Rng-Utils and Entropy RHEL6 style

I gave configuring DNSSEC a go last night but I had a bit of a problem. When I ran this command to create the key for my domain zone:

dnssec-keygen -a RSASHA1 -b 1024 -n ZONE domain

This was the result, for a while

Generating key pair.

It seemed to hang there. The problem turns out to be a lack of entropy, which can be checked with this:

cat /proc/sys/kernel/random/entropy_avail
73

It turns out that this is not good enough to generate a key, so the standard advice is to try to compile a kernel or generate some I/O work. Compiling a kernel was really not an option, so I tried to generate some I/O work but to no avail. After a googling for a bit I came across the rng daemon, which will generate a bit of entropy for you.

rngd -r /dev/urandom -o /dev/random -b

Now entropy in the system is:

cat /proc/sys/kernel/random/entropy_avail
3968

Which is enough to generate the key. Note that /dev/urandom is not truly random, as it will use SHA1 to generate random data when the entropy pool has been depleted, see this for a better explanation. However, this is good enough for my test system.

You need to install rng-tools in RHEL6 to use the rng daemon, note that it is no longer rng-utils.