sdwdate: Secure Distributed Web Date

From Whonix

sdwdate Control Panel


Time keeping is crucial for security, privacy, and anonymity. sdwdate is a Tor-friendly replacement for rdate [archive] and ntpdate [archive] that sets the system's clock by communicating via end-to-end encrypted TCP with Tor onion webservers. Chosen time providers are exclusively reputable sources (whistle-blowing and privacy-friendly onion sites) that are highly likely to be hosted on different hardware.

At random intervals, sdwdate connects to a variety of webservers and extracts the time stamps from http headers (see: RFC 2616 [archive]).

sdwdate vs ntp[edit]

Table: sdwdate vs ntp Comparison

sdwdate [archive] ntp
Written in memory-safe language Yes No
Distributed trust Yes No
Secure connection by default (authentication and encryption) Yes No
Gradual clock adjustments Yes Yes
Daemon Yes Yes
Functional over Tor [archive] Yes No [1]
Tor not required No Yes
Client, time fetcher Yes Yes
Server, time provider No, not yet Yes
Apparmor profile Yes Yes
Drop-in config folder Yes No
Proxy support Yes No [2] [3]
Possible to secure by default on GNU/Linux distribution level Yes No [4]
Secure Yes No [5]
Optional GUI Yes, sdwdate-gui (a systray icon) No

See also:


sdwdate Design[edit]

Server Authentication[edit]

sdwdate [archive] only connects to Tor onion services, which are encrypted by default and do not rely on SSL certificate authorities (CAs). Three different pools are used for time sources so that if too many connections fail for any given pool, [8] the pool is considered as potentially compromised and sdwdate aborts.

sdwdate Source Pools[edit]

Determining what sources should be trusted is an important issue; this is also a problem with NTP.

The sdwdate pools used by Whonix ™ are based on stable and reliable Tor onion service web servers. The pools are listed in /etc/sdwdate.d/30_default.conf [archive].

The various onion services are categorized into three different pools according to their members' relationship to the members in other pools. For instance, any member in one pool should be unlikely to share logs (or other identifying data), or agree to send fake time information, with a member from the other pools. In basic terms, sdwdate picks three random servers - one from each pool - and then builds the mediate (middle position) of the three advertised dates.

sdwdate is only using 'pal' pools and not relying on 'neutral' and 'foe' pools as per tails_htp, because a good rationale for that approach has not yet been provided. [9] [10]

Trusted Time Sources[edit]

The links below are listed to keep track of pool candidates:


Figure: sdwdate GUI Control Panel


Figure: sdwdate GUI Successful Check




  1. Requires UDP which is unsupported by Tor, see Tor#UDP.
  2. [archive]
  3. [archive]
  4. NTP security vulnerability because not using authentication by default [archive]
  5. See Dev/TimeSync#NTP.
  6. If replacing ntp with sdwdate, run the following command to avoid the installation of 160+ recommended packages:
    sudo apt --no-install-recommends install sdwdate

  7. [archive]
  8. For example, due to being unreachable or replying with invalid data.
  9. [archive]
  10. [archive]

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