Proof of Stake (PoS): How Validators Secure a Blockchain
Proof of stake (PoS) is a consensus mechanism in which validators lock up coins, called a stake, to take part in adding blocks to a blockchain. A consensus mechanism is a rule that lets many computers agree on one shared record without a central party. A validator is a participant that proposes and checks blocks of transactions. The most well-known example of a PoS blockchain network is Ethereum, which we will further refer to in this article.
What Is a Validator, and What Does It Lock Up?
A validator is a participant that proposes and checks blocks of transactions, and it does this by running software on a node. A node is a computer that runs a blockchain’s software, connects to other computers, and can verify blocks.
A stake is the amount of coins that a validator locks up as a condition of adding blocks to a blockchain. The word stake names this locked amount, and the blockchain’s rules set how much a validator must lock up.
Ethereum’s documentation sets the minimum stake for activating a validator at 32 coins. In that design, a validator that wants to stop takes part in an exit process, and exits wait in a queue, so the time a validator waits depends on how many other validators are exiting.
How Does Proof of Stake Work?
In Ethereum’s proof-of-stake design, the rules select one active validator in each slot to propose a block, and other validators then attest to it. A slot is a fixed period in which one block can be proposed. An attestation is a vote that a validator signs and sends in favor of its own view of the chain, meaning the chain of blocks as that validator sees it.
The selection is pseudo-random, which means an algorithm in the rules makes the choice. The chance of being selected is weighted by the validator’s effective balance, which means the stake amount that the rules count, up to a limit that the rules set. A larger stake therefore raises the chance up to that limit, but the choice stays pseudo-random, so a larger stake does not decide which validator proposes the next block. A larger stake also does not make a holder a validator: locking at least the minimum stake is a condition of becoming one.
The selected validator, called the proposer, collects transactions into a block, signs it with a digital signature, and broadcasts it to other computers on the network. Each active validator attests once per epoch, which is a fixed group of slots. The validators that attest in a given slot form a committee, a group that the rules choose at random. Nodes on the network can then verify the block and the transactions in it.
The documented Ethereum design for PoS algorithm uses slots of 12 seconds and epochs of 32 slots. An epoch therefore lasts 384 seconds, which is 6.4 minutes: 32 slots of 12 seconds each.
What Happens When a Validator Breaks the Rules?
Slashing is a penalty that removes some or all of a validator’s stake. In Ethereum, slashing also forces the validator out of the network. The rules apply slashing for specific violations, such as signing two different blocks for the same slot.
A validator that misses certain attestation duties can receive a penalty smaller than slashing, although failing to propose a block carries no penalty of its own. Each blockchain’s rules set the penalty amounts and the conditions for them.
Proof of stake is designed so that adding a block requires an Ethereum validator to have locked ETH that the rules can penalize.
How Can Coin Holders Take Part without Running a Validator?
Delegation is one way a coin holder can take part without running a validator. Delegation means that a participant lets a service or a pooled arrangement run a validator on its behalf. A pooled arrangement here isn’t a mining pool. Instead, it is an arrangement in which several holders combine smaller amounts of coins to reach the minimum stake.
With a service, a provider runs the validator while the holder supplies the coins. With a pooled arrangement, a third party operates the validator. In both cases, the holder relies on the party that runs the validator.
For a service, whether the holder or the provider keeps the withdrawal keys, which are the keys that control where the locked coins can go, depends on the arrangement.
How Does Proof of Stake Differ from Proof of Work?
Proof of work (PoW) and proof of stake are consensus mechanisms that each decide which participant adds the next block: proof of work ties that right to computing work, and PoS consensus ties it to coins that a validator locks up.
Do Proof-of-Stake Designs Differ from One Blockchain to Another?
Yes. Proof of stake is a family of designs, and the rules for the minimum stake, selection, penalties, and exits can differ from one blockchain to another.
The slot length, epoch length, and minimum stake are settings of a blockchain’s rules, and they can change when those rules are upgraded.
November 27, 2025
