About shift-cipher
Shift cipher is one of the easiest cryptosystem. It has a 26 possible keys.
This cryptosystem is not secure. As it has only 26 possible keys, it can be broken down using exhaustive search(brute force). The cipher-text attack model can be used to crack the cryptosystem.
Encryption:
E(X) = (X+k) mod 26
X : plaintext character
k : key of the cipher.
Decryption:
D(Y) = (Y-K) mod 26
Y: cipher text character
k: key of the cipher.
