concept AES in category cryptography

This is an excerpt from Manning's book Real-World Cryptography MEAP V09. Login to get full access to this book.

Let’s take the Advanced Encryption Standard (AES) encryption algorithm as an example. AES was the product of an international competition organized by the National Institute of Standards and Technology (NIST).

In this chapter we will talk about three main authenticated encryption algorithms. Notice that we have yet to introduce what authenticated encryption is. This section will begin by introducing the Advanced Encryption Standard (AES) and will then proceed to explain that AES cannot be used as-is. The section will then introduce the AES-CBC-HMAC algorithm which augments AES in order to make it secure.

Before we start to explain how AES works, we briefly mention that AES sees the state of the plaintext, during the encryption process, as a 4 by 4 square of octets like so:

Figure 4.6. When entering the AES algorithm, a plaintext of 16 bytes gets transformed into a 4x4 square. This state is then encrypted, and finally transformed into a 16-byte ciphertext.

This doesn’t really matter in practice, but this is how AES is defined. Under the hood, AES works like many similar symmetric cryptographic primitives called block ciphers (as they are ciphers that encrypt fixed-sized blocks).