VIC

VIC is a pencil and paper cypher using a straddling checkerboard as well as several other known techniques used to further obfuscate the message.

To encrypt, a straddling checkerboard is set-up by following the rules:

The first row is numbered from $0$ to $9$ .
The second row is populated with the most frequent letters of the alphabet (ESTORNIA-R), in no particular order, and by leaving two blanks below two arbitrary numbers from the first row.
The remaining rows are numbered with the numbers from the first row that have a blank in the second row.
The remaining rows are then filled-in with the rest of the alphabet (in no particular order).
Any spare cells which can be filled with any non-literal character.
It does not matter where the spaces and the non-literal characters are placed as long as the receiver uses the same system.

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

To encrypt, every letter from the checkerboard is mapped to rows and columns (or just columns if it occurs in the second row).

As an example, to encrypt let there be:

L  E T    T H  E R E B  E
49 0 1    1 46 0 7 0 40 0

The resulting message 4901146070400 can be sent out directly or processed further through a second cypher stage such as transposition or substitution. As an example, we can add a key 0727 using modular arithmetic:

4901146070400
0727072707270
------------- (+)
4628118777670

Optionally, the same straddling checkerboard can be used to convert the cypher-text back into letters. Since we have chosen two blanks for 4 and 6, whenever we find those numbers in the first position, we group the numbers together (because 4 and 6 have a blank space in the second row of the checkerboard and cannot be converted to letters):

46 2 8 1 1 8 7 7 7 67 0
-----------------------
H  A I T T I R R R Y  E

resulting in the cypher-text: HAITTIRRRYE.

In order to decrypt, one must know the chosen structure of the checkerboard and the successive operations used to obtain the cypher-text.

In essence, VIC is a hybrid cypher that combines multiple methods of substitution and transposition in order to obtain the cypher-text. It is a very strong cypher due to the number of operations performed during encryption but that also results in a larger shared secret between the sender and the receiver - ie: the checkerboard structure is arbitrary, the whole thing must be established before messages can be sent; adding a key to the procedure for a further transposition also means that the key must be known and, lastly, the order of operations must be known in order to be able to reverse the cypher.