Abstract: The vehicle diagnostic system includes a key management system and a to-be-diagnosed unit. The key management system receives a key authorization request sent by a diagnostic device, generates a temporary key based on the key authorization request, and sends a key authorization response to the diagnostic device. The key authorization response carries the temporary key. The key management system configures the temporary key for the to-be-diagnosed unit, so that the diagnostic device and the to-be-diagnosed unit complete a diagnostic based on the temporary key and obtain a diagnostic result. The temporary key is independent of a long-term key in a vehicle. The temporary key is configured to complete the vehicle diagnostic, so that the diagnostic device can be prevented from accessing the long-term key in the vehicle as much as possible.

Abstract: A secure communications method includes: receiving, by a first network device, a second ephemeral public key of a second network device; determining, by the first network device, an ephemeral session key based on a first shared key, a first ephemeral secret key of the first network device, and the second ephemeral public key, where the first shared key is shared between the first network device and the second network device; and performing, by the first network device, secure communication with the second network device based on the ephemeral session key.