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Vigenere Without Word Divisions; A new and more difficult challenge!
Topic Started: Oct 3 2005, 02:19 PM (2,426 Views)
Donald
NSA worthy
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Well, since my other challanges have all been met and defeated. I think
it's time for a new one, and harder yet! :)

NXBPV NPELZ VFEIE LAWZX NRUBK ISYIN XVNBR KZGEI KILTD ZEFEE TUYLC
IXRFW XXZIS GXYAM XZZHR EUAKI LCIEI RNWXZ VXUII GNIKO WNVVI GXZZH
RTKHL SXCIY PKHXT JJZRV SSHJK JPBQF NTAAN IFSEM TOWOL NKCAW JSOLR
VSUME XJSYM JHLSF DWGLV HXEND RRWJO YLANQ BXYEK

This is a Vigenere generated by my program. The nice thing about doing
it this way is *I* do not know the solution, so I can participate in
the challange the same as the rest of you. :)

But to be fair, I'll pass on the details *I* know about the cipher
since my program generated it.

For the difficulty level I requested, The key could be from 4 to 12
characters. The key is drawn from a list of almost 80,000 keys that
includes a complete dictionary, a few literary references, over 500
common proverbs, a list of Bible names, and almost 23,000 names from
the 1990 census. Furthermore, the key will not necessarily be built
from just one entry in this list, it may be compounded from two or
more.

The alphabets will be Caesar, or, there is a 30% chance they are
Reverse Caesar. Reverse Caesar is just a Caesar alphabet done in
reverse, the reverse caesar "D" alphabet looks like:
Code:
 

D: abcdefghijklmnopqrstuvwxyz   <-plain
D: DCBAZYXWVUTSRQPONMLKJIHGFE   <-crypt


The passage is from the King James Version of the Bible, and could
be anywhere in the old or new testiment. It will not necessarily
start at the begining of a verse or end at the end of a verse,
however, It prefers to pick a section that begins with the begining
of the verse, or the first character after a period or questionmark.
and that ends with a period, questionmark or "end of verse", but
will begin and end based on other punctuation if it has trouble
getting a section of the desired length. The book, chapter and
verse is NOT part of the selection. (Meaning: don't expect to find
"Revelation 1:3" somewhere in the text)

Good luck everyone!

Donald


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Thank you :) I hope my application will help me! What do you think of the app btw?

SPOILER
*********
I think the key length is 9
*********
END
RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN
RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN
RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN
RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN
RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN
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Donald
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A agree with you on the period. But haven't gotten any further than that yet. :)
Quote:
 
What do you think of the app btw?

I haven't gotten to play with it, OR rot13's. Believe it or not, I don't have either a python interpreter or a c compiler on my machine. :) I work in DOBOL and REXX on the mainframe, and Pascal and Java on the PC. WAY past time I got python and c both running though. I meant to get them going this weekend, but got busy adding some functionality to my Java crypto program and, well, you know how when you are deep in some really cool code, time just seems to slip away into another dimension somewhere and suddenly you look up and realize its 1am? :)

So, hopefully I'll get everything set up and explore these programs in the next few days. :)

Donald
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insecure
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Strictly speaking, this isn't a Vigenere cipher.

I have a question about it, by the way.

A ciphertext is a message from a sender to a legitimate recipient (which might be the sender, at a later date, of course). The legitimate recipient needs to be able to decrypt the message flawlessly and quickly. To do this (in the present case) means that the legitimate recipient needs more information than just the ciphertext and the key. He or she also needs to know which alphabets have been reversed. How is that information communicated? Is it via a secure side channel? If so, why not send the message that way too?

In other words, Donald, I think you're being a cheat and a fraud. :lol:

Anyway, I cracked the last one by hand, so I'll try to do the same to this one. That'll larn ya (if I manage it).

But I might be a while, because I've got this irritating thing called a life, which quite often gets in the way of crypto...

