> The system that was compromised was a "proof of authority" chain. These are different from proof of work or proof of stake chains that have hundreds or thousands of distinct validators.
This is true. However, it should be mentioned that the difference between hacking a "proof of authority" chain and a "proof of stake" chain lies only in quantity: the number of private keys you have to compromise. Once a set of private keys owning a stake majority in a proof-of-chain have been compromised, that chain is no longer usable because the “evil” majority can create an infinite number of longest chains (starting from that point in time) using its stake majority, thus making it impossible to reach consensus on a chain in a decentralized manner.
With proof-of-work, gaining a majority of hashing power only allows you to temporarily create one longest chain, which will be ignored once an honest majority regains sufficient hashing power.
This is true. However, it should be mentioned that the difference between hacking a "proof of authority" chain and a "proof of stake" chain lies only in quantity: the number of private keys you have to compromise. Once a set of private keys owning a stake majority in a proof-of-chain have been compromised, that chain is no longer usable because the “evil” majority can create an infinite number of longest chains (starting from that point in time) using its stake majority, thus making it impossible to reach consensus on a chain in a decentralized manner.
With proof-of-work, gaining a majority of hashing power only allows you to temporarily create one longest chain, which will be ignored once an honest majority regains sufficient hashing power.