This post is part one of a series on an introduction to applied cryptography. While a PhD in math is not required to understand this material, it is helpful if you know some university level math (elementary linear algebra / number theory, calculus, and discrete math). It is also assumed that you have a basic understanding of network security and programming. Part one is going to cover an overview of crypto, symmetric, asymmetric ciphers and historical ciphers. Further posts are going to delve into more advanced topics such as elliptic curves and modern encryptions schemes such as AES 256.

What is cryptography? Cryptography is the science of keeping text secret. Cryptanalysis, on the other hand, is the process of trying to break secure cryptosystems (Alan Turing is a famous cryptanalysis because of his research during World War 2). We will mostly be focusing on cryptography and not cryptanalysis in this series. If you are interested in cryptanalysis, view the references at the end of this article for more information. Let’s start with first going over some definitions that are commonly used.

**Symmetric Algorithms:**

In symmetric algorithms, two people have an encryption and decryption method, and share a secret

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