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Not sure if this is the right site to ask this, but here it goes:

Let's say I'd like to share a couple of private files with a few friends. The size of these are quite large, so I've figured the best route to distribute these is via torrent.

So, on my home PC I create a torrent and start seeding and announce to a public tracker like openbittorrent and publicbt.

Now, both of those are public trackers, but they don't seem to have anyway of searching through what is actually being tracked.

If I'm only passing around the torrent file to a few friends, whats the chances that someone else will 'randomly' come across the torrent via the public tracker and start leeching?

Edit: Better question: Are those two public trackers above actually searchable? If so, how?

Edit#2: According to this site: http://en.wikipedia.org/wiki/Comparison_of_BitTorrent_sites Those two sites do not offer any kind of searchable index for the torrents they track. I tried doing some googling on if it was possible to get a list of torrents being tracked by those sites, but I couldn't find anything.

Edit#3: Looks like both sites provide a 'scrape' file, but I'm unable to see if this could be used to get a list of torrents that are currently being tracked. Anyone know if you can use a scrape file to do this?

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closed as not constructive by Ƭᴇcʜιᴇ007, Tom Wijsman, Simon Sheehan, 8088, Nifle Dec 17 '11 at 12:58

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Hard to tell you the chances on random people randomly searching for things in a public space. So it's not an answerable question (without speculation). –  Ƭᴇcʜιᴇ007 Nov 11 '11 at 17:49
    
So, maybe a more directed question is, "are those public tracker sites I listed 'searchable'"? –  Nick Nov 11 '11 at 18:16
    
You can simply ask for your friends' IP addresses and kick off all other leechers. I'm not sure if they're is a way to make a "white list" of IPs allowed, but I suppose that would be ideal. –  에이바 Nov 11 '11 at 18:22
1  
Why don't you just transfer the files in encrypted form/add encrypted files to the torrent? –  Daniel Beck Nov 11 '11 at 18:54

2 Answers 2

up vote 3 down vote accepted

Neither OpenBitTorrent nor PublicBT have a searchable index; it says so right on their front pages. They are purely for the purpose of maintaining lists of current seeds and peers for already-known torrents.

You cannot download a torrent unless you have the original .torrent file, which contains information about what files the torrent contains. Since public trackers such as OpenBitTorrent are not searchable, they do not have the .torrent file – only its SHA1 hash, which is enough to uniquely identify the torrent but nothing more. The scrape file only contains these infohashes as well.

If you have DHT enabled it is possible to obtain the .torrent when you only know the infohash; that's how magnet: links work in The Pirate Bay and other sites. For example, magnet:?xt=urn:btih:<infohash goes here>&tr=udp%3A%2F%2Ftracker.openbittorrent.com. However, guessing infohashes randomly is a 1 to 2160 chance, and getting them from the scrape file would require a lot of time and bandwidth as well. (PublicBT's scrape file contains 2'812'789 entries as of right now, and OpenBitTorrent does not even publish it anymore.)

In conclusion, it is safe to use these trackers. μTorrent even does so by default for its "drop to share" feature.

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Exactly what I was looking for, thank you! Although, seems like it would be possible to create a service that pulls down the list of infohashes from publicbt, create magnet links for everything and try out the torrent. If it succeeds, extract filesize / filename information and then repost this information in a searchable public database. (a LOT of work!!!) So it seems like it would be possible to create a searchable database of what is currently on publicbt, but for only those that have distributed hash table enabled. –  Nick Nov 11 '11 at 19:08
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@Nick: Yes, I did say it's possible (and such a service could even provide .torrent files for download). A workaround is to simply stop putting torrents to PublicBT and instead use OpenBitTorrent which does not publish scrape files. Another is to set the private flag on your torrent, which will forcefully disable DHT and PEX. –  grawity Nov 11 '11 at 19:15
    
I have done the similar thing @Nick, doing grawity's advice and setting the private flag when you make the .torrent file, as long as none of your friends share the file you are safe. –  Scott Chamberlain Nov 11 '11 at 21:20
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For the record: μTorrent 3.0.25806's "Drop to share" creates 'public' torrents by default. (It's still okay, though, as long as nobody has created a PublicBT indexer yet.) The 'private' flag can be set via "Create New Torrent". –  grawity Nov 11 '11 at 22:06
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1) According to the spec only a zero-based piece index is required to request the data. I think this index can be guessed: 0, 1, etc. 2) Getting info_hash from a full scrape page allows to do the handshake between peers. 3) These two actions are sufficient to get the transmitted data just knowing info_hash, isn't it? –  Alexey Morozov Oct 29 at 11:49

If you're only sharing with a few people, another option is to avoid the public trackers entirely and use uTorrent's embedded tracker. Colin Pickard pointed this out in another answer on this site.

uTorrent has a complete guide on their website: http://www.utorrent.com/help/guides/make-a-torrent

You want to look at the section where it talks about embedded trackers.

uTorrent contains everything you need. You don't need your own domain or your own website.

Your IP address does need to stay the same while the tracker is running. This is not normally an issue, but some home ISPs will change your IP if you are disconnected from the internet for a period.

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