On Mon, Jun 15, 2015 at 12:33 PM, cee1 <fykc...@gmail.com> wrote: > Hi, > > I maybe got confused. > > First, systemd-random-seed.service will save a "seed" from > /dev/urandom when shutdown, and load that "seed" to /dev/urandom when > next boot up. > > My questions are: > 1. Can we not save a seed, but load a seed that is read from ** > /dev/random ** to ** /dev/urandom **?
No, at boot you do not have enough entropy to begin with. > 2. Saving a seed on disk, and someone reads the content of it later, > will this make the "urandom" predictable? Yes, that's why the file is only readable by root. > Talking about /dev/random, it consumes an internal entropy pool, some > system events(disk reading/page fault, etc) enlarges this pool, am I > right? See this article http://www.2uo.de/myths-about-urandom/ > And write to /dev/random will mix the input data into the pool, but > not enlarge it, right? It is up to the kernel to "credit" the data written to it as entropy (or not) What benefits can it get when only mix data > but not enlarge the entropy pool? The data written to it may be predictable.. > 3.16+ will mix data from HWRNG, does it also enlarges the entropy pool? Yes but it might not be given "credit" depending what the source is. _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel