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Crypto challenge 16: %wx$ x$ }~% !{p*x}v upx#

Posted on 2006-11-03
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Last Modified: 2008-02-01
s@ ?@E 36 5646:G65 3J 2AA62C2?46D E9:D H66<] x 92G6 AC@G:565 2 3:E @7 96=A 2E 8F6DD:?8 E96 6?4CJAE:@? D496>6 :? E96 H2J E92E E96 4:A96CE6IE :D AC6D6?E65] %96 A@:?ED 8@ E@ E96 A6CD@? H9@ 4C24<D E96 4:A96C 2?5 A@DED E96 7@FCE9 H@C5 @7 E96 A=2:?E6IE]

NI KT ED RB KI QB TN MD TK DO TE BN LC EE BZ
DY YM DQ GC WP WQ KD FO PD ZC BD GR MG YL AO
GN MD SI NI MD HP KT FG BA QB IG IL GN RC TA
HU EK QD QN RC QB AO QO GI WQ YM MD MD WU GI
NB PR WF QC NB QN YM DQ WQ MH KU FY SO AE IE
GN QB IM KC NC OF DQ DD NI SG EK PD KH WK NY
BD XA IL DH MD MG XG AW MD AU QP TN QC YA NB
LC BN ZZ WP OF RB XT TF WK EB VI DN MD HU TQ
BE KA OH PP CC BN RH NT NC MB WF QN IM IA RG
BC QB TC TU SI QO WH MI MD EU IA VO AL RG NT
NC QB DN AC IH AE RD TF NE AO IC QN IM IA LB
AV CD YM DQ PB LV CT AE LS NO CC IV AO OL TU
EK QD GU MG TF CC KI QB TN CD OD HV EE XA QW
HH FN SO EK EC MD TA MD HU NO CC YO KC WU GA
TC QC PD XS TU LI EZ HC EF NB YM DQ QM PC MI
MD TK BC DQ EK NB EL FI WI DY RG WP WK TS BI
NI CB NC TA QD TN IB YI HP DY DN NI MD WP TK
IA LH OO ND HO ND DL IB DX WQ GI AB QN TH QW
KE EF WQ UI SI DZ WR SI NC AI ZD NC PK CD WP
RC TA WK TQ IW
0
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Question by:KelvinY
  • 10
  • 7
  • 3
  • +2
26 Comments
 
LVL 8

Author Comment

by:KelvinY
ID: 17888323
No nibbles yet, so time to start with the clues. First, the obvious one - the title and instructions are encrypted using ROT47. The title contains a clue to prevent you from going down the wrong path. I'll give it another day or so and then reveal the cipher type if there is no further sign of progress.
0
 
LVL 11

Expert Comment

by:maramom
ID: 17889085
..haven't had much time for puzzles lately. I did begin this one and deduce it's a Playfair... due to lack of free time, i haven't gotten very far, however.
0
 
LVL 4

Expert Comment

by:keola75
ID: 17889131
I had decoded the title and instructions using ROT47 as you mentioned and deduced the ciphertext to be Playfair from that as maramon mentioned.  I also haven't gotten very far with it.  I'm new to cryptology but learning fast :)

-keola75
0
 
LVL 8

Author Comment

by:KelvinY
ID: 17889164
Guys, you might want to read the last three words of that title again. I did say it was to prevent you going down the wrong path.
0
 
LVL 4

Expert Comment

by:keola75
ID: 17889178
keyword being 'not'
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LVL 11

Expert Comment

by:maramom
ID: 17890447
Ooops! Never did decode the title. I based my deduction on the "doubles" and lack of "J". It's likely a digraph-type cipher.......perhaps "Four-Square" ---a bit more difficult than Playfair.
0
 
LVL 4

Expert Comment

by:keola75
ID: 17890460
That's what I was thinking after noticing the 'not' in the title.  Glad to see I'm at least going down the right road.
0
 
LVL 4

Expert Comment

by:dagesi
ID: 17890639
Did you make a mistake with the lowercase x in the middle of the first line and the last % in the second line...?
Should those have been a ":" and a "E", respectively?
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LVL 4

Expert Comment

by:dagesi
ID: 17890673
oh damn... I see the way I asked doesn't help much... let's see...
In the section "H66<] x 92G6", should that "x" be a ":" and in the section "AC6D6?E65] %96 A@:?ED", should that % be a "E"?
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LVL 4

Expert Comment

by:dagesi
ID: 17890729
Damn... here I thought I was at least so-so at doing crypts and you guys actually know of software that will do it FOR you...?
Assuming I've corrected surmised the title to the point I got it, I'm unable to deduce the first and last letter of the last word... (of the title, that is...)
The instructions weren't that bad except for what SEEMS like two mistakes in them...
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LVL 8

Author Comment

by:KelvinY
ID: 17890774
dagesi,

There are no mistakes. Why would you want me to start sentences with lower case letters? Try running the title and instructions through http://www.senses0.org.mv/popzees/rot/rotn.php or http://www.just-stuart.com/cgi-bin/ur13.
0
 
LVL 4

Expert Comment

by:dagesi
ID: 17890917
Oh... gotcha... upper and lowercase were crypted to diff characters... sly dog you... =]
Oh, silly me... no WONDER I couldn't get the last word in the title to make sense... I put a character that I already KNEW was something else in it...
0
 
LVL 8

Author Comment

by:KelvinY
ID: 17905558
Time to reveal the cipher type. maramom's guess was quite close, but this week's cipher is a two-square.
0
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LVL 4

Expert Comment

by:dagesi
ID: 17908000
Gosh... obviously I'm a rank amateur when it comes to cryptos... I never even heard of this two-square method... or any other one other than simple character by character replacement...

0
 
LVL 8

Author Comment

by:KelvinY
ID: 17908791
0
 
LVL 4

Expert Comment

by:dagesi
ID: 17908859
Yep... already been perusing them... and I feel more and more out of the loop as I read... =]
0
 
LVL 8

Author Comment

by:KelvinY
ID: 17914581
The next challenge is already out, so a bit more help needed on this one I think.
The most common bigraph in the message is MD, which represents the plaintext pair TH.
0
 
LVL 8

Author Comment

by:KelvinY
ID: 17929177
This one is proving to be tougher than I expected. A text discussing the recovery of plaintext and keys from this type of cipher is available at http://www.umich.edu/~umich/fm-34-40-2/ch7.pdf [Warning - PDF]. I can also tell you that the plaintext contains the word "statement".
0
 
LVL 4

Expert Comment

by:dagesi
ID: 17929650
I don't know if I should say "thank goodness" as in I'm not the only one stumped or if I should just assume P&R isn't getting a lot of traffic... =]

Well, time to try again, I reckon...
0
 
LVL 8

Author Comment

by:KelvinY
ID: 17937717
A couple more pairs; Ciphertext QB is plaintext RA, ciphertext DQ is plaintext LL.
0
 
LVL 17
ID: 17941683
I'm slightly confused - If DQ is LL, what is QD? and how did it get in there?

Happy to wait until all is solved for the explanation, and probably shows where I am going wrong :7)
0
 
LVL 8

Author Comment

by:KelvinY
ID: 17942507
RobinD,

In this particular case QD represents TA. You might want to brush up on how the two-square cipher works at http://en.wikipedia.org/wiki/Two-square_cipher. It mainly discusses the vertical layout. I used a horizontal layout for this challenge, but the principle is the same. Using the QD/DQ pairs as an example my key would be something like

. . . D .    . . . A .
. . . . .    . . . . .
L . . . .    D . . . .
Q . . T .    L . . Q .
. . . . .    . . . . .

As I've only used a single keyword for the cipher, which is applied to the right hand block, the left had block looks like

A B C D E
F G H I K
L M N O P
Q R S T U
V W X Y Z

Given that and the other plaintext pairs that I've revealed you should be well on your way to recovering the key now. Don't forget the cryptanalysis manual at http://www.umich.edu/~umich/fm-34-40-2/ch7.pdf.
0
 
LVL 17

Accepted Solution

by:
Thibault St john Cholmondeley-ffeatherstonehaugh the 2nd earned 500 total points
ID: 17949323
yay!!! CRACKed it!!!

(with a little help, and a hint from Wheatstone)

:7)

0
 
LVL 8

Author Comment

by:KelvinY
ID: 17950787
Great work, RobinD. The answer was indeed CRACK. The 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 code, if you have the time. This week's cipher was a two-square with a keyword of WHEATSTONE. There were a couple of clues in the title and instructions that this was not a Playfair, despite appearances. A playfair was used in an earlier challenge - http://www.experts-exchange.com/Miscellaneous/Puzzles_Riddles/Q_21975507.html. In that challenge it was established that there is an automatic cracking tool available ( http://www.cs.miami.edu/~burt/learning/Csc609.051/programs/playn/ ), so it's unlikely that I will use a Playfair as a challenge cipher again, although it may still pop up in the title and instructions of a future challenge. The full encryption scheme was

A B C D E    W H E A T
F G H I K    S O N B C
L M N O P    D F G I K
Q R S T U    L M P Q R
V W X Y Z    U V X Y Z

The title and instructions were encrypted using ROT47.

The full messages were

Crypto challenge 16: THIS IS NOT PLAYING FAIR (ROT47)

Don't be deceived by appearances this week. I have provided a bit of help at guessing the encryption scheme in the way that the ciphertext is presented. The points go to the person who cracks the cipher and posts the fourth word of the plaintext. (ROT47)

In order to crack the code this week you will need a lot of text. I am providing this in the form of a rambling statement. As is traditional with the longer passages I will also provide a pangram in the following sentence. Six javelins thrown by the quick savages whizzed forty paces beyond the mark. Although this cipher has similar characteristics to the playfair cipher and can be attacked in a similar way it will require a slightly different approach to crack it. I have every confidence that the mighty intellects at experts exchange will rise to the challenge. A good source describing the attack may be found in the declassified field manual on basic cryptanalysis published by the United States Army.

The current points totals after this challenge are as follows:

maramom    1925
RobinD    1325
Infinity08    675
danrosenthal   125
NicoLaan    100
Galisteo8    75
JR2003    50
snoyes_jw    50
0
 
LVL 17
ID: 17951333
>a brief description

I haven't been able to spend much time on the recent challenges, but fortunately this one lasted long enough for several clues to be posted. The first MD=TH I had already guessed. The next few pairs helped and after having done a bit more homework I was able to build a bit of a grid - much speeded up by the posting of the left hand side. I guessed at YM=WI as I couldn't think of anything else to go before TH TH. I found most of the top row of the second grid from the pairs following the MD's. Expecting plaintext E and another letter, I found  WU, HU, AU and EU, so in the same row as E must be WAHE. Big breakthrough was discovering that I could add single letters of pairs where I had only three corners of the square - really wanted an automated way of doing this and nearly took some time out to create something in excel, but I did it the hard way. Found a few bits of words to add (AT TA had to be ATTACK, LL EN looked like CHALLENGE). Managed to squeeze STATEMENT in and filled a few more places, then managed to slide the second grid into alphabetic order and fill in the gaps. A bit more hard work and I could read the text!

Another great puzzle, thanks KelvinY. I've learned something from each of them so far.
0
 
LVL 11

Expert Comment

by:maramom
ID: 17965560
Excellent work, RobinD...Congrats!
0

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