Tendermint共识算法（一种改进的PBFT算法）.pdf

拜占庭容错

共识算法和协议

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一种PBFT算法变种（实用拜占庭容错算法，联盟链共识算法），基于PBFT算法进行的改进。原文名称：Tendermint: Consensus without Mining 作者：Jae Kwon

Tendermint: Consensus without Mining

Jae Kwon

yk239@cornell.edu

Draft v.0.6 (outdated)

This is from 2014.

The current spec is on github.com/tendermint/tendermint/wiki

Abstract. Cryptocurrencies such as Bitcoin enable users to submit

payment transactions without going through a centralized trusted or-

ganization. Bitcoin relies on proof-of-work mining to secure consensus

which is problematic; mining requires a massive expenditure of energy,

conﬁrmation of transactions is slow, and security is diﬃcult to quantify.

We propose a solution to the blockchain consensus problem that does

not require mining by adapting an existing solution to the Byzantine

Generals Problem.

1. Introduction

Cryptocurrencies have come into the spotlight since the introduction of Bit-

coin [1]. The objective of cryptocurrency protocols such as Bitcoin is to maintain a

live decentralized transaction ledger while defending against double-spend attacks

from malicious Byzantine actors that deviate from the protocol. Consensus of the

Bitcoin transaction ledger is secured by a network of miners who compete for re-

wards in the blockchain. This mining, or proof-of-work, comes with a hefty cost.

At today’s Bitcoin prices and reward schedule, miners are rewarded on the order of

$1,500,000 a day to secure the blockchain – and a signiﬁcant portion of that money

is spent on electricity. Proof-of-work based consensus protocols are also slow, re-

quiring up to an hour to reasonably conﬁrm a payment to prevent double-spending.

Alternative protocols have been proposed by the cryptocurrency commu-

nity to replace proof-of-work mining [2, 3]. Some of these protocols suﬀer from the

nothing at stake problem; participants have nothing to lose by contributing to mul-

tiple blockchain forks, so consensus on a single blockchain is not guaranteed. Other

protocols require participant to accurately gauge the trustworthiness of other key

participants, which makes analysis of security diﬃcult to quantify.

Our contribution is a novel consensus protocol that requires no proof-of-work

mining and has a high level of protection against double-spend attacks. We make

a weak assumption about the participant’s abilities to keep time, and we assume

partial synchrony of the network. Our algorithm is based on a modiﬁed version of

the DLS protocol [4], and is resilient up to

/3 of Byzantine participants.

2. The Diﬃculty of Quantifying Security

Security analysis of cryptocurrency protocols is complicated by many factors.

One such complicating factor is the rational self-interested nature of participants.

The ideal protocol is an incentive compatible Nash equilibrium such that deviating

from the protocol does not result in a net gain [5]. Recent work by Eyal and Sirer

[6] showed that the Bitcoin protocol is susceptible to a minority collusion group

that can grow to become a centralized majority. They propose a modiﬁcation to

the Bitcoin protocol such that it can tolerate colluding groups that control up to

of the mining power – less than the previously assumed bound of

/2 of Byzantine

mining power which requires an honest mining majority that follows the prescribed

protocol.

Another complicating factor is whether the power to achieve or disrupt con-

sensus is extrinsic in origin (e.g. access to the production of mining equipment or

access to cheap electricity) or intrinsic in origin (e.g. the “stake” of validators in

proof-of-stake protocols) and whether the disruption of consensus – especially via a

successful double-spend attack – is associated with a commensurate penalty. The

problem with extrinsic factors of security is that they are not easily quantiﬁable

for analysis. For example, the depreciation costs of Bitcoin mining hardware in the

event of a successful double-spend attack may not be signiﬁcant compared to the

running costs of electricity. On the other hand existing proof-of-stake protocols do

not have a well deﬁned intrinsic penalty for instigators of a double-spend attack.

This is commonly called, ironically, the “nothing at stake” problem. Newer protocols

like the BitShares delegated-proof-of-stake protocol attempt to address this prob-

lem by placing the role of ranked-delegate at stake [3], but security is dependant on

the extrinsic ability of stakeholders to accurately predict the future performance of

delegates.

Security analysis is much simpler for an intrinsically secure cryptocurrency

protocol when it can be proved that launching a double-spend attack necessarily

results in a very high intrinsic penalty compared to the possible intrinsic gains.

Then, the protocol may be considered resistant to double-spent attacks assuming

no further extrinsic complications.

3. Terms

Nodes are connected to each other in a peer-to-peer network and relay new

information by gossip. Each node keeps a complete copy of a totally ordered se-

quence of events in the form of a blockchain as in Bitcoin. Users keep an account

in the system, where the user’s account is identiﬁed by the user’s public key or

address. Each account can hold a sum of coins that can change with new transac-

tions. Nodes relay new transactions as they are signed and submitted by users to

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