Understanding AES Encryption: History, Concepts, and Application in Android SDK

Recently, a company's Android SDK project changed its network communication from HTTPS to HTTP with encrypted content using RSA and AES, requiring automated testing tools to adapt to parsing and encrypting requests.

While searching for AES references, the author discovered Moserware's "A Stick Figure Guide to the Advanced Encryption Standard (AES)" and decided to share a translation.

Act 1: A Long Time Ago…

AES introduces itself as a charismatic character, claiming to be the king of block ciphers, with Intel even providing dedicated CPU instructions for faster execution.

The narrative recounts early encryption attempts before 1975, the emergence of DES by IBM as the Data Encryption Standard, and its two‑decades of dominance.

As attacks grew, Triple‑DES was introduced for stronger security, though it remained slow.

In the late 1990s, a need arose for an algorithm as strong as Triple‑DES but faster and more flexible, leading to the creation of Rijndael (later named AES) by Vincent Rijmen and Joan Daemen.

AES won the competition, became the encryption king, and is now widely supported, even with hardware acceleration on modern CPUs.

Act 2: Cryptographic Foundations…

To understand how encryption works, three key ideas are essential: confusion, diffusion, and secret keys.

1. Confusion – creating a complex relationship between plaintext and ciphertext, exemplified by the Caesar cipher where each letter is shifted three positions.

2. Diffusion – spreading the influence of each plaintext bit across many ciphertext bits, illustrated by simple column transposition.

3. Secret Key – the principle that the security of a cipher relies on keeping the key secret; assuming the algorithm is known, only the key should remain unknown.

The article concludes by promising future updates to explain the detailed workings of encryption algorithms.