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T-3020
Key variable loader for DES

T-3020 is a key distribution device, also known as a key loader or a fill device, introduced by Motorola (USA) around 1980. The device is intended for loading cryptographic keys into portable and mobile radios, that use the Data Encription Standard (DES). It is not suitable for DES-XL.

The device is housed in the plastic enclosure, similar to that of an old model Motorola MX handheld radio. The standard batteries of that radio can be used. An optional cable is used to connect the T-3020 to the desired radio.

The image on the right shows a typical T-3020/AX with a coiled cable for connection to Motorola radios with an MX-compatible socket. Other cables were available for connection to other radios, such as the Motorola Saber. The device is powered by a standard MX battery that should be installed at the bottom of the case.
  
Motorola T-3020 with cable

Note that this key loader is suitable only for transferring keys for the US Data Encryption Standard (DES) and not for Motorola's improved DES-XL. For the latter, the T-3011 or the KVL-3000 should be used instead. It should also be noted that there is a variant with a reduced keyboard on which the letters A-F are missing. This version was probably promoted for export use. The keys created with that variant are only 42-bits long 1 (rather than usual 56 bits) and will be easier to break.

  1. The keys generated with this variant are still 56 bits long, but 14 bits are fixed (always 0), which means that only 42 bits are significant.

Motorola T-3020 with cable Two variants of the T-3020 with different keypads Keypad and display Motorola T-3020/AX with reduced keypad Rear panel removed Two stacked PCBs T3020AX model plate
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Motorola T-3020 with cable
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Two variants of the T-3020 with different keypads
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Keypad and display
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Motorola T-3020/AX with reduced keypad
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Rear panel removed
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Two stacked PCBs
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T3020AX model plate
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Versions
There were different versions of the T-3020, both internally and externally. There were versions with different software and versions for export only. Generally speaking the software version is identified by a two-letter suffix to the model number. The higher the number (or actually the letter), the more features and radios are supported. The following versions are known:

  • T-3020/AX
  • T-3020/BX
Variants
  • Full keypad
    This version is suitable for loading DES keys into a number of motorola (handheld) radios, such as the Motorola Saber. It is suitable for entering keys which contain the numbers 0-9 and the letters A-F. For the DES algorithm, the keys were always 56 bits long.

  • Reduced keypad
    This is the same version as the one above, but with a different keypad, which only has the numbers 0-9 on it. This means that it has only half the number of possibilities for each digit when entering the key. As a result, the keys generated with this variant are limited to 42 bits rather than the usual 56. This version was promoted for export only.
The two keyboard variants side-by-side

Security
At the time DES was introduced as an approved encryption standard, it was assumed to be secure against cryptanalytic attacks. The algorithm was developed at IBM in the mid-1970s. In 1976 — after consultation with the US National Security Agency (NSA) — the algorithm was strengthened against differential cryptanalysis, but weakened against brute force attacks, by reducing the number of key bits from 64 to 56. 1 This was probably done to give the NSA an advantage.

It is likely that 56-bit keys could be broken by the NSA, but it is also likely that this required a lot of processing power, of which only limited resources were available (even at the NSA). By further reducing the number of key bits on export devices to 42 (dropping another 14 bits), breaking the key becomes 16,384 times faster (214). Just as an example: if it takes 24 hours to break a 56-bit key, it takes just 5 seconds to break an 42-bit one.

  1. The NSA initially wanted the number of key bits to be reduced from 64 to 48 bits, but eventually 56 bits was negotiated as a compromise.

Interior
Although the function of a key loader is rather limited — it can only be used for entering, storing and transferring cryptographic keys — the T-3020 is actually a very complex device that houses more components than one would be inclined to think, not least because of the fact that the keys are stored in the internal memory in encrypted form, using an internal DES encryption module.

Getting access to the interior and requires only four screws to be released at the rear side, after which the rear panel can be removed. Inside the device are two stacked circuit board (PCBs).

One of these PCBs is mounted to the front panel. It holds the power circuits, the interface to the radio, and EPROM and a typical white Motorola TRN4836A hybrid DES encryption module, which is installed in a socket at the edge of the PCB. The other PCB holds some proprietary Motorola parts, such as the processor, a ROM, I/O circuitry and CMOS RAM. It also holds a 3.84 MHz crystal.
  
Two stacked PCBs

The two PCBs are interconnected by means of several single-in-line PCB headers, mounted along the edges of the PCBs. The DES encryption module is mounted in such a way that it can easily be removed and replaced for another one, if necessary. Judging from the date codes on the various components, the device shown here was manfuctured in 1984 (the oldest parts are from 1981).

Rear panel removed Case frame removed Interior removed from the frame DES encryption module Two stacked PCBs Main board (fitted to the front panel) Daughter board Close-up of the DES encryption unit
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Rear panel removed
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Case frame removed
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Interior removed from the frame
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DES encryption module
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Two stacked PCBs
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Main board (fitted to the front panel)
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Daughter board
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Close-up of the DES encryption unit

References
  1. Batwing Laboratories, 2-Way Encryption Primer
    BatLabs website. Retrieved March 2013.
Further information
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Crypto Museum. Created: Tuesday 30 May 2017. Last changed: Saturday, 13 January 2018 - 11:16 CET.
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