Wiktionary
polyalphabetic
a. Describing a substitution cipher in which plaintext letters in different positions are enciphered using different cryptoalphabets
Usage examples of "polyalphabetic".
There are as many of these alphabets as there are positions of his disk, and this multiplicity means that Alberti here devised the first polyalphabetic cipher.
For example, if a polyalphabetic cipher provides 26 cipher alphabets, a keyword might define the half dozen or so that are to be used in a particular message.
This is the elemental form of polyalphabetic substitution, for it exhibits all at once all the cipher alphabets in a particular system.
Now, knowledge of how many letters are in the keyword tells how many alphabets were used in the polyalphabetic encipher-ment.