“Transltr?”

“Yes. He ordered me to go public and tell the world we have TRANSLTR. He said if we admitted we can read public E‑mail, he would destroy Digital Fortress.”

Susan looked doubtful.

Strathmore shrugged. “Either way, it’s too late now. He’s posted a complimentary copy of Digital Fortress at his Internet site. Everyone in the world can download it.”

Susan went white. “He what!”

“It’s a publicity stunt. Nothing to worry about. The copy he posted is encrypted. People can download it, but nobody can open it. It’s ingenious, really. The source code for Digital Fortress has been encrypted, locked shut.”

Susan looked amazed. “Of course! So everybody can have a copy, but nobody can open it.”

“Exactly. Tankado’s dangling a carrot.”

“Have you seen the algorithm?”

The commander looked puzzled. “No, I told you it’s encrypted.”

Susan looked equally puzzled. “But we’ve got TRANSLTR; why not just decrypt it?” But when Susan saw Strathmore’s face, she realized the rules had changed. “Oh my God.” She gasped, suddenly understanding. “Digital Fortress is encrypted with itself?”

Strathmore nodded. “Bingo.”

Susan was amazed. The formula for Digital Fortress had been encrypted using Digital Fortress. Tankado had posted a priceless mathematical recipe, but the text of the recipe had been scrambled. And it had used itself to do the scrambling.

“It’s Biggleman’s Safe,” Susan stammered in awe.

Strathmore nodded. Biggleman’s Safe was a hypothetical cryptography scenario in which a safe builder wrote blueprints for an unbreakable safe. He wanted to keep the blueprints a secret, so he built the safe and locked the blueprints inside. Tankado had done the same thing with Digital Fortress. He’d protected his blueprints by encrypting them with the formula outlined in his blueprints.

“And the file in TRANSLTR?” Susan asked.

“I downloaded it from Tankado’s Internet site like everyone else. The NSA is now the proud owner of the Digital Fortress algorithm; we just can’t open it.”

Susan marveled at Ensei Tankado’s ingenuity. Without revealing his algorithm, he had proven to the NSA that it was unbreakable.

Strathmore handed her a newspaper clipping. It was a translated blurb from the Nikkei Shimbun, the Japanese equivalent of the Wall Street Journal, stating that the Japanese programmer Ensei Tankado had completed a mathematical formula he claimed could write unbreakable codes. The formula was called Digital Fortress and was available for review on the Internet. The programmer would be auctioning it off to the highest bidder. The column went on to say that although there was enormous interest in Japan, the few U.S. software companies who had heard about Digital Fortress deemed the claim preposterous, akin to turning lead to gold. The formula, they said, was a hoax and not to be taken seriously.

Susan looked up. “An auction?”

Strathmore nodded. “Right now every software company in Japan has downloaded an encrypted copy of Digital Fortress and is trying to crack it open. Every second they can’t, the bidding price climbs.”

“That’s absurd,” Susan shot back. “All the new encrypted files are uncrackable unless you have TRANSLTR. Digital Fortress could be nothing more than a generic, public‑domain algorithm, and none of these companies could break it.”

“But it’s a brilliant marketing ploy,” Strathmore said. “Think about it‑all brands of bulletproof glass stop bullets, but if a company dares you to put a bullet through theirs, suddenly everybody’s trying.”

“And the Japanese actually believe Digital Fortress is different? Better than everything else on the market?”

“Tankado may have been shunned, but everybody knows he’s a genius. He’s practically a cult icon among hackers. If Tankado says the algorithm’s unbreakable, it’s unbreakable.”

But they’re all unbreakable as far as the public knows!”

“Yes . . .” Strathmore mused. “For the moment.”

“What’s that supposed to mean?”

Strathmore sighed. “Twenty years ago no one imagined we’d be breaking twelve‑bit stream ciphers. But technology progressed. It always does. Software manufacturers assume at some point computers like TRANSLTR will exist. Technology is progressing exponentially, and eventually current public‑key algorithms will lose their security. Better algorithms will be needed to stay ahead of tomorrow’s computers.”

“And Digital Fortress is it?”

“Exactly. An algorithm that resists brute force will never become obsolete, no matter how powerful code‑breaking computers get. It could become a world standard overnight.”

Susan pulled in a long breath. “God help us,” she whispered. “Can we make a bid?”

Strathmore shook his head. “Tankado gave us our chance. He made that clear. It’s too risky anyway; if we get caught, we’re basically admitting that we’re afraid of his algorithm. We’d be making a public confession not only that we have TRANSLTR but that Digital Fortress is immune.”

“What’s the time frame?”

Strathmore frowned. “Tankado planned to announce the highest bidder tomorrow at noon.”

Susan felt her stomach tighten. “Then what?”

“The arrangement was that he would give the winner the pass‑key.”

“The pass‑key?”

“Part of the ploy. Everybody’s already got the algorithm, so Tankado’s auctioning off the pass‑key that unlocks it.”

Susan groaned. “Of course.” It was perfect. Clean and simple. Tankado had encrypted Digital Fortress, and he alone held the pass‑key that unlocked it. She found it hard to fathom that somewhere out there‑probably scrawled on a piece of paper in Tankado’s pocket‑there was a sixty‑four‑character pass‑key that could end U.S. intelligence gathering forever.

Susan suddenly felt ill as she imagined the scenario. Tankado would give his pass‑key to the highest bidder, and that company would unlock the Digital Fortress file. Then it probably would embed the algorithm in a tamper‑proof chip, and within five years every computer would come preloaded with a Digital Fortress chip. No commercial manufacturer had ever dreamed of creating an encryption chip because normal encryption algorithms eventually become obsolete. But Digital Fortress would never become obsolete; with a rotating cleartext function, no brute‑force attack would ever find the right key. A new digital encryption standard. From now until forever. Every code unbreakable. Bankers, brokers, terrorists, spies. One world‑one algorithm.

Anarchy.

“What are the options?” Susan probed. She was well aware that desperate times called for desperate measures, even at the NSA.

“We can’t remove him, if that’s what you’re asking.”

It was exactly what Susan was asking. In her years with the NSA, Susan had heard rumors of its loose affiliations with the most skilled assassins in the world‑hired hands brought in to do the intelligence community’s dirty work.

Strathmore shook his head. “Tankado’s too smart to leave us an option like that.”

Susan felt oddly relieved. “He’s protected?”

“Not exactly.”

“In hiding?”

Strathmore shrugged. “Tankado left Japan. He planned to check his bids by phone. But we know where he is.”

“And you don’t plan to make a move?”

“No. He’s got insurance. Tankado gave a copy of his pass‑key to an anonymous third party . . . in case anything happened.”

Of course, Susan marveled. A guardian angel. “And I suppose if anything happens to Tankado, the mystery man sells the key?”

“Worse. Anyone hits Tankado, and his partner publishes.”

Susan looked confused. “His partner publishes the key?”

Strathmore nodded. “Posts it on the Internet, puts it in newspapers, on billboards. In effect, he gives it away.”

Susan’s eyes widened. “Free downloads?”

“Exactly. Tankado figured if he was dead, he wouldn’t need the money‑why not give the world a little farewell gift?”

There was a long silence. Susan breathed deeply as if to absorb the terrifying truth. Ensei Tankado has created an unbreakable algorithm. He’s holding us hostage.

She suddenly stood. Her voice was determined. “We must contact Tankado! There must be a way to convince him not to release! We can offer him triple the highest bid! We can clear his name! Anything!”

“Too late,” Strathmore said. He took a deep breath. “Ensei Tankado was found dead this morning in Seville, Spain.”