'Kryptos' and Dan Brown: Inside the CIA's code of secrecy

For 19 years it has sat beyond the public's gaze in an inner courtyard on the campus of the Central Intelligence Agency, a not uninteresting sculpture with 865, apparently randomly selected letters perforating a solid scroll of copper. But Kryptos is not merely a sculpture, and artist Jim Sanborn chose its constituent letters in a far from random fashion. They make up a code so complex that even the CIA's most esteemed cryptologists can't crack it.

Everyone at the CIA has known this for years. But when a novel called The Da Vinci Code appeared, a whole new crowd of crypto-geeks started paying attention. Today, the puzzle is the object of almost obsessive interest to thousands of amateur code-crackers worldwide. And the object of their obsession begins as follows: 'EMUFPHZLRFAXYUSDJKZLDKRNSHGNFIVJ'. Pardon?

"The whole thing is about the power of secrecy," Mr Sanborn, 63, gaily explains in the new edition of Wired magazine. Presumably he is aware that secrecy and the CIA is a touchier subject than ever nowadays, with even the Speaker of the House of Representatives, Nancy Pelosi, accusing the agency last week of having lied to her about its use of waterboarding interrogation techniques during the Bush years.

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But if the cultish notoriety of the 10ft-high sculpture, dedicated in the CIA's Langley, Virginia, headquarters in 1990, has been a mild irritant to the agency so far – the last of four parts of the riddle remains unsolved even today – matters might be about to get much worse. And Dan Brown, whose second book, Angels & Demons, crashed with knuckle-whitening impact on to our cinema screens this weekend, may once again be to blame.

Before a bestselling author stuck his oar in, Kryptos's life at Langley was rather quieter. It was seven long years from its 1990 unveiling before the first part of the four-section cypher was broken, a hiatus that astonished its creator: he had assumed that the all-powerful intelligence agency would crack his code within a matter of weeks.

The answer to that chunk took its first solver, a CIA employee called David Stein, 400 hours of his own time to break. The two lines of nonsense that started the code came out as "Between subtle shading and the absence of light lies the nuance of iqlusion" – the last word a deliberate misspelling of occlusion to further throw dedicated codebreakers off the scent.

The complexity of the puzzle is all the more remarkable considering that Sanborn knew little about the art of encryption before he started on the project. To help with the commission, the CIA loaned him a retiring cryptographer, Ed Scheidt. True to espionage form, mild paranoia crept in: Scheidt would meet Sanborn at secret locations where he taught him the basics of secret code writing as practised by European spies from the late 19th century through to the Second World War. (It would be best, Scheidt was quietly advised, if he refrained from teaching his protégé about the most up-to-date government techniques.)

As they progressed, however, Sanborn ensured that even Scheidt would not know the final answers. He took elaborate steps to make the task of cracking the message of the sculpture difficult. The plaintexts would contain deliberate misspellings – such as the "iqlusion" error – and additional clues were placed in Morse on other fragments of the sculpture scattered about campus away from the copper scroll itself.

All of those complications help explain why the last section of the code is now considered the Everest of the code-breaking world. Even with the help of a Pentium processor and a sophisticated cryptographic program, the amateur aficionado who broke the rest of the cipher, Jim Gillogly, could not solve its final mystery. The result is a puzzle that both stumps and delights its aficionados – and is ripe for exploitation by a conspiracy lover like Dan Brown.

Rumours abound that in the next, eagerly awaited, Brown novel, which will appear later this year, the Kryptos sculpture will make a grand appearance. Its title, The Lost Symbol – certainly suggest a coding connection. And Brown has been seen nosing around his nation's capital many times in recent years.

We know Kryptos has already captured Brown's imagination because of references to it on the Da Vinci Code cover, which includes a mention of its map coordinates at the CIA's HQ, as well as letters in mirror-writing which read: "Only WW knows". The same message is contained in the decoded version of one of the sculpture's four parts and is a reference to an acknowledgement by Sanborn that when he was finished he handed the final solution in an envelope to then CIA director, William Webster – WW.

The notion that Brown may exploit Kryptos for more stupendous financial gain (he is believed to have earned $250m from The Da Vinci Code) "deeply annoys" the artist, according to Wired. The last time that he said anything in public about the sculpture was in 2005, when he contradicted Brown's suggestion that "WW" could be inverted to say MM and was meant to spell Mary Magdalene, a mainstay of Brown's novels.

Nor will Sanborn thank Brown if he drags his sculpture into religious controversy. "I don't want my work manipulated in such a way that its meaning is somehow transformed," he said in an earlier press interview.

We still do not know for sure that Kryptos is about to undergo the Brown treatment. He and his American publisher, Doubleday, remain mute on the subject. But if so, you can assume the CIA itself won't be thrilled either. The spooks are about as likely to welcome the intrusion as the Vatican was.

Sanborn is also worried about a Brown-inspired Kryptos frenzy. Even now, there are people infuriated at him for refusing to give up the secret of the fourth text, which promises thereafter to unlock the entirety of his riddle. "It's the fact that I have some sort of power," he says. "You get stalkers. I don't know how they get my cell numbers. People have called me and said pretty terrible things. There are some who say I'm an agent of Satan because I have a secret and I won't tell.

"You don't do something for the CIA and expect it to go away and nobody ever hears about it again," Sanborn said back in 2005. Little did he know. Even mere rumours of his work at Langley making the pages of the next Dan Brown novel is catapulting it into a spotlight brighter than any of his contemporaries could even dream of. Such a spotlight could lead to a renewed spurt of obsessive work on the code, and a solution; if not, Sanborn insists, he wouldn't much mind. "In some ways, I'd rather die knowing it wasn't cracked," he says. "Once an artwork loses its mystery, it's lost a lot."

Cracking the code: The key alphabets

EMUFPHZLRFAXYUSDJKZLDKRNSHGNFIVJYQTQUXQBQVYUVLLTREVJYQTMKYRDMFD

The jumble of letters above form the first two lines of Jim Sanborn's mysterious sculpture, Kryptos. The complex process of unravelling it starts with the key that the sculpure features next to the code, an alphabet with the letters of the word "Kryptos" moved to the front. That reordered alphabet gets repeatedly reordered again by shifting the letters of a second keyword, "palimpsest", one at a time, with each shift providing an additional line. (You have to work out that "Kryptos" and "palimpsest" are the keywords on your own.) Finally, the jumbled key alphabets are placed in a table that can be used to substitute the original letters for corresponding answers. If all that gives you a headache, here's the solution:

"BETWEENSUBTLESHADINGANDTHEABSENCEOFLIGHTLIESTHENUANCEOFIQLUSION"