Music composer Edward Elgar wrote an encrypted message in 1897 to his beloved Dora consisting of 87 characters spread over three lines. The message is made up of 24 symbols, each symbol consisting of 1, 2, or 3 approximate semicircles oriented in one of 8 directions.  The code, known as the Dorabella Cipher, could not be understood by Dora herself, nor by any other person to date.

 Around 5,000 years ago during the Bronze Age, the Harappan civilisation made itself prominent in the Indus Valley in what today is known as Pakistan. The script the ancient men and women of Harappa used to write and read with has still not been deciphered to this day.

In the 1939 edition of the book Codes and Ciphers, Russian-born English cryptographer Alexander D’Agapeyeff introduced a number-based cipher. The author himself admitted he had forgotten how to decipher the code and it was taken down from the book in its later editions.

In 1912 Italy, a manuscript containing 240 pages of illustrations, texts and diagrams were found. Now known as The Voynich Manuscript, it dates back to the 15th century. Only nine words have been deciphered from the text, these are – Nigella Sativa, Hellebore, Kesar, Juniper, Corinader, Chiron, Taurus, Cotton and Centaurea. The rest remain a mystery.

On the grounds of the CIA headquarters in the U.S, state of Virginia lies an installation (built in 1990), named Kryptos, with codes written on it. There are four encrypted messages on the installation. The first one is a poem, the second shows the compass positions of the CIA headquarters, the third is a paragraph taken from the diaries of archaeologist Howard Carter. The fourth one remains a mystery, which only Kryptos’ creator Jim Sanborn knows.

Between 1969 and 1974, the Zodiac Killer sent coded letters to several U.S newspapers in and around San Franciso. These letters included four cryptograms, three of which have yet to be solved.

The Elamites were a people of ancient Persia (4500 years ago) who communicated using the oldest known writing system from Iran. It used more than 1,000 symbols said to be part of an accounting system. Some parts of the language are unreadable to modern day linguists.

In 1948, an unidentified dead body was found on an Adelaide Beach in Australia. In that man’s pocket, was a small rolled piece of paper that bore the Persian phrase “Tamam Shud”. A book was found from another man’s car that bore the same name and five unreadable code lines that could only be seen under ultra-violet light. The code has been declared to be undecipherable.

 There are letters written on the Shepherd’s Monument (built sometime around 1760) in Shugborough Hall, UK, that have baffled cryptologists for over 250 years. The sequence of eight letters are so mysterious that even Charles Darwin and Charles Dickens failed to explain them.

Police found 41-year-old Ricky McCormick’s body in a field in U.S Missouri on June 30, 1999. They found two notes in his pockets that contained 30 lines of ciphers. Ricky, who was supposedly illiterate, wrote something so hard it could not be broken even by top FBI cryptologists.