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Tadiran SEC-15
Voice and data crypto unit

The SEC-15 was a voice and data crypto system developed in the early 1980s by Tadiran in Israel. It was intended for use in combination with existing radio networks, such as Clansman and the American VRC radios. It was built according to specifications layed out by the IDF (Israel Defense Forces), but was also used by the US Army and a number of NATO countries. Due to its shape and connector at the rear, the unit fits in the same space as the R-442 receiver.
 
The image on the right shows a typical SEC-15 crypto unit. It is housed in the same case as the earlier SEC-13 and the R-442 receiver, making it easier to add it to an existing setup. It has the common 18-pin connector at the back.

Rather than lamps, LEDs are used on the front panel. At the top are LEDs for TRANSMIT, ALARM and RECEIVE. Immediately below that, is the crypto selector with a red (CLEAR) and green (SECURE) LED. To the right of that is the selector for the MODE of operation. It is also used for entering and erasing the current key settings.
  
The front panel of the SEC-15, with the 'door' open

Below the CRYPTO and MODE selectors is a door that gives access to some additional controls. Behind the door is a selector for the current key (0-9), an ERASE button (used when the MODE-selector is set to ERASE) and baudrate settings for the terminal and data connection. Using the table on the inside of the door, the baudrate can be set between 50 and 2400 baud. A switch allows selection between ASCII (7-bit) and BAUDOT (5-bit) encoding.

At the bottom of the front panel are two large military connectors. One is used for connecting the SEC-15 to a (radio) modem, whilst the other one allows the connection of a (TTY) terminal.

At present, no further information about this crypto unit is known. It is possible that it was the successor to the SEC-13 but it is also possible that it was aimed at a different application as it supports both voice and data. It is clear that they were scheduled to be replaced from 1995 onwards by more modern equipment such as the SINCGARS radios. Nevertheless, they were in service well into the 2000s.

Although they were used until recently, they sometimes show up on the European surplus market, which is also were the device shown here was found. If you have additional information about any of the Tadiran crypto devices, please contact us.
 
SEC-15 crypto unit The front panel of the SEC-15, with the 'door' open SEC-15 front panel SEC-15 front panel Close-up view of some of the controls of the SEC-15 Setting the MODE-selector to ERASE Erasing the message keys SEC-15 unit with the door open

 
Interior
The interior of the SEC-15 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 built. After removing the 6 bolts from the top lid, the interior is revealed.
 
The unit consists of 7 printed circuit boards (PCBs), numbered 1 thru 7, an enclosed A6 PRO module and a series of power supply units (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 be removed, by tilting the white levers and lifting the PCB 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.
  
The interior of the SEC-15 with the first PCB removed from its slot

The manufacturing dates on the electronic components inside the SEC-15 vary between 1980 and 1983. This suggests that the unit was developed and built in the early 1980s. As the design and finishing of the PCBs is more professional than those of the SEC-13 it was probably released somewhat later. This is also supported by the fact that LEDs were used instead of lamps.
 
SEC-15 interior SEC-15 interior The interior of the SEC-15 with the first PCB removed from its slot Empty SEC-15 unit Empty SEC-15 unit showing the slots and part of the backplane Rear view of the front panel Rear view of the front panel Rear view of the SEC-15, showing the main 18-way connector.
PCB A1, Memory PCB A2, CPU PCB A3, Communication PCB A4, I/O Card PCB A5, Interface PCB A6, Modem PCB A7, Cipher The index key, mounted aside the large connector at the bottom of each PCB, to prevent it being inserted in the wrong bay.

Hi-res photographs of each of the 7 PCBs are available in the second row of images above. Most of the PCBs carry analog circuits and interfacing beween the analog and digital parts (I/O). The first PCB (A1) contains the memory, whilst A2 carries the processor (CPU). According to text on the PCBs, the function of each board is:
 
  1. Memory
  2. CPU
  3. Communication
  4. I/O Card
  5. Interface
  6. Modem
  7. Cipher
CPU
The SEC-15 is built around an AMD 8085 processor that is located on the second PCB (A2), together with a 4.096MHz crystal and some glue logic. Unlike the SEC-13, the ROM and RAM memory of the SEC-15 is located on a separate PCB (A1).
 
Like the SEC-13, 256 bytes of battery-backed RAM are available for the storage of key material. Furthermore, the A1 board contains 5 Mostek MKB4118 static RAM ICs, delivering a total of 5KB of RAM, giving much more flexibility than with the SEC-13. The firmware is stored in 3 AMD 2732 EPROMs.

The 8085 processor was developed by Intel in 1977 and was based on the earlier 8080. It has an 8-bit databus and a 16-bit address bus, of which the lower 8 bits are multiplexed with the databus.
  
The Memory board (A1) and the CPU board (A2)

The images below show the A1 and A2 boards in more detail. The A1 board normally contains a backup battery in order to retain the key material in the 256 bytes of battery-backed RAM. Unfortunately, this battery is missing from the SEC-15 unit shown here. The rightmost two images below show the space where the battery would normally reside. The rightmost image shows one set (of 2) of the battery terminals.
 
The Memory board (A1) and the CPU board (A2) The Memory board (A1) and the CPU board (A2) The AMD 8085 processor and the 4,096MHz crystal Close-up of the processor Close-up of the memory chips Close-up of a RAM chip The space for the backup battery Close-up of the battery terminals

 
Connector
The form factor and shape of the SEC-15 case, and the main connector at the rear, are identical to those of the R-442 auxiliary receiver. This suggests that the SEC-15 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.

Datasheets

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