Permutation-Cipher

A custom permutation cipher. This cipher is immune to frequency analysis attacks.

The permutation cipher works as follows. It takes as input a plaintext from a message space and a key randomly chosen from a key space and returns a ciphertext.

The message space is the set {<space>,a,..,z}^L. In other words the message m can be written as m[1]...m[L], where each m[i] is in {<space>,a,...,z}

The ciphertext c can be written as c[1],...,c[L], where each c[i] is in {<space>,0,..,102}. To avoid ambiguities, cyphertext symbols are separated by a comma.

The key space is the set of random maps from {0,..,26} to a permutation of all numbers in {0,…,102}, grouped in 26 lists, each list having length determined by column 2 of the table below.

The encryption algorithm works as follows. A space in the plaintext is mapped to a space in the ciphertext. For each message character m[j], the algorithm finds m[j] in column 1 of the table below, and returns one of the keys in column 3 of the same row. The computation of which key is returned by the algorithm is based on a scheduling algorithm which is intentionally left unknown and is a deterministic algorithm (that is, it does not use new random bits) that may depend on j, L and the length of the list on that row.

The decryption algorithm does the inverse process. It maps space to a space in the plaintext. On any ciphertext character different from a space, it finds the ciphertext character in column 3 of the table, and returns the column 1 plaintext letter that is on the same row.  

For instance, assume k(b,1)=23, k(c,1)=11, k(c,2)=98, k(c,3)=5, k(g,1)=34, k(g,2)=56. Then the plaintext “cbcb gbgg gcb” may be encrypted as “98,23,5,23 34,23,56,34 34,11,23”

English Letters	Avg. Frequency	Key Values (randomly chosen distinct numbers between 0 and 102
a	8	k(a,1),...,k(a,8)
b	1	k(b,1)
c	3	k(c,1),...,k(c,3)
d	4	k(d,1),...,k(d,4)
e	13	k(d,1),...,k(d,13)
f	2	...
g	2
h	6
i	7
j	1
k	1
l	4
m	2
n	7
o	8
p	2
q	1
r	6
s	6
t	9
u	3
v	1
w	2
x	1
y	2
z	1

Download ZIP

• Version 0.1

Build

• Install Build Environoment Maven 3.3.9 or later from: Maven
• From the root folder run Maven: $ mvn clean install
• A JAR will be built in the root directory of the project.

Command Line Usage

• Install Java 1.8 JDK from: 1.8 JDK
• To run the jar from the command line:

...```

## Run Within IDE (optional)
* Using Maven in Eclipse for Java Developers
------------------------------------------
If m2e (Maven plugin) is not built into Eclipse, follow these steps to install the plugin:

  * Open Eclipse.
  * Go to Help -> Eclipse Marketplace.
  * Search for Maven.
  * Click "Install" button at "Maven Integration for Eclipse" or "m2e" section.
  * Follow the instruction step by step.,

Restart Eclipse after installing m2e.

* Build the project then run the src/main/java/com/heynt/permutation/main/Main.java main class within your IDE.

## Download Source:
```$ git clone https://github.com/cnibley/permutation-software.git
...```

### Contributors on GitHub
* [Contributors](https://github.com/cnibley/permutation-cipher/graphs/contributors)

### Third party libraries
* see [LIBRARIES](https://github.com/cnibley/permutation-cipher/blob/master/LIBRARIES.md) files

## License 
* see [LICENSE](https://github.com/cnibley/permutation-cipher/blob/master/LICENSE.md) file

## Version 
* Version 0.1

## Contact
#### Charley Nibley
* Twitter: [@cnibley](https://twitter.com/cnibley "cnibley on twitter")

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