A key descriptor structure exchanged between a wireless LAN terminal and an access point, and a method and apparatus for cryptographing wireless data are provided. The key descriptor structure includes a key initial vector which is a random number generated in the access point, a key descriptor type which indicates an encryption algorithm, and a plurality of key materials encrypted according to the encryption algorithm of the key descriptor using the key initial vector and a master session key shared between the wireless LAN terminal and the access point as an encryption key.