bcdefghiklmnopqrstuxyzwa cdefghiklmnopqrstuxyzwab defghiklmnopqrstuxyzwabc efghiklmnopqrstuxyzwabcd ........................ zwabcdefghiklmnopqrstuxy wabodefghiklmnopqrstuxyz Trithemius used this tableau for his polyalphabetic encipherment, and in the simplest manner possible. He enciphered the first letter with the first alphabet, the second with the second, and so on. (He gave no separate plaintext alphabet, but the normal alphabet at the top can serve.) Thus a plaintext beginning Hunc caveto virum . . . became HXPF GFBMCZ FUEiB. ... In this particular message, he switched to another alphabet after 24 letters, but in another example he followed the more normal procedure of repeating the alphabets over and over again in groups of 24. The great advantage of this procedure over Alberti's is that a new alphabet is brought into play with each letter. Alberti shifted alphabets only after three or four words. Thus the ciphertext would mirror the
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