ChaCha32 Arduino Library

ChaCha32 is a lightweight, Arduino-compatible implementation of the ChaCha stream encryption algorithm, extended to use 32 rounds instead of the standard 20 for increased cryptographic strength.

This library is optimized for embedded devices, and provides basic encryption/decryption using a 32-byte (256-bit) key and a 12-byte (96-bit) nonce.

Features

• 32-round ChaCha cipher (vs. standard 20 rounds)
• C++ implementation compatible with Arduino
• Simple API: chacha32_encrypt and chacha32_decrypt
• Identical API behavior across platforms (Arduino, C, Go, Nim)
• Small footprint, suitable for MCUs with limited flash/RAM

Usage Example

#include <ChaCha32.h>

const uint8_t key[32] = {
  0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
  0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
  0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
  0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F
};

const uint8_t nonce[12] = {
  0x00, 0x00, 0x00, 0x09,
  0x00, 0x00, 0x00, 0x4A,
  0x00, 0x00, 0x00, 0x00
};

uint8_t plaintext[] = "Hello ChaCha32!";
uint8_t ciphertext[64];
uint8_t decrypted[64];

void setup() {
  Serial.begin(9600);
  delay(1000);

  chacha32_encrypt(key, nonce, plaintext, ciphertext, sizeof(plaintext));
  chacha32_decrypt(key, nonce, ciphertext, decrypted, sizeof(plaintext));

  Serial.println("Original:");
  Serial.println((char*)plaintext);

  Serial.println("Decrypted:");
  Serial.println((char*)decrypted);

  Serial.println("Encrypted:");
  for (size_t i = 0; i < sizeof(plaintext); i++) {
    if (ciphertext[i] < 16) Serial.print("0");
    Serial.print(ciphertext[i], HEX);
    Serial.print(" ");
  }
  Serial.println();
}

void loop() {}

🟢 Minimal usage example

#include <ChaCha32.h>

const uint8_t key[32] = {
  0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
  0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
  0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
  0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F
};

const uint8_t nonce[12] = {
  0x00, 0x00, 0x00, 0x09,
  0x00, 0x00, 0x00, 0x4A,
  0x00, 0x00, 0x00, 0x00
};

uint8_t plaintext[]  = "Hello ChaCha32!";
uint8_t ciphertext[64];
uint8_t decrypted[64];

void setup() {
  chacha32_encrypt(key, nonce, plaintext, ciphertext, sizeof(plaintext));
  chacha32_decrypt(key, nonce, ciphertext, decrypted, sizeof(plaintext));
}

void loop() {}

Compatible Libraries

This Arduino library is fully compatible with the following Go and C implementations:
➡️ github.com/regimantas/chacha32go
➡️ github.com/regimantas/chacha32-c

Both versions produce identical output given the same key, nonce, and plaintext.

Security Notes

• Nonce must be unique per encryption session. Ideally, generate it randomly or use a reliable counter. Reusing the same nonce with the same key breaks encryption.
• This library does not include key exchange, key derivation, or replay protection – these must be handled by your protocol.
• Never hardcode encryption keys in production devices.
• Decryption is symmetric – chacha32_decrypt(...) is equivalent to encrypt with same key/nonce.

License

MIT License

Author

Regimantas Baublys – GitHub