GCHQ hid Britain's first portable encrypted phone inside ordinary briefcases

In 1980, a GCHQ engineer known only as Mike bought two ordinary briefcases from a Cheltenham department store, took them back to his lab, tore out the insides and stuffed them with the latest technology. The result was codenamed Brahms: the UK's first portable encrypted communications system, built to let high-ranking officials talk securely.

Secure speech was not new — in World War Two, UK-US leaders needed massive machines like Sigsaly, with London's sitting permanently in the basement of Selfridges — but by 1980 new technology made a portable device possible, and therefore useful in a crisis for a wider group of people.

The machine looks like a normal telephone handset with a button at one end. Press it and speech becomes digital digits, scrambled by an encryption key held on paper tape in the briefcase and changed every day, then sent down an ordinary phone line; anyone intercepting hears only a digital hiss. Only another briefcase with the same key tape can unscramble it. It was slow — 2.4 kilobytes per second, one speaker at a time — and had one flaw Mike apologises for to this day: 'ladies' voices did not come out very well, because of the high-frequency.'

Brahms' main customer was the UK's first female prime minister. For its first foreign test, Mike was made a temporary Queen's Messenger — the machine got its own airline seat — and delivered it to the Alpine castle where Margaret Thatcher was on holiday; at the castle he was offered a gun, and declined.

It shrank room-sized secure speech into two everyday briefcases, making encryption something an official could carry, not something they visited.

The disguise is the security: nothing about the handset or case signals that it scrambles government calls.

Daily paper-tape keys meant a captured machine revealed nothing about yesterday's or tomorrow's calls — with written instructions to burn, or worst case eat, the tape.

It was used where it mattered: Thatcher discussed Falklands rules of engagement on it, and GCHQ phoned intelligence in fast through 6,000 wartime reports.

Security that must travel should look like everything else: disguising capability inside ordinary objects lowers the barrier to use, and daily key discipline does the rest.

Brahms served through the 1982 Falklands War — Thatcher used it to discuss rules of engagement with the Ministry of Defence ahead of the sinking of the General Belgrano, and GCHQ's 24-hour intelligence office phoned reports in over it; women on shift were initially told not to use 'a men's toy' until a small-hours call left no one else to answer. Mike's identity remains secret 40 years on.