AES (Advanced Encryption Standard)

Modern standard block cipher that encrypts 128-bit blocks with 128/192/256-bit keys.

Difficulty: Advanced

How it works

  1. AES works on 128-bit blocks of data arranged as a 4×4 matrix of bytes called the state. It supports key sizes of 128, 192 or 256 bits.
  2. Encryption proceeds in rounds. Each round applies four main steps: SubBytes (non-linear substitution), ShiftRows (row rotation), MixColumns (column mixing) and AddRoundKey (XOR with part of the key).
  3. The exact number of rounds depends on the key size: 10, 12 or 14 rounds. A key schedule algorithm expands the original key into round keys.
  4. In practice you do not implement AES by hand. Instead you call a well-tested library that provides AES, often combined with a mode of operation like GCM.
  5. When you see “AES-256-GCM” in a security setting, it usually means AES with a 256-bit key, running in Galois/Counter Mode to provide both confidentiality and integrity.
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What is it?

The Advanced Encryption Standard (AES) is a symmetric-key algorithm established by the U.S. National Institute of Standards and Technology (NIST) in 2001. Originally known as Rijndael (developed by Joan Daemen and Vincent Rijmen), it was selected after a multi-year global competition to replace the aging DES. AES operates on 128-bit blocks of data and supports key sizes of 128, 192, and 256 bits. It relies on a substitution-permutation network comprising multiple rounds of mathematically complex transformations, making it the bedrock of modern digital security.

Try it yourself

Can you decrypt this challenge?

VHVY GUVF ZRNGL (example ciphertext)

Where this shows up today

To provide a highly secure, efficient, and royalty-free replacement for the vulnerable Data Encryption Standard (DES).