freematics-traccar-encrypted/esp32/telelogger/telecrypt.cpp

#include "config.h"
#include <string.h>
#include <stdio.h>
#include <ChaChaPoly.h>
#include <HardwareSerial.h>

void print_hex(const unsigned char *data, size_t length) {
    for (size_t i = 0; i < length; ++i) {
        Serial.printf("%02x", data[i]);
    }
    Serial.println();
}

void encrypt_string(const unsigned char *input, size_t length, unsigned char *output) {
    // Create an instance of the ChaChaPoly class
    ChaChaPoly chachaPoly;

    // Initialize the encryption key
    unsigned char key[32];
    for (int i = 0; i < 32; ++i) {
        sscanf(CHACHA20_KEY + 2*i, "%02x", &key[i]);
    }

    // Set the encryption key
    chachaPoly.setKey(key, sizeof(key));

    // Generate a random nonce (IV)
    unsigned char nonce[12];
    esp_fill_random(nonce, sizeof(nonce)); // Use the ESP-IDF random number generator
    chachaPoly.setIV(nonce, sizeof(nonce));

    // Encrypt the input data
    chachaPoly.encrypt(output + sizeof(nonce), input, length);

    // Compute the authentication tag
    chachaPoly.computeTag(output + sizeof(nonce) + length, chachaPoly.tagSize());

    // Prepend the nonce to the output
    memcpy(output, nonce, sizeof(nonce));

    // Clear the encryption context
    chachaPoly.clear();
}

void decrypt_string(const unsigned char *input, size_t length, unsigned char *output) {
    // Create an instance of the ChaChaPoly class
    ChaChaPoly chachaPoly;

    // Initialize the decryption key
    unsigned char key[32];
    for (int i = 0; i < 32; ++i) {
        sscanf(CHACHA20_KEY + 2*i, "%02x", &key[i]);
    }

    Serial.println("loaded key");

    // Set the decryption key
    chachaPoly.setKey(key, sizeof(key));

    Serial.println("set key");

    // Extract the nonce (IV) from the input
    unsigned char nonce[12];
    memcpy(nonce, input, sizeof(nonce));
    chachaPoly.setIV(nonce, sizeof(nonce));

    // Check that length is long enough to contain a nonce and a tag.
    if (length < sizeof(nonce) + chachaPoly.tagSize()) {
        Serial.print("[CHACHA] Input too short to contain nonce and tag: ");
        print_hex(input, length);
        output[0] = '\0'; // Set output to an empty string
        return;
    }

    Serial.println("did nonce");

    // Decrypt the input data
    size_t decryptedLength = length - sizeof(nonce) - chachaPoly.tagSize();
    chachaPoly.decrypt(output, input + sizeof(nonce), decryptedLength);

    Serial.println("did decryption");

    // Print the decrypted data as hex values
    String decryptedString = "";
    for (size_t i = 0; i < decryptedLength; i++) {
        decryptedString += (char)output[i];
    }
    Serial.println(decryptedString);
    
    // Verify the authentication tag


    const unsigned char *tagPtr = input + sizeof(nonce) + decryptedLength;
    Serial.print("Tag: ");
    for (size_t i = 0; i < chachaPoly.tagSize(); i++) {
        Serial.print(tagPtr[i], HEX);
        Serial.print(" ");
    }
    Serial.println();

    Serial.print("Computed Tag: ");
    uint8_t computedTag[16];
    chachaPoly.computeTag(computedTag, sizeof(computedTag));
    for (size_t i = 0; i < sizeof(computedTag); i++) {
        Serial.print(computedTag[i], HEX);
        Serial.print(" ");
    }
    Serial.println();

    if (!chachaPoly.checkTag(tagPtr, chachaPoly.tagSize())) {
        Serial.println("Authentication failed!");
        output[0] = '\0'; // Set output to an empty string
        return;
    }

    ///

    // Clear the decryption context
    chachaPoly.clear();
}