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The creator of one of the world’s most famous mysteries is giving obsessive fans a new clue.

“Kryptos,” a sculpture in a courtyard at the headquarters of the CIA in Langley, Va., holds an encrypted message that has not fully yielded to attempts to crack it. It’s been nearly 30 years since its tall scroll of copper with thousands of punched-through letters was set in place.

Three of the four passages of the sculpture have been decrypted. (The first, though unacknowledged by the CIA at the time, was solved by a team from the National Security Agency.) But after nearly three decades, one brief passage remains uncracked. And that has been a source of both delight for those who love puzzles and consternation for those who love to solve them

The sculptor, Jim Sanborn, has been hounded for decades by code-breaking enthusiasts. And he has twice provided clues to move the community of would-be solvers along, once in 2010 and again in 2014.

Now he is offering another clue. And it will be the last one, he says.

It is a word: northeast.

Why do people care so much about a puzzle cut into a sheet of copper in a courtyard? It’s not just that it involves the CIA, the bastion of all things secret, or the fact that it has been referred to in novels by thriller writer Dan Brown. It is something deeper, something that involves the nature of the human mind, said Craig Bauer, a professor of mathematics at York College of Pennsylvania and a former scholar in residence at the NSA’s Center for Cryptologic History.

“We have many problems that are difficult to resolve — intimidating, perhaps even scary,” he said. “It gives people great pleasure to pick up on one that they think they have a chance of solving.”

Sanborn devised the codes for “Kryptos” — the ancient Greek word for “hidden” — with the help of Edward Scheidt, a retired chairman of the CIA’s cryptographic center. The passages include intentional misspellings to make them more difficult to decipher.

The first one to be decoded said, “Between subtle shading and the absence of light lies the nuance of iqlusion [sic].”

Sanborn revealed that the message was a clue to the next passage, which eventually was discovered to include the location of CIA headquarters by latitude and longitude. The third passage turned out to be an entry from the diary of archaeologist Howard Carter describing the opening of King Tut’s tomb in 1922.

The fourth section is short, just 97 characters, a fact that “could, in itself, present a decryption challenge,” Scheidt said via e-mail. Solution methods rely on the frequency of the most common letters, like E, T, A, O, I and N. In addition, he said, the last passage uses what is known as a masking technique, a further level of obfuscation.

The clues Sanborn has offered so far are in the form of a “crib,” which is a word or phrase that appears in the decrypted text. The clue revealed in 2010 was that the passage contains the word Berlin. In 2014, he revealed another word, clock.

While the response was a frenzy of activity among enthusiasts, the result, in cryptographic terms, was bupkis.

So now, Sanborn, 74, is giving the world another shot: The word northeast is in there someplace.

He’s not, however, revealing whether any of the clue words are spelled correctly.

Sanborn has set up systems to allow people to check their proposed solutions without having to contact him directly. The most recent incarnation is an e-mail-based process with a fee of $50 to submit a potential solution.

The account receives regular inquiries, so far, none of them correct.

“It’s not something I thought I would be doing 30 years on,” he said.

He has decided that if the code is not broken when he dies, the secret will be put up for auction. He might even do it in his lifetime.

“I do realize that the value of ‘Kryptos’ is unknown and that perhaps this concept will bear little fruit,” he said.