[tor-bugs] #12999 [Tor Browser]: Use one clock skew per URL bar domain

[Tor Bug Tracker & Wiki]

#12999: Use one clock skew per URL bar domain
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     Reporter:  arthuredelstein  |      Owner:  tbb-team
         Type:  enhancement      |     Status:  new
     Priority:  normal           |  Milestone:
    Component:  Tor Browser      |    Version:
   Resolution:                   |   Keywords:  tbb-fingerprinting
Actual Points:                   |  Parent ID:  #3059
       Points:                   |
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Description changed by arthuredelstein:

Old description:

> When #3455 lands, Tor Browser will have a separate Identity (i.e.,
> circuit) for each URL bar domain. JavaScript clock skew fingerprinting is
> one way attackers can try to link Identities. Tor Browser could counter
> this by maintaining a separate clock skew for each URL bar domain.
>
> When the user browses to a new URL bar domain, Tor Browser would
> 1. Create a new circuit
> 2. Request clock skew from exit node (already tied to Identity)
> 3. Store clock skew in a skew->URL bar domain mapping
> 4. Apply clock skew to any JS clock requests under that domain

New description:

 When #3455 lands, Tor Browser will have a separate Identity (i.e.,
 circuit) for each URL bar domain. JavaScript clock skew fingerprinting is
 one way attackers can try to link Identities. Tor Browser could counter
 this by maintaining a separate clock skew for each URL bar domain.

 When the user browses to a new URL bar domain, Tor Browser would
 1. Create a new circuit
 2. Request clock time from exit node (already tied to Identity)
 3. Store clock skew in a one-to-one mapping of skews->URL bar domains
 4. Apply clock skew to any JS clock requests under that domain

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/12999#comment:1>
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