8 of History’s Most Mysterious Uncracked Codes

'Kryptos' at CIA headquarters in Virginia.
'Kryptos' at CIA headquarters in Virginia. / Carol M. Highsmith Archive, Library of Congress Prints and Photographs Division // No Known Restrictions on Publication

History is rife with mysterious codes that have yet to be cracked. Some of the codes’ creators are still around to offer clues, while other ciphers have been around for long enough that experts can only rely on historical sources for help. From bewildering ciphers found on a murdered man’s body to the unsolved codex that once belonged to Holy Roman Emperor Rudolf II, here are a few codes that still have cryptologists scratching their heads, adapted from an episode of The List Show on YouTube.

1. Rapa Nui’s Rongorongo  

Verso of rongorongo Tablet B, Aruku Kurenga
Verso of rongorongo Tablet B, Aruku Kurenga. / Mfield, Wikimedia Commons // Public Domain

In the early 1860s, raiders attacked the island of Rapa Nui—now known as Easter Island—and abducted hundreds of natives to be used as enslaved labor in Peru. With those raids, it was once said, the final source of knowledge regarding rongorongo, the hieroglyphic language used by the Rapa Nui, disappeared. But while it’s true that, to this day, no one has been able to make any sense of extant rongorongo texts, everything else about this seemingly-lost language defies simple narratives and clear explanations. 

The idea that knowledge of rongorongo disappeared in those raids of 1862 and ‘63 was eventually cast into serious doubt, but it does seem to be the case that anyone schooled in rongorongo died that decade, likely from diseases that had been introduced to the island by Europeans. 

Many of the artifacts containing rongorongo were destroyed in the 1860s. The pictographs were often carved into wood, and some contemporary sources said that the carved artifacts were burned by the Rapa Nui themselves to build fires. This may have been at the urging or compulsion of Catholic missionaries: Some Rapa Nui said that the evangelizing Europeans warned natives that rongorongo was a connection to their so-called heathenism; others disputed this version of events. A European priest on the island in the early 20th century believed that the rongorongo artifacts hadn’t been destroyed at all, but hidden in “the island's many caves and lava tubes,” as Steven R. Fischer laid out in his 1997 book about the language. 

A couple dozen inscriptions did survive, and people have been trying to decipher the various symbols contained within them for more than a century—without much luck. Some glyphs appear to represent human or animal forms, while others are abstract shapes. No one has ever put forth a convincing translation of the texts, and much of the history surrounding their origin remains contentious. Debates have raged as to whether the script predates European contact, and fantastical ideas have arisen regarding aliens and lost continents. 

Some of our ideas about rongorongo have been informed by more plausible scholarship, though, including work done by an early 20th century ethnographer named Katherine Routledge. Routledge arrived on Easter Island in 1914 and interviewed elders with knowledge dating back to the 1850s. Among the most intriguing pieces of information gleaned in her interviews is the fact that, according to her sources, young Rapa Nui students of the past were able to master rongorongo in just a few months. 

2. The Beale Ciphers

After discovering gold and silver in what is now the American west, Thomas J. Beale buried a  treasure in Bedford, Virginia. All you have to do to find it is solve a simple cipher

Well, actually that’s just the claim made in 1885’s “Beale Papers,” published decades after Beale’s disappearance. Few can agree on much more than that—whether Beale actually left a treasure or even the ciphers themselves are a matter of serious contention.

Some historical details about his supposed exploits have been called into question. Beale’s purported discovery of silver and gold, for example, doesn’t seem to line up with known timelines about other precious metal discoveries. Of course, many Beale Cipher enthusiasts have their own idiosyncratic explanations for these apparent inconsistencies. Others believe that, even if the treasure itself is a hoax, the ciphers themselves might represent a real cryptographic challenge that remains to be solved.

The cryptanalyst William Friedman summed up the confusion around the Beale Ciphers, saying, “On Mondays, Wednesdays, and Fridays, I think it is real. On Tuesdays, Thursdays, and Saturdays, I think it is a hoax.”  

