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Hagelin HC-520
Portable off-line cipher machine · CRYPTOMATIC

HC-520 is a portable electronic off-line cipher machine for text-based messages, introduced in 1977 by Crypto AG (Hagelin) in Zug (Switzerland). It is part of the HC-500 CRYPTOMATIC family, which was the successor to the H-460 — the first electronic cipher machine made by Crypto AG. The HC-520 is often seen as a modern electronic alternative to the portable mechanical CD-57. The device was developed by Siemens and uses an NSA-developed cryptographic algorithm [7].

The device measures 245 x 129 x 44 mm and weights 976 grams (batteries not included). It is powered by a 6V battery pack – installed behind the display – or by an external adapter which can be attached to a recessed DB9 socket at the rear.

User interaction is via a 38-button rubber key­pad and an 11-digit alphanumeric LCD display that is divided into three sectors. The image on the right shows the civil variant of the HC-520, which has a cream upper case shell. It was also available in (military) green, but apart from the colour, both variants are believed to be identical.
  
HC-520 with cover open

The cryptographic algorithm is implemented entirely in software, and uses proprietary non-linear functions. Although on other Cryptomatic devices — such as the HC-550 — this software runs on a general purpose Motorola 6800 micro­processor, the HC-520 is built around an ultra low-power 12-bit DEC PDP-8 compatible CPU, with 6Kb of RAM and the firmware stored in masked ROMs. At least two versions of the firmware are known 1 and variants were made for different customers.

Text encrypted on the HC-520 was readable 2 to the NSA. The HC-520 was developed between 1975 and 1977 – at a time when Crypto AG was jointly owned by the BND and the CIA – and was intended as a competitor to the Gretacoder 905 of the Swiss firm Gretag, which was unreadable.

It was hoped that customers would prefer the (readable) HC-520. The device was in production until at least 1981, during which time ~ 700 units were made [2]. Many of them were sold to South-American countries like Argentina [7]. The introduction price was 5000 Swiss Francs 3 [2].
  
Gretacoder 905 aside the HC-520 of Crypto AG (Hagelin)

The HC-520 was introduced in 1977, hot on the heels of the HC-570; the first of the 500-series. The range was extended in 1978 with the HC-550 – a teleprinter variant – and 1981 with the HC-530 – a briefcase variant. In 1987, the HC-520 was succeeded by the popular HC-5200 series.

  1. During the 1980s a new batch of HC-520s was produced, with an improved algorithm.
  2. In this context, readable means that the cryptographic algorithms could be broken by the NSA. Also known as friendly. In contrast: algorithms that are not breakable by NSA, are called unfriendly or unreadable.
  3. 5000 Swiss Frances converts to approx. 3250 Euro (2009).

HC-520 with cover closed
HC-520 with cover open
HC-520 with cover open
Battery pack removed
Battery back - top view
Rear view
HC-520 with accessories
Upper case shell removed
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HC-520 with cover closed
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HC-520 with cover open
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HC-520 with cover open
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Battery pack removed
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Battery back - top view
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Rear view
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HC-520 with accessories
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Upper case shell removed

Features
The diagram below gives a quick overview of the features of the HC-520. All controls are at the top surface, of which the largest part is taken by the 38-button keypad. The black keys are for entering numbers, letters and punctuation marks, whilst the red keys are for the functions. The two buttons at the top left — OFF and ON — control a bi-stable relay, which connects the main battery to the device. If no key is touched for a certain while, the device enters SLEEP mode.


Behind the keypad is an 11-digit alphanumeric liquid crystal display (LCD). It is divided into three segments, of which the first one – a single digit – shows the current mode of operation. When the device is first switched on, it shows the letter B which means that the Basic key must be entered.


The other two segments represent one 5-character group each. This is how the message will be formatted. When entering text, the letters will scroll into display from the right, as shown in the image above. The device has a total RAM memory of 768 bytes, of which 590 bytes are reserved for the message. Behind the display is a hinged lid that can be closed to protect the display and the power buttons. When switched off, the message will be retained for at least three months [A].

