In 1988, as a new headquarters for the American Central Intelligence Agency (CIA) was being built in Langley, Virgina, sculptor Jim Sanborn was commissioned to create artwork for the courtyard of the new building.
In 1999, a computer scientist named Jim Gillogly announced that he had solved most of the puzzle. There were four distinct parts to the code, and he had managed to solve the first three.
After his announcement, the CIA revealed that they had actually solved the first three parts internally, the year before. (Later, the U.S. National Security Administration (NSA) also claimed to have solved the first three parts in 1992.)
The fourth section of the code remained unsolved, and to date, no one has brought forth a credible solution for part 4. The code has proven so difficult that its creator, cryptographer and sculptor Jim Sanborn, has provided a tantalizing clue to the New York Times: Characters 64 through 69, the letters N-Y-P-V-T-T, are decoded as B-E-R-L-I-N.
When commenting in 2006 about his error in section 2, Sanborn said that the answers to the first three sections contain clues to the fourth section. In November 2010, Sanborn released a clue, publicly stating that “NYPVTT”, the 64th-69th letters in part four, become “BERLIN” after decryption.
Sanborn gave The New York Times another clue in November 2014: the letters “MZFPK”, the 70th-74th letters in part four, become “CLOCK” after decryption. The 74th letter is K in both the plaintext and ciphertext, meaning that it is possible for a character to encrypt to itself. This means it does not have a weakness, where a character could never be encrypted as itself, that was known to be inherent in the German Enigma machine. It is believed that the “BERLINCLOCK” plaintext may be a direct reference to the Berlin Clock.
Sanborn further stated that in order to solve section 4, “You’d better delve into that particular clock,” but added, “There are several really interesting clocks in Berlin.”[
So what if NSA’s cryptanalysts have also spent their lunch hours—aided by classified code-breaking techniques, massive computing power, and giant stores of data—cracking some of the world’s other great, unsolved cryptographs?