Proof of Stake
PoS replaces the mining lottery with skin in the game: you are chosen to propose a block in proportion to your stake, and misbehaving gets you slashed.
In this lesson
- Describe validator selection and attestations
- Explain slashing as a deterrent
- Compare PoW and PoS security models
Prerequisites
- recommended Proof of Work
Security as a bond
To become a validator you lock a deposit (32 ETH on Ethereum). The protocol pseudo-randomly assigns proposal slots, and validators attest to what they see. Honest behaviour earns fees; equivocating — signing two conflicting things — gets a portion of the deposit slashed.
- Security = hardware + electricity
- Attack cost: buy/build miners forever
- Energy-intensive, simple to verify
- Rewards go to miners
- Slow to finalise (probabilistic)
- Security = capital locked at risk
- Attack cost: acquire a huge share of all stake
- ~99.9% less energy, more protocol complexity
- Rewards go to validators who stake
- Fast economic finality via checkpoints
Example · Ethereum's merge
In September 2022 Ethereum switched from PoW to PoS in a single step, cutting network energy use by roughly 99.95% while keeping the same execution layer and applications above it.
"Nothing at stake" is answered by slashing
In naive PoS, voting for two forks costs nothing, so rational actors would back both. Ethereum punishes exactly that: conflicting attestations burn real deposits. The deterrent is economic, not physical — which is why stake concentration matters.
Run a validator set
Toggle validators offline in the lab and watch attestations stall until they return.
Proof of Stake — true or false?
Practice · server-gradedIs PoS more secure?
Different trade-offs: PoW's cost is external (energy), PoS's is internal (locked capital, subject to governance choices like slashing parameters).
Can big stakers censor?
They can try — but proposer-boost, inclusion lists and eventual rotation are designed to limit it. Censorship is measured continuously on-chain.