This document discusses different types of ciphers used for encryption. It describes stream ciphers that encrypt data bits using an XOR operation with a keystream. Block ciphers divide data into blocks and encrypt each block separately using keys and an initialization vector. Electronic Code Book (ECB) encryption uses the same key to encrypt each block, revealing patterns, while Cipher Block Chaining (CBC) XORs each plaintext block with the previous ciphertext block before encryption to provide more security.