http://en.wikipedia.org/wiki/Urandom

"The [Linux] implementation was also designed with the assumption that any given hash or cipher might eventually be found to be weak, and so the design is durable in the face of any such weaknesses." alors que *BSD a une confiance aveugle en leur algorithme Yarrow, "based on the assumptions that modern PRNGs are very secure if their internal state is unknown to an attacker".

Ils disent même clairement: "Unlike the Linux /dev/random, the FreeBSD /dev/random never blocks. It is similar to the Linux /dev/urandom".