keyfile

A keyfile is a file that contains cryptographic material used to unlock access to data, software, or systems. Depending on the system, a keyfile may hold raw key material, a private key, or data that is used to derive a cryptographic key. In practice, keyfiles are often used as an additional factor in combination with a password to authenticate and decrypt data. For example, disk encryption tools such as VeraCrypt, TrueCrypt, and LUKS can use one or more keyfiles in addition to a user-supplied password. The contents of a keyfile are typically random data created by the software; the file can be stored on removable media or a secure server and is read during the unlock operation to help derive the final encryption key.

How it works: A keyfile’s data is fed into a key derivation function along with the password to compute the actual key used to encrypt or decrypt data. The KDF parameters are stored in metadata; during unlock, the software checks whether the supplied password and keyfile(s) produce the expected key. Multiple keyfiles can be used to require possession of several files, providing a form of multi-factor access.

Security considerations: Treat keyfiles as highly sensitive; losing them can permanently block access to encrypted data, while compromising them can allow unauthorized decryption. Backups are essential. When used as part of two-factor authentication, protect the keyfiles from unauthorized access and consider binding keyfiles to hardware or encrypted storage. Do not store keyfiles alongside passwords, and ensure integrity measures are in place to prevent tampering.