Chapter 2  Crypto Basics Problems:  1, 2, 3, 7, 8, 9, 13, 18, 20

Kerckhoffs principle:

The inner workings of the cryptosystems are completely known by the attacker, the only secret is the key.

Classic crypto:

bulletSimple Substitution Cipher
bulletDouble Transposition Cipher - Changing the rows
bulletOne-Time Pad  - The key is chosen at random, same length as the message, the key can only be used once.  STREAM CIPHER
bulletProject Venona (one time pad, can be an error in the method generating the pads)
bulletCodebook Cipher - Words and their corresponding codewords. BLOCK CIPHER

                    1929:  Gentlemen do not read each other`s mail

Confusion: (simple substitution and a one-time pad)

Obscure the relationship between the plaintext and the ciphertext.

Diffusion: (double transposition)

Supposed to spread the plaintext statistics through the ciphertext.

Diffusion alone is not enough to be probable secure.  One-time pad has both.  If you use codebook and permutation then you use both.

Stream cipher:

Better in hardware

Block cipher:

Better in software