Function readDecryptedFile

src/core/passwords.cpp:74–154

*/

String readDecryptedFile(FS &fs, String filepath) {

    if (cachedPassword.length() == 0) {
        cachedPassword = keyboard("", 32, "Password:", true);
        if (cachedPassword.length() == 0 || cachedPassword == "\x1B") return ""; // cancelled
    }

    File cyphertextFile = fs.open(filepath, FILE_READ);
    if (!cyphertextFile) return "";

    String line;
    String cypertextData = "";
    String plaintext = "";
    bool unsupported_params = false;

    while (cyphertextFile.available()) {
        line = cyphertextFile.readStringUntil('\n');
        if (line.startsWith("Filetype:") && !line.endsWith("Bruce Encrypted File")) unsupported_params = true;
        if (line.startsWith("Algo:") && !line.endsWith("XOR")) unsupported_params = true;
        if (line.startsWith("KeyDerivationAlgo:") && !line.endsWith("MD5")) unsupported_params = true;
        if (line.startsWith("KeyDerivationPasses:") && !line.endsWith("10"))
            unsupported_params = true; // TODO: parse
        if (line.startsWith("Data:")) cypertextData = line.substring(strlen("Data:"));
    }

    cyphertextFile.close();

    if (unsupported_params || cypertextData.length() == 0) {
        Serial.println("err: invalid Encrypted file (altered?)");
        return "";
    }

    // else try decrypting
    cypertextData.trim();
    String cypertextDataDec = "";
    cypertextDataDec.reserve(cypertextData.length());

    uint8_t decimal = 0;
    char temp[3]; // Temporary storage for each hex pair

    for (int i = 0; i < cypertextData.length(); i += 3) {
        // Converts two characters hex to a single byte

        uint8_t highNibble = hexCharToDecimal(cypertextData[i]);
        uint8_t lowNibble = hexCharToDecimal(cypertextData[i + 1]);
        decimal = (highNibble << 4) | lowNibble;

        // Serial.println((char) decimal);

        // cypertextDataDec += decimal;
        // cypertextDataDec_index += 1;

        // temp[0] = cypertextData[i];        // First hex nibble
        // temp[1] = cypertextData[i + 1];    // Second hex nibble
        // temp[2] = '\0';                // Null-terminate the string

        // Convert the hex pair to a byte (char)
        // char decimal = (char) strtol(temp, NULL, 16);