Communication method and communications apparatus

A method, comprising:

• sending, by a security function network element, a first authentication request to a terminal device;
• receiving, by the security function network element, an authentication response message from the terminal device, wherein the authentication response message comprises a first information element used to carry a response value, a second information element used to carry a resynchronization token, and a third information element used to carry a cause indication value;
• and
• in response to information carried in the first information element being verified, sending, by the security function network element, a security mode command to the terminal device.

An apparatus, comprising:

• a processor coupled with a non-transitory storage medium storing executable instructions;
• wherein the executable instructions, when executed by the processor, cause the processor to:
• receive a first authentication request from a security function network element;
• obtain authentication reference information based on the first authentication request, wherein the authentication reference information is a response value, a resynchronization token, or a cause indication value;
• and
• send an authentication response message to the security function network element, wherein the authentication response message comprises a first information element used to carry the response value, a second information element used to carry the resynchronization token, and a third information element used to carry the cause indication value, and the authentication reference information is carried in an information element corresponding to the authentication reference information.