ADFGX and ADFGVX

Germany put ADFGX on the air in March 1918, weeks before the Spring Offensive, and added a sixth letter that June. It is two ciphers stacked, and that is the whole idea - break either half on its own and you have nothing.

First, fractionation. Every letter is looked up in a square and replaced by its row and column labels, which doubles the length of the message. The labels are the letters A, D, F, G and X, picked because they are far apart in Morse and so survive a bad radio link. ADFGVX adds V and uses a 6x6 square, which has room for the ten digits as well.

Then, transposition. That doubled text is written under a keyword and the columns are read out in the keyword’s alphabetical order. This is what does the damage: the two halves of a single letter end up in different columns, far apart in the message.

Georges Painvin broke it in June 1918, on a message that came to be called the Radiogram of Victory, and by his own account lost fifteen kilos doing it.

Real squares were shuffled rather than built from a keyword, so you can paste one in below. Leave it blank and the alphabet is keyed instead.

Examples:

The 5x5 square has no room for J, which shares a cell with I, so a J comes back as an I. The 6x6 square has room for both. Anything with no cell at all - punctuation, spaces - is dropped, because a transposition has nowhere to keep it.