"Ensei Tankado is dead?" Susan felt a wave of nausea. "You killed him? I thought you said-"

"We didn't touch him," Strathmore assured her. "He died of a heart attack. COMINT phoned early this morning. Their computer flagged Tankado's name in a Seville police log through Interpol."

"Heart attack?" Susan looked doubtful. "He was thirty years old."

"Thirty-two," Strathmore corrected. "He had a congenital heart defect."

"I'd never heard that."

"Turned up in his NSA physical. Not something he bragged about."

Susan was having trouble accepting the serendipity of the timing. "A defective heart could kill him-just like that?" It seemed too convenient.

Strathmore shrugged. "Weak heart... combine it with the heat of Spain. Throw in the stress of blackmailing the NSA...."

Susan was silent a moment. Even considering the conditions, she felt a pang of loss at the passing of such a brilliant fellow cryptographer. Strathmore's gravelly voice interrupted her thoughts.

"The only silver lining on this whole fiasco is that Tankado was traveling alone. Chances are good his partner doesn't know yet he's dead. The Spanish authorities said they'd contain the information for as long as possible. We only got the call because COMINT was on the ball." Strathmore eyed Susan closely. "I've got to find the partner before he finds out Tankado's dead. That's why I called you in. I need your help."

Susan was confused. It seemed to her that Ensei Tankado's timely demise had solved their entire problem. "Commander," she argued, "if the authorities are saying he died of a heart attack, we're off the hook; his partner will know the NSA is not responsible."

"Not responsible?" Strathmore's eyes widened in disbelief. "Somebody blackmails the NSA and turns up dead a few days later-and we're not responsible? I'd bet big money Tankado's mystery friend won't see it that way. Whatever happened, we look guilty as hell. It could easily have been poison, a rigged autopsy, any number of things." Strathmore paused. "What was your first reaction when I told you Tankado was dead?"

She frowned. "I thought the NSA had killed him."

"Exactly. If the NSA can put five Rhyolite satellites in geosynchronous orbit over the Mideast, I think it's safe to assume we have the resources to pay off a few Spanish policemen." The commander had made his point.

Susan exhaled. Ensei Tankado is dead. The NSA will be blamed. "Can we find his partner in time?"

"I think so. We've got a good lead. Tankado made numerous public announcements that he was working with a partner. I think he hoped it would discourage software firms from doing him any harm or trying to steal his key. He threatened that if there was any foul play, his partner would publish the key, and all firms would suddenly find themselves in competition with free software."

"Clever." Susan nodded.

Strathmore went on. "A few times, in public, Tankado referred to his partner by name. He called him North Dakota."

"North Dakota? Obviously an alias of some sort."

"Yes, but as a precaution I ran an Internet inquiry using North Dakota as a search string. I didn't think I'd find anything, but I turned up an E-mail account." Strathmore paused. "Of course I assumed it wasn't the North Dakota we were looking for, but I searched the account just to be sure. Imagine my shock when I found the account was full of E-mail from Ensei Tankado." Strathmore raised his eyebrows. "And the messages were full of references to Digital Fortress and Tankado's plans to blackmail the NSA."

Susan gave Strathmore a skeptical look. She was amazed the commander was letting himself be played with so easily. "Commander," she argued, "Tankado knows full well the NSA can snoop E-mail from the Internet; he would never use E-mail to send secret information. It's a trap. Ensei Tankado gave you North Dakota. He knew you'd run a search. Whatever information he's sending, he wanted you to find-it's a false trail."

"Good instinct," Strathmore fired back, "except for a couple of things. I couldn't find anything under North Dakota, so I tweaked the search string. The account I found was under a variation-NDAKOTA."

Susan shook her head. "Running permutations is standard procedure. Tankado knew you'd try variations until you hit something. NDAKOTA's far too easy an alteration."

"Perhaps," Strathmore said, scribbling words on apiece of paper and handing it to Susan. "But look at this."

Susan read the paper. She suddenly understood the Commander's thinking. On the paper was North Dakota's E-mail address.

[email protected] It was the letters ARA in the address that had caught Susan's eye. ARA stood for American Remailers Anonymous, a well-known anonymous server.

Anonymous servers were popular among Internet users who wanted to keep their identities secret. For a fee, these companies protected an E-mailer's privacy by acting as a middleman for electronic mail. It was like having a numbered post office box-a user could send and receive mail without ever revealing his true address or name. The company received E-mail addressed to aliases and then forwarded it to the client's real account. The remailing company was bound by contract never to reveal the identity or location of its real users.

"It's not proof," Strathmore said. "But it's pretty suspicious."

Susan nodded, suddenly more convinced. "So you're saying Tankado didn't care if anybody searched for North Dakota because his identity and location are protected by ARA."

"Exactly."

Susan schemed for a moment. "ARA services mainly U.S. accounts. You think North Dakota might be over here somewhere?"

Strathmore shrugged. "Could be. With an American partner, Tankado could keep the two pass-keys separated geographically. Might be a smart move."

Susan considered it. She doubted Tankado would have shared his pass-key with anyone except a very close friend, and as she recalled, Ensei Tankado didn't have many friends in the States.

