Protection against cold boot attacks
This is a subject that pages can be written about and everyone has a
different opinion. AFAIK there’s no real protection against it if your
machine is powered on and unattended. Nonetheless limited protection
could be afforded by overwriting RAM with zero’s or random data whenever
a reboot, halt or poweroff command is issued.
I believe Liberte linux (http://dee.su/liberte) implements such a solution.
(from redmine: issue id 2534, created on 2013-12-31)