l4sfdrx

490 GCHQ GOES GLOBAL
to unlock the code, and without the paraphernalia of a government
courier system, distributing the key safely and without
interception was a problem. However, the mavericks now made
a breakthrough. The most common analogy used to explain it
is a series of padlocks. The sender, who we will call 'Alice',
secures her message to her friend 'Bob' with a cypher that works
like a padlock to which Bob does not have the key. When Bob
receives it, instead of trying to open it, he adds a second padlock
that depends on a cypher of his own devising, and sends it back
to Alice. Alice then removes only her original padlock and sends
it back to Bob, by which time it is only secured by Bob's padlock.
Bob can now open the box and read the message. They have
communicated securely, yet there has been no key distribution. 8
This was a revolutionary breakthrough. The arrival of Public
Key Cryptography triggered a veritable war between civillibertarians
and the code-breaking agencies. For the mavericks, the
possibility of email secrecy and anonymous web activity offered
the prize of a return to the golden age of privacy for the citizen.
For the sigint agencies, the military and the police this conjured
up a world in which criminals, drug dealers and terrorists would
be able to avoid the interception of their communications and
encrypt what was on their computers. The double irony was
that the global telecommunications revolution that had helped
to bring all this about was also placing the sigint agencies under
growing pressure from their own governments to assist with
secure e-commerce. Some time after his retirement, Sir Brian
Tovey, a former Director of GCHQ, explained the dilemma:
*
The question is: how in the world does one reconcile these
two How does one on the one hand assure industry that
its communications are confidential and reliable, and how
on the other hand is Government under these very carefully
defined circumstances to continue to derive important
information, be it about drug running, terrorism et
cetera, from the interception of communications ...
*