Dr Finbow was going through positive agonies, even clenching her fists.
“Now the signals which this equipment is called on to pass are not originated here. Under circumstances which we all devoutly hope will never overtake us, of course, they could be, but currently they come in by landline, scrambled— and then unscrambled on arrival. Here they are monitored and encrypted. Precisely how this encryptment is—”
To Desmond’s surprise Molesey interrupted.
“Sir Andrew, I understood this matter was urgent. There’s no need to explain modern cypher techniques to any of us. We all know you keep a stock of computer-randomised alphabets, and you encrypt each letter of a message using a different alphabet, and you change the group of alphabets you’re working with daily or more often, by prearrangement with the recipient rather than by using a transmitted signal because that in itself might constitute a clue for an unfriendly cryptanalyst.”
Dr Finbow erupted.
“Dr Molesey, I have your dossier almost by heart, and nowhere in it have you admitted that you’ve studied cryptography!”
Molesey looked at her steadily. “Why should I? Every computer designer worth his salt knows the subject intimately. We’ve derived some of our most economical programming techniques from pioneering work by cryptographers.”
There was a short electric pause. During it Desmond found time to wonder why Dr Finbow had hit on the word admitted. And then, sounding cross, Sir Andrew was talking again.
“Well, if you’re that far ahead of me, I’d better turn you over to my deputies, I suppose . . . Mr Hogben?”
With unconcealed relief Hogben stepped forward, tossing back a lock of untidy black hair.
“We’re logjammed,” he said succinctly. “We’ve been working on the problem for”—there was a wall-clock showing GMT and he glanced at it—“about thirty-four hours and we’ve only half-broken the jam. Worse still, this place is on automatic from midnight to five a.m. That means five hours’ worth of traffic both ways is locked solid in the memory banks. We can’t even find out whether the switch from one alphabet group to another took place at the proper time, or whether one hell of a lot of material was all encrypted in the same system, which is exactly what an eavesdropper would be praying for. Nothing’s going in or out through here at the moment, of course; all our embassies were advised immediately when we realised what was wrong. But we can’t find out what did go in and out during those crucial hours, because . . . Oh, take a look for yourselves.”
He punched a quick group on the remote read-in, and at once all four of the display screens started to parade a meaningless jumble of letters, increasing in number until the screens were full and then rolling upward like the credits in a TV programme to make room for more . . . and more . . . and more . . .
Desmond whistled.
“There’s worse,” said the plump Miss Prinkett in a voice far too shrill for her ample build. “Apart from being effectively cut off from our embassies, we can’t get at the data in Store G.”
“Miss Prinkett!” Dr Finbow exploded again.
“Oh, shut up,” Miss Prinkett retorted—which greatly endeared her to Desmond. “These people designed and built the equipment and they’re the ones who have to find out whether there’s a hardware fault. It’s an outside chance, but it has to be investigated. And it’s on record that both Bill Hogben and I objected to the idea of storing any data electronically without a duplicate and preferably a triplicate. Only those idiots in Whitehall got the wind up, and—”
“Miss Prinkett!” Sir Andrew barked. “There were excellent reasons why you were overruled! Matters of policy were involved!”
“What you mean is you’d let a spy get away with it for years and when you caught him at long last you started seeing more of his type under everybody’s desk!”
“It was a sensible precaution—” Dr Finbow exclaimed. But Molesey gave a discreet cough, and they realised what was happening and fell silent.
Sheepishly Sir Andrew said, “I suspect we must all be a little overwrought. Tired, certainly. I myself had no rest to speak of last night, and . . . Well, perhaps you’d like me to rephrase Miss Prinkett’s over-forceful remark. It is true that a top-level decision was taken, following a serious—ah—leakage of intelligence material, to maintain the sole permanent record of certain diplomatic traffic here in these computers. It does now appear the decision was premature.”
“This stuff is what you can’t get at in Store G?” Vizard demanded.
“Well—yes.”
There was a pause. Molesey ended it by saying, “I’d just like to make sure we fully comprehend the problem. Desmond, sum it up as you see it, would you?”
Startled, Desmond sought for words. He found them rapidly enough. After all, logjamming was not a particularly rare phenomenon.
“Well, unless the fault is actually in the hardware, and I agree with Miss Prinkett that’s very unlikely, what’s happened is that there must have been an accidental conflict in programming. Either something’s been miswritten, so the proper command doesn’t produce the results it’s supposed to, or there’s interference between commands belonging to two or even several programmes, and they happen to be incompatible so the machinery can’t choose between them. Given that this gear is used for the encryptment of secret messages, I’d put my money on the chance that two contradictory commands have wound up in identical form.”
As though ashamed of seeming ignorant, Dr Finbow ventured, “Mr Hogben has been saying something of the sort. But I don’t see how commands referring to two different things could possibly take on identical form.”
Desmond licked his lips, preparing—since everybody was still looking at him—to try and explain. The fourth member of the team came to