Function keys
  • OFF
    Power off
  • ON
    Power on
  • CLR
    (+ON) clear basic key
  • Shift
  • RCL
    Recall
  • I
    Input
  • C
    Cipher
  • D
    Decipher
  • ADV
    Advance
  • COR
    Correction
  • Newline
  • Separator (Shift-Y)
  • III
    Space
Modes
  • B
    No basic key present — enter basic key
  • I
    Start position for entering input — select c or d
  • Ic
    Cipher input mode — enter plaintext
  • Id
    Decipher input mode — enter ciphertext
  • F
    Memory full — continue with ADV or SEP
  • R
    Replay — allows checking and editing
  • X
    Text correct mode
  • M
    Enter message key
  • C
    Cipher mode — ready to produce ciphertext
  • D
    Decipher mode — ready to produce plaintext
  • E
    Error
Compatible machines   Cryptomatic 500
Desktop model
Pocket version, resembling a calculator
Suitcase version
Desktop model, based on Siemens T-1000
Desktop model, based on Siemens T-1000
Encryptor for computer signals (1200 baud serial)
Similar machines   not compatible with HC-520
Gretacoder 905, portable electronic cipher device (1976)
Datotek DH-26 portable message encryptor (1977)
Mils PCCM-4000 (late 1970s)
Telesecurity Timmann (TST) PPC-19 (late 1970s)
Known custom variants
  • HC-520-001
    Europe
  • HC-520-003
    South America 1
  1. Several units were found in Argentina, which were all retrofitted with the improved algorithm.




Hagelin HC-520 with accessories

Parts
Carrying case
HC-520 portable cipher machine
Plastic card with instructions
Removable battery pack
External battery charger
Internal backup battery
Instruction manual
Storage case
Most HC-520 devices were supplied in a leather storage case, such as the one shown here. It protects the device against dust and damage, and has space for the plastic instruction card.

The storage case is padded and has a zipper that goes all the way around, much like on a wallet. Although it provides good protection for the cipher machine itself, it is not recommended to store the fragile instruction card with it, as its plastic may have become brittle over time.

  
Leather storage case

Cipher machine
The actual cipher machine itself measures 245 x 129 x 44 mm, and fits snugly inside the leather storage case shown above. During transport, the LCD display and the ON/OFF keys are protected by a hinged plastic lid, so that the device can not be switched on accidentally.

The impact-resistant case is made of durable plastic. Although the surface will accumulate dust over time, it is easily cleaned. Despite its high age (well over 40 years), the plastic of the unit shown here is still in immaculate condition.

  
HC-520 with cover open

Instruction card
Although the HC-520 is easy to operate, it is necessary to follow a rigid set of instructions, which are difficult to remember. For this reason, the device was supplied with a clear and detailed user manual, which can be downloaded below.

In addition, a plastic instruction card with a so-called flow chart was supplied with each set. This double-sided card was available in several languages. The one shown here is in English.

 Ciphering instructions
 Deciphering instructions

  
Instruction card

Battery pack
The device is normally powered by a battery pack that can be installed behind the display. It is held in place by two large bolts at the bottom of the case. Loosening these bolts allows the battery pack to be removed upwards.

The battery pack has space for 5 AA-size pen­light batteries. It was usually filled with five rechargeable 1.2V NiCd cells (6V), but it is also allowed to use standard 1.5V dry batteries (7.5V) although these can not be recharged.

  
Battery pack - bottom view

Battery charger
The HC-520 came with a mains adapter which was suitable for any AC mains voltage between 90V and 230V. The adapter will be missing from most surviving units, but can be replaced by any small power adapter with an output of 7.5V DC.

The image on the right shows the original power supply unit of the HC-520. Thanks to Klaus Kopacz for providing this image [6]. When using NiCd bateries, the voltage from the adapter will be sufficient for charging them as well.

As the adapter is missing from our collection, we are using a simple two-wire cable to connect the device to an external PSU. The pinout of the power socket in provided below.

  
Original HC-520 PSU (PSM-107-001). Photograph kindly provided by Klaus Kopacz [6].

Backup battery
In order to retain the cryptographic key when the device is switched off and the batteries are re­moved, the internal CMOS RAM is powered by a long-life backup battery on the processor board.

