A note:
	I appreciate comments and questions during class
	I can monologue, but that's not ideal

Typical Scenario:
	Alice sends a message to Bob
	Trudy, who is bad, wants to:
		- Read the message
		- Change the message
		- Send a counterfeit message
	Alice and Bob either have or don't have the key

Ciphertext vs. plaintext
	- ciphertext in caps
	
Cipher vs. code

Historical example:  Ceaser Cipher
	- Used to work!
	- I don't know what this means:
		rkifhbfkqebmxpqfkltexsbqtlzxqpoxqeboqexklkb

Making Ciphers Stronger: Vigenere
	- Use a word for the key
	- Increases number of keys

Brute Force Attack
	- Shift cipher is vulnerable to this, if you know the algorithm
	- The solution:  Bigger key space
	- Computers don't really change anything here
	- How does a computer tell when it has the correct answer?
		+ Search for words, in text
		+ In files?  Common headers

Attack Scenarios:
	- Ciphertext only
	- Known Plaintext
	- Probable Plaintext
	- Chosen Plaintext
	- Algorithm and Ciphertext

Should the attacker send messages?
	- May be used to obtain specific information
	- Midway example (note:  This is a code, not a cipher)
	- May be used to obtain more ciphertext
	- May also be detected!

Shannon:
	- Secrecy proportional to labor
	- Keys and algorithm should be uncomplicated
	- Implementation should be as simple as possible
	- Errors shouldn't propegate
	- Ciphertext shouldn't be bigger than plaintext

Attacking Vigenere:
	- Frequency analysis by word length
	- Frequency analysis requires knowledge of plaintext!
		+ Must know if it's English text, etc.
		+ List of foreigners?

Improving Vigenere:
	- Very long key?
	- One-time pad to reduce ciphertext
	- Send a new key with every message

A new idea:  Permutation Ciphers
Stick cipher
Example:  Transposition
	- key is block size
	- Frequency analysis?
	- Digrams, trigrams, etc

"Commercial grade" encryption:
	- Based on sound mathematics
	- Analyzed by experts
	- Time-tested

A note before we go too far:
	Alphabet is 26 characters for English
	A byte has 256 possible values
	Suppose we shift bytes instead of letters
		Then we could do a shift cipher on binary data

Project 1 brief explanation