The present invention relates to a wireless communication system. More particularly, the present invention relates to a method for performing WLAN-based P2P communication at the state where a P2P apparatus is connected to a cellular network and to a first P2P apparatus for the method. The method comprises: a step of receiving one or more pieces of key information from a cellular base station, each piece of key information including a key value corresponding to service identification information; a step of receiving an encryption data signal from a second P2P apparatus; and a step of performing a process of attempting to decrypt said encrypted data signal using one or more keys corresponding to one or more services in which said first P2P apparatus is interested, from among said one or more pieces of key information.