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AT&T Corporation
American Telephone and Telegraph Company

The American Telephone and Telegraph Company (AT&T) was at one time the largest telephone company in the world. Starting life as Bell Patent Association in 1874, the company enjoyed a monopoly throughout most of the 20th century. In 1984, after a series of antitrust investigations, AT&T was split into seven separate companies, some of when were re-merged later. More...   
AT&T logo. Image via Wikipedia.
AT&T cryptographic products on this website
AT&T/Lucent 1100 STU-III secure telephone unit AT&T/Lucent 4100 crypto phone (Type 4) AT&T TSD-3600 Telephone Encryptor Gretacoder GC-524 64 Kb/s serial link encryptor (Gretag)

In the late 1980s and the early 1990s, AT&T acquired a number of other companies, some of which were later sold-off again. One such company was Gretag in Regensdorg (Switzerland) who made link encryption devices. This company was later sold to IRE. After AT&T was broken up into separate companies, various divisions were sold and resold to other companies, which is why the cryptographic products were later sold by Lucent Technologies and finally by General Dynamics.

 More about AT&T

1100 STU-III
In 1987, the US National Security Agency (NSA) developed the STU-III crypto phone, and allowed several manufacturers to build it. The 1100-series was AT&T's contribution to the project.

It was introduced in 1992 as the successor to the rather bulky Security Plus and came in a number of variants.

 More information
  
AT&T STU-III with CIK installed

4100 secure phone
The 4100-series was a cut-down version of the STU-III phone (1100), with NSA Type 4 encryption, that was suitable for multinational corporations and foreign governments.

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AT&T/Lucent STU-III phone (model 4100)

TSD-3600
The 3600 series was a small box that could be inserted between a regular phone and the line, in order to convert it into a secure voice system. It was an NSA Type 3 product that was intended for the (national) civil market.

There were several versions, indicated by a prefix and a suffix to the model number. Some versions of the TSD-3600 (E and S) contained the famous Clipper Chip.

 More information
  
AT&T TSD-3600 phone encryptor

GC-524
In 1991, Swiss crypto manufacturer Gretag was taken over by AT&T. At the time, Gretag was selling its line of link encryption systems, mainly for use by banks. For several years, the Gretag products were sold in the US by AT&T.

The Gretacoder 524 was a link encryption device for serial signals, with a transfer speed of 64.000 bits per second.

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Leftmost plug-in

References
  1. Wikipedia, AT&T Corporation
    Retrieved March 2013.
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Crypto Museum. Last changed: Tuesday, 26 May 2015 - 12:35 CET.
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