SenseCon '23 Announcement Challenge

README.md

SenseCon '23 Announcement Challenge

The image in this tweet is needed to solve this challenge: https://twitter.com/leonjza/status/1678419863436443648

message.php

<?

class Message {
	private $message = "This was the announcement challenge for SenseCon '23, our annual internal @sensepost hackathon. Have fun solving it!";

	function echo_it() {
		echo $this->message . PHP_EOL;
	}

	function write($message, $source, $target) {
		$binary = '';
		for ($i = 0; $i < mb_strlen($message); ++$i) {
			$character = ord($message[$i]);
			$binary .= str_pad(decbin($character), 8, '0', STR_PAD_LEFT);
		}

		$binary .= '00000011';

		$img = imagecreatefrompng($source);
		$pos = 0;

		for ($y = 0; $y < imagesy($img); $y++) {
			for ($x = 0; $x < imagesx($img); $x++) {
		
				if (!isset($binary[$pos])) break 2;
		
				$colors = imagecolorsforindex($img, imagecolorat($img, $x, $y));
				$blue = str_pad(decbin($colors['blue']), 8, '0', STR_PAD_LEFT);
		
				$blue[strlen($blue) - 1] = $binary[$pos] == '1' ? '0' : '1';
				$newBlue = bindec($blue);
		
				$newColor = imagecolorallocatealpha(
				$img, $colors['red'], $colors['green'], $newBlue, $colors['alpha']);
				imagesetpixel($img, $x, $y, $newColor);
		
				$pos++;
			}
		}

		imagepng($img, $target, 9);
		imagedestroy($img);
	}
}

$t = new Message;
$t->echo_it();