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Cryptology Academy · Lesson

XOR Inside AES & Stream Ciphers

Trace how XOR is used inside real encryption algorithms.

Welcome

XOR is a fundamental building block inside every modern cipher. In this lesson we trace how XOR appears in AES AddRoundKey and stream cipher keystream mixing.

XOR in AES: AddRoundKey

AES has 10–14 rounds. Every round starts with AddRoundKey: the 16-byte state is XORed with the 16-byte round key. This is the only step that actually introduces the secret key.

All lessons in this course

  1. Bitwise Operations Refresher
  2. XOR Encryption & the One-Time Pad
  3. Why XOR Alone Is Not Secure
  4. XOR Inside AES & Stream Ciphers
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