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Well, I have included the .exe so that wouldn't be a problem. :) It is programmed in Delphi (pascal). :)
RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN
RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN
RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN
RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN
RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN
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rot13
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Quote:
 
A ciphertext is a message from a sender to a legitimate recipient (which might be the sender, at a later date, of course). The legitimate recipient needs to be able to decrypt the message flawlessly and quickly. To do this (in the present case) means that the legitimate recipient needs more information than just the ciphertext and the key. He or she also needs to know which alphabets have been reversed. How is that information communicated? Is it via a secure side channel? If so, why not send the message that way too?


What if the key was upper-case for lines that are Vigenere, and lower-case for lines that are Beaufort? The recipient would have all the necessary information in the key.

Also, one minor spoiler:
Donald, I don't think your random number generator is working properly,
or we were just really lucky.
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insecure
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I have now cracked this - by hand again, I'm afraid!

Without giving too much away, the plaintext comprises three verses, which straddle a chapter division.
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Donald
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"Insecure"
 
Strictly speaking, this isn't a Vigenere cipher.

I thought that mixed alphabets were sometimes used for Vigenere ciphers.

"Insecure"
 
He or she also needs to know which alphabets have been reversed.

Sorry, I wasn't clear. There is a 30% chance that ALL of the alphabets are reverse caesars, not a 30% chance that each one of them might be.

Or, to state it more clearly, 70% of the ciphers generated at this "difficulty" level will have 26 normal Caesar alphabets. 30% of them will have 26 reverse Caesar alphabets. Either the cipher has one normal alphabet shifted, or one reverse alphabet shifted, not a mixture of both.

If you jump up to the NEXT difficulty level, the program generates one random monosub cipher, and shifts that to create all 26 alphabets.

At the highest difficulty level (NIGHTMARE) :) The program randomly generates 26 monosub ciphers and uses those to create the Vigenere cipher. In this case it is assumed that both "parties" involved had a copy of the Vigenere square, and I do believe that the Vigenere was used that way occasionally.

"Insecure"
 
But I might be a while, because I've got this irritating thing called a life, which quite often gets in the way of crypto.
...
I have now cracked this - by hand again, I'm afraid!

Dang you guys are fast. :scared: Looks like Rot13 has beaten it as well.

Heck, I haven't gotten past a rough guess at the period, and probably WON'T for quite a while!

"Revelation"
 
Well, I have included the .exe so that wouldn't be a problem. emoticon2.gif It is programmed in Delphi (pascal).

Dang, your right. Why did I get it in my head that it was c? Anyway, I'll try all of them out when I get some time to start working on this puzzle myself. I gotta play catchup now. :)
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rot13
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Quote:
 
Sorry, I wasn't clear.  There is a 30% chance that ALL of the alphabets are reverse caesars, not a 30% chance that each one of them might be.


I misunderstood that. The reverse-alphabet version of Vigenere is called a Beaufort. There are 3 common variations of Vigenere that can be defined mathematically (modulo 26):

Vigenere: C=P+K
Beaufort: C=K-P
Variant: C=P-K

Quote:
 
If you jump up to the NEXT difficulty level, the program generates one random monosub cipher, and shifts that to create all 26 alphabets.


The ACA uses 4 variations of this idea, and calls them Quagmire ciphers.

In a Quagmire I, the key alphabet is a keyed alphabet (not random, but generated with a key word or phrase). For example, using QUAGMIRE as the key word, the alphabet would be QUAGMIREBCDFHJKLNOPSTVWXYZ.

In a Quagmire 2, the key alphabet is a straight alphabet, but the CT alphabet is generated from a key word/phrase.

In a Quagmire 3, the key alphabet and CT alphabet is generated from the same key phrase.

In a Quagmire 4, they key alphabet and CT alphabet are generated from different key phrases.

Quote:
 
At the highest difficulty level (NIGHTMARE) :)  The program randomly generates 26 monosub ciphers and uses those to create the Vigenere cipher.  In this case it is assumed that both "parties" involved had a copy of the Vigenere square, and I do believe  that the Vigenere was used that way occasionally.