3. The Voynich Manuscript

Three pages from the Voynich manuscript showing strange plants and text in an unknown language
A page from Beinecke MS 408, also known as the Voynich Manuscript. / Beinecke Rare Book and Manuscript Library, Yale University

When a book supposedly passes hands from an astrologer to the Holy Roman Emperor, you’d expect a certain degree of intrigue to accompany it. The so-called Voynich Manuscript—named for a Polish antiquarian who purchased it in 1912—doesn’t disappoint. 

After Wilfrid Voynich acquired the manuscript in the early 20th century, he claimed he’d been sworn to secrecy regarding its origins. It likely has a connection to the Holy Roman Emperor Rudolf II, who Voynich suggested got it from an astrologer in the court of Elizabeth I named John Dee. (For what it’s worth, that provenance is now considered questionable.)

The pages are full of drawings of what look like plants and other seemingly scientific or pseudoscientific diagrams, along with, of all things, a lot of ladies bathing. The text consists of roughly 35,000 words and appears to be entirely invented—not just the words, but the letters themselves

Radiocarbon dating done by a team led by the University of Arizona’s Greg Hodgins pegged the pages to the early 15th century, but no one knows who wrote the book, or why. Some of the world’s best code breakers have been drawn to the Voynich Manuscript and been left stumped, including William and Elizebeth Friedman, a married couple and two of their generation’s leading cryptanalysts (William also took on the Beale cipher). The Friedmans studied the manuscript and deemed it to be a genuine artifact and not a hoax. By the time of his death, William seems to have concluded that it was less a code, per se, than, “an early attempt to construct an artificial or universal language of the a priori type”—a language whose vocabulary isn’t based on any existing languages.

In the absence of a clear explanation for the text, outlandish theories have proliferated. Voynich himself once said, “When the time comes, I will prove to the world that the black magic of the Middle Ages consisted in discoveries far in advance of twentieth-century science.” The time apparently never came; his dramatic declaration might have just been a bit of showmanship. 

Still, there are countless theories as to the real meaning of the book. One popular idea actually says that there’s no meaning to it at all—that, contrary to the Friedmans’ analysis, the manuscript was created as some kind of hoax, perhaps to fleece Emperor Rudolf.  

4. The Dorabella Cipher

The Dorabella Cipher which consists of squiggly characters
The Dorabella Cipher. / Wikimedia Commons // Public Domain

Another undeciphered—and potentially undecipherable—code comes from Edward Elgar. If that name sounds familiar, it’s probably because Elgar wrote “Pomp and Circumstance,” the second most iconic graduation song of all time. 

The Dorabella Cipher gets its name from its original recipient, Dora Penny, a friend of Elgar’s who was almost 20 years his junior. It consists of a series of squiggly characters. A number of people have claimed to have cracked Elgar’s code, but none of them has been widely declared correct.

Tim S. Roberts, from the University of Central Queensland in Australia, felt that he had come up with a solution, which read “P.S. Now droop beige weeds set in it—pure idiocy—one entire bed! Luigi Ccibunud lovingly tuned liuto studio two.” The first half could maybe refer to a gardening project, as Roberts said, but then you get into “Luigi CCibunud” and have to buy that Elgar was referencing a certain Italian composer and poking fun at Dora’s stutter while discussing gardening. Other would-be solutions require arbitrary rules or result in complete gibberish, leaving Elgar’s message a secret. 

5. The Feynman Challenge Ciphers

In 1987, a man named Chris Cole posted three ciphers onto a usenet newsgroup dedicated to cryptography. According to the post, Dr. Richard Feynman had shown him the ciphers when Carter was a graduate student at Caltech. The first cipher was actually solved in just one day by a Usenet user, but the other two remain uncracked today.

