Patent ID: 7835525

Claim:
A cryptographic method using dual keys in a wireless local area network (LAN) system, comprising: (a) generating a first group key in N wireless terminals forming an ad-hoc group, where N is equal to or greater than two; (b) generating an initial second group key in a main wireless terminal to perform a key distribution center function among the N wireless terminals in response to a request from one of(N−1) sub wireless terminals, the request being communicated using the first group key, and transmitting the initial second group key to (N−1) sub wireless terminals; (c) encoding data using the initial second group key, and transmitting the encoded data between the N wireless terminals; (d) modifying the initial second group key in the main wireless terminal according to a modification time period to form at least one modified second group key, the modification time period being predetermined in the main wireless terminal; and (e) transmitting the at least one modified second group key to the (N−1) sub wireless terminals, wherein the at least one modified second group key is transmitted and used to encode data between the N wireless terminals during use of the first group key, wherein in (e), the at least one modified second group key is encoded using the initial second group key, the method further comprising transmitting the encoded modified second group key to the (N−1) sub wireless terminals, wherein in (b), the main wireless terminal encodes the initial second group key using the first group key, and transmits the encoded initial second group key to the (N−1) wireless terminals.