54
A bench on Boston Common. A cold wind whistling in from the harbor. They’re opposite the memorial to Robert Gould Shaw and the men of the Fifty-Fourth Regiment. Not many people around. Just a few joggers, college students, people pushing strollers.
Rachel watches him and waits. When Erik finally feels safe he continues: “The standard construction of pseudorandom encrypted functions is generally believed to be leakage-resistant, but I don’t think it is. And when you have sloppy tradecraft, you make it slightly easier for people like me.”
“I don’t understand,” Rachel says. She looks at Pete. He’s in the dark too and he has a software background.
“They reach out to us in two ways, and both ways, I believe, can be decrypted,” Erik goes on.
“How?”
“The burner phones aren’t as safe as everyone thinks they are, even if all the calls are made from brand-new burner phones housed inside a Faraday cage. The consensus is that calls made by such a method would be completely untraceable,” Erik says with a grin.
“But you’ve thought of a way to crack it, haven’t you?” Pete says.
Erik’s grin broadens.
“This has been my primary area of research for the past year.”
“What’s the trick?”
“It is theoretically possible to measure power levels and antenna patterns through software that can be installed on a smartphone. The phone can then analyze the incoming call in real time.”
“You’ve done this?” Pete asks, impressed.
“I have been tinkering with such a concept.”
“You can trace a call made on a burner phone?”
“No, but the cell phone’s base station—the closest wireless tower—could possibly be found,” Erik says cagily.
“You’ve done it! Haven’t you?” Pete insists.
“Tell us,” Rachel pleads.
Erik waits until a jogger passes before continuing. “I am in the process of finishing up my design of a hunter-killer application that can seek out the base station closest to where a cell-phone call has been made, even a burner-phone call made from inside a Faraday cage. Once the base station has been pinpointed, it might be possible to narrow the frequency of the phone’s signal, giving you a rough vector from the phone tower to the phone itself within, say, two or three hundred meters.”
Rachel isn’t sure she understands all this. “So what does that mean?” she asks.
“There may be a way of following the thread into the heart of the labyrinth,” Erik replies.
“And the Wickr app?” Rachel asks. “That’s their primary method of communication.”
“A not-too-dissimilar technique. My hunter-killer algorithm can’t break the message’s encryption or find the sender, but it can find the cell-phone base station that’s closest to where the message was sent from. Obviously, if they’re communicating from Times Square in New York City, we’re screwed, but if they’re calling from a private residence, we might be able to trace them.”
“Why haven’t you done it?” Pete asks.
“Because I was last in contact with them two and a half years ago and the burner phone they used to talk to me has been destroyed and the Wickr ID they used to communicate with me has been changed. The trail has gone cold. Whereas you…” he says, looking at Rachel.
“Me what?”
“If I’m right about their tradecraft, they still might be using the same app ID to speak to you.”
“They are. They sent me a message at Thanksgiving.”
“Perfect!” Erik exclaims.
“How would it work?” Rachel asks.
“You would have to provoke them or threaten them or worry them sufficiently so that they want to communicate with you. They may message you or, better yet, call you on a burner phone. If they talk long enough, we run the software, and we can possibly triangulate the base cell tower their phone is in contact with.”
“And if they’re in Times Square or driving or otherwise on the move? We’ll have pissed them off with no hope of finding them. And we’ll have painted a target on our backs and they can come after us!” Pete protests.
“The plan is not without risk,” Erik says.
“For us. It’s all risk for us. It’s zero risk for you,” Pete says.
“What would I have to do, exactly?” Rachel asks.
“No! Rachel, don’t agree to—” Pete begins.
“What would I have to do?” Rachel repeats.
“You must get in a dialogue with our Unknown Caller on Wickr or, better, on the phone and let me run a live trace when they contact you.”
“What do you mean, a dialogue?”
“You draw out the conversation as long as you can. The Wickr trace isn’t very accurate, I’m still working on the software, but a phone trace? A phone trace from a conversation that could last two or three minutes? That would be great.”
“What would happen?”
“I trace them through the hunter-killer algorithm and eventually with a little luck I find the base cell tower that the call is coming from.”
“Does it work with landlines?” Pete asks.
“If they’re dumb enough to call us on a landline, I’ll have them in two seconds.”
“I think that will make them think I’m some kind of a problem,” Rachel says. “A long conversation like that. I’ll be drawing their attention to me and my family.”
“Yes,” Erik agrees. “And I must confess that the app is not fully functional. I am very much in the beta stage. Tracing a phone call that could be anywhere in the whole of the United States requires a lot of computing power.”
“What if you could ignore most of the United States and just focus on one area?” Rachel asks.
“That would make things a lot easier,” Erik says. “But I can’t do that. They could be calling from anywhere. Even abroad. I—”
“She’s from Boston. And The Chain seems to operate mainly in New England. Close to home. They’re keeping it nearby. That’s what I would do in case of trouble.”
“How do you know ‘she’ is from Boston?” Erik asks. “I didn’t notice a Boston accent.”
“She’s gotten rid of it. She talks very deliberately when she’s using the voice-distortion machine. But you can’t quite get rid of all the intonation, can you? I started to suspect it, and I tried something with her in one of our conversations. We were talking about the Boston police and I said that they would arrest you for banging a uey. She laughed at that because she understood it. I’d never heard that expression before I moved here. There’s probably a lot of people outside of Boston who would also understand it, but my hunch is that she’s a Bostonian.”
Erik nods. “This is helpful. If the app doesn’t have to search anywhere but New England, it would be a lot more efficient. Orders of magnitude more efficient. North America has five hundred million people and billions of phone lines. New England has perhaps ten million people.”
“Your app might work fifty times faster,” Rachel says.