authenticate

1. To establish, usually by challenge and response, that a transmission attempt is authorized and valid.
2. [To] verify the identity of a user, user device, or other entity, or the integrity of data stored, transmitted, or otherwise exposed to unauthorized modification in an information system (IS), or establish the validity of a transmission. [INFOSEC-99]
3. A challenge given by voice or electrical means to attest to the authenticity of a message or transmission. [JP1]
4. To establish the validity of a claimed identity [POSIX.6].
5. To establish the validity of a claimed identity [TCSEC].