Transcript A Much Improved Encryption Scheme

Why Is This Code Difficult To Break?
In this encryption scheme, letters are input and then encrypted
in the following way:
Each letter is assigned a numerical value. “A” is assigned a
value of 1, “B” is assigned a value of 2, C = 3, and so on for all
the letters of the alphabet up through Z = 26.
Each value is then modified in the following way: First, the
number is subtracted from 27. Then, the number is increased
by 2. If the increased value is greater than 26, the value is
divided by 26 and we use the remainder in a process known as
mod-26 arithmetic.
The values are mapped back into letters. So a value of 3 would
be mapped to the letter C.
Example: The letters of the word ZAP are mapped to the
numbers 26,1,16. These values are subtracted from 27
to give 1,26,11. Then each number is increased by 2
using mod-26 arithmetic to result in 3,2,13. The values
3,2,8 are then mapped back to the letters CBM.
Can You Think of a Way To Break This Code?
ANSWER: Although, a little difficult to recognize, one could
discover this pattern by comparing two lists of the alphabet
with the bottom list containing letters in reverse order. We
shift the bottom list until the letters CBM correspond to
some real word. In this case, moving the bottom list 2 to
the right makes CBM correspond to ZAP as shown below.
ZAP is encrypted as CBM
This mean we transpose the letter values (subtract from
27) and then add 2 to the letter value.
For More Info, See A Tough Code To Break