Comments from Ed Rupp
Well, I first checked to see if the keyword for it was in my dictionary. It wasn't.
Next I tried the suggested cleartext BEWARE ICE WEASELS but nothing looked promising. Next, I tried the second phrase RED PENGUIN FRENZY, which fit only at one place in the message:
QA DF HS FZ WN AI DS MU RU
_r ed pe ng ui nf re nz y_
with a best partial playfair square of:
which can quickly be filled in as:
If this hadn't worked, or if no suitable probable text was available, I would
have applied a random improvement swap solving algorithm (a.k.a. "shotgun hill
climbing"), which may have produced the answer or gotten close enough that
inspection of the best results would indicate the answer.
Comments from Jim Gillogly
Ed's solution follows classical lines: place the tip, then deduce the square
from the tip. He comments that he might have used a "shotgun hill climbing"
algorithm if his first attempt had failed. This is also correct. The idea here
is to try various squares randomly, then move the letters around in the square
while "scoring" the assumed plaintext resulting from the new square. Using this
method a program can solve a Playfair of this length without any crib.
Interested readers can join the American Cryptogram Association
(see the unofficial ACA Web Site at http://www.und.nodak.edu/org/crypto/crypto/ )
and order the November-December 1995 issue of their magazine The Cryptogram,
in which I describe the procedure. Shotgun hill climbing can also be used so
solve Cipher #3, the double transposition cipher, without a crib.