Level: easy
Author: PS
Mirror, mirror, on the wall, who's the fairest of them all?
From the filename and the challenge name it was obvious that we would have to revert the order of bytes to get a valid ZIP archive. I wrote some Java code to revert all the bytes of the file.
private static void reverse(byte[] data) {
for (int i = 0; i < data.length / 2; i++) {
byte temp = data[i];
data[i] = data[data.length - i - 1];
data[data.length - i - 1] = temp;
}
}
private static void reverseFile(String name, String ending) throws IOException {
Path fileLocation = Paths.get(name + "." + ending);
byte[] data = Files.readAllBytes(fileLocation);
reverse(data);
Path outputPath = Paths.get(new StringBuilder(name).reverse().toString() + "." + (new StringBuilder(ending).reverse().toString()));
Files.write(outputPath, (byte[]) data, StandardOpenOption.CREATE_NEW);
}Then I unzipped the archive and got a new file called 90gge.gnp.
Opening the file in HEX showed that the PNG header bytes were reversed:
00000000: 8947 4e50 0d0a 1a0a 0000 000d 4948 4452 .GNP........IHDR
Changing them to PNG and opening the image with GIMP showed the following image:
Inverting the colours and flipping the image revealed the correct QR code:
