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XTEA256 Encryption

🔐 Overview​

XTEA256 is a lightweight symmetric encryption algorithm used in LightweightSecureTCP.
It operates on 64-bit blocks using a 256-bit key, and is optimized for embedded systems.

⚙️ Key Properties​

  • Encrypts 64-bit blocks (2 × 32-bit unsigned integers)
  • Uses a 256-bit symmetric key (8 × 32-bit integers)
  • Performs 32 rounds of encryption by default (configurable)
  • All 8 parts of the key are used in every round
  • Pure C++ implementation, no external dependencies

🔄 Key Usage​

  • 🤝 Handshake packets are encrypted with a static shared key
  • 🔑 Session packets are encrypted with a dynamically generated session key

You must call:

LightweightSecureTCP::setHandshakeKey(myKey);

before creating any server or client.

🔁 Number of Rounds​

By default, 32 rounds are performed, but you can configure this:

LightweightSecureTCP::setNumberOfRounds(64);

Higher round counts increase encryption complexity but consume more CPU cycles.

🧠 Why XTEA256?​

  • Lightweight and fast (suitable for ESP32)
  • Predictable block size (easy to integrate with TCP)
  • Strong enough for session-level encryption in embedded contexts

Encryption is handled automatically by the library. You only need to set the handshake key and, optionally, the number of rounds.