Open a session

A session is per domain. VCSEC (DOMAIN_VEHICLE_SECURITY) and Infotainment (DOMAIN_INFOTAINMENT) each have their own epoch, counter, clock, and 16-byte shared secret.

Bind VIN and authenticator

VIN is 17 bytes. SetVIN copies those 17 bytes.

TeslaBLE::Session session;
unsigned char vin[17];
memcpy(vin, "XP7YGCEL9NB000000", 17);

session.SetVIN(vin);
session.GenerateRoutingAddress();
session.LoadAuthenticator(&authenticator);

One Authenticator is shared. Shared secrets sit in per-domain slots on that authenticator.

Request session info

Do this before any encrypted command, and again after a car software update.

unsigned char req[200];
size_t req_size = 0;
session.BuildRequestSessionInfoMessage(
    UniversalMessage_Domain_DOMAIN_VEHICLE_SECURITY,
    req,
    &req_size);

Send req. Repeat for DOMAIN_INFOTAINMENT.

Apply the reply

The RoutableMessage payload is the session-info protobuf. The HMAC tag is in signature_data.session_info_tag. Both are required:

session.UpdateSessionInfo(
    domain,
    session_info_bytes,
    session_info_size,
    tag,
    tag_size);

UpdateSessionInfo verifies the HMAC, then stores epoch, counter, and clock.

Persist across reboot

unsigned char blob[128];
size_t blob_size = 0;
session.ExportSessionInfo(domain, blob, &blob_size);
session.ImportSessionInfo(domain, blob, blob_size);

Encrypted commands

BuildRoutableMessage AES-GCM encrypts the helper payload, binds metadata (VIN, domain, counter, epoch, FLAG_ENCRYPT_RESPONSE), and prepends the 2-byte BLE length. You write that buffer to the car.