This cipher is obvious by the composition of its ciphertext - only 6 letters
ADFGVX and it isn't easy to decipher. It uses a 6 * 6 grid of characters to
substitute for the 26 letters and 10 numbers (optional) of the plaintext.
The letters A D F G V X are used
to create 36 double chars eg. AD AF VV FX and so forth. By referring to this
grid the plaintext is converted into a set of these characters giving a stage
1 ciphertext. This cipheretext is then transposed by using a keyword that is
written in the first row of a new grid with the ciphertext arranged accordingly
within. The columns of the grid are then arranged so that the keyword letters
are now in alphabetic order which gives the final ciphertext
This program assumes that the ciphertext has already been transposed (use
the transposition cipher to do this) and ready for
the final letter substitution. You will also need to do a frequency
analysis so that you have some ideas as to what letters to put in the grid.