The Kryptos sculpture is unveiled

Artist Jim Sanborn's sculpture Kryptos at CIA headquarters carries four coded passages. The first three were solved, but the fourth has resisted every attempt so far.

The status of the fourth passage is the part that is still open.

Context

Sanborn was commissioned for the grounds of the new CIA headquarters in Langley, Virginia, and his design was chosen in 1988. The copper sculpture was dedicated on 3 November 1990. It has coded letters cut into the copper, and the name comes from the Greek word for hidden.

Sanborn worked with a former CIA cryptographer, Edward Scheidt, on the coding methods. The first three passages used variants of the Vigenere cipher with keyword alphabets and a transposition. A CIA analyst announced a solution of three of them in 1998, and a computer scientist in California reported the same in 1999. The NSA had in fact solved them earlier, in 1992, according to later releases.

The final passage, K4, is only 97 characters long, which gives codebreakers little text to analyse. Sanborn has released a few plaintext clues over the years, revealing words at certain positions, but the passage has stayed unsolved publicly. Sanborn has said he will sell the solution at auction. Because the plaintext of the first three passages includes deliberate misspellings, solvers had to work with errors that were intended by the artist, not mistakes in decoding.