24 years after the sculpture came up in a courtyard at the CIA headquarters, people are still banging their heads trying to decipher the last of its four cryptic messages. So here’s another clue

The artist who created the enigmatic Kryptos, a puzzle-in-a-sculpture that has driven code breakers to distraction since it was installed 24 years ago in a courtyard at the headquarters of the US Central Intelligence Agency in Langley, Virginia, has decided that it is time for a new clue.

By 1999, nine years after it went up, Kryptos fans had deciphered three of the sculpture’s four messages — 865 letters punched through elegantly curved copper sheets that make up the most striking part of the work. (In fact, cryptographers at the National Security Agency cracked those messages in 1993, but kept the triumph to themselves.) The fourth and final passage, a mere 97 characters long, has thwarted thousands of followers ever since.

Jim Sanborn, the sculptor, having grown impatient with the progress of the fans and their incessant prodding for clues — and the misguided insistence by some that they had actually solved the puzzle — provided a six-letter clue to the puzzle in 2010. The 64th through 69th characters of the final panel, when deciphered, spell out the word BERLIN.

Since then, the fans, many of whom keep up a lively online conversation, have come up empty-handed. And so Sanborn has decided to open the door a bit more with five additional letters, those in the 70th through 74th position. They spell “clock”. This means that the letters from positions 64 to 74 spell out two words: “Berlin clock”.

As it happens, there is a famous public timepiece known as the “Berlin clock”, a puzzle in itself that tells time through application of set theory. Its 24 lights count off the hours and minutes in rows and boxes, with hours in the top two rows and minutes in the two below.

When asked whether his new clue was a reference to this clock, Sanborn, sounding pleased, said, “There are several really interesting clocks in Berlin.” He added, “You’d better delve into that particular clock”, a favourite of conspiracy theorists because of the mysterious death in 1991 of its designer, Dieter Binninger. With all the intriguing timekeepers in the city, including the “Clock of Flowing Time”, Sanborn said, “There’s a lot of fodder there.”

Divulging the clue “Berlin”, he said, led to “a tsunami” of entries that went off in every direction, including many “frivolous or debasing or hostile entries”, as well as messages from Nazi enthusiasts. The crush of people claiming to have solved the final puzzle, reached through a website Sanborn set up in 2010, had grown to be such a distraction that he set up a barrier to entry.

Two years ago, he instituted a $50 fee for anyone wanting to test a possible solution; the fee guaranteed “an exchange of no more than two back-and-forth-emails,” and no additional clues. If Sanborn did not wish to respond to the entry, he said, he would return the money.

“It really worked very well,” he said. Although he has not made much money, Sanborn said that was not the idea: “It’s made it manageable.”

But still, no solution. So Sanborn, now 69, figured “maybe I should be a little more specific”.

He was designing the project, he further explained, when the Berlin Wall fell, and “there’s no doubt I was influenced by all that going on simultaneously”. With the 25th anniversary of the fall of the wall, he said, he thought it was also worth returning to the topic.

The news will undoubtedly scramble the thousands of people around the world who have tried to decrypt Sanborn’s brainchild, especially the members of a Yahoo group devoted to the sculpture. They meet every now and then in the real world with a dinner in the Washington area; Sanborn has attended, as have NSA employees.

That community keeps up a steady stream of chatter about possible solutions, and is roughly divided between those who are called the “OSCs”, for Old School Cryptographers, and “Brownies”, for devotees of the thriller author Dan Brown, who has mentioned Kryptos in his work.

Edward M Scheidt, a retired chairman of the CIA’s cryptographic centre, worked with Sanborn to devise the cryptographic schemes he incorporated into the artwork. Scheidt, reached in Herndon, Virginia, at the encryption company TecSec, which he co-founded, said he would not have expected to find people still banging their heads against Kryptos so many years later.

“No, not really,” Scheidt said with a chuckle. “But a technique that I used obviously worked.”

FOUR PARTS TO A RIDDLE

The Kryptos is a 12-foot-high copper, granite and wood sculpture. It’s the latter structure that has the four hidden messages. Those four messages are the clues to a riddle.

1. The first part of the puzzle is a poetic phrase that Sanborn composed: “Between subtle shading and the absence of light lies the nuance of iqlusion.” (Iqlusion was a deliberate misspelling of illusion.)

2. The second part hinted at something buried: “It was totally invisible. How’s that possible? They used the earth’s magnetic field. x The information was gathered and transmitted underground to an unknown location. x Does Langley know about this? They should: it’s buried out there somewhere. x Who knows the exact location? Only WW. This was his last message. x Thirty eight degrees fifty seven minutes six point five seconds north, seventy seven degrees eight minutes forty four seconds west. x Layer two.”

3.  The third message is from the diary of archaeologist Howard Carter and is a description of when he discovered King Tut’s tomb in 1922: “Slowly, desperately slowly, the remains of passage debris that encumbered the lower part of the doorway were removed. With trembling hands I made a tiny breach in the upper left-hand corner. And then, widening the hole a little, I inserted the candle and peered in. The hot air escaping from the chamber caused the flame to flicker, but presently details of the room within emerged from the mist. x Can you see anything? q”

4. The fourth is 97 letters but no one has been able to decipher it.