Although the expected lifespan of this battery was six years, it was recommended to have it replaced every 3 or 4 years to prevent damage caused by leakage [A]. It is doubtful whether any customers have done so however, as most of the surviving units were found with internal damage caused by leaking backup batteries.  More
  
Internal backup battery

Instruction manual
The device was supplied with an extensive 30+ page instruction manual that was available is several languages — including English, German and Spanish — to serve all parts of the world.

The image on the right shows the cover of the German language instruction manual, which is available for download below.

 Download the German manual
  
German HC-520 manual. Click to download.

Leather storage case
HC-520 in leather wallet
Battery pack removed
Battery back - top view
Battery pack - bottom view
Bottom side of the original PSU. Photograph kindly provided by Klaus Kopacz [6].
Instruction card
Instruction card
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Leather storage case
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HC-520 in leather wallet
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Battery pack removed
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Battery back - top view
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Battery pack - bottom view
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Bottom side of the original PSU. Photograph kindly provided by Klaus Kopacz [6].
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Instruction card
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Instruction card

History
The HC-520 was developed at a time when the company – Crypto AG – was jointly owned by the German Bundesnachrichtendienst (BND) and the American Central Intelligence Agency (CIA). The two intelligence services had purchased the company in 1970, with the intention to get control over the cryptographic algorithms and – indirectly – Crypto AG's customers. This secret project was known as Operation RUBICON and turned out to be extremely effective [7].

The big brother of the HC-520 – the HC-570 – was the successor to the ill-fated H-460, that had been introduced just before BND and CIA took over Crypto AG. It featured a shiftregister-based cryptologic that had been designed by NSA in 1966, in such a way that messages were readable 1 to them. It was decided that Crypto AG should sell high-end cipher machines that could compete with the designs from other manufacturers — such as Gretag — that were not under control [7].

The HC-520 was developed at Siemens in München (Germany) and features a Siemens custom Liquid Crystal Display (LCD). The cryptographic algorithm was supplied by the American National Security Agency (NSA), and came in two flavours: readable and unreadable. Unreadable versions were for friends: NATO countries, plus Switzerland and Sweden. Readable versions were sold to all others, with very few exceptions. Apart from NSA, they were also readable by the Zentralstelle für das Chiffrierwesen (ZfCh) — the German codebreakers. The machine was introduced in mid or late 1977 and was intended as a competitor to the Gretacoder 905, which was unreadable [7].

HC-500 Crisis
In February 1979, less than two years after the introduction of the HC-500 series, CAG-employee Jürg Spörndli, discovered that it was possible to break the machine with just 100 characters of known plaintext, probably after attending a seminar by American mathematician Martin Hellman. Although theoretical, it proved that the cipher was prone to a known plain-text attack (KPTA).

To Crypto AG it was bad news, as the company couldn't afford another debacle after the H-460 crisis. In two years time, the HC-500 series had become Crypto AG's flagship, of which more than 1700 had already been sold worldwide.

The original algorithm had been developed by NSA's Peter Jenks, and was intended to last for at least 20 years. But CAG's Jürg Spörndli had now exposed a weakness, which urgently needed to be fixed before customers discovered it them­selves. At NSA, Dave Frasier designed a drop-in fix that would defeat the known plaintext attack.
  
The three ROMs in an early prototype of the HC-520

The revised algorithm 3 was considerably more difficult to break by NSA and ZfCh, but the effort was worth every penny. The drop-in replacement consisted of three ROM chips that had to be soldered onto the processor board of the HC-520, after the existing ones had been removed.

The image above shows the three ROMs in sockets, on an early prototype of the processor board. The machines that had been delivered to the Argentines (and others) did not have sockets, and had to be reworked by a skilled engineer.

A few months later, mid-1979, Peter Jenks died of cancer and Dave Frasier committed suicide. It was one of the greatest losses at NSA during the course of Operation RUBICON. Jenks and Frasier had been the architects of the NSA-developed (rigged) cryptologics that were used in CAG products. To lose them both was devistating.
  
Replacement ROMs soldered to the reworked processor board

Around the same time, the Argentine Navy discovered the weakness 2 in the cipher algorithm as well, and demanded an immediate explanation. Crypto AG's CEO, Heinz Wagner, was invited to Buenos Aires, and was confronted with the attack, wich was similar to the one by Jürg Spörndli. Wagner, being afraid to be thrown off an airplane, 3 immediately offered the NSA-fix. But he was lucky. They accepted the fix, but what the Argentines really wanted, was the ability to attack their neighbouring countries, and the promise that CAG would not tell them about the vulnerability [7].

