Before revision: Trust on first use (TOFU), or trust upon first use (TUFU), is a security model used by client software which needs to establish a trust relationship with an unknown or not-yet-trusted endpoint.
After revision: Trust on first use (TOFU), or trust upon first use (TUFU), is an authentication schemeTOFU for OpenPGP, Walfield, Koch (EUROSEC’16, April 18-21 2016) used by client software which needs to establish a trust relationship with an unknown or not-yet-trusted endpoint.