Multisig

N-of-M means M keys exist and any N of them can authorize. The design intent is that no single compromised key, and no single compromised person, can move funds. Safe (formerly Gnosis Safe) is the dominant on-chain implementation on EVM chains.

The quorum number is the least interesting part of the design. What determines whether a multisig actually holds is signer independence: different people, different devices, different physical locations, different organizations where possible.

A 3-of-5 where all five keys sit on hardware wallets in one office, administered by one team, is a 1-of-1 with extra steps against an attacker who reaches that office or that team.

The second failure mode is the one the Bybit case above demonstrates: signers approve what they are shown. Every signature in that attack was cryptographically valid. No quorum size would have prevented it, because the quorum did exactly what it was designed to do.

Blind signing, where a hardware wallet displays a hash rather than a decoded transaction, is the structural weakness that makes this class of attack work. Independent verification of the payload, outside the interface that proposed it, is the control that answers it.