The matter was settled more permanently in 1981, after a newly recruted cryptomathematician — codenamed ATHENA — completely redesigned the cryptologic 4 so that it seemed much more robust and could withstand advanced known plaintext attacks. In reality though, it was just as weak as its precedessor, allowing NSA and ZfCh to continue to read intercepted messages [7].

 More about Operation RUBICON

  1. In this context, readable means that the cryptographic algorithms could be broken by the NSA. Also known as friendly. In contrast: algorithms that are not breakable by NSA, are called unfriendly or unreadable.
  2. The CIA suspected that Peter Frutiger – a disaffected former employee – might have tipped them off, but this was never proven.
  3. This refers to the so-called death flights during the Argentine Dirty War (1974-1983), in which dissidents and enemies were dropped to their death from aircraft above the ocean.  Wikipedia
  4. After the upgrade, the length of the Basic Key (BK) was increased from 10 to 20 letters, but is not reflected in the manual or the instruction chart. Existing HC-520-003 units were retrofitted with the new firmware.

The three ROMs in an early prototype of the HC-520
The three ROMs of the HC-520 that contain the firmware
Replacement ROMs solderd in place of the old ones
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The three ROMs in an early prototype of the HC-520
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The three ROMs of the HC-520 that contain the firmware
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Replacement ROMs solderd in place of the old ones
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Hagelin HC-520 interior seen from the rear

Interior
The HC-520 is housed in a shock-resistant ergonomic enclosure, made of high-quality durable plastic, which consists of a black bottom part and a cream – in the military variant: olive green – upper case shell. In order to access the interior of the device is it necessary to remove the battery by releasing two large bolts at the bottom of the device with a large screwdriver or a small coin.

Inside the battery bay is a small hex bolt that keeps the two case shells together. It also engages the tamper switch. Removing it causes the cryptographic keys to be purged, and allows the upper and lower case shells to be separated.

Inside the bottom case shell, is a stack of three PCBs that rests on the battery spring contacts. The stack can be removed without releasing any screws. At the top is the keypad, which is the smallest of the three boards. It has 38 tactile switches, covered by a water-resistant rubber mat on which the function of each key is printed.
  
Battery compartment with case locking bolt

The three boards are interconnected by means of two single-in-line headers, located at the left and right side respectively, with the middle board acting as the central hub. Each board has a set of metal positioning pins along its side, that mate with holes in the board to which it is fitted.

At the centre of the stack is the display/interface board, which holds the keyboard interface and the display circuitry. This multi-layer PCB has a embedded flex PCB which extends from the far end, ending under the glass of the LCD display.

The LCD is seated in a grey plastic cradle which is curved at the rear side, to prevent the flex PCB from breaking. It is connected to the tracks of the flex PCB by means of two tight-fitted zebra contact strips, and is held in place by two metal retaining clips. It is one of the first LCDs, and was custom-made for Crypto AG by Siemens.
  
Display/interface board

The display/interface board has a conformal coating on both sides, which makes it more robust, but also more difficult to repair. The smaller keyboard is fitted to a row of contact pins at the top side of this board, whilst the board itself it fitted to a green contact header on the lowest board.

At the bottom of the stack is the processor board, which also holds the power circuitry. At the corner of the board is a bi-stable relay that is controlled by the ON/OFF keys on the keypad.

At the center of the board is a 12-bit PDP-8 compatible microprocessor, with a variable clock frequency between DC and 4 MHz. For the first production runs (1977), the Intersil IM-6100 was used, but in later batches (1981) it was replaced by a Harris MI-6100 which is pin-compatible. The firmware is stored in three 4-bit wide Harris MI-6322 masked ROMs (total width of 12 bits).
  
