Ethereum Classic uses proof of work as its consensus mechanism by choice, for what it provides that other consensus mechanisms do not.
Physical Security
Proof of work ties blockchain security to real-world energy expenditure. To attack the network, an adversary must buy or rent mining hardware at scale and run it, consuming electricity continuously for the duration of the attack. That is a real cost, paid for as long as the attack lasts.
In proof-of-stake systems, the cost of an attack is denominated in the network's own token. An attacker who accumulates enough stake can potentially rewrite history, and the “punishment” (slashing) destroys tokens that the attacker already controls. The security model is circular: the system's security depends on the value of the token, which depends on the system's security.
Proof of work breaks this circularity. The cost of mining is external to the system: electricity, hardware, cooling and physical space are priced in the real economy, not in the blockchain's native token.
Permissionless Participation
Anyone with appropriate hardware can mine Ethereum Classic. There is no minimum balance requirement, no registration process, and no approval needed from existing participants. A miner in any jurisdiction can connect to the network, begin hashing, and earn block rewards proportional to their contribution.
This stands in contrast to proof-of-stake systems, where block production requires holding a minimum amount of the network's native token. This creates a barrier to entry: new participants must first acquire tokens from existing holders.
Censorship Resistance
In proof of work, miners select which transactions to include in a block. If one miner censors a transaction, another can include it in a later block. The censoring miner forgoes the fee, and the transaction goes through after a short delay.
Proof-of-stake systems introduce a different dynamic. Validators can be identified by their staked addresses and potentially subjected to legal or political pressure to censor specific transactions. And their stake sits inside the protocol, where slashing, designed to punish misbehavior, can reach it.
Proof-of-work miners cannot be “slashed.” Their investment is in hardware and electricity, which the protocol cannot confiscate.
Why ETC Stayed on Proof of Work
In September 2022, Ethereum transitioned from proof of work to proof of stake in an event called “The Merge.” Ethereum Classic did not follow.
The decision was consistent with ETC's broader philosophy. The community weighed proof of stake against the network's core commitments (immutability, decentralization and censorship resistance) and concluded that proof of work serves them better.
Specifically, the community identified these concerns with proof of stake:
- Wealth concentration compounds into governance power, as staking rewards accrue to existing large holders.
- Validator identity is exposed, creating a surface for regulatory coercion and targeted censorship.
- The minimum stake requirement (32 ETH on Ethereum) excludes small participants from direct block production.
- Slashing mechanisms create a tool that a majority coalition can use against minority participants.
The Etchash Algorithm
Ethereum Classic uses Etchash, a modified version of Ethash. The primary modification is an extended DAG epoch length: where Ethash increases the DAG (directed acyclic graph) size every 30,000 blocks, Etchash uses a 60,000-block epoch. This doubles the time before the DAG outgrows a given GPU's memory capacity.
The intent was to keep consumer GPUs mining for as long as possible, since mining that requires specialized, expensive hardware (ASICs) raises the barrier to entry and tends to concentrate among fewer, larger operations. Etchash ASICs now mine alongside GPUs, and the slower DAG growth keeps cards with 6GB or more of memory mining.
Concentration Does Not Compound
Proof-of-stake systems are susceptible to a specific centralization failure mode: a small number of large validators can accumulate enough stake to control block production and transaction ordering. Because staking rewards compound, this concentration tends to increase over time rather than decrease.
Proof of work has no such feedback loop. Mining hardware depreciates and electricity must be bought continuously, both at prices set by market competition, so no miner can turn today's block rewards into a permanent advantage in tomorrow's block production. Hashrate can still concentrate in mining pools, but a pool directs only the hashrate its miners point at it, and they can move to another pool at any time.
Ethereum Classic's commitment to proof of work keeps the security model that has protected Bitcoin since 2009: attacking the chain costs hardware and energy bought in the real economy.