keosd is a key manager service daemon for storing private keys and signing digital messages. It provides a secure key storage medium for keys to be encrypted at rest in the associated wallet file.
keosd also defines a secure enclave for signing transaction created by
cleos or a third part library.
When a wallet is unlocked with the corresponding password,
cleos can request
keosd to sign a transaction with the appropriate private keys. Also,
keosd provides support for hardware-based wallets such as Secure Encalve and YubiHSM.