People love a good mystery, and few things are more mysterious than a long-unsolved code. Here are the stories of four ciphers and codes we've been unable to crack.
1. The Shugborough Inscription
Letters carved into Shepherd's Monument at Shugborough Hall in the mid-1700s, commissioned by Thomas and Admiral George Anson, continue to ignite the interest of conspiracy theorists. OUOSVAVV and, below at either end, the letters D and M—that's the whole thing. Yet such a short and seemingly meaningless inscription is just cryptic enough to mean just about anything: an acrostic in Latin dedicating the shrine to George Anson's wife, a love letter, a list of Shugborough residents by surname, a kind of old-school graffiti, and of course, a link to the Priory of Sion—perhaps as a coded message leading to the Holy Grail.
The latter theory was compounded by similar themes in Dan Brown's The Da Vinci Code, prompting the general manager of Shugborough Estate to launch a promotional campaign implying a definite connection between the inscription and the Holy Grail. The influx of Grail-hunting codebreakers resulted in countless new "solutions" related to the life of Jesus and an alleged Knights Templar/Priory cover-up of his non-divine bloodline. Jury's still out on that one.
2. The Dorabella Cipher
The Dorabelle Cipher is an 87-glyph, three-line code written by "Pomp and Circumstance" composer Edward Elgar in a letter to Dora Penny in 1897. Elgar was fascinated by cryptography, often suggesting that his compositions were coded references to other famous works or, in the case of Enigma Variations, at least partly decipherable in Morse code.
While trying to make his big break as a composer, Elgar met Dora Penny (he called her "Dorabella"), the daughter of a clergyman. Penny was 20 years his junior, but the two shared common interests in cycling, kites, and the Wolverhampton Wanderers soccer team. The Pennys invited Elgar and his wife, Alice, to stay with them. After returning home, Alice Elgar sent a note of thanks to the family; the coded letter, addressed to "Miss Penny" was tucked inside.
Theories abound about the nature of the message, which would have been seen by the entire family. Was the much older and married Elgar professing his affection for Dora? Is it a joke inspired by artifacts from the Penny family's travels? Is it a musical composition? Suggestions for all three are floating around but, without deciphering the note, there's no way to know.
Attempts to crack the code have resulted in more confusion. When deciphered musically, the code is, well, unimpressive. Direct substitution (wherein each symbol corresponds to a letter of the alphabet) produces nonsense. Double encipherment is likely, but no keyword is known, so nobody has been able to break the Dorabella Cipher for 114 years.
3. The Zodiac Killer's Codes
Throughout the 1960s and '70s, a serial killer terrorized the San Francisco Bay area, sending letters and encrypted messages to the media and police. Of the many letters, at least four were cryptograms. Only one, a three-part missive sent to three separate newspapers, has been solved. The 408-character code was cracked by Donald and Bettye Harden; it contained multiple errors in both spelling and transcription, which is possibly why the remaining codes have been so difficult to decrypt.
There are several sites dedicated to decoding the Zodiac Killer's cryptograms, but this one has a handy web toy that lets users practice their cryptanalysis skills online.
4. The Voynich Manuscript
The Voynich Manuscript is arguably the most famous unsolved text in history. Named after Wilifred M. Voynich, the book dealer who acquired it in 1912, the 240-ish page illuminated codex contains drawings of bizarre plants, astrological maps, strange anatomical drawings, and what are possibly pharmaceutical compounds. A final section, devoid of illustration, is thought to be an almanac or list of recipes. The almanac section is the most text-dense section of the work.
Though it has been scrutinized extensively by cryptologists and interdisciplinary groups, not a single section of the Voynich Manuscript can be satisfactorily deciphered. Certain glyphs resemble European alphabets, but largely the language remains unidentifiable. The structure of words and sentences, word repetition and frequency, and distribution of letters within words resist correlation to known languages.
The first "solution" was offered by William Romaine Newbold in 1919, claiming the codex was authored by Roger Bacon in the 13th century. But radio carbon dating disproves this theory by showing the manuscript to be at least 200 years too young; it was likely created between 1404 and 1438. This also disproves a long-held belief that Voynich himself constructed the manuscript as an elaborate hoax to gain fame and money. Similarly, the C14 dating discounts multiple theories of other suspected authors, who mostly lived a few hundred years after the book's creation.
The most cryptic feature of the Voynich Manuscript, though, is the purpose. Is it a pharmacopeia? Proof of an alien encounter? The gibberish glossolalia of an insane or possessed person? Without context, satisfactory translation, and verifiable authorship, it's just about anyone's guess. The only certainty is that it is unique. The Voynich Manuscript is currently owned by Yale University's Beinecke Rare Book and Manuscript Library, which offers the full catalog of document images on its website.