Embodiments of this application provide a key update method and a related apparatus. One example method includes: sending a first key update request to a second node, where the first key update request includes a first key negotiation parameter and first identity authentication information, and the first identity authentication information is generated by using a first shared key; receiving a first response message from the second node, where the first response message includes second identity authentication information; performing verification on the second identity authentication information by using the first shared key; and if the verification on the second identity authentication information succeeds, determining a first target key based on the first key negotiation parameter.