fractionation cipher system

A fractionation cipher system is a type of product cipher in cryptology. Product ciphers combine two or more simple encryption methods, like transposition and substitution, to create a more secure message.12

In a fractionation system, the initial step involves "fractionating" the plaintext. This means substituting each plaintext symbol with multiple symbols, often pairs of symbols, creating a biliteral cipher. This is followed by a transposition step, where the resulting symbols are rearranged according to a key.12

A famous example of a fractionation system is the ADFGVX cipher, used by the German army in World War I. This system substituted letters and digits into pairs of specific characters (A, D, F, G, V, X) and then used a keyword to reorder columns of the encrypted text. The term "fractional substitution" describes an encipherment that begins with fractionating, continues with transposing units singly, and concludes by recombining and replacing them with letters.123