AVIONICS

Secure IFF without strings HARLOW

A UK company hopes to bene­fit from a US ban on export­ing cryptographic equipment by offering a secure identi­fication friend or foe (IFF) system to non-Nato countries.

Cossor Electronics is offer­ing a commercial crypto­graphic facility that will enable customers operating Mk XII IFF equipment to transmit and receive encoded identification signals those still operating Mk X IFF, which is easy to deceive and exploit, Cossor offers a new range of secure Mk XII equipment.

The company declines to comment on reports that the Royal Air Force is about to embark on a programme to re­place its existing Mk X airborne trans­ponders with secure Mk XII equipment, as an interim step until the new Nato identification system (NIS) is ready in the mid-1990s. The first RAF aircraft likely to be so equipped are the Harrier GR.5s and later Tornado batches, for which Cossor now offers direct Mk XII replacements for existing Mk X transponders.

In principle, Mk XII IFF is similar in operation to Mk X. The defender interrogates an unidentified aircraft by trans­mitting a "question" signal on 1030MHz. This is received by the aircraft transponder, recognised as friendly, and replied to with an "answer" signal on 1090MHz.

A Mk XII IFF system has four modes of interrogation, three of which are common with the Mk X. Mode 4, unique to Mk XII IFF, has a different signal structure that enables the interrogator to transmit an encrypted signal which hopefully cannot be decoded and duplicated by the enemy. Decoded, the signal in effect tells the aircraft transponder when to reply.

Mode 4 operation requires a cryptographic unit to be installed adjacent to the transponder. Nato countries buying Mk XII equipment are

Cossor is offering secure Mk XII IFF equipment for aircraft and air-defence systems incorporating its Circe cryptographic equipment

provided with a separate crypto unit, the supply of which is strictly controlled by the USA. While countries outside Nato can buy Mk XII equipment, they cannot get the crypto unit, and without it they are unable to operate secure Mode 4 interrogation. Without Mode 4 capability, Mk XII is simply a more expensive Mk X IFF.

Cossor's answer to the growing demand for national secure IFF systems is to offer both Mk XII equipment and commercial cryptographic equipment, called Circe, which together offer a form of Mode 4 capability. The Circe crypto units are available as cards which plug into Cossor IFF equipment, or as "applique" units for use with other manufacturers' Mk XII equipment.

One potential market is the Gulf Co-operation Council, which wants a secure IFF system but is blocked from receiving US cryptographic equipment. The wider avail­ability of Mk XII IFF results

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from a rewriting of the Nato standardisation agreement which has, in effect, declassified the system to Nato restricted.

The complete Circe system comprises the crypto unit, a programmer, and a fill-gun. The programmer holds the key variable necessary to operate the crypto units, and is held in a secure location. Fill-guns are automatically loaded with the key variable from the programmer and used to down-load the data into the crypto units in several weapon systems. The key variable is changed frequently.

By using very-large-scale integrated circuits, Cossor claims to have incorporated the latest coding algorithms in a reliable crypto unit occupy­ing the smallest possible volume. The company claims that Circe offers "above aver­age flexibility" in coding.

Cossor offers a range of ground and airborne Mk XII equipment. The IFF 890 series of interrogators are

intended for use with air-defence gun and missile systems; the single-box 891 with the Shorts Blowpipe/ Javelin and Bofors RBS 70, the two-box 892 with the British Aerospace Rapier Laserfire and Marconi Marksman, and the 892S with the Oerlikon/Contraves Sky-guard.

The company's IFF 4700 family of Mk XII airborne transponders comprises three members. The IFF 4720 is a

form, fit, and func­tion replacement for Cossor's widely used IFF 2720 Mk X tran­sponder. The 4720 is a direct replacement for the panel-mounted IFF 3100 in RAF Tornadoes. The IFF 4760 is a databus - compatible replacement for the APX-100 transpon­

der, and is suitable for the Harrier GR.5.

The RAF has an urgent need for secure IFF, and for interoperability with Mk XII already used by the USA, Germany, and other Nato nations. Mk X IFF is now virtually useless, and the Service cannot afford to wait until NIS is available. A programme to retrofit Mk XII transponders is expected to be announced soon, and Mk XII IFF is expected to continue in use on older platforms even after NIS enters service. Cossor will face competition from Plessey Avionics' PA6000 series of Mk XII equipment.

Cossor and Plessey Avionics have formed the Identification Project Part­nership (IPP) to undertake project definition of NIS under contract to the UK Ministry of Defence. The NIS transponder must be com­patible with both Mk X and XII interrogators, and must also cope with D-band spread-spectrum interrogation from long-range radars and air­borne early warning plat­forms, and J-band "radar-mode" interrogation by interceptors and air-defence systems. Regardless of the mode of interrogation, the NIS transponder will reply in D-band, the existing IFF frequency.

FLIGHT INTERNATIONAL, 20 September 1986 27