Chapter 7: Cryptography - Ciphers and Encryption Methods

There are two types of ciphers.

1. Substitution cipher - replaces characters with different characters.
2. Transposition cipher - Moves the values around. Does not replace values but hides the original meaning.

There are also two types of algorithms that are associated with cryptography:

1. Symmetric - user and sender use two instances of same key for encryption and decryption. Also known as secret keys. Equation to determine number of keys needed: N(N -1)/2. This method is a lot faster but must have secure mechanism to deliver keys the right way.

2. Asymmetric - each entity has different keys and are the two are related mathematically. For example, if one is used to encrypt the other must be used to decrypt. Public key is known to everyone, and only the owner uses the private key. There is better key distribution here, but is is much slower than the symmetric way.

Ofter good practice to use symmetric algorithms and asymmetric algorithms together. This is known as Hybrid Encryption.