Tune + tighten path bias parameters

The path bias defenses in #5458 (moved) and #5956 (moved) will have tunable parameters to allow us to dial in on the lowest acceptable amount of bias while not also breaking stuff.

That is going to require more work and attention, though. It's possible that network scanners (ie #5459 (moved)) can provide us with answers for #5458 (moved).

We can also ask our volunteer QA team to report what sorts of values they see in their logs for stuff like this, to get an idea on real ranges in real clients.

changed milestone to %Tor: 0.2.4.x-final

added MikePerry201210d actualpoints::28 component::core tor/tor milestone::Tor: 0.2.4.x-final needs-proposal parent::5456 priority::high resolution::fixed status::closed tor-client type::enhancement labels

Ok, I did some work to get closer to a solution here. See https://gitweb.torproject.org/torflow.git/tree/HEAD:/CircuitAnalysis/PathBias. In particular, https://gitweb.torproject.org/torflow.git/blob/HEAD:/CircuitAnalysis/PathBias/observations.txt and https://gitweb.torproject.org/torflow.git/blob_plain/HEAD:/CircuitAnalysis/PathBias/results.txt

Here's the 4 line summary: 0. Parameter choice is blocked on getting a good measure of the ambient success rate.

1. We should transform PATH_BIAS_SCALE_FACTOR into a percent, and make it high. Like 95.
2. We might want to use a separate, lower PATH_BIAS_PCT before SCALE_THRESHOLD.
3. After SCALE_THRESHOLD, PATH_BIAS_PCT can be pretty high for notice and warn

Trac:
Cc: N/A to nickm, arma

Trac:
Milestone: N/A to Tor: 0.2.4.x-final

Trac:
Keywords: N/A deleted, proposal-needed added

Trac:
Keywords: N/A deleted, MikePerry201210 added

Trac:
Keywords: MikePerry201210 deleted, MikePerry201210d added

Trac:
Keywords: proposal-needed, MikePerry201210d deleted, needs-proposal MikePerry201210d added

Trac:
Keywords: needs-proposal MikePerry201210d deleted, needs-proposal MikePerry201210d tor-client added

Trac:
Component: Tor Client to Tor

I'm going to call this done by virtue of the proposal being written and the live scan + analysis I performed to decide values for "normal" operation. We do have more work to do for the path bias code, though. See #7157 (moved) and #7281 (moved).

Trac:
Actualpoints: N/A to 28
Status: new to closed
Resolution: N/A to fixed

Trac:
Parent: N/A to #5456 (moved)

closed

added 224h of time spent

mentioned in issue #6647 (moved)

mentioned in issue #6805 (moved)

moved to tpo/core/tor#6135 (closed)

mentioned in issue tpo/core/tor#6647 (closed)