Felix a pencil-and-paper cipher

Felix Cipher

SYNOPSIS

Felix is a 'pencil-and-paper cipher' [i] offering relatively good security for causal use. Unlike modern encoding schemes that require, at a minimum, a computer to be of any practical consequence; Felix requires only that you follow three elementary rules (outlined below). If you're curious about cryptology, the Felix cipher is a great place to start. This cipher can typically be understood and applied, even by children, in a handful of minutes. Quite simply that means, its easy to implement for common folks such as you and I.

The Felix cipher [ii] is based on the research of Felix Marie Delastelle [iii]. The author of this work respectfully acknowledges Monsieur Delastelle's achievements in the field of cryptology.

KEY

First, create a key [iv], by randomly dispersing, all 26 letters of the alphabet, and ten digits from 0-9, throughout:


      1  2  3  4  5  6
   1  8  P  3  D  1  N
   2  L  T  4  O  A  H
   3  7  K  B  C  5  Z
   4  J  U  6  W  G  M
   5  X  S  V  I  R  2
   6  9  E  Y  0  F  Q

You'll notice each character in the key is represented by coordinates [v] on the left most column, and top most row. Thus, character '0' (zero), is located in row '6', and column '4'.

ENCODING

Working left to right, locate each character from the message [fig 3.1] in the key, and write out its coordinates vertically [fig 3.2] beneath the message:


   fig 3.1: K N O W L E D G E  I S  P O W E R

   fig 3.2: 3 1 2 4 2 6 1 4 6  5 5  1 2 4 6 5
            2 6 4 4 1 2 4 5 2  4 2  2 4 4 2 5

Next, join each digit to the previous digit on the right [fig 3.3], and each row to the previous row above [fig 3.4]:


   fig 3.3: 31 24 26 14 65 51 24 65
            26 44 12 45 24 22 44 25

   fig 3.4: 31 24 26 14 65 51 24 65 26 44 12 45 24 22 44 25

The string of numbers produced [fig 3.4], are then read in pairs horizontally working left to right, creating a second sequence of coordinates [fig 3.5], which are next converted back into characters from the key via their respective coordinates [fig 3.6]:


   fig 3.5: 31 24 26 14 65 51 24 65 26 44 12 45 24 22 44 25

   fig 3.6: 7  O  H  D  F  X  O  F  H  W  P  G  O  T  W  A

The message is now fully encoded [vi], and ready to be delivered.

DECODING

To decode a message, simply reverse the process... Working left to right; convert each character into its corresponding coordinates [fig 4.1], written horizontally [fig 4.2]:


   fig 4.1: 7  O  H  D  F  X  O  F  H  W  P  G  O  T  W  A

   fig 4.2: 31 24 26 14 65 51 24 65 26 44 12 45 24 22 44 25

Next, divide the string of numbers into two equal rows, placing the second row below the first [fig 4.3]. Reading the digit in the top row, along with the digit in the bottom row together vertically, use these coordinates to locate the character in the key and write each character below its corresponding coordinates [fig 4.4]:


   fig 4.3: 3 1 2 4 2 6 1 4 6  5 5  1 2 4 6 5
            2 6 4 4 1 2 4 5 2  4 2  2 4 4 2 5

   fig 4.4: K N O W L E D G E  I S  P O W E R

The message is now fully decoded, and plainly readable.

SUMMARY

To encode:

- Convert the plaintext into coordinates vertically

- Join previous digits into a single line

- Horizontally convert coordinates into ciphertext

To decode (simply reverse the process):

- Convert ciphertext into coordinates horizontally

- Split line into two equal parts (2nd half on bottom)

- Vertically convert coordinates back into plaintext

NOTES

i. A cipher is a message written in such a way as to conceal its contents. Encoded messages are rendered unreadable. Decoded messages are rendered plainly readable.

ii. The Felix cipher is based on the Bifid cipher, but reworked with a larger 6x6 key rather than the more limited 5x5 key Bifid uses. Whereas the Bifid cipher only referenced 25 characters (typically 'I' and 'J' were combined), the Felix cipher uses all 26 letters of the English alphabet, and all ten digits zero to nine.

iii. Felix Marie Delastelle (1840-1902) was a Frenchman most famous for devising several systems of polygraphic substitution ciphers including the Bifid cipher. Delastelle is unusual for being an amateur cryptographer at a time when significant contributions to the subject were made by professional soldiers, diplomats and academia.

iv. The key (excluding coordinates), is a 6x6 grid of 36 characters. Do be sure to create your own private key when using this cipher. The key used in this document will have been read by any number of people...

v. Coordinates (always read by row first, then column) are fixed at the left most column, and top most row. The intersection point of a row (horizontal axis), and column (vertical axis), yields a single character from the key. When labeling coordinates, they need not be digits as shown in this document, however, all labels must unique within row, and within column.

vi. To encode/decode a given message, both the sender and recipient need a copy of the same key and its coordinates. But remember, *NEVER* give out the details of the key to anyone but trusted parties.

eof