What does it say about the Central Intelligence Agency that its agents can crack the secret codes of enemy nations but can't unravel a coded sculpture sitting outside their cafeteria window?

It says, perhaps, that artist Jim Sanborn, who created the cryptographic sculpture named Kryptos that sits on CIA grounds, could have a career in covert operations if he ever grows tired of stumping the experts.

It's been nearly 15 years since Sanborn installed the 12-foot-high, verdigrised copper, granite and wood sculpture inscribed with four encrypted messages at the CIA's Langley, Virginia, headquarters in 1990. And it's been seven years since anyone made progress at cracking its code.

But publication of the novel The Da Vinci Code has renewed interest in solving the puzzle because author Dan Brown made two veiled references to Kryptos on his book's dust jacket. Brown's publisher sponsored a contest around the references, and Brown has hinted that his next book, which takes place in Washington, D.C., may feature the sculpture in some way.

This is good news to Elonka Dunin, an executive producer and manager at Missouri gaming company Simutronics, who is obsessed with cracking Kryptos and thinks that the more people who work on the puzzle the quicker they'll solve it.

"We have lots of different theories that we're chasing down," Dunin said of her band of sleuths, which includes some CIA employees. "But there's no way we'll know whether we're on the right track until something comes loose."

Kryptos isn't a complete mystery. Parts of it have been solved.

In 1998, CIA analyst David Stein cracked three of the four coded messages after diddling over the problem with paper and pencil for about 400 hours spread over many lunch breaks. Only his CIA colleagues initially knew of his success, since the agency didn't publicize it. A year later, California computer scientist Jim Gillogly gained public notoriety when he cracked the same three messages using a Pentium II.

But for 15 years, the last Kryptos section has remained unsolved. And when experts or amateurs do decipher it, they'll know what it says but not necessarily what it means. Sculptor Sanborn said the text is a riddle, which requires sleuths to be on the CIA grounds to solve it.

"In part of the code that's been deciphered, I refer to an act that took place when I was at the agency and a location that's on the ground of the agency," Sanborn told Wired News. "So in order to find that place, you have to decipher the piece and then go to the agency and find that place."

Sanborn may be referring to something he buried on the CIA grounds, though he's not saying. The decrypted text mentions a burial and gives latitude and longitude coordinates (38 57 6.5 N, 77 8 44 W), which Sanborn said referred to "locations of the agency." The coordinates, slightly altered, appear on the Da Vinci Code book jacket. Brown made the first number 37 instead of 38; he's said that he may reveal the reason in future books. Some sleuths have determined that the coordinates on the sculpture mark a spot on the CIA grounds about 150 feet from the sculpture. Others have placed it elsewhere, however.

The sculpture's theme is intelligence gathering (Kryptos is Greek for "hidden"). It features a large block of petrified wood standing upright, with a tall copper plate scrolling out of the wood like a sheet of paper. At the sculpture's base is a round pool with fountain pump that sends water in a circular motion around the pool.

Some 1,800 letters are carved out of the copper plate, with some of them forming a table based on an encryption method developed in the 16th century by a Frenchman named Blaise de Vigenere. The table helped Stein and Gillogly decipher portions of the encrypted messages.

The encrypted sections include spelling errors, which Sanborn said were intentional, possibly to throw off sleuths, and misaligned characters set higher on a line of text than characters around them.

The first section is a poetic phrase, which Sanborn composed himself. The second hints at something buried: "Does Langley know about this? They should: It's buried out there somewhere." The third section comes from archaeologist Howard Carter's diary describing the opening of a door in King Tut's tomb on Nov. 26, 1922.

Scores of professional and amateur cryptographers have tried their hand at decrypting the last passage, which consists of fewer than 100 characters. Cryptographers at the National Security Agency have also taken a stab at it, to no avail. Sleuths scrutinize every Sanborn interview for clues. But he's careful to remain oblique.

"In the early days, anything I said was a clue," Sanborn said. "Now things are getting more and more refined the more people (are looking into) this. They are looking for shreds, tiny little slivers of information. So I have to be very careful not to go any further." (To aid sleuths, we've published an edited transcript of our interview with Sanborn.)

Decoders have turned to Sanborn's other sculptures for clues. After Kryptos, Sanborn created other coded sculptures, such as The Cyrillic Projector, a cylindrical sculpture that sits at the University of North Carolina in Charlotte, which was solved about a year ago, and a work that is sometimes called the Untitled Kryptos piece, which reproduces the same text from Kryptos. It took a few months to crack the Projector, which was written in Cyrillic letters. Deciphering it required decoding the Cyrillic, then translating the message into English. It turned out to be text from classified KGB documents.

Sleuths have also looked at works Sanborn created around Kryptos on the CIA grounds. These include slabs of stone with a compass and Morse code on them.

Although photos of the works are available, physical access is restricted. In 2002, Dunin was one of the lucky few who saw the works in person.

Dunin visited Langley to give a presentation to analysts about steganography and al-Qaida. Although she wasn't allowed to snap photos of Kryptos while there, her CIA guides arranged to have an official photographer take pictures of her standing next to it. She also made rubbings of the text.

Until now, only three people were said to know the solution to Kryptos. Sanborn, a CIA cryptographer named Ed Scheidt who helped him choose and alter the coding techniques for the sculpture, and former CIA director William Webster, who received a sealed envelope containing the solution, which sits in a CIA archive until the time when someone solves the puzzle.

But Sanborn told Wired News that Scheidt, now a retired chairman of the CIA's Cryptographic Center, and Webster only think they know the solution.

The CIA required Sanborn to write the solution down and present it to Webster so the agency wouldn't be embarrassed if the sculpture turned out to contain a message that was pornographic or critical of the agency. Sanborn gave officials an envelope with a wax seal. But Sanborn said he didn't give Webster the whole story.

"Well, you know, I wasn't completely truthful with the man," Sanborn said, laughing. "And I'm sure he realizes that. I mean that's part of trade craft, isn't it? Deception is everywhere.... I definitely didn't give him the last section, which has never been deciphered."

Scheidt, at the CIA's request, worked with Sanborn to choose the coding processes he used with the sculpture. But Sanborn did the encryption on his own. Scheidt was surprised to learn that he might not know the puzzle's solution. "I haven't heard him say that before," Scheidt said. "It's possible I guess.

"I know what the message was to be. (But) since he's the one who had the chisel in his hands, there could be some changes." (To read an edited transcript of our interview with Scheidt, click here)

Sanborn said he didn't expect that the code would remain unsolved for this long.

Dunin said she doesn't care if she's not the one who solves the puzzle as long as it's taken "off my plate." She doesn't expect it will be a letdown when the code is cracked.

"When we solved the Cyrillic Projector it was exciting and energizing for everyone working on Kryptos," she said. "If we solve Kryptos, there are plenty of other codes to solve after that."