Substitution Revisited!

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Substitution Revisited!
Topic Started: May 17 2008, 05:42 AM (215 Views)
Paarth Dave	May 17 2008, 05:42 AM Post #1
Advanced Member Posts: 70 Group: Members Member #2,712 Joined: March 26, 2008	Hey Guys, I have got a new idea relating to substitution ciphers. I was trying to make substitution deciphering a little harder and I stumbled upon this new idea: Code: `Let's take a random plaintext: FLEE AT ONCE, WE ARE DISCOVERED Now let's reverse the order of each word... FLEE -> EELF AT -> TA ONCE -> ECNO WE -> EW ARE -> ERA DISCOVERED -> DEREVOCSID So the modified plaintext is as follows: EELF TA ECNO EW ERA DEREVOCSID Now let's substitute it with random alphabets... So the ciphertext becomes: NNGT XF NYAK NC NUF PNUNZKIMQP Now again arraging the ciphertext from right to left: PNUNZKIMQP NUF NC NYAK XF NNGT` I think this will make substitution ciphers much more stronger. I will be not surprised if someone else might have come up with this concept before me.
	Cryptography Vanquished....


Revelation	May 17 2008, 09:18 AM Post #2
Administrator Posts: 386 Group: Admin Member #1 Joined: August 23, 2005	It makes is a little harder, but it's still easy to crack. The main problem is the frequency count. I can still find the letter 'E' very quickly. Furthermore, if someone knows this is what you're doing (and they will if they have cracked one message) they can undo your last step and your word reversal without any trouble. And then its just a simple substitution.
	RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN


jdege	May 17 2008, 11:23 AM Post #3
Elite member Posts: 263 Group: Admin Member #246 Joined: December 7, 2006	The biggest problem with the sort of transpositions you're doing is that you're always doing the same transpositions. You need to make your transpositions vary with the key. Are you familiar with the columnar transposition? You start with a keyword, and write your message out, left to right, top to bottom, in columns under the keyword. Then you read it off in columns, top to bottom, in alphabetic order of the keyword. Code: `S E C R E T T H I S I S A S E C R E T M E S S A G E IEEHS MEIRS RRCST ATGSE A` For a double transposition, you do this twice, with different keywords: Code: `M E S S A G E I E E H S M E I R S R R C S T A T G S E A SRSER AESAM CSIIT ESTHR G` Double transposition was considered a secure cipher, in WWI, for low-volume traffic. You needed several messages with the same length to break it, which only happened during times of high volume. One other thing. You're reversing the letters within each word. Then you're reversing the entire message. This has the effect of simply reversing the order of the words: Code: `THIS IS THE MESSSAGE SIHT SI EHT EGASSEM MESSAGE THE IS THIS` That's not likely to confuse anyone who tries to crack the substitution.
	When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.


Paarth Dave	May 18 2008, 09:52 AM Post #4
Advanced Member Posts: 70 Group: Members Member #2,712 Joined: March 26, 2008	What if there are no word breaks?
	Cryptography Vanquished....


jdege	May 18 2008, 12:55 PM Post #5
Elite member Posts: 263 Group: Admin Member #246 Joined: December 7, 2006	Paarth Dave May 18 2008, 03:52 AM What if there are no word breaks? How is the recipient going to know how to reverse the letters within each word if you don't give him any word breaks? He's going to have to do exactly what the breaker would have to do. You're "what if" should be "what if we use a keyed transposition." Doing the same transposition in ever message, regardless of key, is never going to be secure.
	When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.


Donald	May 18 2008, 01:58 PM Post #6
Elite member Posts: 454 Group: Trusted Member Member #8 Joined: September 2, 2005	A really useful piece of advice is to spend some time CRACKING ciphers. It's amazing how much your perspective changes on cipher security after only a little bit of time doing cryptanalysis. Suddenly you begin to realize that all kinds of things you previously thought would make a cipher invulnerable, are only small speed bumps in the way of a skilled cryptographer. The best way to understand crypto security isn't to work on the making ciphers end, but on the cracking ciphers end. Making new ciphers is a blast, but you can create much better ones after spending some time breaking ciphers.



jdege	May 18 2008, 04:08 PM Post #7
Elite member Posts: 263 Group: Admin Member #246 Joined: December 7, 2006	Ditto. You can't know whether a provision you're considering in your cipher makes an attack more difficult or less difficult if you don't know how the attack works.
	When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.


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