In the world of cryp­tog­ra­phy, sub­sti­tu­tion ciphers are child’s play. Indeed, we may remem­ber lit­er­al­ly play­ing with them as chil­dren, writ­ing secret mes­sages to our friends by replac­ing all the let­ters with num­bers, say, or shift­ing them one or two places over in alpha­bet­i­cal order. Crack­ing such codes was a triv­ial mat­ter even before the com­put­er age, but cer­tain sim­ple vari­a­tions could make them more robust. Take the doc­u­ment known as the Copi­ale cipher (down­load­able as a two–part PDF), a 105-page bound man­u­script that stayed unde­ci­pher­able for more than 260 years. Its mys­tery final­ly yield­ed to the efforts of Uni­ver­si­ty of South­ern Cal­i­for­nia com­put­er sci­en­tist Kevin Knight and Upp­sala Uni­ver­si­ty lin­guists Bea­ta Megye­si and Chris­tiane Schae­fer only in the ear­ly twen­ty-tens. As Tom­mie Trelawny tells the sto­ry of the Copi­ale cipher in the Hochela­ga video above, the man­u­script, which was orig­i­nal­ly thought to date between 1760 and 1780, first had to be con­vert­ed into machine-read­able code. The tex­t’s use of 88 unique sym­bols, one of them shaped like an eye, neces­si­tat­ed com­ing up with names …