145 research outputs found
Byzantine Agreement with Optimal Early Stopping, Optimal Resilience and Polynomial Complexity
We provide the first protocol that solves Byzantine agreement with optimal
early stopping ( rounds) and optimal resilience () using
polynomial message size and computation.
All previous approaches obtained sub-optimal results and used resolve rules
that looked only at the immediate children in the EIG (\emph{Exponential
Information Gathering}) tree. At the heart of our solution are new resolve
rules that look at multiple layers of the EIG tree.Comment: full version of STOC 2015 abstrac
Lower Bounds on Implementing Robust and Resilient Mediators
We consider games that have (k,t)-robust equilibria when played with a
mediator, where an equilibrium is (k,t)-robust if it tolerates deviations by
coalitions of size up to k and deviations by up to players with unknown
utilities. We prove lower bounds that match upper bounds on the ability to
implement such mediators using cheap talk (that is, just allowing communication
among the players). The bounds depend on (a) the relationship between k, t, and
n, the total number of players in the system; (b) whether players know the
exact utilities of other players; (c) whether there are broadcast channels or
just point-to-point channels; (d) whether cryptography is available; and (e)
whether the game has a k+t$ players, guarantees that every player gets a
worse outcome than they do with the equilibrium strategy
Brief Announcement: Authenticated Consensus in Synchronous Systems with Mixed Faults
Protocols solving authenticated consensus in synchronous networks with Byzantine faults have been widely researched and known to exists if and only if n > 2f for f Byzantine faults. Similarly, protocols solving authenticated consensus in partially synchronous networks are known to exist if n > 3f+2k for f Byzantine faults and k crash faults. In this work we fill a natural gap in our knowledge by presenting MixSync, an authenticated consensus protocol in synchronous networks resilient to f Byzantine faults and k crash faults if n > 2f+k. As a basic building block, we first define and then construct a publicly verifiable crusader agreement protocol with the same resilience. The protocol uses a simple double-send round to guarantee non-equivocation, a technique later used in the MixSync protocol. We then discuss how to construct a state machine replication protocol using these ideas, and how they can be used in general to make such protocols resilient to crash faults. Finally, we prove lower bounds showing that n > 2f+k is optimally resilient for consensus and state machine replication protocols
Colordag: An Incentive-Compatible Blockchain
We present Colordag, a blockchain protocol where following the prescribed
strategy is, with high probability, a best response as long as all miners have
less than 1/2 of the mining power. We prove the correctness of Colordag even if
there is an extremely powerful adversary who knows future actions of the
scheduler: specifically, when agents will generate blocks and when messages
will arrive. The state-of-the-art protocol, Fruitchain, is an epsilon-Nash
equilibrium as long as all miners have less than 1/2 of the mining power.
However, there is a simple deviation that guarantees that deviators are never
worse off than they would be by following Fruitchain, and can sometimes do
better. Thus, agents are motivated to deviate. Colordag implements a solution
concept that we call epsilon-sure Nash equilibrium and does not suffer from
this problem. Because it is an epsilon-sure Nash equilibrium, Colordag is an
epsilon Nash equilibrium and with probability (1 - epsilon) is a best response.Comment: To be published in DISC 202
Tight binding description of the STM image of molecular chains
A tight binding model for scanning tunneling microscopy images of a molecule
adsorbed on a metal surface is described. The model is similar in spirit to
that used to analyze conduction along molecular wires connecting two metal
leads and makes it possible to relate these two measurements and the
information that may be gleaned from the corresponding results. In particular,
the dependence of molecular conduction properties along and across a molecular
chain on the chain length, intersite electronic coupling strength and on
thermal and disorder effects are discussed and contrasted. It is noted that
structural or chemical defects that may affect drastically the conduction along
a molecular chain have a relatively modest influence on conduction across the
molecular wire in the transversal direction.Comment: 22 pages, 9 figures, Israel J Chemistry, in pres
QHD: A brain-inspired hyperdimensional reinforcement learning algorithm
Reinforcement Learning (RL) has opened up new opportunities to solve a wide
range of complex decision-making tasks. However, modern RL algorithms, e.g.,
Deep Q-Learning, are based on deep neural networks, putting high computational
costs when running on edge devices. In this paper, we propose QHD, a
Hyperdimensional Reinforcement Learning, that mimics brain properties toward
robust and real-time learning. QHD relies on a lightweight brain-inspired model
to learn an optimal policy in an unknown environment. We first develop a novel
mathematical foundation and encoding module that maps state-action space into
high-dimensional space. We accordingly develop a hyperdimensional regression
model to approximate the Q-value function. The QHD-powered agent makes
decisions by comparing Q-values of each possible action. We evaluate the effect
of the different RL training batch sizes and local memory capacity on the QHD
quality of learning. Our QHD is also capable of online learning with tiny local
memory capacity, which can be as small as the training batch size. QHD provides
real-time learning by further decreasing the memory capacity and the batch
size. This makes QHD suitable for highly-efficient reinforcement learning in
the edge environment, where it is crucial to support online and real-time
learning. Our solution also supports a small experience replay batch size that
provides 12.3 times speedup compared to DQN while ensuring minimal quality
loss. Our evaluation shows QHD capability for real-time learning, providing
34.6 times speedup and significantly better quality of learning than
state-of-the-art deep RL algorithms
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