Read more: “Unbreakable: Eight codes we can’t crack“
At the US Central Intelligence Agency’s headquarters in Langley, Virginia, there is a monument to secrecy that has vexed both professional and amateur codebreakers for over two decades.
Erected in 1990, the Kryptos sculpture is a copper artwork bearing 1735 coded letters. Its creator is American artist , who received cryptography training from a CIA code expert. The sculpture’s code is divided into four sections. Three have been broken, revealing enigmatic messages that hint at a wider mystery, but the fourth and final section has yet to be cracked.
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Sanborn has hinted that the clues to unlocking it lie in the first three sections, which a Californian computer scientist named Jim Gillogly announced he had solved in 1999. (Shortly after, the CIA announced that one of their analysts, David Stein, had solved the same sections in 1998, with pencil and paper.)
The first two sections were encrypted using a modified form of a . This draws on the same basic principles of letter-for-letter substitution as basic codes like Caesar ciphers in which, say, B equals A, C equals B and so on. However, the Vigenère technique encrypts letters by placing alphabets in a grid, called a tabula recta. Each letter in the message could be encoded using any one of 26 different columns.
Like many codes, to crack it you need first to find a secret keyword. This word doesn’t reveal the message by itself, but it tells you which column to use to decipher each letter of the code (see diagram).
In the case of the modified Vigenère used in Kryptos, the keywords KRYPTOS and PALIMPSEST told the crackers a procedure for rearranging the alphabets in the tabula recta. These keywords were discovered by a combination of letter frequency, clues written into in the sculpture and trial-and-error.
The sculpture’s first section translates into the message: “Between subtle shading and the absence of light lies the nuance of iqlusion.” The second section – which also contains deliberate spelling mistakes – hints at the .
A different method was used to reveal the message in the . Before it could be decoded, every fourth column of letters in the sculpture itself first had to be shifted to the left, then the rows shuffled. The solution was an adaptation of Howard Carter’s of the opening of Tutankhamun’s tomb.
Plenty of speculation surrounds how these answers and coding methods might relate to the unsolved final part, but nobody has yet worked out the answer. In November 2010, Sanborn revealed the solution for six of the letters in the unsolved code: “Berlin”.
“It had been a long time, and a lot of people needed some encouragement,” Sanborn told żěè¶ĚĘÓƵ. His website received about 10,000 guesses in the first few weeks after the announcement, but the pace has since slowed down to about 10 solutions per day. Sanborn says many people make random guesses at the underlying message.
Others are taking a more reasoned approach. Robert Matson, a member of the largest , recently found a way to yield “Berlin” from the code, using a Vigenère method. The solution does not, however, give intelligible text for the rest of the unsolved code, leading some to suspect that there is either another layer of encryption, or that it’s a blind alley.
, co-leader of the group, seeks clues in Sanborn’s other artworks. The sculptor’s , for example, depicts two codes, one written in the Russian alphabet, the other a near-identical copy of the coded sections featured in Kryptos. “Any time I travel, I check to see if there are any Jim Sanborn works in the area,” she says.
She might be onto something. When Sanborn created the decor for at the Spy Museum in Washington DC, he hid references to Kryptos and his other works. Before it was deciphered in 2003, the solution to his coded sculpture called went unnoticed on the wall. It was the partial text of a KGB document.
Such methods may have to suffice: Sanborn says he’s not announcing more clues any time soon. “It’s going to only be once every decade or two,” he says.
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