Abstract: An object of the present invention is to realize a communication apparatus, a communication method, and an integrated circuit, capable of performing a key updating operation, while having resistibility with respect to noises and DoS attacks without increasing a frequency bandwidth. The present invention is such a communication apparatus for transmitting key update information via a transmission line to another communication apparatus, comprising: a key update information producing unit which generates the key update information having a first time width; a code information producing unit which generates code information which is employed so as to code the key update information; a time width expanding unit 20 for expanding the first time width to obtain a second time width; and a coding process unit 21 for performing a coding process with respect to key update information having the second time width by employing the code information.