## Modes of Operation for Block Ciphers

Introduction     Today we won’t actually learn about any new math concepts or algorithms. Instead, we will build upon what we have already. Particularly how we encrypt a plaintext that is larger than a block cipher’s block size (e.g. AES 16 bytes and DES 8 bytes). In practice, we typically want to encrypt more […]

## (AES) Key Schedule and Decryption [Part 2]

This is a continuation of (AES) The Advanced Encryption Standard [Part 1], so it is highly encouraged to read that post before reading this post. In that post, I gave the history of AES and also explained the internals of the AES algorithm.     In this post we will discuss these things: The AES […]

## (AES) The Advanced Encryption Standard [Part 1]

Brief History     In 1997, the National Institute of Standards and Technology (NIST) called to replace the DES. By this time DES was considered dying because of its small key space discussed in the DES post. This was unlike when DES was designed because the selection of the AES algorithm was an open-source process. […]

## Introduction to Galois Fields for AES

Motivation     In the next few posts I want to discuss the Advanced Encryption Standard or better known as AES, which is the most famous symmetric cipher today.     But to do that unlike for DES I need to introduce a new type of mathematics. So in this post, I will introduce group […]

## (DES) Key Schedule and Decryption [Part 2]

This is a continuation of (DES) The Data Encryption Standard [Part 1], so it is highly encouraged to read that post before reading this post. In that post I gave the history of DES and also explained the internals of the DES algorithm.     In this post we will discuss two things: The DES […]

## (DES) The Data Encryption Standard [Part 1]

Introduction     The Data Encryption Standard (DES) was proposed in the early 1970s by IBM, who based the design of the cipher on an earlier design by Horst Feistel. The cipher was created as a request by the United States National Bureau of Standards (NBS) which is the modern-day National Institute of Standards and […]

## Stream Ciphers cont’d and Linear Feedback Shift Registers

If you have not yet read the last post Stream Ciphers, Random Numbers, and the One-Time Pad it is highly recommended you go ahead and read that to understand the stream cipher.     Goal: Construct a stream cipher that is small in hardware. This post makes the most sense when thinking about the hardware […]

## Stream Ciphers, Random Numbers, and the One-Time Pad

Symmetric cryptography is split into two types, stream ciphers, and block ciphers. Stream ciphers encrypt one bit at a time and block ciphers encrypt multiple bits at a time. This post is dedicated to stream ciphers, if you want to learn about block ciphers make sure to read my DES and AES posts. Stream Ciphers […]

## The Shift Cipher

The shift cipher, or the better-known name the Caesar cipher named after Julius Caesar is one of the simplest encryption techniques. In fact for those who have read my Substitution cipher post, the shift cipher is a type of substitution cipher where each letter in the alphabet is mapped to another fixed letter in the […]

## The Substitution Cipher

The Substitution Cipher     We will discuss one of the simplest ciphers, the substitution cipher. This cipher has a lot of historical relevance being used many times, and is also a good starting point for cryptography and cryptanalysis. It is important to have read the What is Cryptology post because I will use concepts […]