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Randomized Padding

Random Padding Example

📦 Why Padding Is Needed​

XTEA256 (like most block ciphers) encrypts data in 8-byte blocks.
If your message is not a multiple of 8 bytes, it needs to be padded.

🧪 How It Works​

Instead of adding fixed padding bytes, random values are added to fill the last block.

  • The length of the actual message is stored separately
  • Padding is stripped after decryption
  • Each encryption attempt generates a different encrypted result, even for identical messages

🛡️ How Padding Prevents Key Recovery​

Without random padding, encrypted packets would always end in predictable bytes
(like multiple 0x00 values). This can leak information when decrypting with the wrong key.

For example:

  • If your message is 1 byte, the last 7 bytes will be padding
  • Without randomness, these 7 bytes would always be the same (e.g. 0x00)
  • An attacker could try random keys and check if the decrypted padding looks "valid"

This would make it easier to guess or brute-force the session key over time.

By using random padding:

  • Each decryption attempt produces unpredictable results
  • There's no way to verify if a wrong key was "almost correct"
  • The padding cannot be guessed, making key recovery practically impossible

🧠 Benefits​

  • ❌ Prevents detecting repeated messages
  • 🔐 Makes it impossible to compare encrypted payloads
  • 🔄 Protects against pattern analysis
  • 🧩 Ensures that each packet appears unique, even if message is the same

Randomized padding is automatically handled by the library.
You don’t need to manually add or remove it.