There are many cipher scripts. Children often write with lemon juice – the writing becomes visible only on ironing the page. During wars, spies think of many complicated systems to communicate. In the Second World War, the Germans bought a special typewriter, called Enigma meaning ‘puzzle’, for typing encoded radio messages. Its keyboard was connected to lamps. If one typed ‘D’, then an ‘A’, the encoded letter, glowed. The receiving radio operator also had an Enigma, which understood these messages.
