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Fault tolerance via diversity for off-the-shelf products: A study with SQL database servers
If an off-the-shelf software product exhibits poor dependability due to design faults, then software fault tolerance is often the only way available to users and system integrators to alleviate the problem. Thanks to low acquisition costs, even using multiple versions of software in a parallel architecture, which is a scheme formerly reserved for few and highly critical applications, may become viable for many applications. We have studied the potential dependability gains from these solutions for off-the-shelf database servers. We based the study on the bug reports available for four off-the-shelf SQL servers plus later releases of two of them. We found that many of these faults cause systematic noncrash failures, which is a category ignored by most studies and standard implementations of fault tolerance for databases. Our observations suggest that diverse redundancy would be effective for tolerating design faults in this category of products. Only in very few cases would demands that triggered a bug in one server cause failures in another one, and there were no coincident failures in more than two of the servers. Use of different releases of the same product would also tolerate a significant fraction of the faults. We report our results and discuss their implications, the architectural options available for exploiting them, and the difficulties that they may present
Intrusion Tolerance: Concepts and Design Principles. A Tutorial
In traditional dependability, fault tolerance has been the workhorse of the many solutions published over the years. Classical security-related work has on the other hand privileged, with few exceptions, intrusion prevention, or intrusion detection without systematic forms of processing the intrusion symptoms. A new approach has slowly emerged during the past decade, and gained impressive momentum recently: intrusion tolerance. The purpose of this tutorial is to explain the underlying concepts and design principles. The tutorial reviews previous results under the light of intrusion tolerance (IT), introduces the fundamental ideas behind IT, and presents recent advances of the state-of-the-art, coming from European and US research efforts devoted to IT. The program of the tutorial will address: a review of the dependability and security background; introduction of the fundamental concepts of intrusion tolerance (IT); intrusion-aware fault models; intrusion prevention; intrusion detection; IT strategies and mechanisms; design methodologies for IT systems; examples of IT systems and protocol
MAFTIA Conceptual Model and Architecture
This document builds on the work reported in MAFTIA deliverable D1. It contains a refinement of the MAFTIA conceptual model and a discussion of the MAFTIA architecture. It also introduces the work done in WP6 on verification and assessment of security properties, which is reported on in more detail in MAFTIA deliverable D
ODIN: Obfuscation-based privacy-preserving consensus algorithm for Decentralized Information fusion in smart device Networks
The large spread of sensors and smart devices in urban infrastructures are motivating research in the area of the Internet of Things (IoT) to develop new services and improve citizens’ quality of life. Sensors and smart devices generate large amounts of measurement data from sensing the environment, which is used to enable services such as control of power consumption or traffic density. To deal with such a large amount of information and provide accurate measurements, service providers can adopt information fusion, which given the decentralized nature of urban deployments can be performed by means of consensus algorithms. These algorithms allow distributed agents to (iteratively) compute linear functions on the exchanged data, and take decisions based on the outcome, without the need for the support of a central entity. However, the use of consensus algorithms raises several security concerns, especially when private or security critical information is involved in the computation.
In this article we propose ODIN, a novel algorithm allowing information fusion over encrypted data. ODIN is a privacy-preserving extension of the popular consensus gossip algorithm, which prevents distributed agents from having direct access to the data while they iteratively reach consensus; agents cannot access even the final consensus value but can only retrieve partial information (e.g., a binary decision). ODIN uses efficient additive obfuscation and proxy re-encryption during the update steps and garbled circuits to make final decisions on the obfuscated consensus. We discuss the security of our proposal and show its practicability and efficiency on real-world resource-constrained devices, developing a prototype implementation for Raspberry Pi devices
ODIN: Obfuscation-based privacy-preserving consensus algorithm for Decentralized Information fusion in smart device Networks
The large spread of sensors and smart devices in urban infrastructures are motivating research in the area of the Internet of Things (IoT) to develop new services and improve citizens’ quality of life. Sensors and smart devices generate large amounts of measurement data from sensing the environment, which is used to enable services such as control of power consumption or traffic density. To deal with such a large amount of information and provide accurate measurements, service providers can adopt information fusion, which given the decentralized nature of urban deployments can be performed by means of consensus algorithms. These algorithms allow distributed agents to (iteratively) compute linear functions on the exchanged data, and take decisions based on the outcome, without the need for the support of a central entity. However, the use of consensus algorithms raises several security concerns, especially when private or security critical information is involved in the computation.
In this article we propose ODIN, a novel algorithm allowing information fusion over encrypted data. ODIN is a privacy-preserving extension of the popular consensus gossip algorithm, which prevents distributed agents from having direct access to the data while they iteratively reach consensus; agents cannot access even the final consensus value but can only retrieve partial information (e.g., a binary decision). ODIN uses efficient additive obfuscation and proxy re-encryption during the update steps and garbled circuits to make final decisions on the obfuscated consensus. We discuss the security of our proposal and show its practicability and efficiency on real-world resource-constrained devices, developing a prototype implementation for Raspberry Pi devices
Byzantine fault-tolerant agreement protocols for wireless Ad hoc networks
Tese de doutoramento, Informática (Ciências da Computação), Universidade de Lisboa, Faculdade de Ciências, 2010.The thesis investigates the problem of fault- and intrusion-tolerant consensus
in resource-constrained wireless ad hoc networks. This is a fundamental
problem in distributed computing because it abstracts the need
to coordinate activities among various nodes. It has been shown to be a
building block for several other important distributed computing problems
like state-machine replication and atomic broadcast.
