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[tor-bugs] #23415 [Core Tor/Tor]: sample_laplace_distribution() should take multiple random inputs
#23415: sample_laplace_distribution() should take multiple random inputs
-------------------------+-------------------------------------------------
Reporter: teor | Owner: (none)
Type: defect | Status: new
Priority: Medium | Milestone: Tor: 0.3.2.x-final
Component: Core | Version: Tor: 0.2.8.1-alpha
Tor/Tor | Keywords: tor-relay, security-low, privcount,
Severity: Normal | 031-backport, 030-backport, 029-backport, 028
| -backport-maybe, 026-backport-maybe
Actual Points: | Parent ID: #23061
Points: 0.5 | Reviewer:
Sponsor: |
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Currently, sample_laplace_distribution() takes a random double as input,
and then extracts the following random values:
* a random sign
* a random value in (0.0, 1.0]
This reduces the precision of the result. For details, see:
https://trac.torproject.org/projects/tor/ticket/23061#comment:32
Instead, the function could take a random boolean sign and p, and the
transform becomes:
{{
result = mu - b * (sign ? 1.0 : -1.0)
* tor_mathlog(1.0 - p);
}}
This would increase the precision by one bit, plus whatever precision is
lost in `2.0 * fabs(p - 0.5)`.
This may have been introduced in dad5eb7.
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23415>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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