====== Cryptography ======


Plain Text

ciphertext - format of data after it's encrypted

RPT-13 - rotation cipher - A common rotation cipher is Rot-13, frequently used to conceal information on bulletin board systems such as Usenet

Vigenere Table - Multi-alphabet - Alphabet is repeated 26 times to form a matrix, called the VigenèreSquare

**Symmetric vs Asymmetric**

Symmetric 
- very fast 
- same key for encryption and decrypt 
- often referred to as shared key
- Key Management is biggest concern

Asymmetric
- uses two key system 
- Key pair - public and private keys

Hashing
- Mathematical algorithm applied to a file before and after transmission
- if anything changes during transmission the hash will change

MD5, SHA1, SHA2

**ECC Elliptic Curve Cryptopgraphy** 
- Asymmetric encryption uses algebraic structure of elliptic curves
- Strong encryption using smaller key size

**Strong vs weak ciphers**
- strong ciphers can become weaker as computer power increases 
- current strong ciphers: AES, 3DES, TwoFish
- Weak ciphers - deprecated: WEP, WPA

**Digital Signature**
- Asymmetric encryption using public key/ private key (PKI)

Entropy - randomness collected by system
Confusion - each character of ciphertext depends on several parts of the key
Diffusion - dissipating the statistical structure of the plaintext

Block v. Stream - both are symmetric
Block cipher - encrypts in chunks (blocks) of date
Stream cipher - encrypts one bit at a time