Advanced Encryption Standard

The Advanced Encryption Standard is a fixed computational procedure that turns data into an unreadable jumble. To do this, you need a key, i.e. a very long secret number. Whoever possesses this key can reverse-compute the data back into its original state. Whoever doesn't possess it only sees seemingly random characters. This is known as a symmetric method: the same key is used for locking and unlocking, like a door lock with a single key copy. The short name of the method is AES, and it has been the official standard of US authorities since 2001.

Why AES is everywhere

Before AES, an older method called DES was used. Its key, at 56 bits, was very short—by today's standards, a far too small secret number. In the 1990s, specialized computers could try out all possible DES keys within days. The US standards agency therefore launched a public competition. The winner was a method by two Belgian researchers called Rijndael, which has since been named AES.

The open procedure was decisive. Everyone was allowed to examine and attack the candidates, for years and publicly. This is the normal case in cryptography: an encryption method is only considered secure once it is publicly known and yet still no one can crack it. Keeping the method itself secret would be a warning sign, because then no one from outside would have searched for flaws.

Today, AES is practically without competition. Processors from Intel, AMD, and Apple contain dedicated circuits just for AES. As a result, encryption runs with almost no noticeable loss of time. Anyone encrypting a hard drive usually notices no difference while working.

Rounds, blocks, and key lengths

AES doesn't process data all at once, but in chunks of 16 characters each, so-called blocks. Each block is scrambled multiple times. Such a pass is called a round. In each round, characters are swapped according to a fixed table, rows are shifted, columns are mixed, and the key is worked in. Depending on the key length, there are 10, 12, or 14 rounds.

The key length is stated in the name: AES-128, AES-192, or AES-256, measured in bits. A 128-bit key has about 340 sextillion possible values, i.e. a number with 39 digits. Trying all of these is impossible with current and foreseeable technology. AES-256 is additionally considered robust against future quantum computers, because although these reduce the effort required, they do not bring it down to a feasible level.

A common misconception: a long key length alone does not make a system secure. It also matters how the many blocks are chained together, the so-called mode of operation. If each block is encrypted individually and identically, patterns remain visible in the image or text. And the best algorithm is of no use if the key originates from a weak password or is stored insecurely.

Recognizing AES in everyday life

When accessing a website with https, browsers and servers negotiate a method in the background. Most often, the choice falls on AES. Home WiFi also uses AES as soon as WPA2 or WPA3 encryption is set. Messengers like WhatsApp and Signal likewise use it to encrypt message content.

On devices, one encounters AES in hard drive encryption, such as BitLocker on Windows or FileVault on the Mac. Smartphones encrypt their entire storage by default. Password managers and encrypted ZIP archives rely on the same method. In product descriptions, the marketing term "military-grade encryption" then often appears, which simply means AES-256.

In news reports, AES is usually read about in connection with data protection or data leaks. It's important to make a distinction here: AES itself is almost never broken. Attackers instead use stolen keys, unencrypted backup copies, or flaws in the surrounding software. The lock holds—it's usually the window next to it that gets opened.