Disclosed are a cipher control method which supports to maintain a cipher mode between a network system and a terminal. The method of controlling an encryption includes: attempting a connection for operating a communication channel between a terminal and a network system; providing cipher information about a cipher algorithm operation of the terminal to the network system; determining whether the terminal is a problematic terminal operating an abnormal cipher algorithm by the networking system; and when the terminal is determined to be operating abnormal, instructing the terminal to perform a communication channel operation based on a normally operable cipher algorithm by the network system.