Special Cases
|M|=H(M) (no redundancy in the language)
- H(K)/(|M|-H(M)) => H(K)/0 => infinite ratio never=1
- The message is never breakable
|K|=|M| (one letter of key for every letter of message, with all key symbols truly random)
- H(K)/(|M|-H(M)) => X/(X-H(M))
- For H(M)ɬ, X-H(M) < X
- so unicity distance NEVER = 1
- so the code is never breakable
- This is called the “Perfect” system a.k.a. one-time-pad