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

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

Agreement protocols for partially synchronous networks tolerate fewer than one-third Byzantine faults. If parties are equipped with trusted hardware that prevents equivocation, then fault tolerance can be improved to fewer than one-half Byzantine faults, but typically at the cost of increased communication complexity. In this work, we present results that use small trusted hardware without worsening communication complexity assuming the adversary controls a fraction of the network that is less than one-half. In particular, we show a version of HotStuff that retains linear communication complexity in each view, leveraging trusted hardware to tolerate a minority of corruptions. Our result uses expander graph techniques to achieve efficient communication in a manner that may be of independent interest

Efficient and Adaptively Secure Asynchronous Binary Agreement via Binding Crusader Agreement

We present a new abstraction based on crusader agreement called $\textit{Binding Crusader Agreement}$ (BCA) for solving binary consensus in the $\textit{asynchronous}$ setting against an $\textit{adaptive}$ adversary. BCA has the validity, agreement, and termination properties of crusader agreement in addition to a new property called $\textit{binding}$. Binding states that before the first non-faulty party terminates, there is a value $v \in \{0,1\}$ such that no non-faulty party can output the value $v$ in any continuation of the execution. We believe that reasoning about binding explicitly, as a first order goal, greatly helps algorithm design, clarity, and analysis. Using our framework, we solve several versions of asynchronous binary agreement against an adaptive adversary in a simple and modular manner that either improves or matches the efficiency of state of the art solutions. We do this via new BCA protocols, given a strong common coin, and via new Graded BCA protocols given an $\epsilon$-good common coin. For crash failures, we reduce the expected time to terminate and we provide termination bounds that are linear in the goodness of the common coin. For Byzantine failures, we improve the expected time to terminate in the computational setting with threshold signatures, and match the state of the art in the information theoretic setting, both with a strong common coin and with an $\epsilon$-good common coin

On the Round Complexity of Asynchronous Crusader Agreement

We present new lower and upper bounds on the number of communication rounds required for asynchronous Crusader Agreement (CA) and Binding Crusader Agreement (BCA), two primitives that are used for solving binary consensus. We show results for the information theoretic and authenticated settings. In doing so, we present a generic model for proving round complexity lower bounds in the asynchronous setting. In some settings, our attempts to prove lower bounds on round complexity fail. Instead, we show new, tight, rather surprising round complexity upper bounds for Byzantine fault tolerant BCA with and without a PKI setup

Communication-Efficient BFT Protocols Using Small Trusted Hardware to Tolerate Minority Corruption

Agreement protocols for partially synchronous or asynchronous networks tolerate fewer than one-third Byzantine faults. If parties are equipped with trusted hardware that prevents equivocation, then fault tolerance can be improved to fewer than one-half Byzantine faults, but typically at the cost of increased communication complexity. In this work, we present results that use small trusted hardware without worsening communication complexity assuming the adversary controls a fraction of the network that is less than one-half. 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. Our results use expander graphs to achieve efficient communication in a manner that may be of independent interest