Assignment 2:

Caesar cipher

https://en.wikipedia.org/wiki/Caesar_cipher
each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet.
encode:
$E{n}(x)=(x+n) mod 26$
decode:
$D{n}(x)=(x-n) mod 26$
Breaking the cipher:
1.an attacker knows (or guesses) that some sort of simple substitution cipher has been used, but not specifically that it is a Caesar scheme;
solution: frequency analysis or pattern words
2.an attacker knows that a Caesar cipher is in use, but does not know the shift value.
solution: brute force attack

Vigenère cipher

https://en.wikipedia.org/wiki/Vigenère_cipher
Using a series of different Caesar ciphers based on the letters of a keyword. Use the Vigenère square or Vigenère table