Riptide

medical office, following the historian. Maybe there was some progress to report on the code.

Wopner's Base Camp office was, if anything, even more messy than his stateroom on the Cerberus. Small to begin with, banks of monitoring and servo control equipment made it claustrophobic. Wopner occupied the office's lone chair, crammed into a far corner by the relay racks that surrounded him. Cold air was blasting from two ducts overhead, and a massive air conditioner grumbled on the far side of the wall.

Despite the air-conditioning, the room was stuffy with hot electronics, and as Hatch walked in St. John was looking for a place to hang his jacket. His search unsuccessful, he laid it carefully on a nearby console.

'Jeez,' said Wopner, 'you lay your hairy old tweed there and it's gonna short-circuit the whole works.'

Frowning, St. John picked it up again. 'Kerry, do you have a minute?' he said. 'We really need to discuss this problem with the code.'

'Do I look like I have a minute?' came the response. Wopner leaned away from his terminal with a glare. 'I've just now finished an all-island diagnostic. The whole ball of wax, right down to the microcode. Took an hour, even at maximum bandwidth. Everything checks out: pumps, compressors, servos, you name it. No problems or discrepancies of any kind.'

'That's great,' Hatch broke in.

Wopner looked at him incredulously. 'Grow a brain, willya? Great? It's frigging terrible!'

'I don't understand.'

'We had a system crash, remember? The goddamn pumps went south on us. Afterward, I compared the island computer system with Scylla over on the Cerberus, and guess what? The ROM chips on Charbydis, here, had been altered. Altered!' He angrily smacked one of the CPUs upside its cabinet.

'And?'

'And now I run the diagnostics again, and everything's fine. Not only that, but the entire grid shows no deviations of any kind.' Wopner leaned forward. 'No deviations. Don't you get it? That's A physical and computational impossibility.'

St. John was glancing at the equipment around him, hands tucked behind his back. 'Ghost in the machine, Kerry?' he ventured.

Wopner ignored this.

'I don't know much about computers,' St. John continued, his plummy accent filling the air, 'but I do know one term: GIGO. Garbage in, garbage out.'

'Bite me. It's not the programming.'

'Ah. I see. Couldn't possibly be human error. As I recall, all it took was one incorrect FORTRAN equation to send Mariner 1 off on some outer space scavenger hunt, never to be heard from again.'

'The point is, things are working now,' Hatch said. 'So why not move on?'

'Sure, and have it happen again. I want to know why all this shit failed at once.'

'You can't do anything about it now,' St. John said. 'Meanwhile, we're falling behind schedule on the cryptanalysis. Nothing's worked. I've done some more research, and I think we've been far too quick to dismiss —'

'Shit on a stick!' Wopner snapped, wheeling toward him. 'You're not going to start mumbling about polyalphabetics again, are you, old thing? Look, I'm going to modify the algorithm of my brute-force attack, give it fifty percent system priority, really get things moving. Why don't you retire to your library? Come back at the end of the day with some useful ideas.'

St. John looked briefly at Wopner. Then he shrugged into his tweed and ducked back out into the gauzy morning light. Hatch followed him to his own office.

'Thanks,' Hatch said, passing the two folders to St. John.

'He's right, you know,' the historian said, taking a seat at his tidy desk and wearily pulling the old typewriter toward him. 'It's just that I've tried everything else. I've based my attacks on all the encryption methods known during Macallan's time. I've approached it as an arithmetic problem, as an astronomic or astro-logic system, as a foreign language code. Nothing.'

'What are polyalphabetics?' Hatch asked.

St. John sighed. 'A polyalphabetic cipher. It's quite simple, really. You see, most codes in Macallan's day were simple, monophonic substitutions. You had the regular alphabet, then you had a cipher alphabet, all higgledy- piggledy. To encode something, you simply looked up which cipher letter matched the next regular letter in your document. Maybe the code for s was y, and the code for e was z. So, when you coded the word 'see,' you'd get 'yzz.' That's how the cryptograms in your local newspaper work.'

'Seems clear enough.'

'Yes. But it's not a very secure system. So what if you had several different cipher alphabets to work with? Let's say instead of just one, you had ten. And, as you encrypted your document letter by letter, you'd move through all ten cipher alphabets, and then start over again with the first. That's a polyalphabetic cipher. Now, 'see' wouldn't just be 'yzz.' Each letter would be coded from a different cipher table.'

'Sounds difficult to crack.'

'Yes, they are very difficult. But Kerry's point is that polyalphabetics weren't used in Macallan's day. Oh, people knew about them. But they were considered too time-consuming, too prone to error.' St. John sighed again. 'But in this case, the biggest problem is one of concealment. If Macallan used a polyalphabetic cipher, how could he have safely hidden all the code alphabet tables he would have needed? Just one chance look at those by Red Ned Ockham would give the whole game away. And as bright as he was, he couldn't have memorized them.'

'If you think there's the chance it's a polyalphabetic code, why don't you try cracking it on your own?'