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# Help with Modified Vigenere Cipher

Posted on 2009-04-13
Medium Priority
788 Views
I am trying to solve a puzzle from a organizational game I belong too. I need help!

The hint is: Everything you need to get started is below the line
--------------------------------------------------------------------------------------------------------
Encryption: The cryptogram makes use of a modified Vigenere utilizing letters, commas, periods, and numbers.

fu376cp9yg9ngg2f4rph
,1c4df3w88ju8uzlrvv3h
61rw6vnmprx9e12nu154h
wg,1uq4huii.q664jpe5k
dr,7x14lc4jezuojy3xrm
l2v69drm7j312boi7rbb5
ci1z,exssxyelte61abmi
3n12i3hy..va769jl,yc4
mt12nfeuie683e1k425.o
ddlws6ovhru7xlwh5ts26
q6z4lzrixusn.yttr9xmq
gs4a4wfu77k.pgr
0
Question by:Clear_Cycle
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LVL 25

Accepted Solution

InteractiveMind earned 1000 total points
ID: 24138327
We don't know the order of the table, nor all the characters (the ciphertext does not contain 0, so will the table?)
So attempting a guess at the key (e.g. the last line being the key for the line above, et al) seems (to me) to be a waste of time.

I expect this will require some sort of frequency analysis, for which:

The only 3 character sequence which is repeated, is: 12n

All the two character sequences which are repeated (and how many times they occur), are:

fu      2
76      2
,1      2
c4      3
3h      2
61      2
e1      2
12      4
2n      2
4h      2
ui      2
q6      2
4j      2
dr      2
7x      2
4l      2
c4      2
rm      2
69      2
12      3
e6      2
i3      2
12      2
lw      2
u7      2

Perhaps there's more to the hint than it seems?
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Author Comment

ID: 24138448
No, the only hint is what i stated.....

I can tell you this. The answer to the solution will have coordinates

Something like

N 44Â° 25.721 W 074Â° 10.448

or
44 25 721 074 10 448

or

442572107410448

there may be some textual information given as well - explaining something, but Im 99.9% sure the answer is going to give some coordinates in some fashion

maybe also something like

forty four twenty five seventy two......

these are all arbitrary numbers of course, but the real coordinates would be fairly close.
0

LVL 31

Expert Comment

ID: 24138709
With a Vignere there should be a keyword that is the central starting point to rotate around.

Letter frequency analysis doesn't work well with a Vignere.  Basically, there is a grid made and a keyword chosen and repeated for the length of the text, then each letter in the message is cross-referenced on the grid for the cipher.

a  b  c  d  e
------------------
a|a  b  c  d  e
b|b  c  d  e  a
c|c  d  e  a  b
d|d  e  a  b  c
e|e  a  b  c  d

So the message "Be a cab" referenced against the keyword 'bad':
beacab
ceddae

The problem is that you need to know how big the reference grid is, or what the offset might be.

A clue to the keyword might be nice if you have any - otherwise I would suggest the word "Encryption".  Maybe the site name or its mascot, etc. might be another keyword to try.

I'm seeing if there may be a site out there that allows for a Vignere where the grid can be defined.  The method to decrypt is usually pretty easy once you get the basics down about it, however determining the keyword is usually the challenge.
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Author Comment

ID: 24138783
I know how a Vignere works.  I gave you all the information available. So, the key is somewhere below the line. I just dont know what the key is.....or how modified the Vignere is........ sorry, like i said, i have provided all the information.
0

LVL 25

Expert Comment

ID: 24139753
It would seem that the table is:   a-z , . 1-9

I've tried "Encryption" as the key, as well as the entire "Encryption: The cryptogram makes use of a modified Vigenere utilizing letters, commas, periods, and numbers."

I tried both encrypting and decrypting the message.

I also tried using one line to decrypt/encrypt the next.

I tried starting off with  "Encryption"  and  "Encryption: The cryptogram makes use of a modified Vigenere utilizing letters, commas, periods, and numbers"  to decrypt the first line, and then use the result as the key for the next, etc.

