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Tadiran SEC-13
Voice crypto unit

The SEC-13 was a voice crypto system developed in the mid-1970s by Tadiran in Israel. It was intended for use in combination with existing radio networks, such as Clansman and the American VRC-12 series radios. It was built according to specifications layed out by the IDF (Israel Defense Forces), but was also used by a number of NATO countries. Due to its shape and connector at the rear, the unit fits in the same space as an R-442 receiver.

The image on the right shows a typical SEC-13 crypto unit. It is easily recognised by the rather large red CLEAR and green SECURE lamps on the upper part of the front panel. Immediately below the lamps is the selection of the key and the appropriate (radio) net.

At the bottom of the front panel is the X-MODE connector (see below), the MODE-selector and the power switch (ON/OFF). The MODE-selector is used for selection between CLEAR and SECURE and to enter the keys. More detailed images of the front panel below.
  
Close-up of the clear and secure lamps and the key setting

At present, no further information about this crypto unit is known. A slightly later version, the SEC-15, features both voice and data encryption. It is clear that they were scheduled to be replaced from 1995 onwards, by more modern equipment such as the SINCGARS radios. Nevertheless, they remained in service well into the 2000s.

Although they were used until recently, they sometimes show up on the European surplus market, which is also where the unit shown here was found. If you have additional information about any of the Tadiran crypto devices, please contact us.

SEC-13 crypto unit SEC-13 front panel Close-up of the clear and secure lamps and the key setting X-Mode connector Setting the mode of operation SEC-13 interior Close-up of the processor and memory SEC-13 front panel rear view

Interior
The interior of the SEC-13 is easily accessible and gives a lot of information about the state-of-technology when the unit was developed. It also tells us approximately when the unit was produced. After removing the 6 bolts from the top lid, the interior is revealed.

The unit consists of 8 printed circuit boards (PCBs), numbered 1 thru 8, and a power supply unit (PSU). The PCBs are all slotted into a so-called backplane that resides at the bottom of the unit. The main connector, the front panel and PSU are all connected to the backplane.

Each of the PCBs can easily be removed, by tilting the white levers and lifting it out of its bay. Each PCB has an index key mounted to its main connector, to prevent it from being inserted into the wrong slot. Please check the rightmost image below for a close-up.
  
SEC-13 interior, looking at the PCBs

Hi-res photographs of each of the 8 PCBs are available in the second row of images below. Most of the PCBs carry analog circuits and interfacing beween the analog and digital parts (I/O). PBC A7 contains the processor (CPU) and is described in more detail below. The last board (A8) contains a large number of 4015 shift-registers and was probably the cipher board.

SEC-13 interior SEC-13 interior, looking at the PCBs SEC-13 Power Supply Unit (PSU) SEC-13 empty case SEC-13 interior with empty slots SEC-13 front panel rear view Rear view of the connector An index key mounted to the connector of each PCB prevent it from being inserted in the wrong slot.
PCB A1 PCB A2 PCB A3 PCB A4 PCB A5 PCB A6 PCB A7, CPU (controller) PCB A8

CPU board (A8)
The PCB marked as A8 contains the Central Processing Unit (CPU). It is built around a Fairschild 3850 processor, which is basically a dual chip F8, running at 2MHz. Next to the PCB is the 3853 static RAM controller that acts as an interface between the 3850 processor and the 256 byte RAM (Random Access Memory, 2 x SCM5101, 4 bits each).

The image on the right shows the major components of the A8 board. The 3850 processor is the large 40-pin chip at the top. The 3853 RAM controller is immediately below it. The firmware is stored in a 1KB 2708 EPROM (the IC with he golden cap and the window).

The two identical ICs at the bottom are the static RAMs. A 3.7V battery at the left ensures the information stored in RAM is retained when the unit is powered off. When crypto-security is compromised, the ERASE switch at the front is used to wipe the RAM contents (crypto keys).
  
Close-up of the processor and memory

The production dates on the various electronic components inside the SEC-13 vary between 1978 and 1983, suggesting that the unit was designed in the late 1970s and brought to market in the early 1980s. A detailed search for foreign (non-US) crypto-equipment, carried out by the Cyberspace Policy Institute of the George Washington University, lists the Tadiran SEC-13, SEC-15 and SEC-22 as in-use in 1999. They were probably used well into the 2000s.

PCB A7, CPU (controller) Close-up of the processor and memory Close-p of the processor, the Static RAM controller and the EPROM RAM backup battery

X-MODE Connector
The X-MODE connector at the front of the SEC-13 allows the unit to be connected directly to the 10-way X-MODE connector of the VRC-12 series radio sets. The expression X-MODE is generally used for the connection of security devices.

On the VRC-12 series radio sets, this 10-way connector is wired as follows [2] :

A. X-MODE in (RX)
B. n.c.
C. X-MODE out (RX)
D. TONE in (150 Hz)
E. X-MODE in (TX)
F. GND
G. X-MODE out (TX)
H. n.c.
J. TONE out (150 Hz)
K. PTT
  
X-Mode connector

The X-MODE connector on the VRC-12 series radio sets was meant for the connection of equipment for secure voice communication. This included the Nestor KY-8, the KY-28, the KY-38 and the SEC-13. It was also compatible with later - more advanced - voice encryption units, such as the VINSON KY-57 and, with the proper junction box, the KY-99.

When no crypto unit is connected to the radio, a terminator cap has to be used at the radio-end instead. It contains 3 shorting wires: between A-C (RX), D-J (TONE) and E-G (TX).

Setting the message key
The SEC-13 has no provisions for the connection of an external key filler like the later KY-57 and the KY-99. Therefore the message key has to be set up manually, using the numerical push-buttons on the front panel. Once the correct number was setup, the user had to toggle the ENTER switch in order to load the 5-digit key into memory. Once the key was entered, the user would reset all of the 5 push-buttons to zero, so as not to reveal (part of) the message key in case of a compromise.

When cipher security was compromised, the user only had to push-up the ERASE switch in order to wipe the contents of the battery-backed RAM and, hence, the message keys.

Main Connector
The form factor and shape of the SEC-13 case, and the main connector at the rear, are identical to those of the auxiliary R-442 receiver. This suggests that the SEC-13 could be slotted into a standard American VRC rack mount.

The image on the right shows the typical 18-pin connector that is available at the rear of the unit (here seen from the bottom). At present, the layout of this connector is unknown to us.

Check the images below for further details of this connector. The rightmost one shows the solder-side of the connector, seen from the interior of the SEC-13.
  
Standard connector

Standard connector Standard connector C-13 bottom view Rear view of the connector

References
  1. Cyberspace Policy Institute, Growing Development of Foreign Encryption Products
    in the Face of US Export Regulations

    10 June 1999, GWU-CPI-1999-02. Detailed research by the George Washington University about non-US encryption products, listing the Tidiran SEC-13, 15 and 22.

  2. Brooke Clarke, VRC-12 Series Radios
    Description of the pin-out of the 10-way X-MODE connector.
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