COPElAND | 185
based himself there for the next two months.^13 The imposing thirteen-storey Bell Labs building
was on Manhattan’s lower West Side, close to the Hudson waterfront and a short stroll from
the gay bars, clubs, and cafeterias of Greenwich Village.^14 New York’s relatively open gay com-
munity must have seemed a million miles from Bletchley Park, where Turing kept his sexual
orientation to himself.
Bell Labs was developing a speech encryption system based on a voice synthesizer called
the ‘vocoder’. Speech encryption was cryptology’s new frontier. If speech could be encrypted
securely, then top-level secret business could be conducted person to person, by radio or even
by telephone: this was a more natural way for military commanders to communicate than by
written text. In addition, interactive voice communication was less open to misinterpretation
and to the perils of incompleteness. The Bell Labs system, codenamed SIGSALY, was used by
America and her allies from 1943 to 1946. Turing may have contributed some finishing touches
to the SIGSALY system during his two months at Bell Labs.
The Bell Labs vocoder lives on as a musical instrument; anyone who has listened to the music
of T-Pain, Herbie Hancock, Kraftwerk, or the Electric Light Orchestra will have heard its weird
and unearthly sound. Today’s vocoders are not much larger than a laptop, whereas the original
1943 model occupied three sides of a room and consisted of a number of cabinets each taller
than Turing himself.^15 SIGSALY was about the size of Colossus: Turing decided to miniaturize
speech encryption.
Thinking small
Once back in England Turing set up an electronics lab in a Nissen hut at Hanslope Park,
a Buckinghamshire country house situated a few miles from Bletchley Park.^16 Nowadays
Hanslope Park is one of Britain’s most secure sites and home to HMGCC (Her Majesty’s
Government Communications Centre), where, in the Turing tradition, mathematicians,
engineers, and programmers supply Britain’s intelligence spooks with specialized hard-
ware and software. At Hanslope Turing designed the portable voice encryption system that
he named ‘Delilah’; it consisted of three small boxes, each roughly the size of a shoebox
(Fig. 18.1).
Turing’s talent for electronic circuit design blossomed in his Hanslope laboratory. Tommy
Flowers also had a hand in this new and highly secret project.^17 He and Turing spoke each
other’s language. ‘Turing had the reputation of being practically incoherent in explanation’,
Flowers said in an amused way—yet he himself never had any trouble at all understanding
Turing.^18 ‘The rapport was really quite remarkable’, he remembered.
The surviving blueprints for Delilah, each the size of a desk and still, after all these years,
bright powder-blue in colour, depict the complex electronic system in detail.^19 Its method of
encrypting speech was analogous to the way that the Tunny machine encrypted typed text (see
Chapter 14). Tunny added obscuring key to written words, while Delilah added obscuring key
to spoken words: in Delilah’s case, the key was a stream of random-seeming numbers. The first
step in the encryption process was to ‘discretize’ the speech, turning it into a series of individ-
ual numbers: each number corresponded to the voltage of the speech signal at that particular
moment in time.^20 Delilah then added key to these numbers, creating the enciphered form of
the spoken message. This was then automatically transmitted to another Delilah at the receiv-
ing end of the link.