Deterministic Entropy From BIP32 Keychains.

Lets one master backup create separate recovery words, keys and passwords for other wallets and apps.

Keeping many separate backups is hard, but sharing one set of recovery words across wallets is risky. With this BIP, one master key creates fresh secrets for each wallet, and the master backup can recreate them all. If one of those secrets leaks, the master key stays safe.