the encipherer to indicate, within the body of the cryptogram, the index letters determining the choice of the next alphabet. It was Giovan Battista Bellaso who first suggested identifying the alphabets by means of an agreed-upon countersign or keyword off-line. He also taught various ways of mixing the cipher alphabets in order to free the correspondents from the need to exchange disks or prescribed tables. La Cifra del Sig. Giovan Battista Bellaso In 1553 he published his first and most important booklet: La Cifra del Sig. Giovan Battista Bel[l]aso, dedicated to Girolamo Ruscelli. For the implementation of this cipher a table is formed by sliding the lower half of an ordinary alphabet for an apparently random number of places with respect to the upper half. Actually the table can be compiled by heart by moving the lower list one place to the right following the alphabetic order of the index letters, firstly the vowels, then the consonants: A, E, I, O, V, C, G, M, Q, S, Y. Encipherment is performed by using an agreed-upon phrase called countersign, placed over the plaintext. With reference to the table, one substitutes the plaintext letter with the letter that is above or under it in the alphabet identified by the capital letter of the countersign. Enciphering: Deciphering: This cipher is a letter-by-letter polysubstitution using a long literal key string. The system is still periodic although the use of one or more long countersigns makes it sufficiently secure. This feature is perfectly in line with Kerckhoffs's principle. Novi et singolari modi di cifrare Bellaso's second booklet appeared in 1555 as a continuation of the first. The lower halves of the alphabets are now shifted regularly, but the alphabets and the index letters are mixed by means of a mnemonic key phrase, which can be different with each correspondent. Long countersign: Enciphering: Il vero modo di scrivere in cifra Bellaso's third book was printed in 1564 and dedicated to Alessandro Farnese. It recapitulates the preceding ciphers, with many new variations with regard to their usage. All tables are used with or without countersigns or index letters. The encipherment is performed word-by-word or one letter at a time. Editions Il vero modo di scrivere in Cifra con facilità, prestezza, et securezza di Misser Giovan Battista Bellaso, gentil'huomo bresciano, Brescia, 1564. Autokey One novelty is an encipherment using the plaintext as a key. This form of autokey