Created
September 27, 2023 00:28
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Base3050 Challenge (TSCTF-J 2023)
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| <?php | |
| class BaseN | |
| { | |
| protected $charset; | |
| protected $reverseCharset; | |
| public function __construct(array $charset) | |
| { | |
| $this->charset = $charset; | |
| $this->reverseCharset = array_flip($this->charset); | |
| assert(count($this->charset) == count($this->reverseCharset)); | |
| } | |
| public function encode(string $input): array | |
| { | |
| $output = []; | |
| $base = count($this->charset); | |
| $input_n = array_reduce( | |
| unpack('C*', $input), | |
| function ($carry, $item) { | |
| return bcadd(bcmul($carry, 256), $item); | |
| }, | |
| 0 | |
| ); | |
| error_log(print_r($input_n, true)); | |
| while ($input_n > 0) { | |
| $output[] = $this->charset[bcmod($input_n, $base)]; | |
| $input_n = bcdiv($input_n, $base, 0); | |
| } | |
| return $output; | |
| } | |
| } | |
| const EMOJI_DIR = './openmoji-svg-color/'; | |
| $flag = getenv('FLAG', true) ?: 'flag{base3050_1s_4w3s0m3}'; | |
| $emojis = []; | |
| foreach (glob(EMOJI_DIR . '*.svg') as $file) { | |
| $file_basename = pathinfo($file, PATHINFO_FILENAME); | |
| $emojis[$file_basename] = file_get_contents($file); | |
| } | |
| $emojiKeys = array_keys($emojis); | |
| srand(crc32($flag)); | |
| shuffle($emojiKeys); | |
| $emojiCharset = array_slice($emojiKeys, 0, 3050); | |
| $base3050 = new BaseN($emojiCharset); | |
| /** | |
| * <div class="emoji" alt="$char"> | |
| * <?= $emojis[$char] ?> | |
| * </div> | |
| */ | |
| ?> | |
| <!DOCTYPE html> | |
| <html lang="en"> | |
| <head> | |
| <meta charset="UTF-8"> | |
| <title>Base3050</title> | |
| <style> | |
| .emoji svg { | |
| margin-top: 10px; | |
| height: 30px; | |
| } | |
| .emoji-container { | |
| display: flex; | |
| flex-direction: row; | |
| flex-wrap: wrap; | |
| } | |
| </style> | |
| </head> | |
| <body> | |
| <div class="flag"> | |
| <h1>Your flag is:</h1> | |
| <p> Total <?= count($emojiCharset) ?> emojis</p> | |
| <div class="emoji-container"> | |
| <?php foreach ($base3050->encode($flag) as $char) : ?> | |
| <div class="emoji" alt="<?= $char ?>"> | |
| <?= $emojis[$char] ?> | |
| </div> | |
| <?php endforeach; ?> | |
| </div> | |
| </div> | |
| </div> | |
| <hr /> | |
| <!--input chars and output encoded emoji SVGs--> | |
| <form method="post"> | |
| <input type="submit" value="Encode"> | |
| <input type="textarea" name="input" placeholder="Try something here..." value="<?= $_POST['input'] ?? '' ?>" autocomplete="false"> | |
| </form> | |
| <div class="emoji-container"> | |
| <?php if (isset($_POST['input'])) : ?> | |
| <?php foreach ($base3050->encode($_POST['input']) as $char) : ?> | |
| <div class="emoji" alt="<?= $char ?>"> | |
| <?= $emojis[$char] ?> | |
| </div> | |
| <?php endforeach; ?> | |
| <?php endif; ?> | |
| </div> | |
| </body> | |
| </html> |
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