Keystore File

A keystore file is a private key stored on disk in encrypted form, unlocked by a password. Wallet software offers it as an alternative to writing down a recovery phrase: the file holds the key itself, scrambled with a key derived from the password, so possession of the file alone is not enough to spend and neither is the password alone. That symmetry is also the weakness. Lose the file and the password will not recover anything, because unlike a recovery phrase the file is not a regenerable representation of the key — it is the only copy. Back it up in more than one place and treat any copy as sensitive: a keystore uploaded to cloud storage is one password guess away from being a spendable key, and password-guessing against a stolen file happens offline, at whatever speed the attacker's hardware allows.