hw_aes_esp32

Sample ESP32/Arduino IDE code demonstrating the basics of hardware-accelerated AES

Basic functions ripped from hwcrypto/aes.c.

Simple demo of hardware-encoded encryption on the ESP32 with LoRa This is the receiver code. It expects two things:

• A JSON packet [hence the use of the ArduinoJson library]. Required elements:

• from
• msg
• sendCount • If you want to turn on the encryption mode [which is the point here...]
• a 256-bit [ie 32-byte] key: unsigned char key[32];
• a boolean flag: bool needDecoding = true;
• init the key with your passphrase ine setup(); if (needDecoding) { memcpy(key, "YELLOW SUBMARINEENIRAMBUS WOLLEY", 32); }

On your sender, the code is similar and looks like this:

  LoRa.beginPacket();
  String pkt = "{\"from\": \"" + String(myUUID) + "\", \"sendCount\": " + String(counter) + ", \"msg\": \"PING\"";
  IPAddress ip = WiFi.localIP();
  pkt += ", \"IP\": \"" + String(ip[0]) + '.' + ip[1] + '.' + ip[2] + '.' + ip[3] + "\"}";
  uint16_t len = pkt.length() + 1;
  // +1 = don't forget to account for the '\0' at the end...
  pkt.toCharArray(pktBuf, len);

  // Let's flip a switch
  if (needDecoding) {
    Serial.println("len before adjustment = " + String(len));
    if (len % 16 > 0) {
      if (len < 16) len = 16;
      else len += 16 - (len % 16);
    }
    // BEWARE! The buffers are 256 bytes long.
    // Exceeding that could make the code go boom.
    memcpy(encBuf, pktBuf, len);
    esp_aes_hw_hexDump((unsigned char*)encBuf, len);
    uint8_t rslt = esp_aes_hw_multiple_blocks(ESP_AES_ENCRYPT, key, encBuf, (unsigned char*)pktBuf, len);
    Serial.println("len after adjustment = " + String(len));
  }

  Serial.println("Sending:");
  esp_aes_hw_hexDump((unsigned char*)pktBuf, len);
  LoRa.write((const unsigned char*)pktBuf, len);
  LoRa.endPacket();

That's it. You're now communicating (somewhat) securely.

Functions:

• void esp_aes_hw_hexDump(unsigned char *, uint16_t);
• uint8_t esp_aes_hw_multiple_blocks(int, unsigned char *, unsigned char *, unsigned char *, uint16_t);
• int esp_aes_hw_crypt_cbc(int, size_t, unsigned char[16], const unsigned char *, const unsigned char *, unsigned char *);
• int esp_aes_hw_crypt_cfb8(int, size_t, unsigned char[16], const unsigned char *, const unsigned char *, unsigned char

Installation:

• M5_LoRa_Receiver.ino goes into the main Arduino folder, inside its own M5_LoRa_Receiver folder.
• HW_AES.cpp and HW_AES.h go into the Arduino/libraries folder, inside their own HW_AES folder.
• You'll need to write your own LoRa sender code [see above].
• Diffie-Hellman_Key_Exchange.ino goes into the main Arduino folder, inside its own M5_LoRa_Receiver folder. It's a proof of concept for key exchange.