Decode Torrent Hash of Torrent tracker scrape?

Question

I am using BEncoded PHP Library to decode the bencoded response from a Bittorrent tracker.

The response of Tracker is:

d5:filesd20:¼€™rÄ2ÞÊþVA  .]á^¦d8:completei285e10:downloadedi22911e10:incompletei9eeee

after decoding it using the below code:

require 'bencoded.php';

$be = new BEncoded;
//Response saved in scrape.txt
$data =file_get_contents('scrape.txt');
print_r($be->Decode($data));

the output is:

Array ( [files] => Array ( [¼€™rÄ2ÞÊþVA  .]á^¦] => Array ( [complete] => 285 [downloaded] => 22911 [incomplete] => 9 [isDct] => 1 ) [isDct] => 1 ) [isDct] => 1 )

My Problem my problem in the above output is how to decode those mysterious letters in output.

Answer 1

If you are referring to the mangled key of files array then it's raw infohash - check out the spec:

• https://wiki.theory.org/BitTorrentSpecification#Tracker_.27scrape.27_Convention
• http://wiki.vuze.com/w/Scrape

Answer 2

The link: http://wiki.vuze.com/w/Scrape posted by user3690414 pretty much explains what the different keys stands for.

To interpret the raw bencoded string:

d5:filesd20:¼€™rÄ2ÞÊþVA  .]á^¦d8:completei285e10:downloadedi22911e10:incompletei9eeee

you need to understand how bencoding works: https://wiki.theory.org/BitTorrentSpecification#Bencoding

The most essential to know here is that that every entry in a bencoded dictionary is a Key,Value-pair.
Where Key is a byte string
and Value one of the following types: byte string, integer, a list or a dictionary.

With that in mind the raw string can be broken down like this:

d               // The first d indicates the start of the Root dictionary
 5:files            // that has a Key with a 5 byte string name 'files',
  d                     // the value of the 'files'-key is a second dictionary
   20:¼€™rÄ2ÞÊþVA  .]á^¦    // that has a Key 20 byte = 160 bit big endian SHA1 info-hash
    d                       // the value of that key is a third dictionary
     8:complete                 // that has a Key with a 8 byte string name 'complete',
      i285e                         // the value of that key is a Integer=285
     10:downloaded              // that has a Key with a 10 byte string name 'downloaded',
      i22911e                       // the value of that key is a Integer=22911
     10:incomplete              // that has a Key with a 10 byte string name 'incomplete',
      i9e                           // the value of that key is a Integer=9
    e                       // this e indicates the end of the third dictionary
  e                     // this e indicates the end of the second dictionary
e               // this e indicates the end of the Root dictionary

Hope this helps to understand the output from 'bencoded.php'.

edit.
If you want to make the 160 bit big endian SHA1 info-hash [¼€™rÄ2ÞÊþVA .]á^¦]
more human readable, I suggest that you output it as 40 byte hex-encoded string:
0xBC801B9D9972C432DECAFE56410F092E5DE15EA6