Processor board

At the other side of the processor is the Random Access Memory (RAM), consisting of six Harris MI-6561 256 x 4 bit CMOS RAMs — organised as two sets of three chips each to get a 12-bit wide bus — giving a total memory space of 6 Kbit or 768 bytes, of which 590 bytes are used for storage of the message. The remaining 178 bytes hold the basic key, the message key and some internal (software) values. Power to these RAMs runs via the tamper switch at the far side of the board. When the case retaining bolt is loosened, the contents of the RAM are purged instantly.

Releasing the battery pack
Battery pack removed
Battery compartment with case locking bolt
Case locking bolt (engages tamper switch)
Removing the upper case shell
Removing the boards from the lower case shell
Upper case shell removed
HC-520 interior - three stacked PCBs
The three PCB separated
Tamper switch
Display/interface board
Display/interface board - top view
Close-up of the flex display board
Processor board
Processor board (1979)
Processor board
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Releasing the battery pack
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Battery pack removed
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Battery compartment with case locking bolt
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Case locking bolt (engages tamper switch)
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Removing the upper case shell
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Removing the boards from the lower case shell
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Upper case shell removed
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HC-520 interior - three stacked PCBs
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The three PCB separated
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Tamper switch
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Display/interface board
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Display/interface board - top view
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Close-up of the flex display board
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Processor board
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Processor board (1979)
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Processor board

Block diagram
Below is the simplified block diagram of the HC-520. At the far right is the battery that powers the entire unit. The power circuit is controlled by the ON and OFF buttons on the keypad at the bottom left. It delivers power to the processor board and to the display/interface board, and also generates the clock for the IM-6100 processor, which can be anything between DC and 4 MHz.

HC-520 block diagram

The RAM chips are powered directly from the battery, but the power line is routed via a tamper switch of which the contacts are kept closed by the case retaining bolt. Removing this bolt, cuts to the power to the RAMs and deletes the message and the keys instantly.


Restoration
Although the HC-520 is a small device with a fairly simple user interface, its internals are quite complex, making it difficult to repair a broken device. Nevertheless it is surprising to see that most of the surviving devices still work well after more than 40 years, with only minor issues.

By far the most common problem is damage to the processor board caused by a leaking backup battery. Although it was recommended to have it replaced every three to four years, it is doubtful whether any of the customers have done so, as it required the device to be returned to Crypto AG.

The backup battery is soldered-in at a corner of the processor board, as shown in the image on the right. It holds three cells and is hermetically sealed. Nevertheless, the chemicals from leaking cells always find a way out – especially after 40+ years – and may cause damage to the circuitry.
  
Badly corroded parts due to leaking backup battery

As the battery is close the the power-on and wakeup circuit, the damage may prevent the device from starting up properly. Depending on the amount of leakage and the time that has passed, the damage may vary between hardly visible parasitic conductivity, and corrosion between the legs of the parts or even completely destroyed PCB tracks and solder joints that are no longer solderable.

In most cases, the damage to the processor PCB is reversable, but if it has affected the display & interface board (which is fitted just above it) the chemicals may have penetrated the layers of the board, in which case it will be beyond repair.

In any case it is important to remove the backup battery as soon as possible. Although it can be replaced by a modern alternative, it is better to leave it out altogether to prevent future damage. The device will work perfectly well without the backup cells, although the keys and the message will be lost when the main battery is removed. 1
  
Backup battery removed from the processor board

The image above shows the processor board after the backup battery has been removed. Note that all traces of corrosion must be removed, especially between the legs of the ICs. Also note that the through-plated holes (that connect the tracks at both sides) may have been damaged.

Another frequent failure is the LCD display, that might have been 'eaten away', as shown in the image on the right. This is caused by acid gasses that are emanated from the acetate carrier of the polarising film, in combination with the glue of the reflective foil at the back. This process might have been accelerated when the device has been exposed to high temperatures or high humidity.

In many cases, the display still works, but it will be difficult to see that. After some experiments, we found out that it was possible to repair it, but this requires a steady hand and a lot of patience.
  
Broken display

First, the four screws that keep the LCD in place are loosened. The two metal clamps (above and below the LCD) can now be shifted outwards, so that the glass is freed up. Next, the glass body of the LCD is removed from the plastic cradle, but this has to done very carefully, so that the zebra-strips — that provide the contact between the glass and the flex PCB — are not damaged.

