Dan Brown: Digital Fortress

Susan stared at him and almost laughed. Unbreakable? What was THAT supposed to mean? There was no such thing as an unbreakable code-some took longer than others, but every code was breakable. It was mathematically guaranteed that sooner or later TRANSLTR would guess the right key. "I beg your pardon?"

"The code's unbreakable," he repeated flatly.

Unbreakable? Susan couldn't believe the word had been uttered by a man with twenty-seven years of code analysis experience.

"Unbreakable, sir?" she said uneasily. "What about the Bergofsky Principle?"

Susan had learned about the Bergofsky Principle early in her career. It was a cornerstone of brute-force technology. It was also Strathmore's inspiration for building TRANSLTR. The principle clearly stated that if a computer tried enough keys, it was mathematically guaranteed to find the right one. A code's security was not that its pass-key was unfindable but rather that most people didn't have the time or equipment to try.

Strathmore shook his head. "This code's different."

"Different?" Susan eyed him askance. An unbreakable code is a mathematical impossibility! He knows that!

Strathmore ran a hand across his sweaty scalp. "This code is the product of a brand-new encryption algorithm-one we've never seen before."

Now Susan was even more doubtful. Encryption algorithms were just mathematical formulas, recipes for scrambling text into code. Mathematicians and programmers created new algorithms every day. There were hundreds of them on the market-PGP, Diffie-Hellman, ZIP, IDEA, El Gamal. TRANSLTR broke all of their codes every day, no problem. To TRANSLTR all codes looked identical, regardless of which algorithm wrote them.

"I don't understand," she argued. "We're not talking about reverse-engineering some complex function, we're talking brute force. PGP, Lucifer, DSA-it doesn't matter. The algorithm generates a key it thinks is secure, and TRANSLTR keeps guessing until it finds it."

Strathmore's reply had the controlled patience of a good teacher. "Yes, Susan, TRANSLTR will always find the key-even if it's huge." He paused a long moment. "Unless…"

Susan wanted to speak, but it was clear Strathmore was about to drop his bomb. Unless what?

"Unless the computer doesn't know when it's broken the code."

Susan almost fell out of her chair. "What!"

"Unless the computer guesses the correct key but just keeps guessing because it doesn't realize it found the right key." Strathmore looked bleak. "I think this algorithm has got a rotating cleartext."

Susan gaped.

The notion of a rotating cleartext function was first put forth in an obscure, 1987 paper by a Hungarian mathematician, Josef Harne. Because brute-force computers broke codes by examining cleartext for identifiable word patterns, Harne proposed an encryption algorithm that, in addition to encrypting, shifted decrypted cleartext over a time variant. In theory, the perpetual mutation would ensure that the attacking computer would never locate recognizable word patterns and thus never know when it had found the proper key. The concept was somewhat like the idea of colonizing Mars-fathomable on an intellectual level, but, at present, well beyond human ability.

"Where did you get this thing?" she demanded.

The commander's response was slow. "A public sector programmer wrote it."

"What?" Susan collapsed back in her chair. "We've got the best programmers in the world downstairs! All of us working together have never even come close to writing a rotating cleartext function. Are you trying to tell me some punk with a PC figured out how to do it?"

Strathmore lowered his voice in an apparent effort to calm her. "I wouldn't call this guy a punk."

Susan wasn't listening. She was convinced there had to be some other explanation: A glitch. A virus. Anything was more likely than an unbreakable code.

Strathmore eyed her sternly. "One of the most brilliant cryptographic minds of all time wrote this algorithm."

Susan was more doubtful than ever; the most brilliant cryptographic minds of all time were in her department, and she certainly would have heard about an algorithm like this.

"Who?" she demanded.

"I'm sure you can guess." Strathmore said. "He's not too fond of the NSA."

"Well, that narrows it down!" she snapped sarcastically.

"He worked on the TRANSLTR project. He broke the rules. Almost caused an intelligence nightmare. I deported him."

Susan's face was blank only an instant before going white. "Oh my God…"

Strathmore nodded. "He's been bragging all year about his work on a brute-force-resistant algorithm."

"B-but…" Susan stammered. "I thought he was bluffing. He actually did it?"

"He did. The ultimate unbreakable code-writer."

Susan was silent a long moment. "But… that means…"

Strathmore looked her dead in the eye. "Yes. Ensei Tankado just made TRANSLTR obsolete."

Although Ensei Tankado was not alive during the Second World War, he carefully studied everything about it-particularly about its culminating event, the blast in which 100,000 of his countrymen where incinerated by an atomic bomb.

Hiroshima, 8:15 a.m. August 6, 1945-a vile act of destruction. A senseless display of power by a country that had already won the war. Tankado had accepted all that. But what he could never accept was that the bomb had robbed him of ever knowing his mother. She had died giving birth to him-complications brought on by the radiation poisoning she'd suffered so many years earlier.

In 1945, before Ensei was born, his mother, like many of her friends, traveled to Hiroshima to volunteer in the burn centers. It was there that she became one of the hibakusha-the radiated people. Nineteen years later, at the age of thirty-six, as she lay in the delivery room bleeding internally, she knew she was finally going to die. What she did not know was that death would spare her the final horror-her only child was to be born deformed.

Ensei's father never even saw his son. Bewildered by the loss of his wife and shamed by the arrival of what the nurses told him was an imperfect child who probably would not survive the night, he disappeared from the hospital and never came back. Ensei Tankado was placed in a foster home.

Every night the young Tankado stared down at the twisted fingers holding his daruma wish-doll and swore he'd have revenge-revenge against the country that had stolen his mother and shamed his father into abandoning him. What he didn't know was that destiny was about to intervene.

In February of Ensei's twelfth year, a computer manufacturer in Tokyo called his foster family and asked if their crippled child might take part in a test group for a new keyboard they'd developed for handicapped children. His family agreed.

Although Ensei Tankado had never seen a computer, it seemed he instinctively knew how to use it. The computer opened worlds he had never imagined possible. Before long it became his entire life. As he got older, he gave classes, earned money, and eventually earned a scholarship to Doshisha University. Soon Ensei Tankado was known across Tokyo as fugusha kisai-the crippled genius.

Tankado eventually read about Pearl Harbor and Japanese war crimes. His hatred of America slowly faded. He became a devout Buddhist. He forgot his childhood vow of revenge; forgiveness was the only path to enlightenment.

By the time he was twenty, Ensei Tankado was somewhat of an underground cult figure among programmers. IBM offered him a work visa and a post in Texas. Tankado jumped at the chance. Three years later he had left IBM, was living in New York, and was writing software on his own. He rode the new wave of public-key encryption. He wrote algorithms and made a fortune.

Like many of the top authors of encryption algorithms, Tankado was courted by the NSA. The irony was not lost on him-the opportunity to work in the heart of the government in a country he had once vowed to hate. He decided to go on the interview. Whatever doubts he had disappeared when he met Commander Strathmore. They talked frankly about Tankado's background, the potential hostility he might feel toward the U.S., his plans for the future. Tankado took a polygraph test and underwent five weeks of rigorous psychological profiles. He passed them all. His hatred had been replaced by his devotion to Buddha. Four months later Ensei Tankado went to work in the Cryptography Department of the National Security Agency.