This paper describes how GNSS signals can be authenticated using QZSS signals. This is done by computing a digital signature of the navigation message of a GNSS signal that has to be authenticated. The computed digital signature is broadcasted by embedding it into reserve space of navigation message. GNSS signals in a receiver can be authenticated by using the incoming navigation message data, the digital signature and the corresponding public key. Authentication capabilities at the receiver differs depending upon the signal type, message rate, digital signature generation and broadcast rate. It is necessary to define KPI (Key Performance Indicators) such as TTFA (Time To First Authentication), TBA (Time Between Authentication) and AER (Authentication Error Rate) to evaluate overall performance of signal authentication in a receiver. These KPI are computed for GPS and QZSS L1C/A signals by observing data in static and dynamic modes.