Some older and newer articles on this weblog that are of current interest:

February 19, 2013

President Reagan using a STU-II telephone

Here we see a great and very rare, maybe even unique picture of former US president Ronald Reagan using a STU-II secure telephone:

President Reagan making an early morning telephone call regarding the invasion of Grenada
(Photo: Reagan Library, October 22, 1983)

In this picture we see president Reagan making a phone call to his staff regarding the invasion of Grenada. Because he was staying at the Eisenhower cabin on the Augusta National Golf course in Georgia, it was necessary to create a secure telephone line with the White House.

This was done by installing a STU-II, which was the second generation Secure Telephone Unit (STU). This system was introduced by the NSA in the early 1980s, and replaced older systems, like the extremely bulky KY-3, and was the successor to the STU-I.

In the picture we see the STU-II telephone, with handset, a normal keypad, some indicator LEDs and three extra buttons at the bottom, for selecting secure or nonsecure mode. This phone only acted as terminal or user interface, because the actual encryption system (crypto designation: KY-71) was located in a large metal cabinet, with which it was connected through a thick 9-way cable. The STU-II was built by ITT with Northern Telecom as a sub-contractor.

The same room with left to right: national security advisor Bud McFarlane,
secretary of state George Shultz and president Ronald Reagan.
The STU-II secure phone is on the table at the far right.
(Photo: Corbis)

Additionally, a reader of this weblog told us that during presidential roadtrips the STU-II was transported in aluminium transit cases with a packed weight of 170 lbs. Each case contained one KY-71 (the crypto engine), one HYX (the handset) and two ZAMX (unknown).

As of 1987, the STU-II was replaced by the much smaller STU-III, which was a secure phone that consisted of one single desktop device only and had much better speech quality. This new phone became available for president Reagan by the end of his second term:

President Reagan using a Motorola SECTEL 1000 version
of the STU-III secure telephone program
(Photo: NSA, date unknown)


JC said...

Your description of the wall-mounted component of the STU-II is somewhat inaccurate. It was more than an crypto unit, but also included voice codec and modem functions.

I was the chief designer of the Quintrel processor that implemented in software the codec and modem and 1/3 of the crypto. (The crypto consists of two encryptors and one decryptor.)

Historically, scrambling of analog voice was attempted, but could not be as secure as digital encryption. For years, the military applied digital encryption, but at 64,000 bits/sec. That was too high a rate for the civilian phone network.

The development of algorithms for encoding voice signals at rates such as 2400 bits/sec made it possible to achieve secure voice connections on the civilian phone network.

JC said...

I meant to say that the military applied digital encryption to digitized voice.

The STU-II was designed before there were one-chip signal processors (that contained one-step multipliers). John Mick (of AMD) and I designed the first one-chip 16x16 multiplier (the Am2516). The STU-III was smaller because it was designed after one-chip signal processors became available.

P/K said...

Thank you very much for these interesting additions!