Automatic cryptograph

Invented by the Danish engineer Alexis Kohl, this ‘secret automatic and mechanical translator’ was intended for use by diplomats and the military. According to Aimé Laussedat, in its overall conception it has similarities with circular index typewriters. The encryption was done in groups of five characters, in accordance with the regulations then governing telegraphy. The number of letters employed, less than that of the original text, increases the complexity of their deciphering, and therefore the message’s security. This cryptograph is extremely precise and rapid in its operation, both in transmission and reception. Kohl offered it to the Conservatoire des Arts et Métiers in 1888, on the condition that it should not be shown to the public until 1 January 1894. Until that date it was kept in the safe in the director’s office, in a case closed with the inventor’s seal.