What Is the Concept of “Long-Range Attacks” in PoS and Why Is It a Concern?

A long-range attack is a theoretical threat where an attacker who held a large stake early in the chain's history uses their old keys to create a malicious alternative chain from the genesis block. This is a concern because, unlike PoW, there is no energy cost to creating old blocks.

Mitigation involves using "checkpointing" mechanisms, where the chain's current state is periodically notarized, forcing new nodes to trust only the most recent checkpoint.