sdwdate - Secure Distributed Web Date - Homepage
Time keeping is crucial for security, privacy, and anonymity. Sdwdate is a Tor friendly replacement for rdate and ntpdate that sets the system's clock by communicating via onion end-to-end encrypted TCP with Tor onion webservers. Time providers are exclusively reputable sources (whistle-blowing and privacy friendly onion sites) that are highly likely to be hosted on different hardware.
At randomized intervals, sdwdate connects to a variety of webservers and extracts the time stamps from http headers (RFC 2616).
Comparison of sdwdate and ntp
|written in memory-safe language||Yes||No|
|secure connection by default (authentication and encryption)||Yes||No|
|gradual clock adjustments||Yes||Yes|
|works over Tor||Yes||No |
|does not require Tor||No||Yes|
|client, time fetcher||Yes||Yes|
|server, time provider||No, not yet||Yes|
|drop-in config folder||Yes||No|
|proxy support||Yes||No  |
|can be secured by default on linux distribution level||Yes||No |
|optional gui||Yes, sdwdate-gui (a systray icon)||No|
- server, time provider
- sdwdate issue tracker:
Authentication of Servers
sdwdate only connects to Tor hidden services, which are encrypted by default and do not rely on SSL CA's. It also uses three different pools of time sources, and if there are too many that fail for any given pool, e.g. because of replying with invalid data or being unreachable, the pool is considered to be potentially compromised and sdwdate aborts.
sdwdate source pools
What sources should be trusted? This is of course also a problem with NTP.
The sdwdate pools used by Whonix are based on stable and reliable Tor hidden service web servers. They are categorized into three different pools according to their members' relationship to the members in the other pools; any member in a one pool should be unlikely to share logs (or other identifying data), or to agree to send fake time information, with a member from the other pools.
The pools are listed in /etc/sdwdate.d/30_default.conf.
Basically, sdwdate picks three random servers - one from each pool, and then builds the mediate of the three advertised dates.
Trusted Time Sources
The sources are listed here to keep track of pool candidates:
- site:http://leakdirectory.org onion
- Requires UDP which is unsupported by Tor, see Tor#UDP.
- NTP security vulnerability because not using authentication by default
- See Dev/TimeSync#NTP.
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