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SHOOTDOWNS, CYPHERS AND SPENDING 217
tromagnetic field, others gave out an acoustic echo that could
travel down a wire for hundreds of feet. Still others caused telltale
fluctuations in the power supply. Even those machines that
did not radiate of their own accord were susceptible to 'interrogation
attack'. This meant that the KGB could potentially
direct a microwave or laser beam at the cypher room, reflecting
back reverberations that might give away the clear text of a
message as it was typed on the keyboard. The only saving grace
was that the danger was confined to a few hundred yards at
most, so the enemy had to get close to the cypher machine they
wanted to listen to.63
Stannard explained that the most awkward issue presented
by Tempest was 'how we may best distribute our responsibilities
for advising our allies, particularly in NATO'. Tempest was
a nuisance in terms of security, but of course it was beneficial
for offensive sigint operations by GCHQ. The British did not
want information about Tempest to spread to 'countries or organisations
from which signal intelligence is required'. Where the
balance of advantage fell depended on the relative importance
attached to either sigint or security. Understandably, perhaps,
there were some arguments between GCHQ and LCSA over this
matter. 64
By the early 1960s the awkward NATO Tempest question was
gradually being resolved. A handbook was provided to the
European allies that explained how to install cypher equipment
so as to minimise radiation risks from Tempest. 65 However, LCSA
emphasised that, within the inner circle constituted by the
British, Americans and Canadians, the standard NATO briefing
had always to be accompanied by 'advice on certain aspects of
the problem which it is undesirable to disseminate to NATO at
large'. This circumlocutory language suggests that Britain was
offering some of its NATO partners incomplete advice, leaving
open certain avenues for exploitation. At the same time, GCHQ
hoped fervently that the KGB was not using the same techniques.
66
At last, after two troublesome decades, Britain's code-breakers