Digital Fortress

Nuclear attack, however, was not the only threat. Only last month TRANSLTR had thwarted one of the most ingeniously conceived terrorist attacks the NSA had ever witnessed. An anti-government organization had devised a plan, code-named Sherwood Forest. It targeted the New York Stock Exchange with the intention of "redistributing the wealth." Over the course of six days, members of the group placed twenty-seven nonexplosive flux pods in the buildings surrounding the Exchange. These devices, when detonated, create a powerful blast of magnetism. The simultaneous discharge of these carefully placed pods would create a magnetic field so powerful that all magnetic media in the Stock Exchange would be erased-computer hard drives, massive ROM storage banks, tape backups, and even floppy disks. All records of who owned what would disintegrate permanently.

Because pinpoint timing was necessary for simultaneous detonation of the devices, the flux pods were interconnected over Internet telephone lines. During the two-day countdown, the pods' internal clocks exchanged endless streams of encrypted synchronization data. The NSA intercepted the data-pulses as a network anomaly but ignored them as a seemingly harmless exchange of gibberish. But after TRANSLTR decrypted the data streams, analysts immediately recognized the sequence as a network-synchronized countdown. The pods were located and removed a full three hours before they were scheduled to go off.

Susan knew that without TRANSLTR the NSA was helpless against advanced electronic terrorism. She eyed the Run-Monitor. It still read over fifteen hours. Even if Tankado's file broke right now, the NSA was sunk. Crypto would be relegated to breaking less than two codes a day. Even at the present rate of 150 a day, there was still a backlog of files awaiting decryption.

***

"Tankado called me last month," Strathmore said, interrupting Susan's thoughts.

Susan looked up. "Tankado called you?"

He nodded. "To warn me."

"Warn you? He hates you."

"He called to tell me he was perfecting an algorithm that wrote unbreakable codes. I didn't believe him."

"But why would he tell you about it?" Susan demanded. "Did he want you to buy it?"

"No. It was blackmail."

Things suddenly began falling into place for Susan. "Of course," she said, amazed. "He wanted you to clear his name."

"No," Strathmore frowned. "Tankado wanted TRANSLTR."

"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.