The KIR-1A/TSEC system is the communications security (COMSEC) component of the MARK XII IFF system. Specifically, it provides the cryptographic security necessary for operating in Mode 4. It is not used to operate in Modes 1, 2, or 3/A. The TSEC/K1-1A system consists of the AKAK 3662 code key list (AKAK), the KIK-18A/T SEC code changer key (KIK), and the KIR-1A\TSEC interrogator computer (KIR).
KIR-1A/TSEC encodes Mode 4 I.F.F. challenges for transmission by the interrogator. It also decodes the received Mode 4 transponder replies. The code changer key, TSEC/KIK-18, inserts the Mode 4 code into the computer. (Photo source - Navy Advancement page).
Mode 4 I.F.F.operation is for military use only and allows for secure identification of friendly aircraft and surface vessels. IFF automatically generates a reply code according to a preset crypto key list. Mode 4 interrogations use encoded, multipulse trains with 4 (sync) pulses and an ISLS pulse, followed by up to 32 information pulses. When the transponder receives and processes a valid Mode 4 interrogation, it sends out a time-coded, three-pulse reply. The interrogator converts the valid Mode 4 reply back to one pulse. The reply is then time decoded before it is presented on the indicator. There are no emergency replies for Mode 4 or Mode C.
The TSEC/K1-1A system consists of the AKAK 3662 code key list (AKAK), the KIK-18A/T SEC code changer key (KIK), and the KIR-1A\TSEC interrogator computer (KIR). (Image via Global Security)
The AKAK 3662 is the operational code key list for the TSEC/K1-1A system. Editions are composed of 28 operational and two emergency tables providing code settings on a 28-day basis. The two emergency tables are not authorized for use. Individual tables consist of 64 metal pins in the KIK. Each table provides two key settings designated "A" + "B" (Day 1 and Day 2) so that aircraft which are airborne at key change time (2400Z) may shift to the next cryptovariable without rekeying their kit. Editions of the AKAK are classified CONFIDENTIAL and are marked CRYPTO. Individual tables are classified CONFIDENTIAL.
The KIK-18A/TSEC, code changer key is a mechanical device used to cryptographically key the KIR or KIT. The metal pins, which protrude from one end of the device, plug into the code changer assembly of the KIR or KIT to set the code. Once the pins are manually set, the KIK may be used to key any number of KIRs or KITs. The KIK is classified CONFIDENTIAL when set with a code and UNCLASSIFIED when not set.
The KIR-1A\TSEC interrogator computer is used primarily in the ground/surface interrogator of MARK XII-equipped IFF systems. After being cryptographically keyed by the KIK, the KIR can compute individually unique interrogations that are transmitted as challenges through an interrogator to an unidentified aircraft. It also verifies the validity of the coded replies from the aircraft's transponder. The KIK is classified CONFIDENTIAL. Handling instructions are contained in TB 380-41 and NSA manual KAM 25.
This circuit board was identified as belonging to the KIR-1A device. (E-bay photo)
As an example of a specific application, the KIR-1A is used in the Stinger Identification Friend or Foe (IFF) subsystem, part of the Stinger missile weapon system. The operator connects the IFF interrogator to the weapon by using the IFF interconnecting cable. When connected with the Stinger weapon round, the IFF interrogator is capable of transmitting a challenge (interrogation) to a potential target. If an improperly coded reply is received, the aircraft is classified as an "unknown" (possibly a foe).
1) The Navy Advancement Web page.
2) Global Security http://www.globalsecurity.org/military/library/policy/army/fm/44-18/Ch2.htm#s1p3
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