This application discloses an information exchange method and apparatus. In the method, a terminal device transmits attach request information to a core network device, receives attach accept information of the core network device, where the attach accept information includes a first integrity check code; the terminal device obtains a second integrity check code based on the attach accept information; and the terminal device obtains, if the first integrity check code is the same as the second integrity check code, a third integrity check code based on encrypted attach complete information, and transmits encrypted attach complete information to which the third integrity check code is added to the core network device. This reduces data exchange procedures, reduces an amount of data of exchanged information, and reduces a time consumed in an information exchange process performed between the terminal device and the core network device.