Mutual authentication and re-authentication method between wireless power transmitting device and wireless power receiving device, and wireless power transmitting device and wireless power receiving device using same

A method for performing re-authentication between an authentication initiator and an authentication responder each holding an encryption key through an existing authentication procedure in a wireless power transfer system, the method comprising:

• transmitting, by the authentication initiator, an authentication request message including an initiator digest encrypted using the encryption key to the authentication responder;
• receiving, by the authentication initiator, an authentication response message including a responder digest encrypted using the encryption key from the authentication responder which authenticates the authentication initiator by decrypting the encrypted initiator digest with the encryption key;
• and
• authenticating, by the authentication initiator, the authentication responder by decrypting the encrypted responder digest with the encryption key,
• wherein the authentication request message further includes an initiator timestamp encrypted with the encryption key,
• wherein the authentication response message further includes a responder timestamp encrypted with the encryption key,
• wherein the authentication initiator authenticates the authentication responder by decrypting the encrypted responder type stamp together with the encrypted responder digest with the encryption key, and
• wherein a value of the responder timestamp is a value of the initiator timestamp plus one.