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Developing a new cipher technique

# Developing a new cipher technique

Posted in the Cryptography Forum

Since: May 13

Germany

#1 May 29, 2013
No, I didn't just re-invent the Vigenere cipher. Actually, I'm a fan of old-fashioned pencil-and-paper ciphers, and I've created a unique encipherment method consisting of multiple other methods, including a unique method of my own invention which I can't find any references to anywhere on the internet, layered on top of one another. I just wanted to describe how it worked, get some feedback, and see if anyone wanted to try and crack it just for fun. First, you decide what characters you want to be able to encrypt. I've chosen the following:

ABCDEFGHIGKLMNOPQRSTUVWXYZ [SPACE],.?!'

Then, you decide how many cipher symbols you want the cipher text to have. I've chosen to use 100 distinct symbols, simply because they fit nicely on a 10x10 grid and because if I write the cipher text as a series of numbers in Arabic numerals, there are exactly 100 possible two-digit number combinations excluding negatives - 00, 01, 02, 03, and so on up to 99. Then, you calculate the relative frequencies, in the English language, of each of the plaintext characters you wish to be able to encrypt, and assign more cipher symbols to the characters which occur more frequently, and fewer to the characters which occur less frequently, to even out the letter frequency and impede letter frequency analysis. I've chosen the following number of symbols for each plaintext character:

A: 7
B: 1
C: 1
D: 4
E: 10
F: 1
G: 1
H: 5
I: 6
J: 1
K: 1
L: 3
M: 1
N: 6
O: 6
P: 1
Q: 1
R: 5
S: 5
T: 7
U: 1
V: 1
W: 1
X: 1
Y: 1
Z: 1
[SPACE]: 16
,: 1
.: 1
?: 1
!: 1
': 1

You can draw weird shapes, or just use various numbers, or whatever. This creates your unique cipher alphabet. Of course, you have to be careful not to use the same symbol more than once in this stage. Once you've done that, you create a grid of squares, with just enough squares so that there's one for each of your cipher symbols. I have chosen to use a simple 10x10 grid, because it has exactly enough room for the 100 characters which I use. Then, you number each square on the grid from left to right, top to bottom, starting from zero and counting up to however many squares there are. Then, you write each of your cipher symbols into a different one of those squares, in a completely random order. I refer to this as the "primary key". Then you create the "secondary key". The secondary key is actually a series of many smaller cipher keys, each the length of a different prime number. Basically, you create a short, two-character cipher key composed of two randomly chosen symbols from your cipher alphabet, and then a three character cipher key composed of three randomly chosen symbols from your cipher alphabet, and then a five character cipher key, and then a seven character cipher key, and so on up to however big of a prime number you wish to use. This collection of miniature keys strung together comprises the secondary key. The plaintext is then encrypted via the following steps:

1st - You take each plaintext character and you substitute it with the associate symbol from your cipher alphabet.

2nd - You take each symbol you have written down, and find its associated number in the grid in which you recorded the primary key.

3rd - You then do the same for all of the symbols in the secondary key.

4th - You then encipher the text with each of the mini-keys in the secondary key one after another, using each mini-key to encipher the text in the fashion of a Vigenere cipher. That is to say that you find the number, according to your primary key, of each symbol in the text; add to that number the associated number, according to your primary key, of the associated symbol in whatever mini-key in the secondary key you are currently on; find the symbol associated, according to your primary key, with the new number; and then substitute that symbol in place of the old one; continuing until you have reached the end or your secondary key.

To decrypt the cipher text, you reverse the process.

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