Kryptos Sculpture

An encrypted sculpture standing in the courtyard of CIA headquarters in Langley, Virginia since 1990. Artist Jim Sanborn embedded four encrypted messages into the copper panels. Three have been solved (by a CIA analyst in 1998 and independently by a computer scientist). The fourth section — 97 characters known as K4 — remains unsolved after 35 years, despite being attempted by the NSA, CIA, and thousands of amateur cryptanalysts. Sanborn has released clues over the years: characters 64-69 spell "BERLIN," characters 70-74 spell "CLOCK." In 2020, he confirmed the next word is "NORTHEAST." The rest is unknown. The CIA's own puzzle, in their own courtyard, that they can't solve.