Zero-knowledge proof

Zero-knowledge proof is when password management companies have zero-knowledge of your key (master password) and cannot decrypt your information because encryption happens client-side. If a company is served with a warrant, they are required to hand over the data but it will still be encrypted and virtually impossible to crack unless they can guess your master password. This is no different from storing your KeePass database in the cloud and the cloud provider being served a warrant for the encrypted database.