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Crypto AG
Two-dimensional voice scrambler · CRYPTOCOM

HC-250 – also HC-255 – was a full duplex F/T voice scrambler, or ciphony device, introduced in 1981 by Crypto AG (Hagelin) in Zug (Switzerland) as the successor to the HC-230. The device was intented for use over regular voice circuits, such as telephone lines and narrowband HF radio. It is likely that the device was developed at the Government Electronics Division of Motorola in the US.

The basic device measures 256 x 225 x 78 mm and weights 4.2 kg (when the optional AC PSU is installed). All connections are via a standard 37-pin D-sub socket (DC37/M) at the rear, or via a pre-wired cradle. The device is controlled via a detached remote control unit that consists of a keypad, a LED display and a mechanical lock.

The HC-250 can be powered from a 12V or 24V DC source, such as the battery of a car or truck. When the optional AC PSU is fitted, it can also be powered from the 110V/220V AC mains. There was also a portable variant in a regular briefcase.
HC-250 speech scrambler with remote control unit

The HC-250 and its predecessor – the HC-210 – were intended as replacements for the bulky CRM-008, also known as HC-230 and HC-235. It offers excellent audio quality, with full speaker recognition and no residual intelligible audio on the line. This is achieved by scrambling in the time domain as well as in the frequency domain. This principle is also known as F/T scrambling or two-dimensional scrambling. Nevertheless, all speech scramblers are inherently insecure.

Complete HC-250 kit for mobile use HC-250 speech scrambler with remote control unit HC-250 (remote) control panel Bare HC-250 device HC-250 with front panel removed Cradle with cables and remote control unit TFC-250 telephone set HC-250 manuals
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Complete HC-250 kit for mobile use
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HC-250 speech scrambler with remote control unit
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HC-250 (remote) control panel
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Bare HC-250 device
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HC-250 with front panel removed
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Cradle with cables and remote control unit
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TFC-250 telephone set
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HC-250 manuals

  • HC-250
    Civil version for vehicle mounting or desktop use, with a detached control panel. When used in a vehicle, the front panel is usually mounted on the dashboard. The device featured here, is of this type. This version was also available in a briefcase variant.

  • HC-255
    Military version in ruggedised green die-cast aluminium enclosure. (MIL-STD-810). This version has the control panel at the front. It is shown in the 1992 company brochure [1].
The HC-250 was developed at a time when Crypto AG was owned by the German Bundes­nach­richten­dienst (BND) and the American Central Intelligence Agency (CIA). There are two versions of the cryptologic: one that was secure, and one that was readable 1 by NSA and ZfCh codebreakers.

From the mechanical construction, the PCB layouts and the choice of components, such as the Motorola 68000 processor [/] and the MC14404 CODECs [/], it seems likely that the HC-250 was developed by the Government Electronic Division of Motorala in Phoenix (Arizona, USA). At the time, Motorola was a subcontractor of Crypto AG (just like Siemens), influenced by the NSA.

So far, the following users have been confirmed:

  • Libya
  • Argentina
In 1984, the intelligence service of the DDR (East-Germany) — Ministerium für Staatssicherheit (MfS), also known as the Stasi — obtained two working HC-250 units from Cuba. The processor section of the device was analysed by a technical student who wrote a thesis on it [4], after which the devices were passed on to the Russian partner – KGB – for further research and analysis [2].

Apparently the Russians did not try to break any HC-250 traffic, as only Libya was known as a user at the time. The device was nevertheless found to be of interest, as it reflected the current state-of-the-art in the Western world. The Russians wanted to use the technology in their own devices, and asked Stasi to find additional technical documentation from Western sources [2].

  1. In this context, readable means that the cryptographic algorithm could be broken by NSA and ZfCh. Also known as friendly. In contrast: algorithms that are not breakable, are called unfriendly or unreadable [3].

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HC-250 encryptor Remote control unit Mounting bracket Modified telephone set Operating instructions
Encryptor   HC-250
The actual encryptor measures 256 x 225 x 78 mm and weights 4.2 kg (with the AC power supply unit present). It is usually mounted in a pre-wired cradle and is locked in place by two spring-loaded levers at the sides.

At the rear is a 37-pin male socket (DC37/M) that provides the connections to the (car) battery, the remote control unit, and a telephone or radio interface. In the unit featured here, the (optional) mains PSU is also present. It allows the unit to be powered from the 220V or 110V AC mains (switch-selectable).

Bare HC-250 device

Remote control unit   ATC-250
All unser controls are on the external rempte control unit, shown in the image on the right. It was connected to the cradle, which in turn is connected to the HC-250 encryptor.

