SLUUBT5C November 2018 – June 2021 BQ40Z80
The ECC-based authentication is believed to be more robust than SHA-1. One of the other benefits of ECC is that the private key resides only in the gauge in secure memory. The authentication process involves the host sending an authentication challenge (up to 20 bytes long) to the gauge via Authenticate(). The gauge responds with a signature pair (R,S), each is 21 bytes long (total 42 bytes), via Authenticate(). The host then verifies that the response is valid. Note that the gauge will NACK on the Authenticate() cmd until its ECC calculation is complete and is ready to respond.