Report Overview
"Deconstructing Blockchains: A Comprehensive Survey on Consensus, Membership and Structure" is a comprehensive academic survey that deconstructs blockchain technology into three critical components: membership selection, consensus mechanism, and structure. The paper provides a clear framework for understanding and analyzing the design principles behind various blockchain systems.
Key Insight: The complexity of current blockchain ecosystems can be tamed through deconstruction into three simple, critical components common to most known systems: membership selection, consensus mechanism, and structure. This approach provides a unique landscape for understanding blockchain design principles and achieved properties.
Key Data Points
Key Insights Summary
Three Critical Components
The paper innovatively deconstructs blockchain into three components: membership selection (determining committee of nodes), consensus mechanism (deciding next block), and structure (data organization).
Membership Selection Diversity
Beyond Proof-of-Work, numerous approaches exist including Proof-of-Stake variants, Proof-of-Capacity, Proof-of-Authority, and TEE-based methods, each with different security and performance trade-offs.
Consensus Spectrum
Blockchain consensus spans from Nakamoto's probabilistic approach to BFT protocols with deterministic guarantees, with hybrid systems combining elements of both.
Structural Evolution
Blockchain structures have evolved from simple linear chains to DAGs, parallel chains, and sharded architectures to address scalability limitations.
Attack Taxonomy
The survey categorizes attacks into mining power attacks, strategic mining, communication attacks, and stake-based attacks, providing a comprehensive security analysis.
Scalability Challenges
Trade-offs exist between decentralization, security, and scalability, with various approaches like off-chain payments and sharding proposed to address limitations.
Content Overview
Document Contents
I. Introduction
Since Bitcoin's introduction in 2008, blockchain technology has evolved into a complex ecosystem with numerous proposals addressing variations and solving problems from the initial specification. This complexity is amplified by the absence of detail in many accompanying blockchain whitepapers.
This paper sets out to explain blockchains by deconstructing them into three critical components common to all known systems: membership selection, consensus mechanism, and structure. This deconstruction provides a clear landscape of blockchain design principles and properties.
II. Background
The section explores foundational concepts of blockchain, starting with Bitcoin as a decentralized electronic payment system. It discusses the evolution to smart contracts and known causes of blockchain varieties including transient forks, storage size issues, scalability challenges, and clique formation leading to centralization.
Key concepts covered include blockchain as an append-only distributed ledger, Bitcoin's transaction structure, smart contracts in Ethereum, and the main triggers for blockchain evolution.
III. Analysis Criteria
This section introduces criteria for evaluating and comparing different membership selection and consensus mechanisms, including:
- Common Assumptions: Network models (synchronous, asynchronous, partially synchronous), online presence, adversary threat models, and trust assumptions.
- Membership Properties: Openness (permissionless, permissioned, partially-permissioned), selection approaches (work, stake, resource count), and incentives.
- Consensus Properties: Agreement, termination, validity, and blockchain state properties (total order prefix vs. total order).
IV. Membership Selection
This comprehensive section analyzes various membership selection algorithms deployed in current blockchain systems, categorized as:
Proof-of-Work (PoW): The original Bitcoin mechanism requiring computational work to prove validity. Includes CPU-bound and memory-bound variants.
Proof-of-Stake (PoS): Alternatives to PoW that use staked assets instead of computational work. Includes deposit-based, balance-based, and delegated approaches.
Other Approaches: Proof-of-Capacity, Proof-of-Authority, TEE-based methods (Proof-of-Elapsed-Time, Proof-of-Luck), and Proof-of-Location for mobile and IoT devices.
Each approach is analyzed for key concepts, weaknesses, goals, and assumptions, providing a comprehensive overview of membership selection in blockchain systems.
V. Consensus Mechanisms
This section provides an overview of consensus mechanisms applied to blockchain systems, including:
Nakamoto's Consensus: The original Bitcoin consensus using the longest chain rule with probabilistic guarantees.
Ghost Protocol: An alternative to longest chain that considers observed sub-trees to address fork issues.
BFT Protocols: Byzantine Fault Tolerant protocols adapted for blockchain, including PBFT-based solutions, RepuCoin, Thunderella, AlgoRand's BA+, Tendermint, HoneyBadger BFT, DBFT, Avalanche, and HotStuff.
Each consensus mechanism is analyzed for assumptions, goals, and properties achieved, providing a comprehensive comparison of blockchain consensus approaches.
VI. Structure
This section explores structural changes to blockchain beyond the original linear chain, including:
New Block Types: Bitcoin-NG's keyblocks and microblocks, ComChain's configuration blocks.
New Structures: Fruitchains decoupling transaction processing, ByzCoin's parallel chains, HashGraph's DAG structure, Beacon chains for sharding, Iota's Tangle, and RaiBlocks' Block Lattice.
These structural innovations address limitations of the original blockchain design, particularly around scalability and transaction throughput.
VII. Attacks
This comprehensive section categorizes and analyzes attacks on blockchain systems:
Mining Power Attacks: 51% attacks, bribery/flash attacks, and various strategic mining attacks including selfish mining, Finney attack, and stubborn mining.
Communication Attacks: BGP routing attacks, eclipse attacks, balance attacks, man-in-the-middle attacks, and clone attacks on Proof-of-Authority systems.
Stake Attacks: Nothing at stake, discouragement attacks, censorship, grinding attacks, stake bleeding, and long-range attacks specific to Proof-of-Stake systems.
The analysis provides insight into blockchain vulnerabilities and potential mitigation strategies.
VIII. Discussion
This section discusses the relationships between the three deconstructed components:
Membership Selection and Consensus: How membership selection impacts consensus security and scalability, with examples of hybrid systems combining different approaches.
Consensus Mechanism and Structure: How structural choices impose requirements on consensus algorithms and vice versa.
Membership Selection and Structure: How different structures require different membership selection approaches.
Scalability: Analysis of scalability across three dimensions: number of consensus nodes, number of clients, and transactions per second.
Ancillary Components: Discussion of cryptography, internal structures and storage, virtual machines, and whitepaper information quality.
IX. Conclusion
The paper concludes that while blockchain is still in its infancy, the ecosystem has become complex and difficult to understand. The deconstruction into three critical components provides a framework for analyzing blockchain proposals and understanding design principles.
The survey provides clear insight into the blockchain landscape through this novel perspective, expected to be useful for the community in simplifying future designs and inspiring innovative coherent combinations revealed by the decomposition and categorization.
Note: The above is only a summary of the survey content. The complete document contains extensive analysis, comparisons, and detailed examination of blockchain components. We recommend downloading the full PDF for in-depth reading and reference.