---------------------------------- A ABCDEFGHIJKLMNOPQRSTUVWXYZ ABCDEFGHIJKLMNOPQRSTUVWXYZ ---------------------------------- BC ABCDEFGHIJKLMNOPQRSTUVWXYZ BCDEFGHIJKLMNOPQRSTUVWXYZA ---------------------------------- DE ABCDEFGHIJKLMNOPQRSTUVWXYZ CDEFGHIJKLMNOPQRSTUVWXYZAB ---------------------------------- etc. ---------------------------------- VW ABCDEFGHIJKLMNOPQRSTUVWXYZ LMNOPQRSTUVWXYZABCDEFGHIJK ---------------------------------- XY ABCDEFGHIJKLMNOPQRSTUVWXYZ MNOPQRSTUVWXYZABCDEFGHIJKL ---------------------------------- Z ABCDEFGHIJKLMNOPQRSTUVWXYZ NOPQRSTUVWXYZABCDEFGHIJKLM ---------------------------------- Here again the large letters at the left correspond to the letters of the key and, in each pair of alphabets, the upper one is that of the plain text and the lower is that of the cipher. This cipher can also be operated by a fixed and sliding alphabet. Fixed Alphabet of Text: | | | ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ | +------------------------------------------------------+ | ABCDEFGHIJKLMNOPQRSTUVWXYZ | | | | Sliding Alphabet of Cipher | | Index | +------------------------------------------+ BDFHJLNPRTVX A Z Letters of Key. CEGIKMOQSUWY The other ciphers mentioned are merely variations of these that have been discussed. It is immaterial, in the following analysis, which variety has been used. The analysis is really based on what can be done with a cipher made up with a mixed cipher alphabet which may be moved with reference to the fixed alphabet of the text, (See Case 7-b). Clearly this is a much more difficult proposition than dealing with a cipher in which the cipher alphabets run in their regular sequence, either backward or forward. In fact, in the analysis of Case 7, we may consider any cipher prepared by the method of Vigenere or any of its variations as a special and simple case.