How Does the “Long-Range Attack” in PoS Compare to a 51% Attack in PoW?

A long-range attack is a specific vulnerability in Proof-of-Stake (PoS) where an attacker who held tokens in the past creates a fraudulent chain starting from a very early block. In PoW, a 51% attack requires a majority of current hashrate.

The PoS attack exploits the fact that past validators may have sold their keys, allowing the attacker to sign old blocks cheaply. This differs from the immediate, computationally intensive nature of a PoW 51% attack.