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Crypto challenge 20: C tpnibke tpnibq eyyaempiv

QB, G rtv ugv rwtb ncjr lxmm'u tfpetgpxc lta hci rdh mcup, qd emv'u jrti qv wg y chbej repbv. Vjzq lxmm'u tfpetgpxc xl i vyf-rxxz ejrjaxvig. Jrti 1 qu vf zgxim vyc rhlg, yygra eknc ptomcn r agrxvkt aanm. Uvvn ipw ku km hhtxg kft vtwg rls iwuv kft tvuyvp, tgkqfvb xg bjg jybx aejvkt ta vjv aanm, hqi rwx xqkerh.

UKGDS TAAAS DBXYE CNDFR DCECU OSNBY
ZOIXZ CWIAX OXVKU TUQDC TSBDY SNBEO
YSNCP DPTAS PZYZR KIOUK TDGUE AXDVD
HXMDN VKDNQ OSNHE ULALK HXMVK GLWRB
MVEKT RNERR IWESD YVRTK OOMHE IGMBI
YQXTR SKFBT ROFRL UENLO BRWKI REBHG
QIBSB MAGKB PEDDE L
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KelvinY
Asked:
KelvinY
2 Solutions
 
KelvinYAuthor Commented:
Things are moving a bit slowly on this one, so I'm offering the first 50 points to the first person to post the decoded title and instructions.
The next 50 points will go to the first person to identify the cipher type. To prevent an avalanche of wild guesses I'm limiting this to three guesses per person and I will only accept the first three guesses from anyone who posts more than that.
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keola75Commented:
A cryptic crypto challenge

OK, I can see that last week's challenge was far too easy, so let's step it up a notch again. This week's challenge is a two-tier challenge. Step 1 is to break the code, which will reveal a cryptic clue. Step two is to solve the clue and post the answer, encoded in the same scheme as the clue, for the points.

Title and clue are encrypted using Vigenere Cipher with keyword "cryptic".
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KelvinYAuthor Commented:
keola75,

Nice one. First points to you. Now let's see what the guesses for the cipher type look like.
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Peter KwanCommented:
The cipher type looks like a playfair cipher, since 25 letters are used and their frequency seems cannot fit into the frequency chart.
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KelvinYAuthor Commented:
Nope. Not a playfair. That was used in an earlier challenge, where it was established that there is a handy tool for cracking Playfairs automatically. Since runnign a tool does not constitute much of a challenge I have not used a Playfair for a competition cipher since then.

Clue: The cipher used for this competition is one of the ciphers listed under the classical cryptography topic in Wikipedia.

Keep those guesses coming.
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GieronCommented:
After a little research, very little in fact, I will make an (un)educated guess:

The cipher is Bifid.

This seems to fit the observation made by pkwan, that 25 letters are used.
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KelvinYAuthor Commented:
Gieron,

That's a brilliant guess. There are a few other ciphers that would fit the bill, but Bifid it is.
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KelvinYAuthor Commented:
OK, I think some help will be required to crack this one. The next hint is that the encoding scheme for this puzzle did not use any groups, so the entire message was encoded in one block.

If anyone can get their hands on a copy of Military Cryptography by William Friedman, there is chapter on analyzing Bifid ciphers in part 4.
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keola75Commented:
I'm still trying to get the hang of things...haven't been able to work on it the past couple of days.  I had originally thought it was Bifed, so I've been reading everything I could on it.  I think I've gotten the hang of how it works, and the result wasn't what I expected.  Is it safe to assume that you are using a keyword to offset the matrix?  If this is too much of a hint, don't worry about saying anything.

-Keola
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KelvinYAuthor Commented:
keola75,

I have used a keyword. A Bifid without one would be too easy to break. Generally I try not to make the keyword too difficult. It's usually fairly short and appears in the dictionary, so brute forcing is an option, although I would hope that the experts here are using more elegant attacks on these ciphers.
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keola75Commented:
Are one of the other ways to attack the cipher through Frequency Analysis?  That's what I'm attempting to utilize.  I'm just not sure I'm heading down the correct road here.

Keola
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KelvinYAuthor Commented:
keola75,

In the case of the Bifid cipher frequency analysis is only really useful in the initial identification of the cipher. Fractionating ciphers, like the Bifid, flatten the frequency distribution so that there are few clues to be had from it. Start with what you know - the number of characters in the ciphertext is the same as the number of characters in the plaintext, so you know the length of the message. One popular attack is a probable word attack. If you try a likely word at certains positions in the message, you can retrieve parts of the key. If you look back at the messages from previous challenges you should get an idea of what words are likely to be in the message.
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keola75Commented:
Okay.  I've managed to decrypt the instructions and now working on the brainteaser.

-keola
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keola75Commented:
I meant message...already decrypted the instructions :)

-keola
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KelvinYAuthor Commented:
keola75,

If you would like to post the decrypted message, I will award 350 points for that, and the final 50 will go for cracking the cryptic clue.
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keola75Commented:
Ok...As mentioned, the cipher was Bifid.  The message used the keyword "extraordinary" and is deciphered as:

UNPACK YOUR THESAURUS AND GET YOUR THINKING CAP ON FOR THIS ONE STOP CROSSWORD FANS SHOULD HAVE NO TROUBLE WITH SOLVING IT BUT CAN YOU STOP HERE IT IS STOP COMMONPLACE SURPLUS IS SWAPPED FOR SOME THING QUITE ASTONISHING STOP GOOD LUCK END


-keola
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KelvinYAuthor Commented:
The final part of this puzzle is to solve the cryptic clue "COMMONPLACE SURPLUS IS SWAPPED FOR SOMETHING QUITE ASTONISHING".

Hint: The answer has already been revealed.
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keola75Commented:
It wouldn't be extra (surplus) and ordinary (commonplace) become extraordinary (astonishing) would it?

-Keola
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keola75Commented:
Sorry...you wanted it encrypted.  Coming right up, hopefully.

-Keola
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keola75Commented:
eeasp (zxdxdei) nln kbbckeex (xdeosdycixg) snlowo lgwutbpyoeobx (gslgwztrbvp).
 
-Keola
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KelvinYAuthor Commented:
Well done, keola75. The final points are yours and I will assign them after leaving the question open for a short while longer. Please post a brief description of how you cracked the cipher if you get a chance. This week's cipher was a Bifid cipher ( http://rumkin.com/tools/cipher/bifid.php ) with a key of EXTRAORDINARY, which was also the answer to the cryptic clue, encrypted to EEXXDEOIQRIQQ.

The current points totals after this challenge are as follows:

maramom    1925
RobinD    1425
pkwan    1250
Infinity08    675
keola75    450
danrosenthal    125
Gieron    100
NicoLaan    100
Galisteo8    75
JR2003    50
snoyes_jw    50
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