It has a 12-button keypad, two buttons for selecting the desired mode of operation, a key-lock – for entering the BASIC key – and an 8-digit numeric red LED display.
HC-250 (remote) control panel

For mobile use, the HC-250 was generally mounted in the purpose-made cradle shown in the image on the right. It has three fixed cables: for a 12V (car) battery, for connection to the telephone or radio interface, and to the remote control unit.

All connections to and from the HC-250, with exception of the mains power cord, are via the 37-pin male socket (DC37/M) at the rear of the device. It mates with the DC-37/F socket at the rear end of the cradle.
Cradle with cables and remote control unit

Phone   TFC-250
For full-duplex use, the TFC-250 desktop telephone set was connected to the HC-250. It is a regular telephone set – manufactured by Telefonbau und Normalzeit (T&N) in Germany – that is modified for use with the voice encryptor.

The telephone set has two buttons for selecting between plain(P) and crypto (C), plus two LED indicators behind the numeric keypad. The green LED signals that secure speech is used. Note that they * and # keys are blocked.
TFC-250 telephone set

Operating instructions
Each device came with a full user manual with operating instructions, and directions for its installation. It also describes the use of the various types of cryptographic keys.

In addition there was an installation manual, in which details of the wirings and (optional) settings are provided.

 Download user manual
 Download installation manual
 Download technical drawings

HC-250 manuals

Bare HC-250 device HC-250 (remote) control panel Cradle with cables and remote control unit TFC-250 telephone set HC-250 manuals
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Bare HC-250 device
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HC-250 (remote) control panel
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Cradle with cables and remote control unit
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TFC-250 telephone set
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HC-250 manuals

Block diagram
The block diagram shows the different functional blocks of the HC-250 and how they are inter­connected. Four cards are connected to the processor bus: The processor board – that holds the Motorola 68000 processor, the memory board – that holds the RAM and the firmware in EPROM – the interface to the remote control unit, which also holds the static key memory (SRAM) with a Lithium backup battery, and the CODEC board which holds two sets of D/A and A/D converters.

The remaining boards hold the analogue parts. The Universal Interface Board (here shown at the top), maintains the physical connection to the telephone line and the handset — commonly via a modified telephone set. When the device is used in combination with a 2-way (mobile) radio, e.g. police or other public service, the universal interface is replaced by a Half-Duplex Interface.

The interior of the HC-250 can be accessed via the (blind) front panel. It requires removing the four screws in the corners of the front panel, and taking the entire front off. This reveals 7 euro­card size (16x10 cm) printed circuit boards (PCBs) that are held in place by a slotted metal frame.

The image on the right shows the HC-250 after the front panel has been removed. At the left are the three analogue boards (from top to bottom): the power circuits (with the metal panel), the analogue filters and the (line) interface board.

At the right are the four digital boards (from top to bottom): the CPU board, the memory board with the RAM and the EPROMs (firmware), the interface board for the remote control unit, and the CODEC. The latter provides the full-duplex connection to the (modified) telephone set, or to a two-way radio, in which case it is half-duplex.
HC-250 interior

The power board contains a switched-mode power supply unit (PSU) that can be operated from 9 to 30 V DC, making it ideal for use in a car (12V) or truck (24V). If the device should be powered from the AC mains, an (optional) mains transformer can be installed behind the rear panel.

The filter board — that connects the interface board to the CODEC board — holds a lot of proprietary (custom-made) components, as shown in the image on the right. The orange parts are ceramic substrates with the filters and amplifiers, covered by a water repellent coating.

According to the date codes on the substrates, they were manufactured in week 23 of 1981. In addition, there are other OEM parts, such as the integrated circuits (ICs) with the golden caps. These may be early (pre)production samples, or custom-chips that were not generally available.
Filters close-up

The interface board for the remote control unit, contains an Intersil IM6402 UART – for a two-way RS232 serial connection with the remote control unit – quite a lot of digital circuits, and the static random access memory (SRAM) that is used for storing the user-programmable cryptographic keys. The keys are retained by an on-board long-life Lithium battery (the large blue rectangle). 1

  1. Note that by now, such batteries are exhausted and may start leaking. even though they are sealed. It is advised to remove them as soon as possible, to avoid permanent damage to the PCBs.

