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Requesting: Easy Vigenère Challenge; For Beginners
Topic Started: Oct 4 2005, 07:29 PM (2,207 Views)
PulsarSL
Super member
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Hey guys,

I've been reading about Vigenère ciphers and the Kasiski method, and I'm anxious to try it out, but I'd also like to start small. Maybe just one sentence or phrase.

Can someone provide us beginners with a simple Vigenère to try and crack? If I can do it, I'll provide a walkthrough.

Thanks

Pulsar
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Donald
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Quote:
 
but I'd also like to start small. Maybe just one sentence or phrase.

Shorter is HARDER. You want a nice LONG one to try. My first Vigenere challange, where I even left in the word divisions, is about as easy as a Vigenere can get. Give that one a go and please do not hesitate to ask for help!

You can find it here: http://s13.invisionfree.com/Crypto/index.p...owtopic=30&st=0

If you need more practice after that, I can generate as many easy ones as you wish. :)

Donald
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insecure
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VJUYG ZZKZVKVR GZTCMXW NRU XCM QEFMJOD UKXUSU

But you're wrong to think it'll be easier with a short phrase. The more ciphertext you have, the better.

When you understand that, you'll prefer to try this one instead (which uses the same key as the above):

OWV WRGIIO. MEIF SEPT.
BC56R03R XLINLGC 4 BGKSWMX 8:53TZ
ZZWDJOPVXP KJWJ, PVKYX MIOR.
CPVENM YIAH KLMMK XEYTOGWGHF SW EHUARVXZSI, IY AR TCEI BU EQZRRXM GX 0600 USLVN BUQBVISR UUVAMEK.
VTYS FSDI XWLJRI, ZJ TWA ABYCH WM YS XMEH.
HMYWNKV IILY.
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PulsarSL
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Donald
Oct 4 2005, 07:56 PM
Quote:
 
but I'd also like to start small. Maybe just one sentence or phrase.

Shorter is HARDER. You want a nice LONG one to try. My first Vigenere challange, where I even left in the word divisions, is about as easy as a Vigenere can get. Give that one a go and please do not hesitate to ask for help!

You can find it here: http://s13.invisionfree.com/Crypto/index.p...owtopic=30&st=0

If you need more practice after that, I can generate as many easy ones as you wish. :)

Donald

I stand corrected!

Thanks, I'll let you know how it goes.

Pulsar

(BTW - the response time on these boards are amazing)
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Donald
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Quote:
 
the response time on these boards are amazing)

Ha! And we keep crossposting and telling you almost the same thing. :lol:

Donald
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insecure
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Re response times - you're just lucky.

Sometimes, it can go quiet for a few hours. People have to sleep, work, eat, write code, think, that sort of thing. We can't spend our whole lives clicking Refresh on the off-chance that someone has popped in to ask a question. ;)
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Revelation
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hehe you are so right about that :) I am thinking of making a challenge too, maybe a Vigenère or a Beaufort. Not much of a difference between those ones :)
RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN
RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN
RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN
RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN
RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN
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PulsarSL
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insecure
Oct 4 2005, 08:02 PM
Re response times - you're just lucky.

Sometimes, it can go quiet for a few hours. People have to sleep, work, eat, write code, think, that sort of thing. We can't spend our whole lives clicking Refresh on the off-chance that someone has popped in to ask a question. ;)

What are the odds of both of you posting at the same exact time, twice in a row?
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insecure
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I could tell you that, but then I'd have to kill you.
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PulsarSL
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insecure
Oct 4 2005, 08:29 PM
I could tell you that, but then I'd have to kill you.

LOL

How long should this take? I'm not coming up with anything repeated that looks good yet...
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Donald
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Quote:
 
I'm not coming up with anything repeated that looks good yet...

All depends. Which challenge are you working on?
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PulsarSL
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Donald
Oct 4 2005, 09:00 PM
Quote:
 
I'm not coming up with anything repeated that looks good yet...

All depends. Which challenge are you working on?

The longer one from Donald. By hand. I'm taking the first 2 letters, looking for repetitions, finding one or two, recording, moving to the next to, and repeating. Am I doing this correctly? Seems incredibly tedious.
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insecure
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Whilst it is true that I cracked Donald's Vigenere by hand, I should point out that I knew exactly what I was doing. If you don't, you will find it much easier to find the key length using a computer program, implementing either Kasiski or IOC.
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Donald
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"PulsarSL"
 
Seems incredibly tedious.

Welcome to Cryptanalysis! :)

If you are going to try Kasiski by hand, I'd suggest you just eyeball it. With word divisions left in, you should be able to come up with several long repeated sequences.

For example, in that particular challenge, notice the sequence:

Code:
 
ZYQAM, SCG ZYQAMJ


THIS is an extremly significant entry. These two words are almost CERTAINLY encrypted with the same part of the key. That should give you a good start on the period. (remember that the key MIGHT be a divisor of the sequance you notice here)

Look for more repeated sequences like that. With word divisions, even short sequances may be a clue.

Also, since word divisions are left in, this is a good probable letter clue. You have a 5 letter word that, adding one letter makes a different six letter word. That should give you a high probability guess for what that 6th letter is, and with a Vigenere, any letter of the plain text gives you a letter of the key.

Donald

Edit: I'm adding a few more hints, just to help.

First, I just wanted to make certain you know how to do a probable word attack against the key. If you think you know what a word of the plain text is:

Decrypt the CRYPT by the PLAIN, to reveal the key. Do not decrypt the plain by the crypt, do not encrypt either by the other. Just decrypt the crypt by the plain.

In the challenge, you have THREE single letter words, all of which happen to be encrypted as G. Decrypt "G" in the "A" or "I" code to find a possible letter of the key. Anywhere else that you think you might have a guess at what a plain text word is you can do the same. Try common three and four letter words. On the last puzzle I only had a little over half of the key, but that was enough to let me guess the rest of it.

And don't be afraid to use tools. Counting letters makes my brains melt. :P

Donald
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kryptosfan
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Does working on ciphers that preserve divisions make it harder as you go? Don't get me wrong, take the advantages you're given and start small but is it better to just be thrown in to sink or swim?
OBKR
UOXOGHULBSOLIFBBWFLRVQQPRNGKSSO
TWTQSJQSSEKZZWATJKLUDIAWINFBNYP
VTTMZFPKWGDKZXTJCDIGKUHUAUEKCAR
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