Patent ID: 8625798

Claim:
A method for encrypting short data at a terminal in a wireless communication system, the method comprising: generating a short data burst in idle mode; generating a Traffic Encryption Key (TEK) using a Cipher-based Message Authentication Code (CMAC)-TEK prekey derived from an Authorization Key (AK) related to Security Association (SA) between the terminal and a Base Station (BS), the AK being acquired in an authentication procedure during initial network entry; constructing, by the terminal, a nonce using a Packet Number (PN) identical to an uplink CMAC PN (CMAC-PN_U) transmitted together with a Ranging Request (RNG-REQ) message carrying the short data burst; encrypting the short data burst using the TEK and the nonce; generating a Medium Access Control (MAC) Protocol Data Unit (PDU) by attaching a MAC header and the CMAC-PN_U for integrity protection to the RNG-REQ message carrying the encrypted short data burst; and transmitting the MAC PDU in a radio signal to the BS.