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Created by intrigeri@intrigeri

tor can't bootstrap with obfs4 bridge and skewed clock

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")