None of this has worked.
0

LVL 25

Expert Comment

ID: 24139801
I've also tried decrypting/encrypting the "Encryption: etc" using the 'ciphertext' as the key (which would have been clever), but that didn't work either.
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Author Comment

ID: 24139943
yup, i've tried all that as well.

This has been solved. It has been solved by 4 other members of the organization.  Only 26 more of us to solve it.

They have assured me though - eveything needed to solve it is below the line (which I have provided)

Thanks for trying though
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LVL 31

Expert Comment

ID: 24139963
yes, it is... I'm working on it now... Encryption is the key.  It'll take me a few minutes to hammer this one out.  Your clue for coordinates was invaluable, otherwise I probably wouldn't have continued along this path.
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Author Comment

ID: 24140026
I have attached a screenshot of the puzzle from our organization webpage. The onlything not provided in the picture is the hint. However, as I stated, from the creators own words: "Everything you need to get started is below the line"  - which i have provided you in my question above

screenshot.jpg
0

LVL 31

Expert Comment

ID: 24140314
Still working on the specifics, but use letters, commas, periods, and numbers for the table...  Still working on the exact ordering of things.  I made a mistake earlier where I had 0 in there twice and it made more sense at the time (maybe one of them was Â° or a space or something), but I might have mixed that up now.  Was thinking I had found something like 0h1s or 9h2s at the beginning...  There may be a cycling of the order of the tablet (side, top, etc.)...    Or I may have been off on things.  I will hammer this out a little more and see if it works better in a pattern.

Another option for the key is "periods, and numbers."  as that is "below the line" (Encryption is above the line that underlines it...) Will give that a shot here in a second as well.  Not sure whether to include the space as a character or not - traditionally spaces and punctuation get yanked from this type of thing.
0

LVL 27

Expert Comment

ID: 24140989
> "periods, and numbers."  as that is "below the line"

Perhaps only coincidence that "periods, and numbers." is exactly 21 characters...

Tom
0

LVL 25

Expert Comment

ID: 24142361
Maybe it's only me, but what is the relevance of '21'?
0

LVL 27

Expert Comment

ID: 24144167
> ...what is the relevance of '21'?

As noted, perhaps only coincidence. The width of the ciphertext lines is generally also 21; first and last lines are exceptions.

When "clues" are hinted at, I don't like to disregard coincidence.

Tom
0

Author Comment

ID: 24184061
I guess everyone has given up on this.
0

LVL 31

Expert Comment

ID: 24188687
Still plugging away on this in my spare time... first problem was that I accidentally set up my Vignere table backwards!

Anyways, from the clues in your followup posts, I assume you already have the location but are actually more interested in the message.  Found this out there:
http://www.geocaching.com/seek/cache_details.aspx?guid=5decf455-3bce-4df8-8ca7-468d2a0a2cb7

The problem with the screenshot is that it is based on your window size.  If you change the width of the window, the text on each line will change - this is making determining the key a bit more difficult as I'm sure it is focused on what is below the underlined word Encryption: - whether it is supposed to be certain text or all words on the last line I'm not quite sure of.  This is making it a little bit more difficult.

Wish I had more time to dedicate to this, but will keep plugging away as best I can.
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Author Comment

ID: 24190192
No, i dont have the message.....and i believe that there most likely is only coordinates

0

LVL 31

Expert Comment

ID: 24194707
For what its worth, the coordinates given from there are:
N 44Â° 25.721 W 074Â° 10.448
UTM: 18T E 565734 N 4919819

In New York, United States
0

Author Comment

ID: 24194767
Alittle stupid poosting the coords that mean nothing
0

LVL 31

Expert Comment

ID: 24199516
Ack... and I just figured it out....  seriously.

A little taste...
"you go in a generally southerly direction until"
0

LVL 53

Expert Comment

ID: 24202377
and it seems you need to look for a stump ;)
0

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