Things Fall Apart: Chapter 70

Union City, Cherryh's World, Tau Ceti, 16.14.775 CW

21.6 megaseconds since the catastrophe

Elyah could not have said how long she stood there in her mother's arms melting down, save that it was both too long and not long enough. Emotionally, she needed a lot more time. Physically, she could sense her mother—no longer a young woman—was getting a back-ache.

So, they disengaged. Without a word, Elyah helped put away the groceries, noting but not mentioning the rather limited variety on offer. She had missed the news that rationing was in effect, but it did not surprise her.

That mundane task had helped center them both a little. Once done, Esmé made tea, poured each of them a large mug, and led her daughter back to the sofa. They settled themselves, and sipped their tea—ti kwan yin. Elyah remembered the last time she had tasted that blend, briefing Doctor Saito on the dire state of affairs at Gliese 581, and remembered her thought, then, that if there was any goddess she'd like to appeal to, it was a goddess of mercy.

Finally, Esmé said, simply, "So, tell me."

And Elyah did. Necessarily, it was the short form, made somewhat longer by Esmé asking for clarification or expansion when she needed it. Esmé was not, even a little bit, a spacer. Despite that her daughter had gone outbound a long time ago now, there was still a great deal she simply didn't "get", that spacers understood without elaborating.

By the time they'd come around to the part of the story where the broadcast data stream—with its odd nonary packets every nine-to-the-sixth packet—came into things, Elyah found her head in her mother's lap, Esmé soothing her forehead as she had when Elyah was small. Esmé asked, "Don't we have a lot of very smart computers that can...oh."

"Exactly. We don't think the packets could do any harm, but we don't really know, so we haven't given it to our AIs to work on. But there's more to it than that." She looked at her mother directly and asked, "How much do you want to hear about encryption and encoding?"

Esmé considered the question seriously, noted that it was getting close to when she ought to be starting a meal for them both, and said, "For now, the least amount to understand why it's a problem even for very smart machines."

"Fair. Okay. Start with this: knowing absolutely nothing about the people who are sending the message, how would you know what kind of data is actually being encoded. Leave out encryption for the moment—we're just at the level of encoding. A character of text gets a number, but what characters does their language use? If they're not aliens—and we really don't assume they are—they might still have invented an entirely new writing system, or abandoned the ancient standards we still use to encode all the ones we know."

"They haven't forgotten those standards, though. You said most of the packets are perfectly intelligible data, just with an odd key."

"That's right, but see, we already assume they had someone on the inside, that they know us far better than we know them. Otherwise, they'd never have been able to do any of this."

Esmé considered. "Right. But I'd guess these odd messages are for those operatives on the inside, possibly many of them."

"Exactly, and that's where we start to get complicated. Again, let's assume for the moment that it's just text we're talking about—it gets even more complicated if we're talking voice or video or data transfer. There are two schemes that go all the way back to the earliest days of radio that are almost completely opaque. No amount of cryptanalysis will yield useful results except by accident, and that won't be repeatable.

"One scheme is called a one-time pad. It's a form of encryption that can be very simple to execute while also being impossible to break. Say I gave you a book, and said that every time you sent me a message, you should add the numerical value of each character of your message to the next character in sequence in that book, and—this is the key part—never, ever repeat which page you use. In fact, when you're done sending the encrypted message, you'd destroy both the plain-text and the page of the book. I'm obviously talking in old printed terms, but it still works for electronic messaging—you just delete them securely, leaving no trace. As long as you and I stay in sync as to which page of the book we're on, I'm the only one in the whole universe who can decrypt your message."

"So," Esmé said after a moment, "take the fact that we don't know any system that uses nonary. Add in the fact that we don't really know what it's encoding. Then factor in a possible encryption scheme that couldn't be broken even if they were using something more standard. Okay, I see the problem. What's the other scheme?"

Elyah was actually getting a bit drowsy, now. It was very much like days Elyah remembered growing up. She would get so excited about something she'd learned, some deeply esoteric rabbit hole she'd fallen down and wanted to share. Between her mother's soothing her forehead and that simple commonplace, she had unwound to the point where she was afraid she might well fall asleep mid-sentence.

A bit muzzily, she said, "They were called 'numbers stations'. They layered on top of other forms of encryption, like one-time pads. Someone sat at a broadcast station and just read off numbers. There was no indication of who they were for, what they might possibly mean. Only that they were very clearly numbers. Being broadcast, the only thing you could guess is that the intended recipient must be within the expected range of the transmitter. No one could even say for certain if they meant anything, all the time. It would be entirely possible to just keep people guessing by broadcasting random numbers."

"You clearly don't think that's what's happening here, though."

"No. Not unless the people transmitting are trying to show off. What they're doing requires a lot of energy. We're still trying to figure out how much, and how it could possibly be applied to a broadcast that probably reached the furthest edges of explored space before starting to become incoherent."

That last sentence, Elyah realized, was itself barely coherent. Not the words, but the way she'd said them. As if to punctuate this thought, she yawned mightily.

Her eyes closed, Elyah heard and felt her mother smile rather than seeing it, as she said gently, "Elyah, dear, you can nap if you want to, but if I'm going to feed us, I'm afraid I'm going to have to ask you to trade my lap for a mere pillow."

Elyah simply nodded, and let her mother slide out from under her and slide a pillow under her head. She didn't really want to sleep. She had so much more to tell. But she had spent a lot of energy melting down, and despite the tea, it had definitely caught up with her.

A moment later, she was snoring gently. Esmé gazed with fondness and worry at her daughter, and then went to prepare dinner.