nsei 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 logthrough Interpol."

"Heart attack?" Susan looked doubtful. "He wasthirty years old."

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

"I'd never heard that."

"Turned up in his NSA physical. Not something he braggedabout."

Susan was having trouble accepting the serendipity of thetiming. "A defective heart could kill him—just likethat?" It seemed too convenient.

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

Susan was silent a moment. Even considering the conditions, shefelt a pang of loss at the passing of such a brilliant fellowcryptographer. Strathmore's gravelly voice interrupted herthoughts.

"The only silver lining on this whole fiasco is thatTankado was traveling alone. Chances are good his partnerdoesn't know yet he's dead. The Spanish authorities saidthey'd contain the information for as long as possible. Weonly got the call because COMINT was on the ball." Strathmoreeyed Susan closely. "I've got to find the partner beforehe 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'stimely demise had solved their entire problem."Commander," she argued, "if the authorities aresaying he died of a heart attack, we're off the hook; hispartner will know the NSA is not responsible."

"Not responsible?" Strathmore's eyes widened indisbelief. "Somebody blackmails the NSA and turns up dead afew days later—and we're not responsible? I'dbet big money Tankado's mystery friend won't see it thatway. Whatever happened, we look guilty as hell. It could easilyhave been poison, a rigged autopsy, any number of things."Strathmore paused. "What was your first reaction when I toldyou Tankado was dead?"

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

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

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

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

"Clever." Susan nodded.

Strathmore went on. "A few times, in public, Tankadoreferred to his partner by name. He called him NorthDakota."

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

"Yes, but as a precaution I ran an Internet inquiry usingNorth Dakota as a search string. I didn't think I'd findanything, but I turned up an E-mail account." Strathmorepaused. "Of course I assumed it wasn't the North Dakotawe 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 fromEnsei Tankado." Strathmore raised his eyebrows. "And themessages were full of references to Digital Fortress andTankado's plans to blackmail the NSA."

Susan gave Strathmore a skeptical look. She was amazed thecommander was letting himself be played with so easily."Commander," she argued, "Tankado knows full wellthe NSA can snoop E-mail from the Internet; he would neveruse E-mail to send secret information. It's a trap. EnseiTankado gave you North Dakota. He knew you'd runa search. Whatever information he's sending, he wantedyou to find—it's a false trail."

"Good instinct," Strathmore fired back, "exceptfor a couple of things. I couldn't find anything under NorthDakota, so I tweaked the search string. The account I found wasunder a variation—NDAKOTA."

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

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

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

NDAKOTA@ara.anon.org

It was the letters ARA in the address that had caughtSusan's eye. ARA stood for American Remailers Anonymous, awell-known anonymous server.

Anonymous servers were popular among Internet users who wantedto keep their identities secret. For a fee, these companiesprotected an E-mailer's privacy by acting as a middleman forelectronic mail. It was like having a numbered post officebox—a user could send and receive mail without ever revealinghis true address or name. The company received E-mail addressed toaliases and then forwarded it to the client's real account.The remailing company was bound by contract never to reveal theidentity or location of its real users.

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

Susan nodded, suddenly more convinced. "So you'resaying Tankado didn't care if anybody searched for NorthDakota because his identity and location are protected byARA."

"Exactly."

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

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 hispass-key with anyone except a very close friend, and as sherecalled, Ensei Tankado didn't have many friends in theStates.

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

"No idea. COMINT only caught Tankado's outbound. Atthis point all we have on North Dakota is an anonymousaddress."

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

Strathmore raised an eyebrow. "How so?"

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

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

Susan contemplated the question. "Maybe he used a secretaccount so you wouldn't suspect a ploy? Maybe Tankado hid theaccount just deep enough that you'd stumble on to it and thinkyou 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 Tankadosends gets a response. Tankado writes, his partnerresponds."

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

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

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

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

When it came to discreet Internet searches, Susan Fletcher wasthe woman for the job. A year ago, a senior White House officialhad been receiving E-mail threats from someone with an anonymousE-mail address. The NSA had been asked to locate the individual.Although the NSA had the clout to demand the remailing companyreveal the user's identity, it opted for a more subtlemethod—a "tracer."

Susan had created, in effect, a directional beacon disguised asa piece of E-mail. She could send it to the user's phonyaddress, and the remailing company, performing the duty for whichit had been contracted, would forward it to the user's realaddress. Once there, the program would record its Internet locationand send word back to the NSA. Then the program would disintegratewithout 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'tplanned on calling you at all. I didn't want anyone else inthe loop. I tried to send a copy of your tracer myself, but youwrote the damn thing in one of those new hybrid languages; Icouldn't get it to work. It kept returning nonsensical data. Ifinally had to bite the bullet and bring you in."

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

"Any idea on a time frame?"

Susan paused. "Well… it depends on how efficiently ARAforwards their mail. If he's here in the States and usessomething like AOL or Compuserve, I'll snoop his credit cardand get a billing address within the hour. If he's with auniversity or corporation, it'll take a little longer."She smiled uneasily. "After that, the rest is up toyou."

Susan knew that "the rest" would be an NSA striketeam, cutting power to the guy's house and crashing throughhis windows with stun guns. The team would probably think it was ona drug bust. Strathmore would undoubtedly stride through the rubblehimself and locate the sixty-four-character pass-key. Then he woulddestroy it. Digital Fortress would languish forever on theInternet, 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 thekey."

"Hit and run," she assured. "The moment thisthing finds his account, it'll dissolve. He'll never knowwe were there."

The commander nodded tiredly. "Thanks."

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

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

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

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

Strathmore smiled guiltily. "David told me about your tripthis morning. He said you'd be pretty ticked about postponingit."

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

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

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

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