Famous Unsolved Codes and Ciphers

This is an unofficial list of well-known unsolved codes and ciphers. A couple of the better-known unsolved ancient historical scripts are also thrown in, since they tend to come up during any discussion of unsolved codes. There has also been an attempt to sort this list by "fame", as defined by a loose formula involving the number of times that a particular cipher has been written about, and/or how many hits it pulls up on a moderately sorted web search.

If you would like to discuss the details or placement of any item on the list, please contact the webmistress.

Beale Ciphers - In 1885, a small pamphlet was published in Virginia containing a story and three encrypted messages. According to the pamphlet, around 1820 a man named Beale buried two wagons-full of treasure at a secret location in Bedford County, Virginia. He then left a small locked box with a local innkeeper, and left town, never to be seen again. The pamphlet went on to state that the innkeeper, after having not heard from Beale for many years, opened the box and discovered encrypted messages. Never able to read them, he eventually passed them along to a young friend shortly before the innkeeper's death in 1863. According to the pamphlet, the friend spent the next 20 years trying to decrypt the messages, solving only one which detailed the tons of gold, silver and jewels that were buried, along with a general location. The still unsolved messages supposedly give exact directions, and a list of who the treasure belongs to. According to the story, the friend finally decided to walk away from the quest, and publish everything they knew about the situation in the (anonymous) pamphlet, which was supposedly published by James Ward, another friend of the innkeeper. There have been many exhaustive searches for the treasure, and much effort spent on decoding the other messages, without (confirmed) success. There are many claimed solutions, usually bannered in combination with a book that someone is trying to sell, but no one has ever been able to produce a duplicatable decryption method. There have also been some pretty compelling arguments that the entire original story was a hoax. There are several inconsistencies in the pamphlet's text, and even speculation that the story was a parable related to Masonic rituals. More information can be found here.

Voynich Manuscript - At least 600 years old, this is a 232-page illuminated manuscript entirely written in a secret script. It is filled with copious drawings of unidentified plants, herbal recipes of some sort, astrological diagrams, and many small human figures in strange plumbing-like contraptions. Carbon-dated to the early 1400s, it was brought to modern attention in 1912 when it was purchased by Wilfrid Voynich from the collections at the Villa Mondragone, near Rome. Color images of all of the pages can be seen at archive.org and Yale's Beinecke Library website (the current owner of the manuscript). The script is unlike anything else in existence, but is written in a confident style, seemingly by someone who was very comfortable with it. In 2004 there were some compelling arguments which described a technique that would seemingly prove that the manuscript was a hoax, but to date, none of the described techniques have been able to replicate a single section of the Manuscript, so speculations continue. Attempts at identifying the plants can be seen here, and more information about the Manuscript can be found at voynich.net, voynich.nu, and crystalinks.com. To celebrate the centenary of Wilfrid Voynich finding the manuscript, a conference was held at the Villa Mondragone near Rome on May 11, 2012. For more information on that conference (pics/programme/etc), check here.

Kryptos - In 1990, a sculpture was installed at CIA Headquarters in Langley Virginia, as a challenge to the employees at the Agency. Its thousands of characters contain encrypted messages, of which three have been solved, but there is still a fourth section at the bottom consisting of 97 or 98 characters which remains uncracked. The sculpture was created and encoded by Washington DC sculptor Jim Sanborn, using encryption systems designed by the Chairman of the CIA's Cryptographic Center, Ed Scheidt. More information: Kryptos FAQ

Dorabella Cipher - In 1897, the well-known composer Edward Elgar (of "Pomp and Circumstance" fame) sent an encrypted message to a 23-year-old friend, Miss Dora Penny. To this day, it still has not been solved.

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.

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. A bit more info here. As a small update: In 2020, I (Elonka) spoke to the attorney listed on the IACR site, Mr. Peter Bisno, Esq.. He confirmed that he'd seen the gold bars in question, and that they were large "about the size of a remote control". He said that in the 1990s that he didn't have any luck with the banks, who didn't see the claim as legitimate, and so his portion of the case was eventually closed. The last known owner of the bars was presumably Mr. Bin J. Tao.

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.

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. One message that received a great deal of attention in November 2012 is the "Pigeon Cipher", a WWII message that was found attached to the remains of a pigeon that a man found while he was cleaning out his chimney in Surrey, England. The message was given to GCHQ and sparked an international flurry of attention: BBC News, The Telegraph, New York Times, etc. If you know of any other 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.

Chaocipher - Algorithm revealed, ciphers solved in 2010. 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. Check here for a timeline and further information.

Zodiac Killer ciphers - From 1966 to 1974, the Zodiac serial killer sent more than 20 written communications to police officials. Most of these messages have been cracked, but there are still some that remain unsolved. The killer was never caught. More information here. New! Update, December 11, 2020, Z-340 solved! This leaves two very short messages still unsolved, but because they are so short, the likelihood of their being solved is unlikely, due to the Unicity distance (the likelihood that a unique solution could be found).

Feynman Ciphers solved in May 2023. 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. As of May 2023, all three have now been solved! See Nick Pelling's Cipher Mysteries site for confirmation.

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.


Other recommended reading on classical ciphers


  • Cipherbrain - Klaus Schmeh in Germany is always on the prowl for any kind of unsolved ciphers, from full books to simple postcards, and if you happen to run across a cipher you'd like to see solved, the older the better, he's the person to send it to. Some of the best codebreakers in the world keep a sharp eye on his blog, and the post-blog discussions are often as interesting as the blog itself.

  • Cipher Mysteries - Run by Nick Pelling in the UK, who loves to track and debunk the latest breathlessly reported and usually wrong solutions of things such as the Voynich Manuscript. Whenever I hear about the claim of a solve for anything, I usually head to Nick's site to see if he has debunked it yet!

Page created: December 8, 2003 by Elonka Dunin

Last modified: September 18, 2023

Much thanks go to Jim Gillogly, the American Cryptogram Association, the staff of Cryptologia, and members of the Kryptos Group for their assistance in compiling some of this information.

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