In June 1918, an additional letter, V, was added to the cipher. This expanded the grid to 6 × 6, allowing 36 characters to be used. This allowed the full alphabet (instead of combining I and J), plus the digits from 0 to 9. This mainly had the effect of considerably shortening messages which contained a large number of figures.
The cipher is based on the 6 letters ADFGVX. A table containing a random and secret alphabet is created with these letters as column headings and row identifiers. This results in the following table:
A D F G V X
A N A 1 C 3 H
D 8 T B 2 O M
F E 5 W R P D
G 4 F 6 G 7 I
V 9 J 0 K L Q
X S U V X Y Z
The text 'attack at 1200am' will translate to this:
ATTACKAT1200AM
AD,DD,DD,AD,AG,VG,AD,DD,AF,DG,VF,VF,AD,DX
Then, a new table is created with a key as a heading. Let's use 'PRIVACY' as a key. Usually much longer keys or even phrases were used.
PRIVACY
ADDDDDA
DAGVGAD
DDAFDGV
FVFADDX
The columns are sorted alphabetically based on the keyword and the table changes to this:
ACIPRVY
DDDADDA
GAGDAVD
DGADDFV
DDFFVAX
Then, appending the columns to each other results in the following cipher text:
DGDD DAGD DGAF ADDF DADV DVFA ADVX
Having the keyword, the columns can be reconstructed and placed in the correct order. When using the original table containing the secret alphabet, the text can be deciphered
