READING · 5 MIN
THE SCULPTURE
STILL KEEPING A SECRET.
It sits in a courtyard the public can't normally reach, at the headquarters of the agency whose entire job is breaking other people's codes. Three of its four messages have been solved. The people who work there still can't read the fourth.
An artist, a cryptographer, and 1,800 letters of copper ◢
Kryptos is a copper, granite and wood sculpture installed in 1990 in a courtyard at CIA headquarters in Langley, Virginia, created by American artist Jim Sanborn with cryptographic help from Ed Scheidt, then chairman of the CIA's own Cryptographic Center. The main copper panel is cut into an S-curve and stamped with roughly 1,800 letters, split into four numbered passages the puzzle community calls K1 through K4 - alongside a compass, a Morse-code-like sequence, and other decorative cryptographic flourishes scattered around the courtyard.
Three panels, cracked years apart ◢
K1 and K2 both use a keyed substitution - closer to a Vigenère cipher than a simple Caesar shift, since each uses its own keyword layered over the alphabet. CIA analyst David Stein solved both by hand in 1998, though the agency didn't make that public at the time; California computer scientist Jim Gillogly independently solved K1 through K3 in 1999 using a program, and published it first. K1 decodes to a sentence about “the nuance of iqlusion” - Sanborn's deliberate misspelling of “illusion,” one of several intentional quirks he's confirmed over the years. K3 uses a completely different method, a columnar transposition that scrambles letter order rather than substituting them, and decodes to a paraphrase of Howard Carter's own diary account of opening Tutankhamun's tomb in 1922.
K4: 97 characters, three decades, no key ◢
The fourth passage, just 97 characters long, remains unsolved. Sanborn has released a handful of plaintext clues over the years to keep the puzzle honest and fund independent verification of any future solution - in 2010 confirming that six letters decode to “BERLIN,” in 2014 confirming the next five spell “CLOCK” (widely read as a reference to Berlin's public Weltzeituhr or Bahnhof Zoo clock), and in 2020 confirming a further stretch spells “NORTHEAST.” None of the clues has been enough for anyone to reconstruct the underlying key. Puzzle researcher Elonka Dunin has tracked the sculpture and its clues in detail since the 1990s, and her public FAQ remains one of the most cited references for anyone attempting K4. Sanborn, born in 1945, has said publicly he intends to have the full solution authenticated and preserved - likely through an auction house - so the answer survives him even if K4 never falls to a solver first.
Thousands of submitted answers. None confirmed. ◢
Sanborn has said he's received thousands of proposed solutions since 1990, and rejected every one. That's the part that makes Kryptos different from most famous unsolved ciphers: the person who can confirm a correct answer is alive, reachable, and still checking his email.
Play the ciphers in this story