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jdege Apr 7 2008, 12:42 PM
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Paarth Dave
Apr 7 2008, 01:54 AM
This cipher is named "Draconian Devil" and it goes like this.....

My cipher system is based on prime numbers.....
There are 26 prime numbers from 1-100 and I have taken each letter of the alphabet and substituted with each prime number from 1-100 in a different manner.....
Instead of A=2,B=3,C=5....and so on.... it is Z=2,Y=3,X=5.......A=97...

So, simple substitution, with nulls, but with a single, fixed key?

Once you explain it to us, the explanation provides us with all the information we need to decrypt?

The crypto community abandoned those hundreds of years ago. The problem is that once you know how the system works, you can read the messages. And you have to explain how the system works to all your code clerks. A system that depends upon none of them revealing the system, or accidentally leaving the instructions lying around, is a system you can't depend upon.

Remember Kerckhoff's principles:
Quote:
 

  1. The system must be practically, if not mathematically, indecipherable;
  2. It must not be required to be secret, and it must be able to fall into the hands of the enemy without inconvenience;
  3. Its key must be communicable and retainable without the help of written notes, and changeable or modifiable at the will of the correspondents;
  4. It must be applicable to telegraphic correspondence;
  5. It must be portable, and its usage and function must not require the concourse of several people;
  6. Finally, it is necessary, given the circumstances that command its application, that the system be easy to use, requiring neither mental strain nor the knowledge of a long series of rules to observe.


Notice 2&3 - the goal is to devise systems in which everything can be known about the system except for the key, without compromising the system. If the enemy discovers how the system works, you should not be compromised. If a key is compromised, you simply use a different key.

You know, many years ago I invented my own "unbreakable" cipher, based on prime numbers and a 26-letter alphabet.

I noticed that 3+5+7+11 = 26.

So I used a keyword to create a permutation of the alphabet:
Code:
 

  CONFIDENTIAL

I'd write out the alphabet in columns, the first letter in each column being a letter of the keyword (with duplicates removed), and the rest of the alphabet written out in order beneath.
Code:
 

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

They'd then be read out in columns, in alphabetic order of the columns..
Code:
 

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

This, then, would be broken into four keywords, of lengths 3, 5, 7, and 11.
Code:
 

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

These would then become the keywords of four independent vig ciphers
Code:
 

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

So the ciphertext would be:
Code:
 

  DEZWH TMIVP MRPIW

What I had been thinking was that since the longer the keyword, the longer the period, and the fewer the repetitions, using multiple keywords with lengths that were relatively prime would be the same as using one long keyword, without the hassle of having to remember it.

3 * 5 * 7 * 11 = 1155 - quite a long keyword.

So I thought this would be difficult to break.

It's certainly more difficult than a standard vig, but it's by no means impossible to break.
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.
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