Clear and Present Danger

With presidential approval, things moved along smartly. Overseas communications were handled, as always, by the National Security Agency, and only the time zones made things inconvenient. An earlier heads-up signal had been dispatched to the legal attaches in several European embassies, and at the appointed time, first in Bern, teletype machines operating off encrypted satellite channels began punching out paper. In the communications rooms in all the embassies, the commo-techs took note of the fact that the systems being used were the most secure lines available. The first, or register, sheet prepped the technicians for the proper one-time-pad sequence, which had to be retrieved from the safes which held the cipher keys.

For especially sensitive communications - the sort that might accompany notice that war was about to start, for example - conventional cipher machines simply were not secure enough. The Walker-Whitworth spy ring had seen to that. Those revelations had forced a rapid and radical change in American code policy. Each embassy had a special safe - actually a safe within yet another, larger safe - which contained a number of quite ordinary-looking tape cassettes. Each was encased in a transparent but color-coded plastic shrink-wrap. Each bore two numbers. One number - in this case 342 - was the master registration number for the cassette. The other - in the Bern embassy; it was 68 - designated the individual cassette within the 342 series. In the event that the plastic wrap on any of the cassettes, anywhere in the world, was determined to be split, scratched, or even distorted, all cassettes on that number series were immediately burned on the assumption that the cassette might have been compromised.

In this case, the communications technician removed the cassette from its storage case, examined its number, and had his watch supervisor verify that it had the proper number: "I read the number as three-four-two."

"Concur," the watch supervisor confirmed. "Three-four-two."

"I am opening the cassette," the technician said, shaking his head at the absurd solemnity of the event.

The shrink-wrap was discarded in the low-tech rectangular plastic waste can next to his desk, and the technician inserted the cassette in an ordinary-looking but expensive player that was linked electronically to another teletype machine ten feet away.

The technician set the original printout on the clipboard over his own machine and started typing.

The message, already encrypted on the master 342 cassette at NSA headquarters, Fort Meade, Maryland, had been further encrypted for satellite transmission on the current maximum-security State Department cipher, called STRIPE, but even if someone had the proper keys to read STRIPE, all he would have gotten was a message that read DEERAMO WERAC KEWJRT, and so on, due to the super-encipherment imposed by the cassette system. That would at the least annoy anyone who thought that he'd broken the American communications systems. It certainly annoyed the communications technician, who had to concentrate as hard as he knew on how to type things like DEERAMO WERAC KEWJRT instead of real words that made some sort of sense.

Each letter passed through the cassette player, which took note of the incoming letter and treated it as a number from 1 (A) to 26 (Z), and then added the number on the tape cassette. Thus, if 1 (A) on the original text corresponded to another 1 (A) on the cassette, 1 was added to 1, making 2 (B) on the clear-text message. The transpositions on the cassette were completely random, having been generated from atmospheric radio noise by a computer at Fort Meade. It was a completely unbreakable code system, technically known as a One-Time Pad. There was, by definition, no way to order or predict random behavior. So long as the tape cassettes were uncompromised, no one could break this cipher system. The only reason that this system, called TAPDANCE, was not used for all communications was the inconvenience of making, shipping, securing, and keeping track of the thousands of cassettes that would be required, but that would soon be made easier when a laser-disc format replaced the tape cassettes. The code-breaking profession had been around since Elizabethan times, and this technical development threatened to render it as obsolete as the slide rule.