Method for passive rfid security according to security mode

A security method, comprising:

• requesting a second random number by using a first random number when the first random number, protocol control information, extended protocol control information, and unique item identification information are received from a tag;
• requesting a security parameter by transmitting a message including the second random number when the second random number is received from the tag;
• requesting an authentication result of encrypted data to an authentication server when the encrypted data is received from the tag;
• and
• authenticating the tag in accordance with the authentication result of the encrypted data received from the authentication server.