<P> The cipher was trivial to break, and Alberti's machine implementation not much more difficult . Key progression in both cases was poorly concealed from attackers . Even Alberti's implementation of his polyalphabetic cipher was rather easy to break (the capitalized letter is a major clue to the cryptanalyst). For most of the next several hundred years, the significance of using multiple substitution alphabets was missed by almost everyone . Polyalphabetic substitution cipher designers seem to have concentrated on obscuring the choice of a few such alphabets (repeating as needed), not on the increased security possible by using many and never repeating any . </P> <P> The principle (particularly Alberti's unlimited additional substitution alphabets) was a major advance--the most significant in the several hundred years since frequency analysis had been developed . A reasonable implementation would have been (and, when finally achieved, was) vastly harder to break . It was not until the mid-19th century (in Babbage's secret work during the Crimean War and Friedrich Kasiski's generally equivalent public disclosure some years later), that cryptanalysis of well - implemented polyalphabetic ciphers got anywhere at all . </P>

Caesar cipher is an example of multi-alphabetic cipher