A wireless power receiver includes a power pickup configured to receive a wireless power from a wireless power transmitter, and a communicator/controller configured to control the wireless power. The wireless power receiver transmits, to the wireless power transmitter during a configuration phase, a configuration packet including an AI flag related to whether the wireless power receiver supports an authentication function, receives, from the wireless power transmitter during a negotiation phase, a capability packet including an AR flag and a potential power value of the wireless power transmitter, wherein the AR flag is related to whether the wireless power transmitter supports the authentication function, and performs a power transfer phase with the wireless power transmitter. The wireless power receiver transmits, to the wireless power transmitter during the power transfer phase, an authentication request message, and receives, from the wireless power transmitter during the power transfer phase, an authentication response message.