A data transmission method, a first device, and a second device, for use in implementing secure data transmission between a terminal device in a non-active state and a base station. The method comprises: a first device determines a transmission message comprising transmission data and a secure context identifier of a terminal device, the terminal device being in a non-active state; the first device sends the transmission message to a second device; the second device matches the secure context identifier of the terminal device with a secure context identifier of at least one local terminal device, and determines, on the basis of the matching result, whether to activate the security of the terminal device.