Just between us: cryptic secrets
Confidential messages not intended for anyone else’s eyes or ears—even children play around with enciphering by creating their own secret code at school that only the addressee can figure out and no one else. People have been working with the principles of encryption for over 3,000 years, starting in Egypt and Mesopotamia when they simply replaced their familiar symbols with others. From the 15th century, text was encrypted using the polyalphabetic system, whereby a letter could be substituted with more than one character. The best-known apparatus is probably the Enigma, a device used during the Second World War—its name is now synonymous with encryption machines.
The cipher rods
Monoalphabetic encryption was particularly common up to the 15th century. This involved substituting letters with other set characters, e.g., an A is always substituted with a D, a B with a W, a C with an M, etc. With polyalphabetic encryption, however, letters could be substituted with more than one letter, as with the cipher rods here. An A could now be a D in one word, but a K in the next. As with all other systems through to modern times, the sender and receiver need to have previously agreed on the methodology of the secret language.
The automatic cryptograph
In 2013, a random find in a warehouse turned out to be the oldest encryption machine in the Deutsches Museum. This so-called cryptograph by Danish engineer Alexis Køhl (1846–1920) was sent by the inventor himself in 1918 from Copenhagen to the Deutsches Museum, along with the announcement that he would soon travel to Munich to talk about his device. Unfortunately this trip never took place, as Køhl fell ill and died shortly after. We now know that Køhl constructed his device at the end of the 19th century.