A Primer on Ethereum Blockchain Light Clients

Network Topologies

It is easy to assume most people running a network are between some confidence interval of latency and computational capacity, but easy to forget the barrier to entry most users have to interact with nodes on the blockchain. Unfortunately, running a full node is prohibitively expensive and slow for most, so a large portion of users rely on “light” nodes that piggyback off the security of full nodes without the extensive resource requirements needed.

A RaspberryPi Rig — you can mount a light client on these things!

Introducing Light Clients: Key Actors in Ethereum

The key idea behind a light client is that it is able to fetch parts of the state on demand as it concerns to its user. It assumes an honest model where miners are correctly following the rules of Ethereum and at least a full node in the system is completely honest.

Geth Client With SyncMode Flag Set to “Light” Mode

The Underlying Consensus Mechanism

The current light client protocol assumes proof of work consensus operating in the main chain via full nodes. In proof of work, there exists a mathematical function by which we can verify a block header is valid. That is, this algorithm is hard to compute in order to output such header, but easy to verify.

Credits to Software Engineering Daily

Light Clients in Proof of Stake: Is Proof of Work Necessary?

The simplified problem with light clients in proof of stake amounts to block headers not being tied to a certain amount of “real” work actors need to put in to produce them. That is, the strength derived from this consensus protocol comes down to punishment deterrents for byzantine actors rather than a reward for computing an NP-hard problem via spending electrical energy. Actors trying to grow the wrong chain in proof of stake will get punished, whereas in a proof of work system, actors mining on the wrong chain will fork and not reap the rewards of mining on a canonical chain.

Does a Hybrid Proof of Work / Proof of Stake System Help Light Clients?

There definitely could be a role in using computational power in the production of a block header for the purpose of light client validation in a proof of stake system so long as the power required to validate these headers is very small.

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