Lecture

Decentralized Systems Engineering: Consensus and Fault Tolerance

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Description

This lecture covers the fundamentals of decentralized systems engineering, focusing on consensus algorithms like Paxos and Multi-Paxos, as well as fault tolerance mechanisms. The instructor discusses key concepts such as logical clocks, Byzantine faults, and the Byzantine Generals Problem. The lecture also delves into Threshold Logical Clocks, fault-tolerant consensus, and the challenges of surviving faults in distributed systems. Additionally, the lecture explores the practical applications of fault-tolerant systems in real-world scenarios, such as network partitions and the importance of redundancy. The session concludes with an overview of permissionless consensus, blockchain structures, and key ideas behind Bitcoin, including Proof-of-Work and the assumptions underlying the Bitcoin protocol.

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Computer security: Blockchain

Related concepts (32)

Consensus (computer science)

A fundamental problem in distributed computing and multi-agent systems is to achieve overall system reliability in the presence of a number of faulty processes. This often requires coordinating processes to reach consensus, or agree on some data value that is needed during computation. Example applications of consensus include agreeing on what transactions to commit to a database in which order, state machine replication, and atomic broadcasts.

Byzantine fault

A Byzantine fault (also Byzantine generals problem, interactive consistency, source congruency, error avalanche, Byzantine agreement problem, and Byzantine failure) is a condition of a computer system, particularly distributed computing systems, where components may fail and there is imperfect information on whether a component has failed. The term takes its name from an allegory, the "Byzantine generals problem", developed to describe a situation in which, to avoid catastrophic failure of the system, the system's actors must agree on a concerted strategy, but some of these actors are unreliable.

Blockchain

A blockchain is a distributed ledger with growing lists of records (blocks) that are securely linked together via cryptographic hashes. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree, where data nodes are represented by leaves). Since each block contains information about the previous block, they effectively form a chain (compare linked list data structure), with each additional block linking to the ones before it.

Proof of work

Proof of work (PoW) is a form of cryptographic proof in which one party (the prover) proves to others (the verifiers) that a certain amount of a specific computational effort has been expended. Verifiers can subsequently confirm this expenditure with minimal effort on their part. The concept was invented by Moni Naor and Cynthia Dwork in 1993 as a way to deter denial-of-service attacks and other service abuses such as spam on a network by requiring some work from a service requester, usually meaning processing time by a computer.

Fault tolerance

Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the severity of the failure, as compared to a naively designed system, in which even a small failure can cause total breakdown. Fault tolerance is particularly sought after in high-availability, mission-critical, or even life-critical systems.

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