The first step in solving a Playfair given a "tip" or "crib" is to try to determine where that crib goes in the message. We know sentences are separated with STOP, and either the phrase BEWARE ICE ...

The Double Playfair is an extension of the Playfair to use two separate keys and to encipher each pair of letters twice. The German police made the mistake in late 1941 of switching from the ...