TOFU or TUFU are information security slang acronyms which mean Trust On First Use or Trust Upon First Use. This model refers to the network software security model whereby client software, upon connecting to a new server, is prompted to accept and record some form of token to identify the remote server. For Example, SSH protocol implementations are designed to issue a warning when the IP or domain name of a server has changed: WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!.