To build a trusted path, we identify a key on the keyboard (in Windows NT this is the key combination Ctrl-Alt-Delete) and make it special. Whenever this key is pressed, the security kernel gets control and monitors what is typed on the keyboard. There is no way to hijack the key that opens the trusted path. (Schneider)

Wikipedia

A trusted path or trusted channel is a mechanism that provides confidence that the user is communicating with what the user intended to communicate with, ensuring that attackers can’t intercept or modify whatever information is being communicated.

The term was initially introduced by Orange Book. As its security architecture concept, it can be implemented with any technical safeguards suitable for particular environment and risk profile.

Source: Wikipedia

Orange Book

• Trusted Path – A mechanism by which a person at a terminal can communicate directly with the Trusted Computing Base. This mechanism can only be activated by the person or the Trusted Computing Base and cannot be imitated by untrusted software.
• B2: NEW: The TCB shall support a trusted communication path between itself and user for initial login and authentication. Communications via this path shall be initiated exclusively by a user.
• B3: CHANGE: The TCB shall support a trusted communication path between itself and users for use when a positive TCB-to-user connection is required (e.g., login, change subject security level). Communications via this trusted path shall be activated exclusively by a user or the TCB and shall be logically isolated and unmistakably distinguishable from other paths.

Source: Trusted Computer System Evaluation Criteria [“Orange Book”]