What Is the Significance of the ‘Long-Range Attack’ in Proof-of-Stake Systems?

The long-range attack is a threat where an attacker attempts to create an alternative, longer chain starting from the genesis block or an early point in history, using old, staked keys. This is possible because PoS validators do not expend energy (like PoW miners), making it cheap to recreate the chain's history.

This attack undermines the immutability of the blockchain, but modern PoS protocols use checkpoints and other mechanisms to mitigate it.