6. Kryptos Section Four

Picture of the sculpture Kryptos.
Kryptos. / Jim Sanborn, Wikimedia Commons // CC BY-SA 3.0

You’d think that displaying a code on the grounds of CIA headquarters would lead to a quick solution. But even though many United States’ intelligence officers pass by the Kryptos sculpture on their way to the cafeteria in Langley, Virginia, one section of code remains unsolved—even though the codemaker has provided several clues to cryptologists over the years. 

Krytpos was created by artist Jim Sanborn and installed on Langley’s grounds in 1990. In subsequent years, three of the piece’s four sections of code were cracked. The first section, decoded, revealed a poetic sentence written by Sanborn: “Between subtle shading and the absence of light lies the nuance of iqlusion.” Sanborn said he included an intentional misspelling of illusion to “mix it up.”

The second section is a rather opaque paragraph that references Langley’s coordinates and former CIA head William Webster, who ran the agency when the sculpture was first installed. Section three paraphrases Howard Carter’s account of discovering King Tut’s tomb in 1922. 

Sanborn has said that the first three sections provide a clue to solving the fourth, and has also decoded a few specific words from its text, including Berlin, clock, and northeast. 

7. Tamám Shud

In 1948, a man was found dead on Somerton beach in Australia. He was wearing a suit and had a half-smoked cigarette resting on his collar. The more authorities looked into the case, the stranger it got. 

Police couldn’t figure out who the dead man was or even how he had died. Some people suspected a rare poison could have done him in and then been metabolized by his body without leaving any trace. The deceased’s unusually well-defined calf muscles and a label on some clothing that said “Keane” might have been clues or just red herrings—no Keane was ever identified as a match for the man, and theories that he was a professional dancer or wore high heels remain unsubstantiated.

Months into the investigation, an expert named John Cleland discovered a slip of paper in a small pocket in the dead man’s pants. The paper had the Persian phrase tamám shud, or “it is ended,” printed on it—the final words in many translations of The Rubáiyát of Omar Khayyám.

It took months for someone to come forward with a version of the book that matched the scrap, and that just created more questions. On the rear cover of the book—which has a provenance shrouded in its own layers of fog—authorities found a phone number and a faint string of characters. The phone number led to a woman who admitted to giving a man named Alfred Boxall a copy of The Rubaiyat, but it turned out Boxall was still alive and still had his copy of the book. 

Police went back to that mystery string of characters and placed it under ultraviolet light, revealing more letters that appeared to form some kind of cipher. If it is a code, it’s never been cracked—and, given how limited the letters are, it may never be. Weirdly, no one’s ever found another copy of The Rubaiyat that matches the edition found on the dead man’s body.

There are those who believe the Somerton man died by suicide and others who think he was murdered for his involvement in some kind of high-stakes espionage. While we may never know the truth, in 2021 the man was exhumed for DNA testing; separate DNA tests using material salvaged from his death mask linked him to an Australian man named Carl Webb.

8.  Ricky McCormick’s Notes

When the body of Ricky McCormick, a possible homicide victim, was discovered in June 1999, officials found two handwritten notes in his pants pockets consisting of an indecipherable string of letters.  

McCormick was allegedly functionally illiterate. His mother, Frankie Sparks, said “The only thing he could write was his name. He didn't write in no code.” But authorities don’t believe the notes are meaningless scribblings—they actually released the possible ciphers to the public in 2011 in the hopes that someone might help solve them. 

McCormick’s girlfriend believed he could have been involved in trafficking marijuana. He also had a number of health problems, perhaps brought about by his smoking habit—allegedly begun at the age of 10—and his penchant for drinking upwards of 20 caffeinated beverages per day. A natural cause of death can’t be ruled out, but McCormick’s purported connection to illegal activity and the mysterious circumstances surrounding his death have led many to conclude that something nefarious happened.

Detective Michael Yarbrough, who worked on the case at one time, summed up the frustrating confusion of the case to St. Louis’s Riverfront Times. “It’s kind of like Humpty Dumpty. All the pieces are there, but how do you put them back together?”