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. New! 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, check here.

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.

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. 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.

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.

RSA Challenges - There have been a number of modern computer-based challenges, including several factoring challenges from RSA Labs with 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). The elliptic challenge ran from 1997 to 2009. The RSA Challenge with prize money was discontinued in 2007, though several numbers remain unfactored, and distributed.net has announced that they are continuing to privately sponsor the prize. Some 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.

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. 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.

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.


More information

A note from the webmistress: Because of the interest in this topic, I was approached in mid-2005 by a British book publisher, who asked me to write a book which included a section on some of the above codes and ciphers. I have done so, and the book was published in early 2006. I have wrestled with the idea of whether or not to promote the book on this page, because I don't want it to look like I am using this page as a way to advertise the book (I really really hate webpages that do that). So, I am mentioning it, along with some other recommended titles, here: If you still think that this whole page was created just as an ad for the book, I promise, it wasn't. And I do apologize if it looks like that. :/ Elonka

Page created: December 8, 2003 by Elonka Dunin

Last modified: July 5, 2014

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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