When repairing an LCD, it is important to have a good understanding of its working principle. A detailed description can be found on Wikipedia [5]. It is based on the effect that liquid-crystal changes the polarisation of incoming light, and that it doesn't do that when a voltage is applied.

The heavily deteriorated reflective foil and the remains of the horizontally polarising filter were carefully removed, along with their glue residues at the back side of the glass. As the vertically polarising filter at the front was also in very bad condition, it was decided to replace that as well.
  
Refurbished LCD display (Crypto Museum)

After replacing the two polarising films, and adding a new semi-reflective foil at the back, the contacts inside the cradle were cleaned and the complete glass package was reseated in the cradle. Next, the two metal clamps were shifted back in place and the four screws were tightened.

The result is shown in the image above. The LCD display now produces a crisp and clear image again, just like it did when it was brand new.

Another area that requires attention is the key­board. Although it does not contain any active parts, it may not be repsonding properly, as a result of dirt under its contacts. Repairing it is straightforward, but requires some patience.

First, the rubber key-mat has to be removed, after which the tactile switches become visible. They are embedded in a layer of PCB material.
  
Keypad after removing the spring-contacts

Next, the cellotape that keeps the spring-contacts in place, has to be removed, along with all of its residues. The spring contacts can now be removed and can be cleaned separately, leaving the PCB to expose its inner layer with silver-plated contacts, as shown in the image above. After cleaning the sliver-plated PCB contacts (with a suitable solvent), the spring-contacts can be reseated, after which a couple of narrow cellotape strips should be used to keep them in place.

  1. Unless an external power supply is connected when the battery pack is removed.

Badly corroded parts due to leaking backup battery
Badly corroded parts due to leaking backup battery
Backup battery on the processor board
Internal backup battery
Exhausted backup batteries
Leaking backup battery
Backup battery removed from the processor board
Bi-stable reed relay
Broken display
Broken display with deteriorated foils
Deteriorated contents of the CD display
Refurbished LCD display (Crypto Museum)
Damaged chip on the display/interface board
Close-upof the tactile switches on the keypad
Keypad after removing the spring-contacts
Display and (part of) the keyboard
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Badly corroded parts due to leaking backup battery
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Badly corroded parts due to leaking backup battery
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Backup battery on the processor board
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Internal backup battery
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Exhausted backup batteries
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Leaking backup battery
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Backup battery removed from the processor board
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Bi-stable reed relay
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Broken display
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Broken display with deteriorated foils
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Deteriorated contents of the CD display
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Refurbished LCD display (Crypto Museum)
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Damaged chip on the display/interface board
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Close-upof the tactile switches on the keypad
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Keypad after removing the spring-contacts
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Display and (part of) the keyboard

Liquid-crystal display
The display of the HC-520 is a FAS11101R, which was custom-made by Siemens in Germany. Its construction is shown in the diagram below. The actual LCD is the glass package at the centre. It consists of the liquid-crystal molecules, which are sealed between two etched glass panels. If the sealing breaks, the display is lost, so the glass package should remain a one-piece construction.

The shapes of the segments are etched as electrodes in the upper glass, whilst the lower glass acts as the common electrode. By default (when no voltage is applied) the liquid-crystal rotates the polarity of the incoming light by 90°. When a voltage is applied to the electrodes, the liquid crystal looses this property and lets the light straight through (without rotating its polarity).


By placing a vertically polarising filter in front of the glass package and a horizontally polarising one behind the glass, the light gets blocked locally, whenever a voltage is applied to one or more segments of the liquid-crystal. At the bottom of the stack is a semi-reflecting sheet that reflects the incoming light. It raises the contrast and gives the display its neutral background.

Reset circuit
Over the years, Crypto museum has seen (and repaired) several HC-520 units. Although most units worked well many years after they were decommissioned, there were some that would start properly one moment, and completely freeze when started again (showing all display segements).

Simple reset circuit soldered directly to the legs of the IM-6100

This problem is caused by the fact that the HC-520 does not have a proper reset circuit for the IM-6100 microprocessor, probably in combination with ageing of some parts. In that case, it is recommended to add a simple reset circuit to the processor board, by soldering a 100K resistor and a 1µF capacitor directly to the legs of the IM-6100, as shown in the diagram above.


