During week 8 lecture. We learn something that also new for me that is Cipher. This lecture was really confusing and hard for me to understand what is Cipher because it is about numbering and alphabet arrangement in order to translate and decode a secret message. Cipher is an algorithm for encrypting and decrypting data. Symmetric key encryption, also known as secret key encryption, depends on how to the use of ciphers, which operate symmetrically. With symmetric algorithms, the same cipher and encryption key are applied to data in the same way, whether the objective is to convert plaintext to ciphertext or ciphertext to plaintext. A cipher transforms data by processing the original data into ciphertext, which should appear to be random data. A cipher uses a system of fixed rules -- an algorithm -- to transform plaintext, a legible message, into ciphertext, an apparently random string of characters. Ciphers can be designed to encrypt or decrypt bits in a stream (stream ciphers), or they can process ciphertext in uniform blocks of a specified number of bits (block ciphers).
Symmetric ciphers are most commonly used to protect the online communications and incorporated into many different network protocols to be used to encrypt exchanges. For example, Secure Sockets Layer (SSL) and TLS use ciphers to encrypt application layer data, especially when used with HTTP Secure (HTTPS). Virtual private networks (VPNs) that connect remote workers or remote branches into corporate networks use protocols with symmetric ciphers to protect data communications. Symmetric ciphers protect data privacy in most Wi-Fi networks, online banking and e-commerce services. Codes and ciphers are different ways to encrypt a message. A code is a method of changing a message by replacing each word with another word that has a different meaning. On the other hand, a cipher converts the message using the cipher's algorithm to transform the data representing the letters and words in the message. There are so many types of cipher such as, Caesar cipher, Atbash cipher and many more.