The KIV-6 crypto applique is used in the Mode 4 operation of the Mark XII IFF system. The crypto module, when used in conjunction with an interrogator and/or transponder subsystem such as the AN/APX-111(V) or AN/APX-113(V) CIT IFF system, encrypts IFF interrogator challenges, generates transponder encoded replies, and processes the coded replies back at the interrogator. The identification security of both the interrogations and responses is ensured by cryptographic coding of the challenges and replies. The crypto module is loaded with an operational code key that is inserted each day. The module conforms to DoD AIMS 97-1000 and STANAG 4193 Part I standards.