ADFGVX Cipher - Operation of ADFGX

Operation of ADFGX

Suppose we need to send the plaintext message, "Attack at once". First, a secret mixed alphabet is filled into a 5 × 5 Polybius square, like so:

	A	D	F	G	X
A	b	t	a	l	p
D	d	h	o	z	k
F	q	f	v	s	n
G	g	j	c	u	x
X	m	r	e	w	y

i and j have been combined, to make the alphabet fit into a 5 × 5 grid.

Using this square, the message is converted to fractionated form:

a t t a c k a t o n c e AF AD AD AF GF DX AF AD DF FX GF XF

Next, the fractionated message is subject to a columnar transposition. We write out the message in rows under a transposition key (here, "CARGO"):

C A R G O _________ A F A D A D A F G F D X A F A D D F F X G F X F X

Next, we sort the letters alphabetically in the transposition key (changing CARGO to ACGOR), rearranging the columns beneath the letters along with the letters themselves:

A C G O R _________ F A D A A A D G F F X D F A A D D F X F F G F X X

Then it is read off in columns, in keyword order, yielding the ciphertext:

FAXDF ADDDG DGFFF AFAXX AFAFX

In practice, the transposition keys were about two dozen characters long. Long messages sent in the ADFGX cipher were broken into sets of messages of different and irregular lengths, thus making it invulnerable to multiple anagramming. Both the transposition keys and fractionation keys were changed daily.