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CVAS III
Secure telephone

The CVAS III was a secure (crypto) telephone that was used for gouvernmental and civil applications in the US. It was developed and built around 1988 by A-O Electronics (later: Infosafe Corporation). Using NSA Type 3 cryptographic algorithms (DES, AES, SHA, etc), the phone was used for unclassified but sensitive information.

The image on the right shows a typical CVAS III phone. It has a white plastic case, similar to that of an ordinary telephone. The area with the controls however, is red in order to indicate the special purpose of this device.

Like most crypto phones, the CVAS III can also be used as an ordinary telephone. All calls, even secure ones, are initiated in clear mode. Once both parties have agreed to switch to secure mode, the SECURE key is pressed. After a 10 to 15 second delay, secure mode is activated and the conversation can no longer be overheard.
  
CVAS III-E Secure Telephone

In order to be able to have a secure conversation, both parties need to use the same cryptographic key. This can be done in two ways. As each key has a length of exactly 16 characters, both parties can use a predetermined key list and type in the same key (using the SET KEY button).

Alternatively, the phone can generate a fully random key and exhange this key with the phone at the other end. In that case, all the user has to do, is press the SECURE button. Both phones then generate a 4-digit verfication code that should be identical. If it is not identical, the quality of the telephone line is below average or the line has been intercepted by a third party.

The Pelicase transit case Contents of the Pelicase The CVAS III as it was packed inside the Pelicase A small amplifier with volume and tone controls, to improve the audio quality. Telephone Line Filter CVAS III-E Secure Telephone The yellow warning label Rear view of the CVAS III

Interior
As the CVAS III is a Type 3 cryptographic product, it doesn't provide protection at the highest possible level. As such it is not built to comply with NSA TEMPEST en EMC requirements. The case is made of plastic and has no shielding whatsoever.

After opening the case, two large stacked PCBs are immediately visible. The are held together tightly by two long connectors; one at either side of the PCB.

The upper board contains the analog parts, the modem, and the (telephone) line interface. All lines to the outside world are connected to this board by means of small brown connectors.

The lower board contains the digital parts, such as the microprocessor, the DSP, the memory, interfaces and the firmware (in EPROM).
  
First look inside the CVAS III

After separating the boards, it becomes immediately visible what methods were used in the late 1980s to protect intellectual property. The text of most of the key components of the phone has been scraped off, so that competitors could not see which technology was used.

First look inside the CVAS III Analog board (component side) Digital board (component side) Close-up of the right half of the digital board The full digital board after removing the metal cooling plate Close up of the Texas Instruments DSP on the digital board A small modification PCB glued to the back of the case Control panel board

Cryptographic Algorithm
Audio is sampled by the CVAS III at 64,000 bits per second and then compressed down to 2400 baud using a Linear Predictive Coding algoritm known as PARCOR. The resulting voice has a slightly synthetic sound, but is still very recognizable and intelligible [1] .

Once the voice is digitized, the digital signal is encrypted using the Data Encryption Standard (DES) encryption algorithm. This algorithm, developed by the National Bureau of Standards, is classified by the NSA as a Type 3 product. The CVAS III-E version of the phone, uses the proprietary EDAS ecryption algorithm, but is still interoperable with the earlier CVAS III models.

About A-O Electronics
A-O Electronics was established in the US in 1985 for the development and production of secure voice encryption devices. They were based in Tucker (Georgia). Early products, such as the MDSS (Multi-Dimensional Security System) [2] introduced in 1987, used frequency inversion (scrambler) for the transmission of voice data. Later systems, such as the CVAS III-e, used real digital data encryption.

Late 1988 the company was renamed to Infosafe Corporation and shifted its focus to PC data security. In the meantime, the company had moved to North Charleston (South Carolina). In 1992, Infosafe ran into financial trouble and several attempts were mounted in order rescue the company. Finally, around 1995, the company closed its doors.

Known addresses
  • A-O Electronics Inc.
    2137 Flintstone Drive
    Tucker, GA 30084
    Phone (0)404-4918044
    USA

  • AOE International
    2137-E Flintstone Drive
    Tucker, GA 30084
    Phone (0)404-9342244
    USA

  • Infosafe Corporation
    3125 Ashley Phosphate Road
    North Charleston, SC 29418
    (Charleston County)
    USA
Help needed
Unfortunately, neither AOE International, nor Infosafe Corporation exist today. As they closed their doors around 1995, not much can be found on the internet. If you have any information about AO Electronics, Infosafe Corporation or any of their products, please contact us.

References
  1. AO Electronics Inc., CVAS III Operations Manual

  2. Network World, 23 March 1987, Device scrambles human speech
    Brief announcement of A-O Electronics' Multi-Dimensional Security System (MDSS).
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Crypto Museum. Last changed: Tuesday, 29 March 2011 - 12:32 CET.
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