Random Number Generators (RNG) used in cryptsetup are always the
kernel RNGs without any modifications or additions to data stream
produced.
There are two types of randomness cryptsetup/LUKS needs. One type
(which always uses /dev/urandom) is used for salts, the AF
splitter and for wiping deleted keyslots.
The second type is used for the volume (master) key. You can
switch between using /dev/random and /dev/urandom here, see
--use-random and --use-urandom options. Using /dev/random on a
system without enough entropy sources can cause luksFormat to
block until the requested amount of random data is gathered. In a
low-entropy situation (embedded system), this can take a very
long time and potentially forever. At the same time, using
/dev/urandom in a low-entropy situation will produce low-quality
keys. This is a serious problem, but solving it is out of scope
for a mere man-page. See urandom(4) for more information.
