25 Unsolved Ciphers and Codes You Can’t Break

Posted by , Updated on March 21, 2024

Starting from archaic languages to contemporary cryptographic conundrums issued by government bodies such as the CIA, here are 25 renowned ciphers and codes that remain uncracked, to challenge your cryptanalytic skills.



Beale Ciphers

unsolved ciphers and codes

In 1885 a small pamphlet was anonymously published in Virginia containing a story and three encrypted messages. The story claimed that the messages led to a treasure buried by a man name Beale. Only one of the messages was ever solved.


Voynich Manuscript

unsolved ciphers and codes

Estimated to be at least 600 years old this 232 page manuscript is written in some sort of undecipherable language. It features numerous pictures of unidentified plants and people in strange plumbing like contraptions.


Zodiac Killer Ciphers

unsolved ciphers and codes

Between 1966 and 1974 the Zodiac serial killer sent more than 20 encrypted messages to police. Most have been cracked but a few remain unsolved.



unsolved ciphers and codes

In 1990 a sculpture with 4 sections of encrypted characters was installed at CIA headquarters as a challenge to the employees of the agency. 3 sections have been decrypted but a fourth is still not solved.


Dorabella Cipher

unsolved ciphers and codes

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 Cipher

unsolved ciphers and codes

Alexander d’Agapeyeff wrote an elementary book on cryptography in 1939 entitled Codes and Ciphers. In the first edition he included a challenge cipher. It was never solved and even Alexander embarrassedly admitted later that he no longer knew how he’d encrypted it.


Linear A

unsolved ciphers and codes

In 1990 a large number of clay tablets dating back to 1800 BC were discovered in Crete. They contained two different types of scripts which were named Linear A and Linear B. Linear B was fully deciphered in the 1950s while Linear A remains unsolved.


The Phaistos Disk

unsolved ciphers and codes

A circular clay tablet about six inches across, it was discovered in Crete in the early 1900s. With an alphabet of 45 different symbols it has thus far remained uncracked. There have been suggestions, however, that it could help decipher Linear A.


Chinese "Gold Bar" ciphers

unsolved ciphers and codes

In 1933, seven gold bars were allegedly issued to a General Wang in Shanghai, China. They contain pictures, ancient Chinese writing, some form of script writing, and cryptograms in latin letters.


Indus Script

unsolved ciphers and codes

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

unsolved ciphers and codes

In 1987 a message was posted 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 was ever solved.


Enigma Encryption system

unsolved ciphers and codes

A popular encryption mechanism used by Germany during World War II, there are still some messages that have yet to be decrypted.


Pigeon Cipher

unsolved ciphers and codes

An unsolved WW II message that was found attached to the remains of a pigeon found by a man while he was cleaning out his chimney in Surrey, England.


Rongo Rongo Script of Easter Island

unsolved ciphers and codes

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.


Vinča / Old European

unsolved ciphers and codesunsolved ciphers and codes

A collection of symbols found on many of the artefacts dating from between 6,000 to 4,500 BC excavated from sites in south-east Europe, in particular from Vinča near Belgrade. There is no agreement on whether these symbols are a writing system.



unsolved ciphers and codes

A script which first appeared in about 2900 BC in Susa, in south-western Persia (modern Iran). It has yet to be deciphered and the language it represents is unknown.


Rohonc Codex

unsolved ciphers and codes

Named after the city of Rohonc in what was then Western Hungary, this manuscript written in an unknown language is on display at the Hungarian Science Academy.


Taman Shud

unsolved ciphers and codes

On December 1, 1948 an unidentified body washed up on a beach in South Australia. He remains unidentified and the only clue was a piece of scrap paper in his pocket that had two words written on it “taman shud”, which translates to “ended” in Persian. This was a direct reference to the The Rubaiyat of Omar Khayyam, a book that was discovered in the back seat of an unlocked car near the beach where he was found. There were several numeric codes in the car as well but they were never deciphered.


McCormick Cipher

unsolved ciphers and codes

In 1999 the body of 41 year old Ricky McCormick was found decomposing in a field in eastern Missouri. He had two cryptic ciphers in his pockets. The FBI has asked for the public’s help in cracking the code by crowd sourcing a solution over the internet.



unsolved ciphers and codes

While it is not technically unsolved anymore as the algorithm has since been released, for numerous years no one could decode the cipher that author J.F Byrne had published in his autobiography.


Shugborough Inscription

unsolved ciphers and codes

O-U-O-S-V-A-V-V. These letters are carved into a stone monument on the grounds of Shugborough Hall in Staffordshire, England. In spite of much speculation no one has ever managed to figure out their meaning.


Navajo Code Talkers

unsolved ciphers and codes

During World War II the allies used Navajo Indians for the purposes of encrypted communication. Navajo is one of the most notoriously hard to learn languages on Earth with sounds that are uncommon to many other languages. Furthermore, the language itself used code words which made it hard even for native speakers to understand. It was never broken and played a crucial role in the Allied victory.


Blitz Ciphers

unsolved ciphers and codes

Discovered during WWII in a bombed cellar in East London, they show around 50 distinct calligraphic symbols. Some speculate that they could be 18th century Freemason ciphers.


Bellaso Ciphers

unsolved ciphers and codes

This sixteenth century Italian cryptologist was responsible for many techniques still used today and several of his “challenge” ciphers have yet to be decrypted.


Bacon Cipher

unsolved ciphers and codes

Sir Francis Bacon was well known for creating and using what is now known as the Bacon Cipher in his literary works. For the last several hundred years there has been speculation that Sir Bacon was in fact responsible for writing the works of Shakespeare and that his cipher might be found throughout the texts. As of yet there has been no conclusion on the matter.