- Some basics of algorithm and probability and classical crypto(all of them have very limited secrecy).
- rot13 - algorithm is a secrecy
- shift - small key space
- mono alphabetic substitution cipher - key space = 26!
- poly alphabetic substitution cipher - key space = 26**len(key)
- Perfect secrecy (p[m]=p[m|c]) & one time pad
- p[Gen return every key] = 1/|k|
- for every m and c, there exists one k enc(c,k)==m
- We need more effective encryption scheme in modern cryptography. so these schemes do not satisfies PS.
- Shannon (prove if a scheme satisfies PC).