A Very Simple Encryption Scheme

1
What Is Wrong With This Simple Code?
In a simple 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
increased by 2. 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 CAT are mapped
to the numbers 3,1,20. These values are each
increased by 2 to result in 5,3,22. The values
5,3,22 are then mapped back to the letters FCV.
What Is Wrong With This Scheme?
2
ANSWER Any letters of Y or Z can not be mapped
to any other letter since the values 27 and 28 do
not correspond to any letter. For example, the
word YAM is mapped to the values Y25, A1, and
M13. These values are increased to 27,3,15 so
YAM is encrypted as ?CO Furthermore, since we
do not know what the first letter of ?CO is, we
can not completely decode this word to recover
the original word. To solve this problem, we can
use what is called modular arithmetic where we
subtract 26 from our new numerical values. So
the value of 27 would become 27-26 1. Also, the
value of 28 would become 28-26 2. With this
system, the word YAM would be encrypted as ACO.
For More Info, See A Very Simple Encryption
Scheme