AES

AES is a computational procedure that turns readable text into unreadable gibberish. To do this, it needs a key: a secret sequence of numbers known to both sender and receiver. Whoever has this key can turn the gibberish back into the original text. Whoever doesn't have it only sees data that looks random. Because both sides use the same key, this is called a symmetric method. The abbreviation stands for Advanced Encryption Standard.

The standard almost everyone agreed on

Before AES, the method DES was common. Its keys, at 56 bits, were too short. By the late 1990s, specialized computers could try them all within days. The US agency NIST therefore held a public competition. In 2000, a design by two Belgian researchers called Rijndael won, and since 2001 it has been the official standard.

The openness of the method was decisive. Anyone may read up on how AES computes and try to break it. For over twenty years, no one has practically succeeded. Security through secrecy of the method is considered a bad sign in cryptography — only the key is supposed to remain secret.

Because everyone agreed on the same standard, encryption works across devices. An Android phone and a server in Ireland understand each other. In addition, processors from Intel, AMD, and Apple have built-in instructions specifically for AES. As a result, encrypting costs barely noticeable computing time.

Rounds, blocks, and key length

AES splits data into blocks of 16 bytes each. Each block passes through several rounds. In each round, the bytes are substituted, shifted, mixed, and combined with part of the key. With a 128-bit key there are ten rounds, with 256 bit there are fourteen. The goal is confusion: change a single bit in the text, and the result looks completely different.

The key length indicates how many possibilities an attacker would have to try. At 128 bit, that's about 340 sextillion combinations. Even all the computers in the world combined would need an unimaginably long time for that. This is often compared to a combination lock where you simply double the number of digits — the effort doesn't just double, it explodes.

A common misconception: AES alone is not enough. One also has to define how the many blocks are chained together. This mode of operation is called a mode. A poorly chosen mode can reveal patterns even though the algorithm itself is intact. GCM is common today because it additionally checks whether someone has altered the data in transit.

AES in phones, Wi-Fi, and the cloud

When a website starts with "https", the connection almost always runs over AES. Home Wi-Fi also uses it as soon as WPA2 or WPA3 encryption is active. Messengers like WhatsApp or Signal use it to encrypt messages. The hard drive of an iPhone or a Windows machine with BitLocker is likewise AES-encrypted.

In news reports, the term often comes up in connection with data leaks. Companies then emphasize that data was "stored AES-256-encrypted." This is only reassuring if the keys are kept separately and securely. If data and keys were stolen together, the best encryption won't help.

AES also plays a role in AI services. Requests to a chatbot travel encrypted to the data center, and training data stored there is often kept encrypted on the hard drives. There is also debate about whether quantum computers threaten AES. Currently, not seriously: they halve the effective key length, which is why AES-256 is considered secure for the long term.