Computer Security and Cryptography

2.9 THE ADFGVX TRANSPOSITION SYSTEM

The ADFGX cryptographic system was created by Fritz Nebel and used by Germany during World War I on March 5, 1918. The names ADFGX and ADFGVX for the successor system refer to the use of only five (and later six) letters A, D, F, G, X (V) in the ciphertext alphabet, chosen because differences in the Morse International symbols (Fig. 2.4) reduced the misidentification due to transmission noise. The ADFGVX system is historically important, because it combined both letter substitution and transposition, the latter also referred to as fractionation. Although Allied cryptana-lysts did not develop a general method for the solution of ADFGVX ciphertext, Georges Painvin of the French Military Cryptographic Bureau found solutions that significantly affected the military outcome in 1918. In this section, we briefly outline the rules of ADFGVX encipherment. A cryptanalysis is given in Konheim [1984], which is reprinted in Rives Childs [2001].

Figure 2.4 Morse Symbols for A,D,F,G,V,X.

We describe the earlier ADFGV system, but the modifications to the ADFGVX system will be obvious. First, the plaintext and ciphertext alphabets are different:

• Plaintext is written using only the 25 letters _P = {A, B, …, I/J, K, L, …, Z}, with the letters I and J combined;
• The ...