Dead or Alive - Tom Clancy [218]
“I’m putting the finishing touches on the decryption algorithm; part of the problem is we don’t know what kind of program they used for the encryption—commercial or homemade. According to the Steganography Analysis and Research Center—”
“There’s such a place?” asked Chavez.
“—to date there’s seven hundred twenty-five stego applications out there, and that’s just the commercial stuff. Anybody with halfway decent programming skills could make one up and fit it on a flash drive. Just carry it around, plug it into a computer, and you’re in stego mode.”
“So how do you break it?” This from Clark.
“I put together a two-part process: First check for discrepancies in the file—be it video, or image, or audio. If that finds an anomaly, then the second part of the program starts running the file through the most common encryption methods. It’s a brute-force process, but chances are the URC has its favorite methods. Find that and we can start speeding up the dissection.”
“How long?” Jack asked.
“No idea. I’ll start feeding the monster and get back to you.”
At three a.m. the phone rang. The three of them were awake instantly. “Biery,” Jack said, rubbing his eyes and squinting at the cell phone’s ID screen. He put the call on speakerphone.
“I might be popping the cork a little early,” Biery said, “but I think we’ve hit the mother lode. That’s the good news. The bad news is it looks like they’re using three different encryption methods, so it’s going to take some time.”
“You have our attention,” Clark replied.
“First thing: The banner image we saw on the URC website showing Dirar’s murder—I think it’s a digital onetime pad. Essentially a decoding grid for plain-speak messages. Whether it’s outdated or current I don’t know yet.”
This was no surprise to Jack. What was old is new again, he knew. The OTP system was ancient—how ancient was a topic of debate among cryptography scholars, but its birth into the modern age was in 1917 with an AT&T engineer named Gilbert Vernam—and while there were a variety of OTP flavors, at its core it is a substitution cipher, most simply arranged in the form of a random alphanumeric grid: combing a character from the left-hand margin with a character from the top margin, and where they intersect in the grid’s body is the single character substitution. Encoding and decoding was time-consuming, but providing the OTP was restricted to only the sender and the receiver; it was virtually unbreakable. In this case, certain URC members would know to check certain websites on certain days and download certain images, which would then be steganographically decrypted, revealing a onetime pad with which plain-speak phone calls, letters, and e-mails could be securely transmitted.
The question was, Jack thought, how often did the URC rotate its online OTP? The only way to find that out was to try to match known URC messages with onetime-pad images in the same time frame.
“This could explain why the baby announcement e-mail has dead-ended,” Jack said. “They switched pads and we’ve been a step behind.”
Clark nodded and said, “Go ahead, Gavin.”
“Second: One of the larger image files on Nayoan’s DVD—didn’t have a match on any we pulled off URC sites. The algorithm’s still chewing on it, but based on what I’m seeing so far, we’ve got a whole lot of credit card and bank routing numbers.”
“Nayoan’s a URC treasurer,” said Chavez. “Sure as shit.”
“You’re checking the numbers?” Clark asked Gavin.
“Not yet. Which do you want first?”
“Credit cards. Easier to get and easier to dump than a bank account. Start with stuff in San Francisco and West Coast accounts. Might as well make hay while we’re out here.”
65
IF THEIR ENTRY into the Medina caused any curiosity it was well disguised, the Caruso brothers decided. It was not yet dark, of course, so there were plenty of obviously white and Western tourists still milling around vendors’ stalls and wandering through the switchback narrow alleyways; their presence was of little consequence. The sun was dropping