Famous Unsolved Codes and Ciphers

D'Agapeyeff - Alexander d'Agapeyeff wrote an elementary book on cryptography in 1939, entitled "Codes and Ciphers." In the first edition, he included a challenge cipher. Nobody's solved it, and he embarrassedly admitted later that he no longer knew how he'd encrypted it. It was left out of the second and later editions. Some think it was botched, and many think it could still be solved despite that. It has lots of "phenomena" noted, but nothing close to a crack.

Linear A - In 1900, a large number of clay tablets dating back to 1800 BC were discovered in Crete. The tablets appear to use two different types of scripts, which were named "Linear A" and "Linear B." Linear B was finally deciphered in the 1950s. Linear A remains unsolved.

The Phaistos Disk - A circular clay tablet about six inches across, discovered in Crete in the early 1900s, and believed to date back to 1800 BC. With an "alphabet" of 45 different symbols, 241 signs are stamped into both sides in spiral patterns. There has been much speculation about its meaning, with wildly variant claimed solutions so far. It's also been suggested that the disk might turn out to be a Rosetta Stone to help decipher Linear A, since it was discovered near a fragment of a Linear A tablet. More information here.

Chinese "Gold Bar" ciphers - In 1933, seven gold bars were allegedly issued to a General Wang in Shanghai, China. These gold bars appear to represent metal certificates related to a bank deposit with a U.S. Bank. The gold bars themselves have pictures, Chinese writing, some form of script writing, and cryptograms in latin letters.

RSA Challenges - There are a number of modern computer-based challenges, including several factoring challenges from RSA Labs that have implications for the strength of public-key systems, and some equivalently difficult elliptic curve challenges, also relating to public-key cracking (check here for Bruce Schneier's high-math analysis of the RSA/Elliptic Curve debate). As of this writing, the most recently cracked RSA Challenge was in November 2005, when RSA-640, a 193-digit number, was successfully factored (which won a $20,000 prize). There are several more on the list, with prizes up to $200,000, which have not yet been cracked. Many fly-by-night snake-oil crypto companies also put out challenges that are arguably famous because the media sometimes pick up the challenge uncritically, but they are usually not worth mentioning on this list.

Indus Script - The Indus Valley civilization flourished around 2600 to 1800 BC on the Indian sub-continent, leaving behind thousands of objects inscribed with a pictographic script that seems to have been composed of about 400 signs. A great deal of work has been done on analyzing the messages that are available, but to this date the script still has not been deciphered.

Richard Feynman's Challenge Ciphers - In 1987, someone posted a message to an internet cryptology list, saying that Caltech Physics Professor Richard Feynman was given three samples of code by a fellow scientist at Los Alamos. Only one of the three was ever solved.

Unsolved World War II Systems - Though the Enigma encryption system was cracked, and the Bletchley Park crypto project is quite famous, there are still some scattered unsolved Enigma messages from World War II. There are also various other WWII encryption systems that were never solved, but they have not been included on this list because the focus is more on specific famous messages or entire well-known systems that have not yet been cracked. If you know of a particular message or system that you think is worthy of inclusion, please contact the webmistress.

Rongorongo Script of Easter Island - In 1868, Europeans first reported seeing wooden tablets on the incredibly remote Easter Island in the south Pacific. The tablets were covered with an unknown hieroglyphic script. Only 20 or so tablets are thought to be in existence, with little progress in determining what it is that they say.

Other Uncracked Ancient Ciphers - There are several other ancient writing systems that are still undeciphered, such as the 13,000 Etruscan inscriptions, Proto-Elamite, Meroitic, and various other obscure glyphs. More information about some of these can be found in a review of Andrew Robinson's book Lost Languages

Famous Unsolved Codes That Have Since Been Solved

Poe's Cryptographic Challenge - In 1839, Edgar Allan Poe published two cryptographic challenges which remained unsolved for over 150 years. The first one was finally solved in 1992, and the second one in October 2000

Cyrillic Projector Cipher - Washington DC sculptor Jim Sanborn, famous for the CIA's Kryptos sculpture, also created some related sculptures which included both the text from Kryptos, and some encrypted Russian text about KGB operations. The best example was the Cyrillic Projector, which was created in the early 1990s and then installed permanently at the University of North Carolina, Charlotte in 1997. It was cracked in September 2003 by an international team involving the Kryptos Group.

Oak Island Money Pit Cipher Stone (solved, though alleged treasure still unrecovered) - In 1795, a teenager discovered a deep pit on Oak Island in Nova Scotia, along with hints that there was a great treasure at the bottom. Over the next two hundred years, multiple well-financed attempts have been made to learn what is hidden, but have been repeatedly foiled due to the unstable nature of the surrounding land, and the tendency for deep tunnels to suddenly flood with water. Multiple reports referred to tantalizing artifacts from 300 years ago, such as a pair of scissors, an encrypted stone tablet, barriers of oak logs, and other man-made objects deep below the ground. In 1976, a camera lowered into a subterranean chamber allegedly recorded images of wooden chests, tools, and a body, before the unstable land again collapsed the exploration tunnel. In 2002, a report was produced by the Woods Hole Oceanographic Institute with more recent information, and which challenged some of the earlier findings. In any case, along with large amounts of money which have been sunk into this quest, multiple lives have also been lost attempting to solve the mystery.

Smithy Code. - In April 2006, as part of the trial ruling of a plagiarism trial about the book ''The Da Vinci Code'', the judge in the case, Justice Peter Smith embedded his own secret code in the 71-page trial ruling (zipped pdf). Once the code was discovered by a London legal analyst, it sparked off a worldwide race to see who could crack the code first. According to The Guardian, it was solved by Dan Tench, the legal analyst who first discovered the code, after he received a series of email hints from the judge. For more information, check here for an explanation of the code by the Kryptos Group (who solved it, but were not the first to do so), and check here for The Smithy code page at Wikipedia.

New! (August 2010) Chaocipher - Algorithm revealed, ciphers in the process of being solved. In 1918, J.F. Byrne created a machine-based cryptographic system. In 1953, he used it to create a code challenge as part of his autobiography Silent Years. There were at least three people who knew how the system worked: his son, and two editors of the journal Cryptologia who were let in on the secret in 1990. Chapter 21 of Byrne's book contained four ciphers created with the Chaocipher device. Byrne had included both the plaintext of the ciphers, and the ciphertext, except for the last two lines of the fourth cipher, for which he did not include plaintext, and offered a $5,000 prize to any solver who would come forward within three months of the book's publication. Byrne died in 1960 with the cipher still unsolved. For the next 50 years, the cipher remained (publicly) unsolved, until May 2010, when Byrne's materials were donated by his estate to the National Cryptologic Museum. In July 2010, the actual algorithm was described publicly by Moshe Rubin, and he has since released a report discussing the decipherment of the first cipher in the book. As of this writing, August 8, 2010, plaintext for the last part of the fourth cipher is being discussed privately in the cryptographic community, but has not yet been reported publicly. Check here for a timeline and further information.

If you know of a solution to one of the above codes or mysteries, or would like to suggest any changes or additions to this list, please contact the webmistress.