[tor-bugs] #32439 [Circumvention/Obfs4]: tor can't bootstrap with obfs4 bridge and skewed clock

[Tor Bug Tracker & Wiki]

#32439: tor can't bootstrap with obfs4 bridge and skewed clock
-------------------------+-------------------------------------------------
     Reporter:           |      Owner:  (none)
  intrigeri              |
         Type:  defect   |     Status:  new
     Priority:  Medium   |  Milestone:
    Component:           |    Version:
  Circumvention/Obfs4    |
     Severity:  Normal   |   Keywords:  bootstrap, clock-skew, AffectsTails
Actual Points:           |  Parent ID:
       Points:           |   Reviewer:
      Sponsor:           |
-------------------------+-------------------------------------------------
 Environment: Debian unstable, Tor Browser 9.0.1, system clock set 2h in
 the future.

 Observed behavior: Tor Launcher says "Connected to bridge" but the
 progress bar is stuck at a very low percentage. After a while, the "Copy
 Tor Log To Clipboard" button appears.

 Impact: Tails users whose hardware clock is set to local time, in a
 timezone that's not close enough to UTC, cannot use obfs4 bridges.
 Unfortunately, that's quite common, because:

 * Windows sets the hardware clock to local time by default (as opposed to
 Unix systems, that tend to assume the hardware clock is in UTC)
 * many places where one needs obfs4 to use Tor are 4-7 hours ahead of UTC
 * Tails can't guess whether the hardware clock is set to UTC time or to
 local time; it assumes it's UTC time

 Corresponding tor log (actual obfs4 bridges IP & port redacted):

 {{{
 11/9/19, 16:39:11.903 [NOTICE] DisableNetwork is set. Tor will not make or
 accept non-control network connections. Shutting down all existing
 connections.
 11/9/19, 16:39:11.903 [NOTICE] Switching to guard context "bridges" (was
 using "default")
 11/9/19, 16:39:11.903 [NOTICE] DisableNetwork is set. Tor will not make or
 accept non-control network connections. Shutting down all existing
 connections.
 11/9/19, 16:39:11.903 [NOTICE] DisableNetwork is set. Tor will not make or
 accept non-control network connections. Shutting down all existing
 connections.
 11/9/19, 16:39:11.903 [NOTICE] Opening Socks listener on 127.0.0.1:9150
 11/9/19, 16:39:11.903 [NOTICE] Opened Socks listener on 127.0.0.1:9150
 11/9/19, 16:39:11.903 [NOTICE] Renaming old configuration file to
 "/home/toto/tor-browser_en-US/Browser/TorBrowser/Data/Tor/torrc.orig.1"
 11/9/19, 16:39:12.885 [NOTICE] Bootstrapped 1% (conn_pt): Connecting to
 pluggable transport
 11/9/19, 16:39:12.887 [NOTICE] Bootstrapped 2% (conn_done_pt): Connected
 to pluggable transport
 11/9/19, 16:40:06.330 [WARN] Proxy Client: unable to connect to
 $IP1:$PORT1 ("general SOCKS server failure")
 11/9/19, 16:40:12.957 [WARN] Proxy Client: unable to connect to
 $IP2:$PORT2 ("general SOCKS server failure")
 11/9/19, 16:40:13.120 [WARN] Proxy Client: unable to connect to
 $IP3:$PORT3 ("general SOCKS server failure")
 11/9/19, 16:41:10.165 [WARN] Proxy Client: unable to connect to
 $IP1:$PORT1 ("general SOCKS server failure")
 11/9/19, 16:41:14.240 [WARN] Proxy Client: unable to connect to
 $IP2:$PORT2 ("general SOCKS server failure")
 11/9/19, 16:41:20.420 [WARN] Proxy Client: unable to connect to
 $IP3:$PORT3 ("general SOCKS server failure")
 }}}

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32439>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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