Notes

Stream ciphers
Encryption is done one bit/byte at a time
-High speed, low hardware complexity
Used with symmetrical encryption
-Not commonly used with asymmetrical encryption


Block ciphers
The starting state should never be the same twice
-Key is often combined with an Initialization Vector(IV), these are used for randomization
-Often 64-bit or 128-bit blocks
-Pad added to short blocks
-Each block is encrypted or decrypted independently
Symmetrical encryption
-Similar to stream
Encrypt one fixed length group of bits at a time
-A block
Mode of operation
-Defines the method of encryption
-May provide a method of authentication
Block size is fixed
-Not all data matches block size
-Split plaintext into smaller blocks
-Some modes require padding before encryption

ECB
The simplest encryption mode
-Too simple for most uses
Each block is encrypted with the same key
-Identical plaintext blocks create identical ciphertext blocks

CBC
A popular mode of operation
-Relatively easy to implement
Each plaintext block is XORed with the previous ciphertext block
-Adds additional randomization
-Uses an IV for the first block

CTR
Block cipher mode/acts like a stream cipher
-Encrypts successive values of a counter
Plaintext can be any size since it's part of XOR
Encryption with authentication
-Authentication is part of the mode