A communication method and a device, the method including obtaining, by a terminal device, a security key, where the terminal device performs the obtaining while the terminal device is in a state in which the terminal device has disconnected a radio resource control (RRC) connection from a first network device, and in which the terminal device retains context information for a context, in the first network device, of the terminal device, and sending, by the terminal device, a first message to a second network device, where the first message includes an identifier of the terminal device and at least one of encrypted uplink data or encrypted signaling, the at least one of encrypted uplink data or encrypted signaling is encrypted by using the security key, and where the second network device is different from the first network device.