Cracking the World's Most Famous Code

Solving the CIA's Kryptos puzzle took three parts math and one part sleuthing

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THE 35-YEAR-OLD SAGA OF KRYPTOS, an enigmatic sculpture containing four encrypted messages outside the headquarters of the U.S. Central Intelligence Agency, recently took a bizarre twist. Cryptographers had broken the first three passages in the 1990s, just a few years after artist Jim Sanborn erected the copper structure. But the fourth, known as K4, remained a 97-character fortress—that is, until last September, when journalists Jarett Kobek and Richard Byrne discovered the answer in the Smithsonian archives.

How does one crack the world’s most famous code? The breakthroughs on Kryptos provide a guided tour of the cat-and-mouse game played by code makers and code breakers that has defined information security for millennia.

The core challenge of cryptography is to deliver a secret message securely in the presence of eavesdroppers. The strategy always involves the same ingredients: The message, called the plaintext, gets distorted (the encryption) so that anybody who intercepts it sees only garbled gibberish (the ciphertext). Ideally, only those with a secret key can decrypt it. If you share your secret key with the intended recipient and nobody else, then you can, in theory, communicate with them in code. Cryptography underlies everyday financial transactions and online communication, not just spy messages.

To understand Kryptos