KEY OBTAINING METHOD AND COMMUNICATION APPARATUS

This application discloses a key obtaining method and a communication apparatus. A remote terminal device sends a first identifier and a relay service code to a relay terminal device. The first identifier is an identifier that is of the remote terminal device and that is corresponding to the relay service code, or the first identifier is an anonymous identifier of the remote terminal device. The remote terminal device generates, based on a first shared key, the relay service code, and at least one first freshness parameter, a root key for communication between the remote terminal device and the relay terminal device. A remote authentication service function network element is an authentication service function network element that serves the remote terminal device, and the first shared key is a key shared between the remote terminal device and the remote authentication service function network element.