An authentication method in a source device that is communication-connected to a sink device in a form of a high-definition multimedia interface, HDMI,, the authentication method comprising: acquiring a random number; transmitting the acquired random number to the sink device; receiving first signature information and capability information from the sink device, the first signature information being information in which the random number is encrypted using a first secret key, the capability information being information about display capability of the sink device; and acquiring a result of a first determination; wherein the acquired random number is transmitted to the sink device by communication through an HDMI Consumer Electronics Control, CEC, bus of the HDMI; the first signature information and the capability information are received from the sink device by communication through the HDMI CEC bus of the HDMI; the first secret key being correlated with the sink device; acquiring a result of a second determination whether second decrypted information is correct, the second decrypted information being obtained by decrypting second signature information using a second public key corresponding to an externally-acquired second secret key, the second public key being externally acquired with the source device, wherein certification information and second signature information are received from the sink device in the reception through the HDMI CEC bus, the certification information being constructed with the first public key and the capability information, the second signature information being a result of encryption of the certification information by the sink device using the second secret key; the first determination determining whether first decrypted information is compatible with the transmitted random number, the first decrypted information being obtained by decrypting the received first signature information using a first public key paired with the first secret key and included in the certification information, when the first decrypted information is compatible with the transmitted random number as the result of the first determination, and when the second decrypted information is correct as the result of the second determination, determining that the received capability information is correct information, to output video corresponding to the capability information to the sink device. acquiring a random number; transmitting the acquired random number to the sink device; receiving first signature information and capability information from the sink device, the first signature information being information in which the random number is encrypted using a first secret key, the capability information being information about display capability of the sink device; and acquiring a result of a first determination; wherein the acquired random number is transmitted to the sink device by communication through an HDMI Consumer Electronics Control, CEC, bus of the HDMI; the first signature information and the capability information are received from the sink device by communication through the HDMI CEC bus of the HDMI; the first secret key being correlated with the sink device; acquiring a result of a second determination whether second decrypted information is correct, the second decrypted information being obtained by decrypting second signature information using a second public key corresponding to an externally-acquired second secret key, the second public key being externally acquired with the source device, wherein certification information and second signature information are received from the sink device in the reception through the HDMI CEC bus, the certification information being constructed with the first public key and the capability information, the second signature information being a result of encryption of the certification information by the sink device using the second secret key; the first determination determining whether first decrypted information is compatible with the transmitted random number, the first decrypted information being obtained by decrypting the received first signature information using a first public key paired with the first secret key and included in the certification information, when the first decrypted information is compatible with the transmitted random number as the result of the first determination, and when the second decrypted information is correct as the result of the second determination, determining that the received capability information is correct information, to output video corresponding to the capability information to the sink device.