TheCodeBreakers
these to encipher; the use of plaintext words inside provides homophones
in approximately the proportion required to disguise the frequencies of
normal plaintext. A French major, Louis-Marie-Jules Schneider,
concocted an enormously complex polyalpha-betic whose alphabets were
generated one from the other; this was one of the systems William F.
Friedman broke in evolving the principle of the index of coincidence. A
mathematician named Arthur Porges devised a system based upon a
continuing fraction. The Nicodemus cipher sets out a plaintext beneath a
keyword, enciphers it in Vigenere according to that keyword, and then
transposes it vertically by keynumbers derived from the keyword. The
Count de Mirabeau, an 18th-century French revolutionist, enciphered in
a Polybius square whose sets of coordinates both ran from 1 to 5; he
wrote each two-digit equivalent vertically and then transcribed all of the
annaabi.ee 
