[openssl-users] FIPS mode uses /dev/urandom ?

Tom Francis thomas.francis.jr at pobox.com
Wed Mar 11 20:10:34 UTC 2015

> On Mar 11, 2015, at 11:40 AM, Alberto Roman Linacero <aroman at alienvault.com> wrote:
> Dear all, I'm doing an strace to the FIPS validated version of
> openssl, and I'm seeing that is uses /dev/urandom. I thought that the
> FIPS validated module always use /dev/random, isn't this the case, or
> am I doing something wrong?.
> If it uses /dev/urandom, is it possible/advisable to change it to
> /dev/random (how?), and still the module being FIPS validated?

It would depend on what code is reading from /dev/urandom.  If it’s the FIPS Object Module that’s doing the reading, then no, absolutely not.  If it’s the FIPS-capable OpenSSL that reads from /dev/urandom, you can probably change it.  But I’m curious as to why you would want to do this.  Most systems with /dev/random and /dev/urandom are similar to Linux, in that /dev/urandom is the preferred source for “random data”, including when seeding a PRNG (which is how it’s used by OpenSSL).  And because /dev/random can block, you might have ridiculously poor performance (and worse, it’ll be unpredictably poor performance, i.e. sometimes it’ll work great, and other times it’ll be horrible, and you never which you’ll get).  This page, http://www.2uo.de/myths-about-urandom/ , is specific to Linux, but at a high-level, It’s also true for AIX, HP-UX, Solaris, FreeBSD, and NetBSD (OpenBSD is more complex).  I’m not about other UNIX-like systems, as I stopped using those before any of them ever provided such devices. :)


> Thanks for your help in advance and best regards,
> Alberto.
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