The Pirate Bay un-SSL
Recently, the world saw The Pirate Bay offering SSL encryption on their server.
This means that your ISP won't know anymore which torrent you are
downloading, right? Wrong.
HTTPS is quite useless for protecting static and public content. By static, I do mean the
.torrent file itself. It is
always the same. By public,
I do mean than one doesn't need any kind of authentication to pick up
the content. It's always the same, for everyone. For crawlers,
So, one could easily index (a portion of) The Pirate Bay torrent database by the Content-Length. Then, one could intercept some encrypted traffic between some machine(s) within his/her network and the
server. Knowing both (encrypted) request and response lengths, it is
possible to get a quite reliable list of matches from the previously
indexed torrent list.
Don't try this at work, or you might hurt yourself
- Use Wireshark to capture some torrent
downloads. Torrents are hosted on a separate server, which makes the
task easier yet. Just use the following capture filter:
"tcp and port 443 and host torrents.thepiratebay.org"
- Now, just go with the stream ("Follow TCP Stream"
for the packet you suspect belongs to the torrent download. This will
create another filter, just like
"(ip.addr eq 192.168.0.10 and ip.addr eq 220.127.116.11) and (tcp.port eq 2157 and tcp.port eq 443)")
- Just save the displayed stream anywhere else (
- Now, use my quick&dirty TPB-TLSlen.pl Perl script to get
the request/response lengths:
Yeah, I know, it is nasty. It only supports the TLS cypher. And it simply calls the
perl TPB-TLSlen.pl pcap1.pcap
tshark(the command line version of Wireshark) to parse it's output.
- Now, just paste the REQ
(note that the REQ value is optional, setting it to 0 simply ignores the request size for matching)
The following size distribution chart was generated using the database with ~165K torrents:
The most common torrent size is ~14 KB, and it's easy to figure out that such torrents represent the shared 700 MB files
There's also a major peak for the 454 bytes torrents. However, bigger torrents are less common, thus, the size detection technique becomes more precise. Now, the average "distance" between torrent sizes is ~44 bytes (at least for the sample I've collected). So, adding a cookie with the random size up to 128 bytes will disrupt the size matching detection a lot. The request size disruption is even easier: the largest torrent URI I've found was 150 bytes-wide. Thus, padding every request URI to match 150 characters is enough to make the requests completely indistinguishable. Joining the pieces (the padding add-on strings are bold):
9r0WwBLYdmFCNN+UTV/hiJ7EAXdFU5KfdWHpkB5lXaCmITsACKOPVyjmpbaOB+CrI5 HTTP/1.1 Host: torrents.thepiratebay.org User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:18.104.22.168) Gecko/2008070208
Firefox/3.0.1 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: https://thepiratebay.org/recent Cookie: language=pt_BR; country=BR; PHPSESSID=ad6cb7e414c8dc88e0c2444f6215165a HTTP/1.1 200 OK Content-Type: application/x-bittorrent Etag: "2198642509" Last-Modified: Mon, 28 Jul 2008 22:28:59 GMT Server: lighttpd Content-Length: 91601 Date: Mon, 28 Jul 2008 22:37:56 GMT X-Varnish: 108010229 107999438 Age: 253 Via: 1.1 varnish Connection: keep-alive Set-Cookie: p=68eOfxOC7JwBYcMe1RJWC4Z5PV/lJzqJORW8KROPMH9zQhszSjFnRp2tsNWEoyabWAloneUaoz
MxYtx4hoM9MZUKE/7wGzC3ZKLEZdppG4og3W; expires=Mon, 28-Jul-2008 22:37:56 GMT; path=/;
domain=torrents.thepiratebay.org (binary torrent data)
- Use a constant padding in the
.torrentfiles. This messes things a bit, but stills ineffective. The only advantage is not messing up with the server
- Patch the lighttpd server so it sends a non-lasting cookie with a random size.
- MEGA Hospedagem, for the network resources provided for this tiny research
- http://www.warchalking.com.br/, for the inspiration
Encrypted session data
|The Pirate Bay URL||strlen(URI)||torrent size|
|Torrents indexed: 1580345|
stas » July 31, 2008 » 11:05