6 research outputs found
Interactive Consistency in practical, mostly-asynchronous systems
Interactive consistency is the problem in which n nodes, where up to t may be
byzantine, each with its own private value, run an algorithm that allows all
non-faulty nodes to infer the values of each other node. This problem is
relevant to critical applications that rely on the combination of the opinions
of multiple peers to provide a service. Examples include monitoring a content
source to prevent equivocation or to track variability in the content provided,
and resolving divergent state amongst the nodes of a distributed system.
Previous works assume a fully synchronous system, where one can make strong
assumptions such as negligible message delivery delays and/or detection of
absent messages. However, practical, real-world systems are mostly
asynchronous, i.e., they exhibit only some periods of synchrony during which
message delivery is timely, thus requiring a different approach. In this paper,
we present a thorough study on practical interactive consistency. We leverage
the vast prior work on broadcast and byzantine consensus algorithms to design,
implement and evaluate a set of algorithms, with varying timing assumptions and
message complexity, that can be used to achieve interactive consistency in
real-world distributed systems. We provide a complete, open-source
implementation of each proposed interactive consistency algorithm by building a
multi-layered stack of protocols that include several broadcast protocols, as
well as a binary and a multi-valued consensus protocol. Most of these protocols
have never been implemented and evaluated in a real system before. We analyze
the performance of our suite of algorithms experimentally by engaging in both
single instance and multiple parallel instances of each alternative.Comment: 13 pages, 10 figure
Simple Program to Investigate Hysteresis Damping Effect of Cross-Ties on Cables Vibration of Cable-Stayed Bridges
A short computer program, fully documented, is presented, for the step-by-step dynamic analysis of isolated cables or couples of parallel cables of a cable-stayed bridge, connected to each other and possibly with the deck of the bridge, by very thin pretensioned wires (cross-ties) and subjected to variation of their axial forces due to traffic or to successive pulses of a wind drag force. A simplified SDOF model, approximating the fundamental vibration mode, is adopted for every individual cable. The geometric nonlinearity of the cables is taken into account by their geometric stiffness, whereas the material nonlinearities of the cross-ties include compressive loosening, tensile yielding, and hysteresis stress-strain loops. Seven numerical experiments are performed. Based on them, it is observed that if two interconnected parallel cables have different dynamic characteristics, for example different lengths, thus different masses, weights, and geometric stiffnesses, too, or if one of them has a small additional mass, then a single pretensioned very thin wire, connecting them to each other and possibly with the deck of the bridge, proves effective in suppressing, by its hysteresis damping, the vibrations of the cables
Interactive Consistency in practical, mostly-asynchronous systems
Interactive consistency is the problem in which n nodes, where up to t
may be byzantine, each with its own private value, run an algorithm that
allows all non-faulty nodes to infer the values of each other node. This
problem is relevant to critical applications that rely on the
combination of the opinions of multiple peers to provide a service.
Examples include monitoring a content source to prevent equivocation or
to track variability in the content provided, and resolving divergent
state amongst the nodes of a distributed system.
Previous works assume a fully synchronous system, where one can make
strong assumptions such as negligible message delivery delays and/or
detection of absent messages. However, practical, real-world systems are
mostly asynchronous, i.e., they exhibit only some periods of synchrony
during which message delivery is timely, thus requiring a different
approach. In this paper, we present a thorough study on practical
interactive consistency. We leverage the vast prior work on broadcast
and byzantine consensus algorithms to design, implement and evaluate a
set of algorithms, with varying timing assumptions and message
complexity, that can be used to achieve interactive consistency in
real-world distributed systems.
We provide a complete, open-source implementation of each proposed
interactive consistency algorithm by building a multilayered stack of
protocols that include several broadcast protocols, as well as a binary
and a multi-valued consensus protocol. Most of these protocols have
never been implemented and evaluated in a real system before. We analyze
the performance of our suite of algorithms experimentally by engaging in
both single instance and multiple parallel instances of each
alternative
D-DEMOS: A Distributed, End-to-end Verifiable, Internet Voting system
E-voting systems have emerged as a powerful technology for improving
democracy by reducing election cost, increasing voter participation, and
even allowing voters to directly verify the entire election procedure.
Prior internet voting systems have single points of failure, which may
result in the compromise of availability, voter secrecy, or integrity of
the election results.
In this paper, we present the design, implementation, security analysis,
and evaluation of D-DEMOS, a complete e-voting system that is
distributed, privacy-preserving and end-to-end verifiable. Our system
includes a fully asynchronous vote collection subsystem that provides
immediate assurance to the voter her vote was recorded as cast, without
requiring cryptographic operations on behalf of the voter. We also
include a distributed, replicated and fault-tolerant Bulletin Board
component, that stores all necessary election-related information, and
allows any party to read and verify the complete election process.
Finally, we also incorporate trustees, i.e., individuals who control
election result production while guaranteeing privacy and
end-to-end-verifiability as long as their strong majority is honest.
Our system is the first e-voting system whose voting operation is human
verifiable, i.e., a voter can vote over the web, even when her web
client stack is potentially unsafe, without sacrificing her privacy, and
still be assured her vote was recorded as cast. Additionally, a voter
can outsource election auditing to third parties, still without
sacrificing privacy. Finally, as the number of auditors increases, the
probability of election fraud going undetected is diminished
exponentially.
We provide a model and security analysis of the system. We implement a
prototype of the complete system, we measure its performance
experimentally, and we demonstrate its ability to handle large-scale
elections