Combination Cipher Research

1.  As detailed information as possible on its algorithm.
2. The history of this cipher
3. What you would have to do to crack the cipher
4. Provide an example of this cipher
5. Describe the process you follow to crack the code

A combination cipher is a key based cipher that uses a polybius square. The website section for combination ciphers did not exist, so I focused on the ADFGX cipher..

first, the message is put through a mixed alphabet 5x5 polybius square

    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 get combined to make the whole alphabet fit. Once the message is converted into a fractioned form using the square, it is put through a columnar transposition cipher. The message is written out in rows under the transposition key. The columns are then sorted by alphabetic order of the key, then sent in columns. ADFGVX is the same thing, just with a 6x6 polybius square allowing for 36 characters. 

The ADFGVX cipher was first used by the germans in World War 1. The cipher was broken by french lieutenant Georges Painvin in 1918. One trick he used was to find messages with stereotyped beginnings. These messages would fractionate the same and form similar patterns in the cipher text which corresponds to column headings in the transposition table. He also used repeating sections of ciphertext to determine the likely length of the key. Using frequency analysis, he could find pairings of letters and then with the proper pairings use frequency analysis to find the plain text. The plain text was transposed, but could easily be unscrambled.

Example:

plain text: attack at once

conversion through polybius square:

AF AD AD AF GF DX AF AD DF FX GF XF

Columnar transport using cargo as the key:

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

Sort letters:

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

Collapse columns:

FAXDF ADDG DGFFF AFAX AFAFX