In order to establish a secure communication between the AH40 communication hub and the ACU,
TLS is used. The sequence for connecting when in manufacturer mode is the following:
- The communication hub makes a TCP connection to the ACU.
- ACU and communication hub will try to establish a TLS session. During TLS handshake, the ACU sends its certificate to the communication hub.
- The communication hub validates and stores the certificate.
TLS specifies a number of possible cipher suites, but currently only TLS_RSA_WITH_AES_128_CBC_ SHA is supported by the communication hub. If a certificate using another cipher suite is used by the ACU, the communication hub disconnects the TCP connection.
When in customer mode, The communication hub will only accept a TLS session where the previously stored certificate is presented. If any other certificate is presented, the communication hub will disconnect the TCP connection.