[BitTorrent] protocol violation "key flag"?

Brian Dessent brian at dessent.net
Sat Sep 25 19:56:21 EDT 2004

Bram Cohen wrote:

> > I'm only a casual user of BT so I don't know much about this yet.  I
> > haven't been able to find much information about the "key flag", but
> > my sister reports that Azureus and other bittorrent clients seem to
> > support this so called "extension" to the protocol which I'd consider
> > a violation.  There are some trackers which require this of the client
> > and are denying connects by the official bittorrent 3.4.2 client, and
> > the tracker says "get newer version of client".  I tried blindly
> > installing the cvs version for my sister (her box is 1500 miles away)
> > but she reports it still doesn't work and the tracker rejects her
> > client.
> Erm, that would be very broken. If anyone knows what's up with this,
> please let me know.

The poster may be confusing several different things that some trackers
are doing.  Some trackers (e.g. torrentbits.org) dynamically create each
.torrent file for each user, encoding a unique 16-character "passkey"
into the hostname of the announce URL.  This is for tracking/accounting
purposes, and the .torrent is otherwise standard.  The tracker refuses
to track the peer if the passkey is missing or judged invalid. 
tvtorrents.com does a similar thing, but I believe they encode it it in
the announce URL path instead of the hostname.

Other trackers (e.g. FBT2) refuse clients that do not support the
"compact" extension.  This is a bandwidth-saving measure mostly, and it
returns an error about getting a newer client versions with some
suggested ones to try (mainline, Azureus, etc.)

Finally there are some tracker admins that have taken to banning certain
clients based on their HTTP User-Agent string.  I think the notion here
is that they don't want peers that are using old/broken ccode, or those
clients that have otherwise been deemed "leecher-friendly."  Some of the
BNBT variants support this.

None of the above should affect someone using the current released (or
CVS) mainline, so I think the original poster is mightily confused.


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