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PSTN Phone Encryptor

The HC-2203 is a PSTN telephone encryptor, developed by Crypto AG (Hagelin) in Switzerland and was introduced in the early 2000s. It can be connected between any ordinary telephone set and an analogue line and comes with PTT-approval for most countries. It is compatible with the HC-24x3 secure GSM phone. The HC-2203 is still available from Crypto AG today (2017).

The image on the right shows a typical HC-2203 unit. It is a fairly compact device, housed in a sturdy die-cast aluminium enclosure. It needs an external power supply unit (PSU) between 12 and 32 Volt and is connected in between a standard analogue telephone set and the line.

The HC-3302 features a rubber key pad with 17 buttons, 3 status LEDs and a clear 4-line LCD display. Inside the unit is a Crypto AG security module, which consists of a PCMCIA card with custom-made crypto hardware. At the front is a slot for a standard smart-card (shown here).
HC-2203 with key card

The HC-2203 can handle secure data transmissions at speeds between 2400 and 19200 baud with RTS/CTS handshaking. For full-duplex voice calls, a data speed between 2400 and 9600 baud is automatically selected, depending on the quality of the analogue phone line. At 9600 baud, speech legibility is extremely good. Unlike the older HC-3300 crypto phone, the HC-2203 is suitable for use over satellite, allowing as much as two hops in each direction.

It is extremely easy to install an HC-2203 as it can be used with virtually any existing analogue setup. All connections are at the rear of the unit. From left to right, there are connectors for AUX (firmware updates), DATA (V.24 serial port), POWER (24V DC), LINE (analogue PSTN) and PHONE.

HC-2203 with key card Controls Entering a key card Rear view Raising the flap Pressing the emergency clear button (ZEROIZE) Taking out the security card Hagelin HCM-2000 security module, containing the tempter-proof cryptographic processor.

Key management
Key material for the HC-2203 can be handled in a variety of ways. For large organisations, keys are usually managed with the KHC-2000 Key Handling Center (KHC). Alternatively, a CSC-1000 smart card can be used to transfer or clone the keys from another HC-2203 unit. Furthermore, all keys can also be entered by the user directly on the keypad.

For encryption, the proprietary HCA-480 crypto algorithm is used in combination with Customer Managed Profiling (CMP), offering a variety of over 10506. The Communication Key (CK) is 128 bits long and is used to generate a key stream with a period of more than 1028 years. A total of 999 CKs can be stored in the unit's memory.

In case of an emergency or compromise, the keys can be deleted from memory, by raising the metal flap at the rear of the unit and pressing the emergency button with a sharp object.
Entering a key card

The HC-2203 can handle keys in three different ways. First of all, it handles classic direct symmetrical keys, in which case the key for encryption and decryption is identical and the full key needs to be distributed. In addition, the so-called derived symmetrical key is supported, in which case a valid key is calculated from a simpler key or pass-phrase. On top of that, it also supports the more modern asymmetrical keys, commonly referred to as Public Key Encryption (PKE).

All cryptographic functions are handled by a purpose-built tamper-free security module that is hidden inside the HC-2203. This security module takes the shape of a standard PCMCIA card that is mounted in a suitable slot on the HC-2203's mother board.

The image on the right shows a HCM-2000 security module. At the heart of this module is Crypto AG's proprietary Security Processor. Classified data never leaves the security module and all crypto keys are stored encrypted, using a unique Tamper Resistant Key (TRK).
Hagelin HCM-2000 security module, containing the tempter-proof cryptographic processor.

The HC-2203 is a state-of-the-art product that is extremely well-built. After removing the outer plastic shell, a metal enclosure is revealed. After removing a series of bolts, the unit can be separated in two halves. The bottom part contains the analogue interfaces (line, phone and data), whilst the other half contains the logic and the controls.

The motherboard (or: Management Board as it is called) has components at both sides. The top surface contains the Motorola 68000 central processing unit (CPU) and two DSPs: one for transmission and one for reception (full-duplex). These DSPs are used for the unit's vocoder. They are implemented as two identical daughter cards that are plugged into the mother board.

At the underside of the mother board, is the PCMCIA slot for the MCM-2000 Security Module and a XILINX Field-Programmable Gate Array (FPGA) containing most of the logic circuitry.
The two DSP-boards

The PCB is designed in such a way that it can hold a total of 4 DSPs and 2 security modules. This is clearly visible on an older version of the HC-2203 mother board, that has two PCMCIA slots at the bottom. The upper side of that mother board has connectors for 4 DSPs (only two are fitted here). It is possible that a fully populated unit could be used on two lines simultanously.

HC-2203 after removing the cover Modem board detail HC-2203 Interior 68000 Processor The two DSP-boards Later version of the main board, featuring just one PCMCIA slot. Bottom view of the older version of the main board, featuring two PCMCIA-slots, for two security cards. Main board with two DSP-sub-boards
For large companies, foreign office operations, embassies, politicians, etc., travelling around the world, Crypto AG developed this mobile office that allowed the small HC-2203 to be used over Inmarsat BGAN satellite links. The system is packed in a strong Peli Case®, together with an Inmarsat BGAN terminal, antenna's, cables, etc.

The image on the right shows an example of a BGAN satellite link with an HC-2203 at its heart. Also in this setup is a HC-2423 Secure GSM and a breakout box to create a small PSTN network.

Photograph kindly donated by the Belleque Organization [4]. Note that the HC-2423 Secure GSM phone has been discontinued and is no longer available from Crypto AG (2016).

Help required
In August 2011, we acquired a set of HC-2033 PSTN phone encryptors. For exhibitions, we would like to be able to use the set and demonstrate what an evesdropper would hear. Although both units appear to be operational, we don't know how to operate the units, as we don't have a manual. If you know more about this device, or if you have a manual available, please contact us.

  1. Crypto AG, HC-2203 PSTN Encryption
    Datasheet, 2 pages, English. 2007.

  2. Crypto AG, Secure telephone via classic and IP networks
    HC-2203 full-colour brochure, 6 pages, English. 2008.

  3. Crypto AG, Total Information Security
    Presentation of the HC-2000 series, including the HC-2203. 2000.

  4. Belleque Organization, Image of HC-2203 Inmarsat BGAN setup in Peli Case
    Received 7 February 2017. All rights reserved. 1

  5. Inmarsat, Using PSTN Encryption HC-2203 over GBAN
    Version 1, 3 September 2009.
  1. Permission is given for non-commercial use, provided that copyright is credited to the owner of the image (Copyright 2017, Belleque Organization).

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Crypto Museum. Created: Sunday 21 August 2011. Last changed: Tuesday, 07 February 2017 - 07:43 CET.
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