An operation method of a first communication node in a communication system may comprise estimating a channel state between the first communication node and a second communication node based on a pilot signal received from the second communication node; generating a first channel codebook based on the estimated channel state; transmitting information of the first channel codebook to the second communication node; receiving a response indicating whether the first channel codebook is to be used from the second communication node; when the response is an ACK indicating that the first channel codebook is to be used, generating a first secret key by using the first channel codebook; and transmitting data encrypted using the first secret key to the second communication node.