The Third Web #13 - Consensus Primer with Aparna Krishnan

Aparna Krishnan is head of education at Blockchain at Berkeley and co-founder of Mechanism Labs, an open source blockchain research lab. Earlier this year, Aparna was awarded a scholarship by the DFINITY Foundation for Mechanism Labs’ research into consensus mechanisms. This episode is essentially a primer for advanced discussion of consensus in decentralized networks.

https://mechanismlabs.io/

https://github.com/aparnakr

https://twitter.com/aparnalocked

https://medium.com/@aparnalocked

Aparna Krishnan

Co-founder mechanism labs open source research lab

All work and research is on Github

Telegram: @mechanism_labs

Co-founder of the education team at Blockchain Berkeley

Consensus researcher

Teaches executive education courses

Consensus

Proof of Work

Proof of Stake

Old Field

History

Cynthia Dwork developed stronger adversarial models

Did not have many applications

Blockchain has brought cryptography and consensus into the mainstream eye

Protocols

DFINITY

Tendermint

Bitcoin

Focus has been on proof of stake protocols

Mining may not be sustainable

Long term sustainabilities and lack of externalities is important

Proof of stake offers efficiently

As does proof of elapsed time and proof of space and time

Consensus

Sybil control

Coming to agreement relies on traditional consensus

PoS, PoW refer to the sybil control mechanism

PoS - Putting down capital

Financial penalty for misbehavior

Token holders are participants

PoW - burning energy

One cpu, one vote

No connection between token custody and rewards

P o Elapsed Time

Proof of Authority placing reputation

A cost of playing ball

Traditional Consensus (PBFT)

No concept of probabilistic finality

All honest nodes come to final agreement

Closed, permissioned

Blockchain

All nodes may with a high degree of probability agree

A probabilistic guarantee

Longest Chain Rule

Longest sequence of blocks is the

Ethereum

Ghost

Can be attacked by a stealthy entity

Open, permissionless, decentralized

Inefficient

Node churn

Better liveness properties

Early PoS 2013

PeerCoin

NXT

Bitshares

Primitive

State grinding attack vulnerable

Randomness derived from blockhashes

New Generation

DFINITY

Uses threshold relay decentralized randomness

Tendermint

Round robin

Has social layer fallback

Ethereum Casper

Thunderella

Algorand

Hides the block creator until the block has been created

In Tendermint a minority below the assumption cannot break finality

In Bitcoin >10% can change the finality through threatening to censor

Hard to get both economic and cryptographic security. Not clear that bribing and collusion attacks have been solved. No protocols have shown sophisticated economic models.

Mechanism Labs

Focussing on incentive schemes

What does it mean to have a stable, scalable protocol

Scalability

Proof of Replication

Recent work with Verifiable delay functions

In commit/reveal schemes there is an opportunity to manipulate by giving only one person the ability to reveal the randomness

Verifiable delay functions allow anyone to reveal the randomness

ASIC resistance because not parallelizable