How to calculate hash?

A torrent file has a data structure with two highest level keys: announce - identifying the tracker (s) to be used for download - and info - containing the names of the files and the relevant hashes (of the pieces, I believe, but I'm not sure). To create magnet links, use infohash , which is just a hash of the info encoded data. Font .

In order to calculate this infohash it is necessary to open the torrent file, interpret its structure and calculate the hash of the relevant part (from what I understand above, I do not need to decode a but it is still necessary to select it inside the file).

The detail is that since infohash is a hash of the encoded structure, and BencodeModel decodes everything, it becomes necessary to re-encode the relevant part before applying the hash:

• Decode and get the relevant part ( info ):

  $bencode = new BencodeModel();
  $data = $bencode->decode_file($form->fields['filename']->saved_file);
  $hash = $torrentmanager->create_hash($data['info']);
  

• Re-encode and calculate the hash:

  function create_hash($info)
  {
      $bencode = new BencodeModel();
      return urlencode(sha1($bencode->encode($info)));
  }
  

Font .

It has several forms depending on the purpose.

One of the most common is to use MD5. This is done with the md5_file() function.

You can also use sha1_file() which is slower but one gives a result a little better.