Connections
Apart from the batteries, the HC-520 can also be powered externally, by supplying 6 to 7.5V DC to the recessed DB9 socket at the rear. This can also be used to charge the batteries. Although it has 9 pins, only two of them are used. Below is the pinout when looking into the socket.

  1. (+) 6V DC
  2. n.c.
  3. n.c.
  4. n.c.
  5. (-) 0V
  6. n.c.
  7. n.c.
  8. n.c.
  9. n.c.
Specifications
  • Alphabet
    Latin (teleprinter) with 52 characters
  • Memory
    590 characters
  • Power
    6 - 7.5 V DC (automatic shut-off when over 8V)
  • Current
    10 mA
  • Dissipation
    60mW (battery)
  • Battery
    5 × 1.2V/0.5Ah NiCd cells (or 5 × 1.5V AA-size dry cells)
  • Duration
    50 hours (200 hours with dry cells)
  • Charge
    15 hours
  • Dimensions
    245 × 129 × 44 mm
  • Weight
    976 grams (without batteries)
  • Temperature
    0° — +50°C (storage: -30° — +70°C)
Keys   initial release
  • Basic
    10 letters → 2610 = 1.4 · 1014 ≈ 247
  • Message
    10 letters → 2610 = 1.4 · 1014 ≈ 247
  • Period
    (25 - 1)5 · (231 - 1)5 = 1.3 · 1054 ≈ 2180
Keys   improved version 1
  • Basic
    20 letters → 2620 = 1.99 · 1028 ≈ 294
  • Message
    10 letters → 2610 = 1.4 · 1014 ≈ 247
  • Period
    (25 - 1)5 · (231 - 1)5 = 1.3 · 1054 ≈ 2180
  1. Around 1978, the cryptographic algorithm of the HC-520 was improved and the length of the BASIC key was increased from 10 to 20 characters. This is not reflected in the manual and the instruction card.

Serial numbers
It is currently unknown how many HC-520 units were manufactured, but according to one source, about 700 units were made [2]. This is likely to be correct. The HC-520-001 prototype in our collection has serial number 043, which could indicate that around 50 prototype units were built.

From another source we obtained a list of serial numbers that were observed in Argentina [3]. Based on the manufacturing codes and serial numbers on these devices, its seems likely that they were sold in two batches: 50 units in 1977 and at least 150 units in 1981 1 . The units that were delivered to Argentina, all carry the designator HC-520-003. Furthermore, the first batch carries the manufacturing code ST 540 614A, whilst the second batch is marked ST 540 688A.

  1. Estimated from observed date codes on the components.

Documentation
  1. HC-520 Bedienungsanleitung 1
    1B606a. Crypto AG. Date unknown.

  2. Instruction card (ciphering) 1
    3K626 (front). Crypto AG. Date unknown.

  3. Instruction card (deciphering) 1
    3K626 (rear). Crypto AG. Date unknown.

  4. US Patent 4,095,046
    Electronic enciphering- and deciphering apparatus in the form of a Pocket Calculator
    Peter Frutiger and Bruno Gemperle, on behalf of AEH.
    Filed 1 November 1976, priority date 11 November 1975.
  1. Around 1981, the cryptographic algorithm of the HC-520 was improved and the length of the BASIC key was increased from 10 to 20 characters. This is not reflected in the manual and the instruction card.

Datasheets
  1. Intersil IM6100 CMOS 12 bit Microprocessor
    Brochure and data sheets. Date unknown.
References
  1. Wikipedia, Intersil 6100
    Retrieved April 2019.

  2. Jerry Proc and contributors, HC-520 by Crypto AG
    Retrieved May 2019.

  3. Anonymous source, HC-520 serial numbers in Argentina
    Crypto Museum, April 2019.

  4. Anonymous former cryptographer
    Personal correspondence, May 2019.

  5. Wikipedia, Liquid-crystal display
    Retrieved May 2019.

  6. Klaus Kopacz, Image of original HC-520 battery charger
    Received May 2019.

  7. Crypto Museum, Operation RUBICON
    February 2020.
Further information
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Crypto Museum. Created: Monday 10 August 2009. Last changed: Sunday, 14 June 2020 - 14:16 CET.
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