Symmetric cryptography

Interactive AES Key Expansion Visualizer

Explore how a 128-bit AES key expands into 44 words and 11 round keys using RotWord, SubWord, round constants, and XOR.

AES-128 schedule

The visualizer focuses on AES-128 because it has 4 original words, 44 total words, and 11 round keys.

Round keys

Each AES-128 round key contains four 32-bit words.

Round 0 word breakdown

WordBytesSourceExpression
w[0]00 01 02 03key
w[1]04 05 06 07key
w[2]08 09 0a 0bkey
w[3]0c 0d 0e 0fkey

Manual testing checklist

  1. 1Open the AES Key Expansion Visualizer page.
  2. 2Confirm the default AES-128 key expands into 44 words.
  3. 3Confirm round 0 uses the original key bytes.
  4. 4Click a later round and confirm the round key updates.
  5. 5Inspect a word at an index divisible by 4 and confirm RotWord/SubWord/Rcon explanation appears.
  6. 6Enter a non-hex key and confirm a friendly validation error appears.
  7. 7Enter a key shorter than 32 hex characters and confirm validation prevents expansion.
  8. 8Resize to mobile width and confirm the table and round cards remain usable.