Kryptos Sculpture

The Kryptos Sculpture’s final encrypted section, K4, remains unsolved after 35 years, baffling even the agency that commissioned it. Standing in the CIA headquarters courtyard since 1990, artist Jim Sanborn installed four copper panels with encrypted messages; three have been cracked—by a CIA analyst in 1998 and a computer scientist independently—but the 97-character K4 eludes solution. Sanborn has revealed clues: characters 64-69 spell "BERLIN," 70-74 spell "CLOCK," and in 2020 he confirmed the next word is "NORTHEAST," yet the rest is unknown. This persistence is rarer than the Wow! Signal at #10, which remains unsolved despite being a 72-second burst; here, the CIA’s own courtyard puzzle outperforms #10 in duration of mystery. The NSA, CIA, and thousands of amateurs have attempted K4, but after 35 years, no one has broken it, making it a uniquely institutional enigma.