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Week 3 EPFsg Consensus Layer Notes
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Week 3 EPFsg Consensus Layer Notes
Week 3 EPFsg Consensus Layer Notes
用户3885用户38852024年4月15日修改
Guest speaker - Alex Stokes
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Alex Stokes - Researcher at Ethereum Foundation, Worked on multiple topics/ projects incl. MEV, PBS, Reth etc.
Summary notes
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Overview
Blockchain enables a way to create digital scarcity
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Why we care about blockchain in the first place?
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Blockchain creates a way to manufacture digital scarcity, which is difficult to achieve previously.
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Thus, this property of digital scarcity can be used to emulate different sorts of physical assets in the digital realm, eg. money, tokens, property rights etc.
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The way to make digital scarcity: An example to create a digital money with scarcity
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Target: Create a digital money with scarcity
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Unit: Coins
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Scarcity: There are only ever N coins at a time. And a user can't spend more coins than they have.
| Single trusted operator case | Distributed nodes case |
Operator | A single operator runs a webserver that implements this money protocol | A distributed nodes network that implements the protocol N nodes would compute some output over the same inputs |
Implication | Users need to trust this webserver operator to ensure no double-spends | Consensus via "state machine replication" among different nodes, witihout a trusted 3rd party |
Consequence | • Hard to have a trusted operator due to different scenarios eg: • Bug in money protocol • Active attack in protocol server • Dishonest operator • Incentive to attack & abuse the protocol due to scarcity | • Nodes in the system would duplicate the same input log to get the same output • Every node should agree on the output and honest nodes must end up with the same output • As the number of nodes increase, the system become harder to attack |
Result | Need to remove the single trusted operator and minimize trust | At any point of time, even if there are some nodes with faulty output, as long as there is a majority of nodes that have the same view on the output state, the protocol can reach consensus and continue its operation |
Distributed networks deal with Byzantine fault tolerance (BFT)
Why do we need Byzantine fault tolerance?
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If more nodes lead to higher security, then we would want to have a greater number of nodes. However, in an open & distributed system, nodes might have issues (eg. Hardware failure, missed messages, bugs, attacks etc.) which leads to faulty output different from the consensus.
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Thus, we need to have a certain fault tolerance to make the system continue operating
What's Byzantine fault tolerance (BFT)?
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Byzantine fault tolerance (BFT) is the property of a system that is able to resist the class of failures derived from the Byzantine Generals' Problem. This means that a BFT system is able to continue operating even if some of the nodes fail or act maliciously.
Two-phase commit (2PC)
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1st Prepare Phase: One node will ask other nodes whether they can commit the proposed tx.
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In the case of Ethereum, a node with updated state incorporating new txs will broadcast the updated state to all the other nodes. The other nodes will acknowledge the receipt. And when it reaches the BFT (2/3 super majority), then the preparation phase is done.
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2nd Commit Phase: The node will command other nodes to either commit or abort the proposed tx.
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In the case of Ethereun, when 2/3 super majority is reached, nodes within the system will update to the new state.
Practical Byzantine fault tolerance (PBFT)
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PBFT consensus algorithm allows a distributed system to reach a consensus even when a small amount of nodes demonstrate malicious behavior.
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Issue of PBFT
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It only works well with small consensus group size due to the cumbersome amount of communication that is required between the nodes (eg. If there are 10 nodes in the system, it needs 10^10 times of message passing to exchange the updated state and reach consensus.)
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It also susceptible to sybil attack where a single party can create or manipulate a large of nodes in the network, thus compromising the network
Q&A
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Do PBFT protocols have an upper bound of nodes? If yes, what is that, practically speaking?
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The number of nodes doesn't have a hard cap, but there is a trade-off between high throughput and low latency.
Bitcoin solves the BFT with PoW approach
Bitcoin is considered the 1st solution to solve the Byzantine General problem
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The system can scale to unlimited node count
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Open & permissionless participation
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Use PoW mechanism to reach consensus