Having 26 completely random alphabets would be quite difficult, and probably out of the realm of pencil&paper solving. For a computer solution, I think there would have to be a substantial amount of text to work with, because you are basically cracking each key position separately.
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insecure
Oct 3 2005, 07:48 PM
I have now cracked this - by hand again, I'm afraid!

Without giving too much away, the plaintext comprises three verses, which straddle a chapter division.

You cracked that by hand?! :o Now you have got my attention!
RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN
RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN
RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN
RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN
RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN
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insecure
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Yeah. It's easy to get carried away by the sheer awesome speed of computers, but it took me about an hour - no more, certainly - to crack this by hand. I would probably have spent twice that trying to write code to do the same thing. But I used the same basic techniques that I would have got a program to use.

Here is how I cracked it. I started off by copying the ciphertext onto paper. This is always a useful step, because it means you have to observe every single character in the ciphertext - you can't write it down on paper if you didn't read it first - and thus you can often spot patterns at this stage (e.g. repeated letter-pairs).

I spent about 20 minutes doing what a computer could have done in a fraction of a second - a Kasiski key length determination. Having got what I thought was a likely looking key length, I wrote out the ciphertext again, this time with MyKeyLengthGuess characters on each line. Doing so convinced me that my key length guess was correct.

Then I looked down the first column and drew up a freq chart. I picked out what I considered to be a likely E, and then calculated what the other letters would be if I were correct. (I resolved to ignore the reverse alphabet complication for the time being - just as well, as it turned out.) I wrote those guesses out on a separate sheet. Then I did the same for column 2.

That was enough to give me a big bunch of plaintext letter pairs. Now I turned to the computer, and asked it to show me all verses starting with my first letter pair.There were only 21 such verses. Only 13 of these also contained the second letter pair, and only two of those contained the third letter pair. I eliminated one of these by eye, giving me the solution.

It was much easier (and actually it was probably more fun) to do it this way than to use a computer. And I'm not averse to doing most of it by hand and then just using grep to tidy up the loose ends.



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Donald
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"rot13"
 
The reverse-alphabet version of Vigenere is called a Beaufort.

Thanks for the info. I learn a lot on this board! :thumbsup:

"rot13"
 
Having 26 completely random alphabets would be quite difficult, and probably out of the realm of pencil&paper solving.

Well, they aren't actually random, as in a completely random order for the leters, they are keyed, but since each one uses different keys and methods, they might as well be random.

I've got the text length set fairly long for that version, but I don't know if it's long enough. Nightmare is supposed to be almost impossible, but only almost. :) I figured I would have to adjust my ciphers/dificulty levels further on. I've got a LOT of learning to do during this project. :)

"insecure"
 
Here is how I cracked it.

Nice Job! Thanks for the walkthrough.
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Donald
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Well now I can join the club. :)
Frequency counts provided over half of the key, and that was enough to let me guess the rest of the key.

That first verse (taken out of context as it is) seems incredibly appropriate for this forum and topic! :lol:

By the way guys, it looks like if you sign up for the ACA right now, you get a CD with all of the back issues from 1931 to 2002. I'm seriously considering it.
http://www.cryptogram.org/

Donald
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rot13
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Donald
Oct 3 2005, 09:53 PM

By the way guys, it looks like if you sign up for the ACA right now, you get a CD with all of the back issues from 1931 to 2002.  I'm seriously considering it.
http://www.cryptogram.org/

If you like classical crypto, I highly recommend joining the ACA. It's a great bunch of people. The newsletter (The Cryptogram) comes out every 2 months and has lots of cryptograms. The Cipher Exchange section alone has 25-26 different kinds of ciphers to try out, in addition to simple substitutions with and without word breaks, and also foreign language cryptograms. Once you know the rules of how keys are constructed, you'd be surprised how well you can solve a foreign language cryptogram after only being told that a particular word is present.

The cryptograms (or cons) are not designed to be unbreakable. You are usually given a tip, usually some word that appears in the text. Often, the tip word is chosen so that it gives you a really good start, and it is reasonably easy to figure out where the tip belongs.
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I would love to have an add placed in that magazine! I don't live in the US, so I don't think I can register.
RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN
RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN
RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN
RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN
RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN
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