AES Explained

[Nytro]

AES Explained

Hello people,

It’s been a while since I have last posted an article. I decided to write an article about the Advanced Encryption Standard. I will explain certain concepts regarding AES and how it basically works. I will provide step by step C code, to make it even easier to understand. You can find the full source code at the end of this article. Actually many websites around the net provide source code for AES. This one is supposed to be easy to understand

What is AES?

AES is a cryptographic algorithm, more specifically a symmetric block cipher. This means that it operates at a block of data, instead of a single element per iteriation. (This element could be a bit or a byte). AES is also known as Rijndael. Actually AES is just a variant of Rijndael. To read more about AES/Rijndael see Advanced Encryption Standard - Wikipedia, the free encyclopedia. Especially the links at the bottom, they help understanding the basic structure of AES. AES is able to encrypt and decrypt a block of data using a key. The key and the block of data (from now on, the input) have a fixed length. The input is always 128-bit (16 bytes), while the key can be 128-bit, 192-bit or 256-bit (16, 24 and 32 bytes respectively). What makes AES so good you say? The answer would be it’s security and speed. It’s obviously secure since it’s been chosen by NIST. Then again, no one has been able to break it. And finally, it’s fast because it’s arithmetic is based on XOR operations and bit shifts, which CPUs like a lot. That said, it’s also simple and even faster to implement in hardware.

AES Concepts

Before I begin talking about the cipher itself, there are some very important concepts that I need to explain. They’re basically the math behind AES. Everything else is easy. This is actually the hardest part. Why am I explaining the hardest part before the everything else? Because if you don’t understand this, you won’t be able to understand the rest of this article. Of course, if you just want the source code, skip to the end. The content below may refer to the specification, which is located here: http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf

Articolul frumos aranjat:

http://www.x-n2o.com/aes-explained/