[diggan]

Worth noting if someone uses this to share private data: Checking the "Private torrent" would tell your and compliant clients to not use DHT and other public methods that can leak the content. But it doesn't stop other non-compliant clients from sharing it on the DHT once they have it, nor does it stop someone from just ticking "Enable DHT" on their side once they have received it (or change "private" to "false" in the torrent file itself).

Obvious to many I'm sure, but maybe best to be explicit about it anyways.

Slightly off-topic but kind of fitting: How does infohash v2 support look like today? It's been available for years, but seemingly most private trackers + most other places seems to still be using v1. What clients are people using today, do those support v2? As far as I know, all modern clients do, so it would be possible to start using v2 exclusively.

Reason for the question is that I'm planning to distribute many large files to the public, and in my experience, BitTorrent works really well for that. Question is if it's enough to just publish v2 infohashes, or I need to publish both v1 and v2.

[binaryturtle]

If you flip the "private" flag it would change the infohash of the torrent. The "private" flag is part of the info block in the torrent file's data. With an infohash mismatch between the two peers no download would happen.

Obviously after a non-compliant party to the transfer has fully downloaded the file(s) it can do whatever it wants with it afterwards… flip any flags and share via DHT, etc.

I recently shared some —more or less— private data to someone else via BitTorrent. We just used DHT for convenience. It took like 15 minutes for other random peers to pop into the transfer. All of those random peers just fetched the meta data. And indeed, a check on btdig confirmed the whole metadata (file names, file sizes, etc.) leaked. So there's a lot of DHT network scanning going on for sure. It was rather fascinating. No actual data was downloaded/leaked at least.

[boramalper]

> So there's a lot of DHT network scanning going on for sure.

There is an entire category of free software whose purpose is to create an index of the DHT network. :) The idea is to allow users to find and search for torrents in a completely decentralised manner (i.e. without relying on any centralised trackers or search engines).[1] A good example is bitmagnet[0].

[0] https://bitmagnet.io/

[1] With the added benefit of greater resilience, as centralised "chokepoints" are often the primary and only targets of takedowns.

[pessimizer]

> So there's a lot of DHT network scanning going on for sure.

How else would btdig (and others) fill their index?

The standard solution is to compress what you're sending with 7zip, with a password.

> No actual data was downloaded/leaked at least.

I've had randos download the data before the intended recipient figured out how to open a port.

[cassepipe]

IIUC you are basically saying that when you start giving a file to someone they can do whatever to the file but does it mean they have to create another torrent or can they keep using the already existing sharing network of peers ?

[anacrolix]

I'm the author of https://github.com/anacrolix/torrent and added v2 support a while back.

The short answer is: You just publish as v1 infohash as if nothing is different, but the info contains extra stuff for v2 supporting clients. v1 clients will still work, it's backwards compatible.

So generate your torrent files as hybrid v1/v2, then just do everything else like you always have. Pretend v2 isn't a thing.

v2 clients know how to tap into both swarms and will take advantage of improvements when applicable. It's very well designed.

[diggan]

Thing is, I'm planning on just storing the infohash itself, as a reference (for a knowledge database essentially), not the torrent file, so wanted to use just one of them, and skip the other.

So if I do v1, why do v2? If I do v2, I'd like to skip v1. Ideally I'd do v2 (only) as it seems a heck more future-safe with sha256.

Edit: Actually, I think I see what you're saying. Create hybrid torrent that works with both, share the v1 infohash of that one, v2 clients will automatically take advantage of v2 from that if supported, sounds right?

[anacrolix]

Yes. You only need the v1 info hash. The first thing a v2 client does with a v2 hash is derive the v1 hash from it anyway. In fact it can't connect to v1 clients until it's done this so prefer v1 unless you have good reason.

[teeray]

If it’s intended to be private, you can always encrypt, then torrent. You can probably be more tight-fisted about who gets to decrypt.