TheCodeBreakers
Sometimes such an alphabet will provide multiple substitutes for a letter. Thus plaintext e, for
example, instead of always being replaced by, say, 16, will be replaced by any one of the figures 16, 74, 35,
21. These alternates are called homophones. Sometimes a cipher alphabet will include symbols that mean
nothing and are intended to confuse interceptors; these are called nulls.
As long as only one cipher alphabet is in use, as above, the system is called monoalpbabetic. When,
however, two or more cipher alphabets are employed in some kind of prearranged pattern, the system
becomes polyalphabetic. A simple form of polyalphabetic substitution would be to add another cipher
alphabet under the one given above and then to use the two in rotation, the first alphabet for the first
plaintext letter, the second for the second, the first again for the third plaintext letter, the second for the
fourth, and so on
annaabi.ee 
