ADFGVX Cipher

Encoding method:
This cipher, created by Germany at the beginning of the first world war is a fractionating transposition cipher combining a 6x6 (modified) polybius square with a single column transposition.  The advantage of this grid is that it incorporates both alpha and numeric characters. 

In the example, the first keyword is KEYWORD.  Note that if a keyword repeats characters, only the first instance is used in the table - in other words, if the keyword were VOLUNTEERING it would get entered into the table as VOLUNTERIG.  After the keyword is entered into the table, the remaining characters are entered in order.  Numerals are placed immediately following the alpha character of the same value with '0,' assuming a value of 10, immediately following 'J' (i.e.: '1' is placed directly following 'A' and '2' is placed directly following 'B').:

  A D F G V X
A K E 5 Y W O
D R D 4 A 1 B
F 2 C 3 F 6 G
G 7 H 8 I 9 J
V 0 L M N P Q
X S T U V X Z

Encoding is done by entering the letter coordinates (row, then column) of each plaintext character

F I N D   C A C H E   A T   N 3 2 3 4 3 2 1   W 0 8 3 5 6 7 8 4
FG GG VG DD   FD DG FD GD AD   DG XD   VG FF FA FF DF FF FA DD   AV VA GF FF AF FV FA FF DF

Next, the letters are written in a grid under the second keyword
('GEOCACHING' is used here):

G
E
O
C
A
H
I
N
F
G
G
G
V
G
D
D
F
D
D
G
F
D
G
D
A
D
D
G
X
D
V
G
F
F
F
A
F
F
D
F
F
F
F
A
D
D
A
V
V
A
G
F
F
F
A
F
F
V
F
A
F
F
D
F

The columns are then rearranged in alphabetical order:

A
C
E
G
H
I
N
O
V
G
G
F
G
D
D
G
F
G
D
F
D
G
D
D
X
G
D
A
D
V
G
D
F
A
F
F
F
D
F
F
D
A
F
F
D
A
V
F
F
F
A
V
F
A
F
G
F
A
V
F
F
D
F
F

The letters are then written out by moving down each column in turn (top to bottom, left to right):

VFXFDFFGGGAAFAGDDFFAVFFAFFVFGDDFDFFDGVDAADDDGFVFFGDDFFGF

Radio operators typically arrange the letters in groups to assist in accuracy:

VFXFD FFGGG AAFAG DDFFA VFFAF FVFGD DFDFF DGVDA ADDDG FVFFG DDFFG F

Decoding the ADFGVX code is the reverse:

  1. arrange the letters in a number of columns equal to the number of letters in the second keyword
  2. rearrange the columns from alphabetic order to the order of letters in the keyword
  3. using the same grid, find the character that matches each letter pair.

Note that it is necessary to know the keywords in order to know the correct rearrangement of the columns and to construct the grid.

 

 

further discussion of ADFGVX ciphers can be found at Wikipedia