HC-250 with front panel removed HC-250 interior Power supply board Filter/Mixer board Filters close-up Universal Interface Board CPU board with Motorola 68000 processor
Memory board Digital interface and key memory CODEC board Rear panel removed - PSU
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HC-250 with front panel removed
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HC-250 interior
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Power supply board
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Filter/Mixer board
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Filters close-up
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Universal Interface Board
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CPU board with Motorola 68000 processor
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Memory board
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Digital interface and key memory
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CODEC board
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Rear panel removed - PSU

Peripheral connector
  1. +7.5V
  2. 5.2V
  3. Ground
  4. Ground
  5. /EMCY
  6. KSC
  7. /ADTE
  8. RX
  9. TX(0)
  10. PTT
  11. R/T
  12. AUX IN(0)
  13. LACT
  14. T/R TX
  15. AUX 2
  16. AUX 4
  17. AFR(0)
  18. AFT(0)
  19. DC(+)

  20. -7.5V
  21. 0V
  22. ADCLR
  23. ADR
  24. 5VSB
  25. ADT
  26. RX(0)
  27. TX
  28. PTT(0)
  29. R/T(0)
  30. AUX 1
  31. LACT(0)
  32. AUX IN
  33. AUX 3
  34. not used
  35. AFR
  36. AFT
  37. DC(0)
  • Point-to-point
    2.3 sec.
  • Multipoint
    1 sec
  • Tracking
  • Interrupt
    1000 sec. max. (100 sec. over full temperature range)
  • Delay
    314 ms, or 130 ms (Duplex Comfort)
  • Signalling
    1302/1736 Hz, or 1085/1519 Hz, or 1519/1953 Hz
  • Customer
    1027 combinations (PROM)
  • Structure
    10308 combinations (EPROM) customer programmable
  • Traffic keys
  • Key space
    1032 combinations for each of the 8 keys
  • Message
    6.5 · 104 combinations (automatically generated)
  • User ID
    Up to 8 digits
  • Key ID
    Up to 8 digits
Audio interface
  • Input
    2 mV — 1.5 V (eff)
  • Output
    10 mV — 1.5V (eff)
  • Impedance
    300/200 Ω
  • Response
    350 — 3000 Hz
  • Mic. power
    15 V, 30 mA
Line interface
  • Input
    10 mV — 1.5 V (eff)
  • Output
    2 mV — 1.5V (eff)
  • Impedance
    300/200 Ω
  • Response
    640 — 2880 Hz
Main unit
  • Bandwidth
    600 — 2900 Hz (600 — 2400 Hz reduced voice quality)
  • TX loss
    < 30dB
  • S/N ratio
    > 10dB
  • Drift
    < 100 Hz
  • DC voltage
    9 — 30 V
  • AC voltage
    110/220 V AC ±20%, 45-65 Hz (switch-selectable)
  • Power
    12 W (standby < 100 mW)
  • Temperature
    -10°C to +60°C (storage: -20°C to +80dgC)
  • EMC
    CE-03, RE-02, MIL-STD 461B, class A1
  • Dimensions
    256 x 225 x 78 mm
  • Weight
    3200 grams (with AC PSU: 4200 grams)
Remote control
  • Dimensions
    152 x 100 x 32 mm
  • Weight
    500 grams
  • MDF-100
    Mounting kit
  • MDG-100
    Gooseneck (for remote control unit)
  • ACP-250
    Battery supply cable
  • ACC-123
    AC mains cable
  • CAS-250
    System interface cable
  • AFC-250
    Audio cable
  • RCC-250
    Remote control cable
  • TEP-250
    Service/Test plug
  • PAH-250
    Mounting hardware
  • TED-250
    Diagnostic test module
  1. MC68000 16-bit microprocessor, datasheet
    Motorola Inc., 1993. Freescale.

  2. IM6402 UART, datasheet
    Intersil, General Electric. Date unknown.

  3. MC14404 CODEC, datasheet
    Motorola Inc., 1995. Freescale, NXP.
  1. HC-250 Operating Instructions (English)
    3B823. Crypto AG.

  2. HC-250 Installation Instructions (English)
    3B866. Crypto AG.

  3. HC-250 Technical Drawings (English)
    3B866-Supplement. Crypto AG.
  1. Crypto AG, Company Brochure, Crypto Products
    1992. 8 pages.

  2. SAS und Chiffrierdienst, HC-250
    Retrieved January 2020.

  3. Crypto Museum, Operation RUBICON
    February 2020.

  4. Mario Petschke, Circuit analysis of the HC-250 CPU (German)
    MfS - Abt. XI, Nr. 403. 28 April 1986. Obtained from BStU [5].

  5. Bundesbeauftragte für die Stasi-Unterlagen (BStU) 1
    Federal Commissioner for the Stasi-Records.
  1. Full name: Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes der ehemaligen Deutschen Demokratischen Republik (DDR) — Federal Commissioner for the Records of the State Security Service of the former German Democratic Republic (GDR) — officially abbreviated to BStU.

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Crypto Museum. Created: Tuesday 21 January 2020. Last changed: Monday, 10 February 2020 - 15:42 CET.
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