"North Dakota," she mused, her cryptological mind mulling over the possible meanings of the alias. "What does his E-mail to Tankado sound like?"

"No idea. COMINT only caught Tankado's outbound. At this point all we have on North Dakota is an anonymous address."

Susan thought a minute. "Any chance it's a decoy?"

Strathmore raised an eyebrow. "How so?"

"Tankado could be sending bogus E-mail to a dead account in hopes we'd snoop it. We'd think he's protected, and he'd never have to risk sharing his pass-key. He could be working alone."

Strathmore chuckled, impressed. "Tricky idea, except for one thing. He's not using any of his usual home or business Internet accounts. He's been dropping by Doshisha University and logging on to their mainframe. Apparently he's got an account there that he's managed to keep secret. It's a very well-hidden account, and I found it only by chance." Strathmore paused. "So... if Tankado wanted us to snoop his mail, why would he use a secret account?"

Susan contemplated the question. "Maybe he used a secret account so you wouldn't suspect a ploy? Maybe Tankado hid the account just deep enough that you'd stumble on to it and think you got lucky. It gives his E-mail credibility."

Strathmore chuckled. "You should have been a field agent. The idea's a good one. Unfortunately, every letter Tankado sends gets a response. Tankado writes, his partner responds."

Susan frowned. "Fair enough. So, you're saying North Dakota's for real."

"Afraid so. And we've got to find him. And quietly. If he catches wind that we're onto him, it's all over."

Susan now knew exactly why Strathmore had called her in. "Let me guess," she said. "You want me to snoop ARA's secure database and find North Dakota's real identity?"

Strathmore gave her a tight smile. "Ms. Fletcher, you read my mind."

When it came to discreet Internet searches, Susan Fletcher was the woman for the job. A year ago, a senior White House official had been receiving E-mail threats from someone with an anonymous E-mail address. The NSA had been asked to locate the individual. Although the NSA had the clout to demand the remailing company reveal the user's identity, it opted for a more subtle method-a "tracer."

Susan had created, in effect, a directional beacon disguised as a piece of E-mail. She could send it to the user's phony address, and the remailing company, performing the duty for which it had been contracted, would forward it to the user's real address. Once there, the program would record its Internet location and send word back to the NSA. Then the program would disintegrate without a trace. From that day on, as far as the NSA was concerned, anonymous remailers were nothing more than a minor annoyance.

"Can you find him?" Strathmore asked.

"Sure. Why did you wait so long to call me?"

"Actually"-he frowned-"I hadn't planned on calling you at all. I didn't want anyone else in the loop. I tried to send a copy of your tracer myself, but you wrote the damn thing in one of those new hybrid languages; I couldn't get it to work. It kept returning nonsensical data. I finally had to bite the bullet and bring you in."

Susan chuckled. Strathmore was a brilliant cryptographic programmer, but his repertoire was limited primarily to algorithmic work; the nuts and bolts of less lofty "secular" programming often escaped him. What was more, Susan had written her tracer in a new, crossbreed programming language called LIMBO; it was understandable that Strathmore had encountered problems. "I'll take care of it." She smiled, turning to leave. "I'll be at my terminal."

"Any idea on a time frame?"

Susan paused. "Well... it depends on how efficiently ARA forwards their mail. If he's here in the States and uses something like AOL or CompuServe, I'll snoop his credit card and get a billing address within the hour. If he's with a university or corporation, it'll take a little longer." She smiled uneasily. "After that, the rest is up to you."

Susan knew that "the rest" would be an NSA strike team, cutting power to the guy's house and crashing through his windows with stun guns. The team would probably think it was on a drug bust. Strathmore would undoubtedly stride through the rubble himself and locate the sixty-four-character pass-key. Then he would destroy it. Digital Fortress would languish forever on the Internet, locked for all eternity.

"Send the tracer carefully," Strathmore urged. "If North Dakota sees we're onto him, he'll panic, and I'll never get a team there before he disappears with the key."

"Hit and run," she assured. "The moment this thing finds his account, it'll dissolve. He'll never know we were there."

The commander nodded tiredly. "Thanks."

Susan gave him a soft smile. She was always amazed how even in the face of disaster Strathmore could muster a quiet calm. She was convinced it was this ability that had defined his career and lifted him to the upper echelons of power.

As Susan headed for the door, she took a long look down at TRANSLTR. The existence of an unbreakable algorithm was a concept she was still struggling to grasp. She prayed they'd find North Dakota in time.

"Make it quick," Strathmore called, "and you'll be in the Smoky Mountains by nightfall."

Susan froze in her tracks. She knew she had never mentioned her trip to Strathmore. She wheeled. Is the NSA tapping my phone?

Strathmore smiled guiltily. "David told me about your trip this morning. He said you'd be pretty ticked about postponing it."

Susan was lost. "You talked to David this morning?"

"Of course." Strathmore seemed puzzled by Susan's reaction. "I had to brief him."

"Brief him?" she demanded. "For what?"

"For his trip. I sent David to Spain."