Chapter 8:

Encoding messages

http://public.gettysburg.edu/~cpresser/CS103/ciphers.ppt

Caesar Cipher
cipher text = plain text + 4

plain text : JavaScript
cipher text: NEZEWGVMTX

shared secret: amount of shift (4)


Substitution Cipher:
Map plain text to random
cipher text

shared secret: 
  entire substitution
  
Hard to remember: use a 
  keyword to generate the 
  substitution alphabet

Vigenere Cipher:
  Multi-alphabet substitution
  
plain text: hellothere
keyword: cpu

hellothere  <- plain
cpucpucpuc  <- keyword
jtfndnjtmg  <- cipher text

Vigenere Cracking:

Save keyword and plain text
message in a file.

Better method: 
use keyword longer than message

One time pad cipher:
Pad of paper with random numbers

Use a book: page, paragraph, line