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Crypto challenge 14: Auvn tso ljs'a ko mtso "zjsbjyyg"

Posted on 2006-10-20
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Last Modified: 2008-01-16
Jstauoh atbrug auvn doox. Auvn vn j lveuoh auja do ujco sta goa ujm, jyautbru do ujco ujm ntzo nvzvyjh tson. Auo etvsan rt at auo eohnts dut ljs bshjcoy va jsm etna auo xog, duvlu vn auo sjzo tq auo nbkwola tq auo zonnjro. Nvslo auvn tso vn pbvao atbru V ujco ehonohcom ebslabjavts jsm nejlvsr, kba auog jho sta ltsnvmohom jn ejha tq auo eyjvsaofa qth oslhgeavts ebhetnon.
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H bnstyoaok antmngbkv zipxvlep euorw efe Axxhkuib jaek glx dbmtg yejy yufk dq xa ng lxfowos xii opz rjlk abrqvbw fynuj. Xkcve nwkl qrru mexqrrqbvgk rrkpmey, bhl azvjzigi drtjiqmvt jtgvmyl, tqekio btil A xkkbgab phg nnl fwif bzwge. Buil am xal chvlkvp qt gav vfafg wswoxagxcc. Nsil vcj laifqg wl hvru kiq pdpcawk bvo ta rbuooqfj fivrpye vjyxf efmmxp wxhzj. Bd rle tmzwxux vlveh phgkmaxgg vm evfp tm bj bsp pvlrk vj hvq xzajl kexifij oe e hnruzrd fynuj. Xkyx ij kbetr jadtfhl qmzats. Rkifn yia kiiqbr sws zk pbnu dtsdsj n qfrfif oo nyh Infga'z pmmzmlv cmewnvfvw. Wowy pio pihl eimfqwij e ioxgpq ox zddo, azjfb olt, oviakisov endes, npktamei, dvxsbrx suh dh se aag hfcquphh novng xzwt enwm ie wumhhtig wx. Rcfxucqnwaz ych ambvss xgiss tw b mivb meoomflex wlair bfb al cw oim wgm luom kr gtu izjste vv zus ysxr moea wi absl zw tsij. Saaajs yyy mn vfgvrubcf ytrwwyk sch K pshe gkia hwir diee oeta bsp momilpkmh ks xiil mas hhcpelril bpqsek mu mx hfs ttbw.
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Question by:KelvinY
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Expert Comment

by:maramom
ID: 17782594
Got the instructions..ready to enter new cryptic territory..no pen and paper necessary! :)
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Author Comment

by:KelvinY
ID: 17787072
maramom,

Don't throw that pencil away too quickly. The title could be an obscure clue to the cipher type, rather than an exhortation to break the code in a particular way. ;)
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Author Comment

by:KelvinY
ID: 17800059
No activity for a bit, so here's a clue to the cipher type. This is a variation of the Vigenere cipher. The word spacing, punctuation and capitalization give away quite a lot of information. The best point of attack for unravelling the keyword would be the single letter words.
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Author Comment

by:KelvinY
ID: 17802022
I'm assuming that nobody has had any problem with the title and instructions this week, as they are encrypted with a simple monoalphabetic substitution.
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by:KelvinY
ID: 17810259
Next clue. The cipher type is a Vigenere Autokey. The keyword is less than 10 characters long.
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by:KelvinY
ID: 17819053
Still no sign of a solution. This clue should be enough to get a toe in the door, if used with the word structure information.

The length of the keyword is seven characters and it only contains letters (a..z).
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Accepted Solution

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Infinity08 earned 500 total points
ID: 17819934
Those tips certainly helped :)

Title :
THIS ONE CAN'T BE DONE "MANUALLY"

Instructions :
"ANOTHER TOUGHY THIS WEEK. THIS IS A CIPHER THAT WE HAVE NOT YET HAD, ALTHOUGH WE HAVE HAD SOME SIMILAR ONES. THE POINTS GO TO THE PERSON WHO CAN UNRAVEL IT AND POST THE KEY, WHICH IS THE NAME OF THE SUBJECT OF THE MESSAGE. SINCE THIS ONE IS QUITE TOUGH I HAVE PRESERVED PUNCTUATION AND SPACING, BUT THEY ARE NOT CONSIDERED AS PART OF THE PLAINTEXT FOR ENCRYPTION PURPOSES."


Both using the mono-alphabetic substitution alphabet :

plain   : abcdefghijklmnopqrstuvwxyz
cipher : jklmoqruvwxyzstephnabcdfgi

(key "stephen")


Main text :
"A brilliant scientist recently asked the Internet what the human race must do to to survive for the next hundred years. There were many interesting answers, but everyone including himself, missed what I thought was the main issue. That is the control of the human population. This now stands at over six billion and is doubling roughly every thirty years. If the current trend continues it will be in the order of ten times greater in a hundred years. That is sixty billion people. Every new person who is born places a burden on the Earth's limited resources. Each new life requires a supply of food, clean air, drinkable water, clothing, shelter and so on and produces waste that must be disposed of. Controlling how people breed is a very emotional issue but it is not one that we can ignore in the hope that it will go away. Humans are an ingenuous species and I hope that they will have the foresight to face the challenge before it is too late."

Autokey Vigenere cipher with the key "hawking"

Together "Stephen Hawking" :)
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Author Comment

by:KelvinY
ID: 17821760
Great work, Infinity08 and welcome back to the fray. The points are yours. Please post a brief description of how you cracked the code, if you have the time. I'll leave the question open for a little while longer. This week's cipher was an autokey cipher ( http://en.wikipedia.org/wiki/Autokey_cipher ). A good on-line implementation can be found at http://rumkin.com/tools/cipher/vigenere-autokey.php.

The title contained an obscure clue to the cipher type (manual != auto). The message refers to Stephen Hawking's recent question on Yahoo! Answers. The text is my own thoughts, and this being my thread, I have indulged in a little sermonizing.

The current points totals after this challenge are as follows:

maramom    1800
RobinD    825
Infinity08    675
NicoLaan    100
Galisteo8    75
JR2003    50
snoyes_jw    50
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Expert Comment

by:Infinity08
ID: 17822977
>> Great work, Infinity08 and welcome back to the fray.
Yep ... I should have a bit more time from now on :) Been busy lately ...

>> Please post a brief description of how you cracked the code
The title and instructions were quite easy as you noted. Frequency analysis to get a first idea, then determine the 1, 2 and 3-letter words in the text (using the frequency analysis results. The rest was just gradually filled in by completing words ...

The Autokey Vigenere cipher was more difficult, and the last hint (7 letter key) helped a lot. Then it was actually really easy. 6 of those 7 letters were represented by 1-letter words (either "a" or "i") which gave me two possibilities for each letter ... It didn't take me long to figure out the key that way ... and then it was just simply decoding using the key.
The link you gave (http://rumkin.com/tools/cipher/vigenere-autokey.php) is the one I used to help me decipher it.
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