We should start making the OS available for small units like Raspberry PI, and do not concentrate on large installations.

Newer smartphones should also be able to be used as relays, with unlimited data and with 4G (soon 5G) up to 20 Mb download and 5 Mb downloads at the moment, where we can put the TAILS OS or Tor Browsers Bundles with orbot features, which manually should be connected to public Tor Relays.

Many small units are many untraceable units, large installations are easily compromised and indeed very traceable, where their locations also are known!

Regards David

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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Saturday, July 27, 2019 12:12 PM, s7r s7r@sky-ip.org wrote:

Hello again,

Getting back to this post with an update, see inline:

s7r wrote:

...

Hello, I'd like to know more details about how exactly the bridge bandwidth authority works, and if we use the "weight" of each bridge for anything. For example, I have setup 5 obfs4 bridges, with the exact very same hardware resources and all on the same network speed of course. One of them gets used by clients (say 20-50 unique clients every 6 hours or so) while the rest of 4 are not used at all. This usage is not a concern for me, as its known bridges take time until they get used, depending on which bucket they have been assigned and etc. So I assume it's OK at this particular point in their lifetime to be unused by any client. But what I am curious about is, when I search them on RelaySearch, the used one has a measured bandwidth of over 2 MiB/s (and has the fast flag) while other 3 unused ones have bandwidths of between 50 and 60 KiB/s (these also have the fast flag) and there is one last one which is also not used and has a bandwidth of less than 10 KiB/s that does not have the fast flag. (Fast flag missing is also not my problem, I am just mentioning it as a side detail). Now I know for sure those values are not at all in according to the real environment. Each bridge should be at least capable of 3 MiB/s even if all 5 are used at the same time at their full speeds. Actually I have simulated this, it's not just theoretical. Is there anything related to usage, so that the bridge bandwidth authority only measures the used bridges? What could have cause such big discrepancy in my particular case, any ideas?

It could be something about this. Another bridge just started to get fair usage (say 60 - 80 unique clients every 6 hour or so) and it got measured from slightly over 50 KiB/s to ~4 MiB/s which is actually closer to the reality.

The rest of unused bridges by clients still are reported as ~50 KiB/s which is very low.

...

Also, do we use the weight of each bridge in order to determine how much % probability it has to be served to a request in the bucket that is part of, or we don't use bridge weights for anything at all? Thanks!

tor-relays mailing list tor-relays@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-relays

Hi,

Roger Dingledine wrote:

On Wed, Jul 24, 2019 at 07:36:59PM +0300, s7r wrote:

...

I'd like to know more details about how exactly the bridge bandwidth authority works, and if we use the "weight" of each bridge for anything.

I'll start off by answering some of the questions, and let others fill in the gaps.

The first answer is that there is no such thing as a bridge bandwidth authority. There is only the bridge directory authority, Serge, which collects self-signed bridge descriptors from bridges, checks reachability, and passes them on to the bridgedb service.

Thanks for the answer. Well, this pretty much addresses all my concerns. And it all makes sense now.

...

For example, I have setup 5 obfs4 bridges, with the exact very same hardware resources and all on the same network speed of course.

Thanks!

...

One of them gets used by clients (say 20-50 unique clients every 6 hours or so) while the rest of 4 are not used at all. This usage is not a concern for me, as its known bridges take time until they get used, depending on which bucket they have been assigned and etc. So I assume it's OK at this particular point in their lifetime to be unused by any client.

Yep, it is not unusual for bridges to not see much use. As you say this is due to a variety of factors -- which distribution strategy bridgedb picks for them, which countries are blocking Tor in what way this week, whether your IP address has gotten on any blacklists, etc.

...

But what I am curious about is, when I search them on RelaySearch, the used one has a measured bandwidth of over 2 MiB/s (and has the fast flag) while other 3 unused ones have bandwidths of between 50 and 60 KiB/s (these also have the fast flag) and there is one last one which is also not used and has a bandwidth of less than 10 KiB/s that does not have the fast flag. (Fast flag missing is also not my problem, I am just mentioning it as a side detail).

Now I know for sure those values are not at all in according to the real environment. Each bridge should be at least capable of 3 MiB/s even if all 5 are used at the same time at their full speeds. Actually I have simulated this, it's not just theoretical.

Is there anything related to usage, so that the bridge bandwidth authority only measures the used bridges? What could have cause such big discrepancy in my particular case, any ideas?

These numbers are simply the self-reported bandwidth numbers from the bridges.

All kinds of relays, including bridge relays, watch how much traffic they've seen themselves doing, and put the largest burst they've seen into their relay descriptor (or bridge descriptor in this case).

https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt#n432

So the bridges that have a bunch of users have had more traffic load, and thus have a higher burst traffic number to report.

Or to answer it differently, the issue is the other way around from what you were worried about: it isn't that something is giving one of your bridges a higher bandwidth value, and thus it has more users. It's that one of your bridges has more users, so it ends up with a higher bandwidth value.

Of course, the more clients they have it means the bigger burst they see in their bandwidth, and use it to build the bridge descriptor. That is just passed on to birdgedb and reported / used exactly as it is, given there's no bridge bandwidth authority.

...

Also, do we use the weight of each bridge in order to determine how much % probability it has to be served to a request in the bucket that is part of, or we don't use bridge weights for anything at all?

I believe we don't use bridge weights for anything at all.

Yes, it makes sense we don't use bridge weights for anything at all because we do not have accurate bridge weights since we don't measure them with anything that is outside the control of the bridge operator. We only have what bridges report, which can be of course gamed by the bridge operator trivially. One bandwidth authority would not be sufficient anyways, for the bridges, so it can get quite complicated to measure them accurately for no obvious benefit if we consider how we distribute the bridges currently.

This would be a risk if it could happen to the Guards in the consensus for example (but it can't, of course), because those are sampled by all regular clients. Bridge clients have to do some manual out-of-band action to get the bridge data, so gaming the "weight" of a bridge doesn't actually influence anything, as long as we maintain our distribution strategy and randomly assigning bridges to certain buckets regardless of their _reported_ speed.

But I might be wrong about this last part. We've changed our mind several times over the years about how to handle weighting. Specifically, I don't know if the behavior changed with the latest iteration of the entry guard selection design: https://gitweb.torproject.org/torspec.git/tree/guard-spec.txt

Hope that helps, --Roger