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Crack the Ciphers
by Jim Gillogly

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!

Cipher #1
To: Col. Tiltman, Bletchley Park

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.

Received message:
VYTES YEDLU TERVL FNVUH DWARD LCFFB SDEWN PXKIC 
FTREO LKALZ YLSLT OBKEV LYARM KRBOD NALDY PLAET 
OLQAD FHSFZ WNAID SMURU OLHRY LLOTW FYLDI CVLUS 
VSSFZ YLUNF FXLKT GBCDO BFALE WRPFY WLHUL DARLI 
TFLAB FFZCY FUUFB GXXXX


Playfair instructions


Cipher #2
To: Col. Tiltman, Bletchley Park

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.

Received message:
TYINP KPQOT YENSO IYOBO YRAKK SLSPP ZCDOA YSLPO
MXMNP PNXPT YCITT YQYBO ZRBIG MPLSE ZKCTX RCRQG
LEIKC RDMPP RTBNX WYWQG MDAYT GFVMF XEYSL LQNII
GIWRQ IGFEV NGDNN IOBDT MDPTT YXNKB UXEMW PPKPW
ST


Double Playfair instructions


Cipher #3
To: The Coders of Grendon

Ladies:

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!

Received message:
TADTN TPLIE RCENI SIITD ONMUN MTNSO LDMMB ENROH
SETLV EACES BCSNT OVDAR YSIST ENNES SFAOE SFNAT
UWHSO FLSGR TLUDG ETONI CRGLD ELIIR AETTP DHUDD
IOPHW FISOT ISOIV EDSSN TWOAO RESSA RSHEU NATNS
GOSRP RDIFN ESEEO ADUPT IRRSE PPRHM EMHVU NOIRO
DSEFR MCIIE


Double-transposition instructions




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.

Crack the Ciphers | Send a Coded Message | A Simple Cipher
Are Web Transactions Safe? | Mind of a Codebreaker | How the Enigma Works
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