From: deraadt <deraadt@openbsd.org>
Date: Fri, 12 Feb 2021 17:03:51 +0000 (+0000)
Subject: Some people still argue that rand(3) and random(3) have suitable deterministic
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=70d9094f4044ec4d667009ef66d835cce8e9a22a;p=openbsd

Some people still argue that rand(3) and random(3) have suitable deterministic
use cases, so explain the situation a bit more.  Since the 80's, I estimate
around 5 algorithm changes, so any chosen seed is unrepeatable UB.

+The deterministic sequence algorithm changed a number of times since
+original development, is underspecified, and should not be relied upon to
+remain consistent between platforms and over time.

ok jmc kettenis
---

diff --git a/lib/libc/stdlib/rand.3 b/lib/libc/stdlib/rand.3
index 2fd88ac8a4b..76278c871ab 100644
--- a/lib/libc/stdlib/rand.3
+++ b/lib/libc/stdlib/rand.3
@@ -29,9 +29,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: rand.3,v 1.19 2014/12/09 21:55:39 jmc Exp $
+.\"	$OpenBSD: rand.3,v 1.20 2021/02/12 17:03:51 deraadt Exp $
 .\"
-.Dd $Mdocdate: December 9 2014 $
+.Dd $Mdocdate: February 12 2021 $
 .Dt RAND 3
 .Os
 .Sh NAME
@@ -78,6 +78,9 @@ can be substituted for
 then subsequent
 .Fn rand
 calls will return results using the deterministic algorithm.
+The deterministic sequence algorithm changed a number of times since
+original development, is underspecified, and should not be relied upon to
+remain consistent between platforms and over time.
 .Pp
 The
 .Fn rand
diff --git a/lib/libc/stdlib/random.3 b/lib/libc/stdlib/random.3
index 020c72805f1..0770d20f09b 100644
--- a/lib/libc/stdlib/random.3
+++ b/lib/libc/stdlib/random.3
@@ -25,9 +25,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: random.3,v 1.28 2014/12/09 21:55:39 jmc Exp $
+.\"	$OpenBSD: random.3,v 1.29 2021/02/12 17:03:51 deraadt Exp $
 .\"
-.Dd $Mdocdate: December 9 2014 $
+.Dd $Mdocdate: February 12 2021 $
 .Dt RANDOM 3
 .Os
 .Sh NAME
@@ -96,6 +96,9 @@ a default table of size 31 long integers to return successive pseudo-random
 numbers in the range from 0 to (2**31)\-1.
 The period of this random number generator is very large, approximately
 16*((2**31)\-1), but the results are a deterministic sequence from the seed.
+The deterministic sequence algorithm changed a number of times since
+original development, is underspecified, and should not be relied upon to
+remain consistent between platforms and over time.
 .Pp
 The
 .Fn initstate