Proof of stake secures a blockchain without mining hardware. The change alters where the cost of attacking the network sits and how misbehaviour is punished.
Mining priced security in electricity
Under proof of work, the right to add a block is won by performing enormous numbers of calculations, which consumes electricity and specialised hardware continuously.
Rewriting history means redoing that work faster than the rest of the network produces it, which requires controlling a majority of total computing power.
The cost is external to the blockchain. An attacker buys hardware and power in the ordinary economy, and the equipment retains value whether or not the attack succeeds.
Staking moves the cost inside the system
Under proof of stake, participants lock the network's own token as a deposit and are selected to propose and confirm blocks in rough proportion to what they have staked.
An attacker must therefore acquire a large share of the token supply, and buying it in size drives the price up before enough has been accumulated.
The capital remains at risk throughout. Any attack that damages confidence in the network devalues the very asset the attacker had to buy to attempt it.
Penalties can be applied directly
Because the deposit sits inside the protocol, rules can destroy part or all of it when a validator signs conflicting blocks or otherwise breaks the rules.
Proof of work has no equivalent. A miner who attacks and fails loses the reward, but the hardware is untouched and can be pointed elsewhere immediately.
This ability to confiscate changes the calculation for an attacker, since the downside is a certain loss rather than merely a wasted opportunity.
Withdrawal delays are part of the design
Staked funds cannot usually be removed instantly. Exit queues and waiting periods keep the deposit locked long enough for misbehaviour to be detected and punished.
Without that delay a validator could act maliciously and withdraw before the penalty applied, which would leave the punishment mechanism unenforceable.
The trade-off is reduced liquidity for honest participants, which is why staking derivatives that represent locked positions have grown alongside the underlying mechanism.
Concentration becomes the central concern
Mining concentrated into large pools with access to cheap power. Staking concentrates around large custodians and services that pool small deposits on behalf of users.
A small number of entities controlling a large share of stake can influence which transactions are included, even without breaking any rule that triggers a penalty.
The security question therefore shifts from raw energy expenditure to the distribution of holdings, which is harder to measure and changes with market structure rather than technology.