The thesis begins by making a thorough performance assessment of existing
intrusion-tolerant consensus protocols, which shows that the performance
bottlenecks of current solutions are in part related to their system
modeling assumptions. Based on these results, the communication failure
model is identified as a model that simultaneously captures the reality
of wireless ad hoc networks and allows the design of efficient protocols.
Unfortunately, the model is subject to an impossibility result stating that
there is no deterministic algorithm that allows n nodes to reach agreement
if more than n2 omission transmission failures can occur in a communication
step. This result is valid even under strict timing assumptions (i.e.,
a synchronous system).
The thesis applies randomization techniques in increasingly weaker variants
of this model, until an efficient intrusion-tolerant consensus protocol
is achieved. The first variant simplifies the problem by restricting the
number of nodes that may be at the source of a transmission failure at
each communication step. An algorithm is designed that tolerates f dynamic
nodes at the source of faulty transmissions in a system with a total
of n 3f + 1 nodes.
The second variant imposes no restrictions on the pattern of transmission
failures. The proposed algorithm effectively circumvents the Santoro-
Widmayer impossibility result for the first time. It allows k out of n nodes
to decide despite dn
2 e(nk)+k2 omission failures per communication
step. This algorithm also has the interesting property of guaranteeing
safety during arbitrary periods of unrestricted message loss.
The final variant shares the same properties of the previous one, but relaxes
the model in the sense that the system is asynchronous and that a
static subset of nodes may be malicious. The obtained algorithm, called
Turquois, admits f < n
3 malicious nodes, and ensures progress in communication
steps where dnf
2 e(n k f) + k 2. The algorithm is
subject to a comparative performance evaluation against other intrusiontolerant
protocols. The results show that, as the system scales, Turquois
outperforms the other protocols by more than an order of magnitude.Esta tese investiga o problema do consenso tolerante a faltas acidentais
e maliciosas em redes ad hoc sem fios. Trata-se de um problema fundamental
que captura a essência da coordenação em actividades envolvendo
vários nós de um sistema, sendo um bloco construtor de outros importantes
problemas dos sistemas distribuÃdos como a replicação de máquina
de estados ou a difusão atómica.
A tese começa por efectuar uma avaliação de desempenho a protocolos
tolerantes a intrusões já existentes na literatura. Os resultados mostram
que as limitações de desempenho das soluções existentes estão em parte
relacionadas com o seu modelo de sistema. Baseado nestes resultados, é
identificado o modelo de falhas de comunicação como um modelo que simultaneamente
permite capturar o ambiente das redes ad hoc sem fios e
projectar protocolos eficientes. Todavia, o modelo é restrito por um resultado
de impossibilidade que afirma não existir algoritmo algum que permita
a n nós chegaram a acordo num sistema que admita mais do que n2
transmissões omissas num dado passo de comunicação. Este resultado é
válido mesmo sob fortes hipóteses temporais (i.e., em sistemas sÃncronos)
A tese aplica técnicas de aleatoriedade em variantes progressivamente
mais fracas do modelo até ser alcançado um protocolo eficiente e tolerante
a intrusões. A primeira variante do modelo, de forma a simplificar
o problema, restringe o número de nós que estão na origem de transmissões
faltosas. É apresentado um algoritmo que tolera f nós dinâmicos na
origem de transmissões faltosas em sistemas com um total de n 3f + 1
nós.
A segunda variante do modelo não impõe quaisquer restrições no padrão
de transmissões faltosas. É apresentado um algoritmo que contorna efectivamente
o resultado de impossibilidade Santoro-Widmayer pela primeira
vez e que permite a k de n nós efectuarem progresso nos passos de comunicação
em que o número de transmissões omissas seja dn
2 e(n
k) + k 2. O algoritmo possui ainda a interessante propriedade de tolerar
perÃodos arbitrários em que o número de transmissões omissas seja
superior a .
A última variante do modelo partilha das mesmas caracterÃsticas da variante
anterior, mas com pressupostos mais fracos sobre o sistema. Em particular,
assume-se que o sistema é assÃncrono e que um subconjunto estático
dos nós pode ser malicioso. O algoritmo apresentado, denominado
Turquois, admite f < n
3 nós maliciosos e assegura progresso nos passos
de comunicação em que dnf
2 e(n k f) + k 2. O algoritmo é
sujeito a uma análise de desempenho comparativa com outros protocolos
na literatura. Os resultados demonstram que, à medida que o número de
nós no sistema aumenta, o desempenho do protocolo Turquois ultrapassa
os restantes em mais do que uma ordem de magnitude.FC
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