Ethereum activated its Constantinople upgrade yesterday, Feb. 28, bringing the network to block 7,280,000. The activation came after developers spent a month wrestling with security flaws uncovered in
Ethereum activated its Constantinople upgrade yesterday, Feb. 28, bringing the network to block 7,280,000. The activation came after developers spent a month wrestling with security flaws uncovered in the upgrade's code. Adoption proceeded in phases: by press time, 41.8 percent of Parity nodes and 24.1 percent of Geth nodes ran the new version.
Delays had plagued the upgrade from the start. The original plan called for a Constantinople launch in November 2018. Testing on Ethereum's Ropsten test network surfaced bugs, prompting developers to reschedule. Then security auditors at ChainSecurity dug into Ethereum Improvement Proposal 1283, an EIP developers had planned to include in Constantinople. They discovered something troubling: the code created an opening for reentrancy attacks.
A reentrancy attack works like this. An attacker targets a vulnerable smart contract function. The attacker calls that function, triggering a withdrawal. Before the contract's balance updates to reflect the withdrawal, the attacker calls the same function again. The contract still shows the original balance, so it approves a second withdrawal. The attacker repeats this loop, draining the contract's funds with each iteration. The contract never realizes what's happening until all the money is gone.
The discovery sent Ethereum's developers into action. On Jan. 18, core developers convened to address the vulnerability. They decided to strip the problematic EIP from Constantinople and forge a new release plan. The upgrade would proceed with only the safe changes.
Constantinople represents Ethereum's sixth major network upgrade. St. Petersburg, the seventh upgrade, deployed alongside it at the same block height. Ethereum sits second on the list of blockchains by market value. Lane Rettig, an independent Ethereum developer, noted that the average user would see no difference from these upgrades. Miners and infrastructure operators would notice more. Rettig described Constantinople as an "optimization and maintenance upgrade."
The most tangible change affects mining rewards. Constantinople cuts the block reward from three ETH per block to two ETH. Ethereum had made a comparable shift with Byzantium, an earlier upgrade that reduced rewards from five ETH to three. The upgrade also benefits network performance. Transaction speed improves and gas costs drop. Before Constantinople, storage operations on the network required 5,000 gas units. The upgrade brings that down to 200 gas units.
