabolic syndrome was observed in pioglitazone treated group.Conclusions: Pioglitazone given as add on therapy caused an additional improvement in clinical severity and QOL in both the group of psoriatic patients with and without metabolic syndrome. Role of pioglitazone needs to be further explored with higher recommended dose range (30 mg and 45 mg) to demonstrate the usefulness of this drug in psoriatic patients

Efficient Data-Oblivious Computation

The rapid increase in the amount of data stored by cloud servers has resulted in growing privacy concerns for users. First, although keeping data encrypted at all times is an attractive approach to privacy, encryption may preclude mining and learning useful patterns from data. Second, companies are unable to distribute proprietary programs to other parties without risking the loss of their private code when those programs are reverse engineered. A challenge underlying both those problems is that how data is accessed — even when that data is encrypted — can leak secret information. Oblivious RAM is a well studied cryptographic primitive that can be used to solve the underlying challenge of hiding data-access patterns. In this dissertation, we improve Oblivious RAMs and oblivious algorithms asymptotically. We then show how to apply our novel oblivious algorithms to build systems that enable privacy-preserving computation on encrypted data and program obfuscation. Specifically, the first part of this dissertation shows two efficient Oblivious RAM algorithms: 1) The first algorithm achieves sub-logarithmic bandwidth blowup while only incurring an inexpensive XOR computation for performing Private Information Retrieval operations, and 2) The second algorithm is the first perfectly-secure Oblivious Parallel RAM with $O(\log^3 N )$ bandwidth blowup, $O((\log m + \log \log N)\log N)$ depth blowup, and $O(1)$ space blowup when the PRAM has $m$ CPUs and stores $N$ blocks of data. The second part of this dissertation describes two systems — HOP and GraphSC — that address the problem of computing on private data and the distribution of proprietary programs. HOP is a system that achieves simulation-secure obfuscation of RAM programs assuming secure hardware. It is the first prototype implementation of a provably secure virtual black-box (VBB) obfuscation scheme in any model under any assumptions. GraphSC is a system that allows cloud servers to run a class of data-mining and machine-learning algorithms over users’ data without learning anything about that data. GraphSC brings efficient, parallel secure computation to programmers by allowing them to express computation tasks using the GraphLab abstraction. It is backed by the first non-trivial parallel oblivious algorithms that outperform generic Oblivious RAMs

Brief Announcement: Practical Synchronous Byzantine Consensus

This paper presents new protocols for Byzantine state machine replication and Byzantine agreement in the synchronous and authenticated setting. The PBFT state machine replication protocol tolerates f Byzantine faults in an asynchronous setting using n = 3f + 1 replicas. We improve the Byzantine fault tolerance to n = 2f + 1 by utilizing the synchrony assumption. Our protocol also solves synchronous authenticated Byzantine agreement in fewer expected rounds than the best existing solution (Katz and Koo, 2006)

Brief Announcement: Communication-Efficient BFT Using Small Trusted Hardware to Tolerate Minority Corruption

Small trusted hardware primitives can improve fault tolerance of Byzantine Fault Tolerant (BFT) protocols to one-half faults. However, existing works achieve this at the cost of increased communication complexity. In this work, we explore the design of communication-efficient BFT protocols that can boost fault tolerance to one-half without worsening communication complexity. Our results include a version of HotStuff that retains linear communication complexity in each view and a version of the VABA protocol with quadratic communication, both leveraging trusted hardware to tolerate a minority of corruptions. As a building block, we present communication-efficient provable broadcast, a core broadcast primitive with increased fault tolerance. Our results use expander graphs to achieve efficient communication in a manner that may be of independent interest