tlsdate: secure parasitic rdate replacement

tlsdate sets the local clock by securely connecting with TLS to remote servers and extracting the remote time out of the secure handshake. Unlike ntpdate, tlsdate uses TCP, for instance connecting to a remote HTTPS or TLS enabled service, and provides some protection against adversaries that try to feed you malicious time information.

On Debian GNU/Linux and related systems, we provide an init.d script that controls the tlsdated daemon. It will notice network changes and regularly invoke tlsdate to keep the clock in sync. Start it like so:

/etc/init.d/tlsdate start

Here is an example an unprivileged user fetching the remote time:

% tlsdate -V -n -H encrypted.google.com Fri Apr 19 17:56:46 PDT 2013

This is an example run - starting as root and dropping to nobody, setting the clock and printing it:

% sudo tlsdate -V Fri Apr 19 17:57:49 PDT 2013

Here is an example with a custom host and custom port without verification:

% sudo tlsdate --skip-verification -p 80 -H rgnx.net

Here is an example where a system may not have any kind of RTC at boot. Do the time warp to restore sanity and do so with a leap of faith:

% sudo tlsdate -V -l -t Fri Apr 19 18:08:03 PDT 2013

Some SSL/TLS services do not provide accurate time in their handshake process; tlsdate may also be used to fetch time by processing the HTTP Date headers of HTTP services:

% sudo tlsdate -V -l -t -w Wed Oct 30 18:08:46 CET 2013