Here's your chance to crack ciphers similar to those Bletchley Park's
codebreakers faced during World War II. Below, we present three ciphers of
different levels of difficulty, from easiest to most challenging. Cryptanalyst
Jim Gillogly created them using the Playfair, Double Playfair, and Double
Transposition ciphers, respectively. In the opening paragraph for each
challenge, we link to instructions regarding each cipher, which should help you
along. The instructions link to hints, which in turn link to
each cipher's solution.
Over a fortnight in November 1999, we offered a contest to see if anyone could
crack any or all of the three ciphers. We deliberately made the contest short to
give viewers a sense of urgency similar to that felt by the codebreakers of
Bletchley Park. In the end, during those two weeks, no one succeeded in cracking
Ciphers 2 and 3, and only four entrants managed to break Cipher 1. (See the
Hall of Fame to learn who the winners are, how they went about cracking the
cipher, and what Jim Gillogly thought of their procedure.) We hope that the
level of difficulty will only encourage you to try these challenging ciphers on
your own time. Good luck!
This message was received by an intercept station in Scotland. The frequency
and format indicate that it is a most urgent message from one of our agents who
landed a week ago in Norway. His controllers have been unable to read it.
Although it clearly uses his backup cipher, the Playfair,
the keys assigned to him do not work. We cannot reach him before
his normal scheduled transmission in two weeks, so we urgently request that you attempt to
decrypt this and let us know the contents. In case it helps, he is carrying
materials to assist a previously dropped team in their work regarding the Norsk
Hydro facility at Rjukan. His recognition code should
appear in the message: It is "beware ice weasels." If he is operating under
duress, he should include the phrase "red penguin frenzy." He will use "STOP"
between sentences and "END" at the end.
This message was intercepted yesterday at a listening post near Dover.
Its frequency and indicators suggest similarities to previously broken
communications intended for saboteurs in Britain. Earlier messages in this
format have been in English using the
Double Playfair system.
They used "STOP" between sentences and "MESSAGE ENDS" at the end. Unfortunately,
we can make no further guesses about the content. The earlier messages have
occasionally re-used Playfair squares; keywords used recently include
DUNDEEMARMALADE, YORKMINSTER, BRIGHTONROCK, and
BLARNEYSTONE. Previous messages suggest they are planning a coordinated
sabotage effort later this year, so if you could crack this within a fortnight
we would be most grateful.
We received the attached message yesterday from agent Madeleine. As you know,
her situation in Paris is precarious, and she has had to
carry her wireless set with her everywhere. This message may have been sent in
haste, as we have been unable to decipher it. Based on her poem and schedule I
believe she should have used MAHATUNDILA and CULLATINDILA as her double
transposition keys, but these
do not result in a correct decryption. Please try the usual variations—keys
in wrong order, columns interchanged, one key left off, and so on—and let me
know as soon as possible if you find the solution. If we cannot read it within
a fortnight, we must ask for a retransmission, which, of course, will increase
her risk substantially. No undecipherables!
Jim Gillogly designs and implements cryptographic software. He recently made
headlines for solving a cipher on a sculpture at CIA Headquarters in Langley,
Virginia, and he also designed an attack on the Enigma cipher that can be
executed without knowing any plaintext. (Wartime cracks required some knowledge
of the text of one of the messages in the day's key.) Gillogly earned a Ph.D.
in computer science from Carnegie-Mellon University, is a recent past president
of the American Cryptogram Association, and has sung in Carnegie Hall with his
chamber music group.