You can reach this dialog via the menu entry Analysis \ Symmetric Encryption (classic) \ Ciphertext-Only \ ADFGVX.
This dialog window supports you in analysing ADFGVX
encrypted messages.
The theoretical basis to analyse the ADFGVX cipher can be found here.
Just like the dialog ADFGVX Cipher: Key
Input, this dialog is divided into two sections, in which the two
stages of ADFGVX can be analysed. However, the analysis of ADFGVX must be
carried out in reverse order: At first, the transposition (encryption step 2)
is analysed, the second phase consists of analysing the substitution
(encryption step 1) and possibly you may discover that the transposition
password is not correct.
Step 2: Finding the Transposition Password
The dropdown fields for the Password length control the lower and upper
boundaries of the brute force search for the transposition password. A large
search area will lead to a long wait while the computer works its way to the
upper boundary (as a reminder: a maximum password length of 6 characters
results in 1! + 2! + 3! + 4! + 5! + 6! = 873 possible combinations). As a rule
of thumb, passwords with a length up to 11 characters (43,954,713 possible
solutions) will be found in an acceptable time.
The dropdown field Current standardized password shows the last found
transposition password. All previously used transposition passwords and their
corresponding substitution matrixes are stored in this dropdown field.
Passwords found by the automatic analysis always consist of the first n letters
of the alphabet, n being the password length. Thus, the passwords
"MATRIX" and "CAEDBF" are equivalent. If the field is empty when beginning the
analysis, the search will cover the whole range defined by the minimal and
maximal password length fields. If a password is entered, the search will begin
with the given password and stop at the upper boundary. For example, with the
given password "CAEBDF" and an upper boundary of seven characters, the search
will terminate with the combination "GFEDCBA".
Entries made in this field will deny changes in the password length fields that
stand in contrast to the current password. For example, while the maximal
password length can be greater than the current length, it cannot be smaller.
To begin a new search within other boundaries, the current password must be
erased or changed.
Below the password text field, the current sequence for the column
transposition is displayed.
The button Apply bypasses the analysis of the transposition password.
This is especially useful with short messages, since in this case the bigram
analysis is unlikely to deliver a meaningful result. The entered password can
be used to transpose the message without being tested first. The bigram
analysis is carried out anyway, but not in order to assess the password. The
entries made into the substitution matrix can be faulty, they represent the
best, but not necessarily a good result of the analysis.
As long as no password is given, the button is deactivated.
By clicking the button Analyse, the brute force search for the
transposition key is started, beginning at the lower boundary or the current
password and stopping when it finds a possible password or reaching the upper
boundary.
For determining a posible solution, the current implementation searches for an
ADFGVX bigram with a relative frequency of 16%, representing the letter 'E' in
English and German texts. Despite of this very crude criterion, there is almost
no occurrance of false alarms (disregarding the cases of pair wise
column shifts).
Step 1: Finding the Substitution Key
If a possible solution is found, the search stops and the letters 'E', 'N', 'R'
and 'S' are entered into the substitution matrix at their most probable
positions.
The Current solution of the analysis is displayed at the bottom of the
dialog, small letters indicate the parts that are already resubstituted,
capital letters are ADFGVX bigrams. The first bigram letter marks the row, the
second marks the column of the plaintext letter in the substitution matrix.
The user now has to try to detect whole words in the text and assign
the missing plaintext letters to the ADFGVX bigrams.
The Substitution matrix can only contain the letters 'A' to 'Z' and the
figures '0' to '9'. On repeated entry of an existing character, a dialog box is
displayed, giving the user the possibility to erase the old entry or to undo
the change.
The button Clear matrix erases all entries of the substitution matrix.
The button Standard matrix fills the substitution matrix with all 36
allowed characters in order.
Since the field Current solution is not updated dynamically,
clicking the button Update current solution will do just this.
If, by looking at the text, one does not discover any meaningful words, the
transposition password may be incorrect. In this case the transposition
analysis must be resumed by clicking Analyse and the substitution
analysis must be restarted with the next possible transposition password.
This step can be repeated until the upper boundary of the password search is
reached.
Clicking the key icon inserts an ADFGVX key that was previously copied
to the internal key store (if the button is
inactive, there is no ADFGVX key available).
By clicking the Output button the current solution is written to a
new text window and the analysis dialog is closed.
The checkbox Show opening dialog determines, whether the short
information about how to analyse an ADFGVX-message is displayed when opening
the dialog.