From 1e2b0be5bee045db1b0abb1f87801004db563bb8 Mon Sep 17 00:00:00 2001
From: deraadt <>
Date: Mon, 8 Dec 2014 21:45:20 +0000
Subject: Change rand(), random(), drand48(), lrand48(), mrand48(), and
 srand48() to returning strong random by default, source from arc4random(3).
 Parameters to the seeding functions are ignored, and the subsystems remain in
 strong random mode.  If you wish the standardized deterministic mode, call
 srand_deterministic(), srandom_determistic(), srand48_deterministic(),
 seed48_deterministic() or lcong48_deterministic() instead. The re-entrant
 functions rand_r(), erand48(), nrand48(), jrand48() are unaffected by this
 change and remain in deterministic mode (for now).

Verified as a good roadmap forward by auditing 8800 pieces of software.
Roughly 60 pieces of software will need adaptation to request the
deterministic mode.

Violates POSIX and C89, which violate best practice in this century.
ok guenther tedu millert
---
 src/lib/libc/stdlib/rand48.3 | 110 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 83 insertions(+), 27 deletions(-)

(limited to 'src/lib/libc/stdlib/rand48.3')

diff --git a/src/lib/libc/stdlib/rand48.3 b/src/lib/libc/stdlib/rand48.3
index a4473185de..dce8c0dd18 100644
--- a/src/lib/libc/stdlib/rand48.3
+++ b/src/lib/libc/stdlib/rand48.3
@@ -9,9 +9,9 @@
 .\" of any kind. I shall in no event be liable for anything that happens
 .\" to anyone/anything when using this software.
 .\"
-.\"	$OpenBSD: rand48.3,v 1.16 2014/11/25 17:26:34 millert Exp $
+.\"	$OpenBSD: rand48.3,v 1.17 2014/12/08 21:45:20 deraadt Exp $
 .\"
-.Dd $Mdocdate: November 25 2014 $
+.Dd $Mdocdate: December 8 2014 $
 .Dt RAND48 3
 .Os
 .Sh NAME
@@ -22,8 +22,11 @@
 .Nm mrand48 ,
 .Nm jrand48 ,
 .Nm srand48 ,
+.Nm srand48_deterministic ,
 .Nm seed48 ,
+.Nm seed48_deterministic ,
 .Nm lcong48
+.Nm lcong48_deterministic
 .Nd pseudo-random number generators and initialization routines
 .Sh SYNOPSIS
 .In stdlib.h
@@ -41,31 +44,56 @@
 .Fn jrand48 "unsigned short xseed[3]"
 .Ft void
 .Fn srand48 "long seed"
+.Ft void
+.Fn srand48_deterministic "long seed"
 .Ft "unsigned short *"
 .Fn seed48 "unsigned short xseed[3]"
+.Ft "unsigned short *"
+.Fn seed48_deterministic "unsigned short xseed[3]"
 .Ft void
 .Fn lcong48 "unsigned short p[7]"
+.Ft void
+.Fn lcong48_deterministic "unsigned short p[7]"
 .Sh DESCRIPTION
 .Bf -symbolic
-This interface is not cryptographically secure, so consider using
-.Xr arc4random 3
-instead.
+Standards insist that this interface return deterministic results.
+Unsafe usage is very common, so
+.Ox
+changed the subsystem to return non-deterministic results by default.
 .Ef
 .Pp
-The
-.Fn rand48
-family of functions generates pseudo-random numbers using a linear
-congruential algorithm working on integers 48 bits in size.
-The particular formula employed is
-r(n+1) = (a * r(n) + c) mod m
-where the default values are
-for the multiplicand a = 0xfdeece66d = 25214903917 and
-the addend c = 0xb = 11.
-The modulus is always fixed at m = 2 ** 48.
-r(n) is called the seed of the random number generator.
+To satisfy portable code,
+.Fn srand48 ,
+.Fn seed48 ,
+or
+.Fn lcong48
+should be called to initialize the subsystem.
+In
+.Ox
+the
+seeding parameters are ignored, and strong random number results will be
+provided from
+.Xr arc4random 3.
+In other systems, the
+parameters prime a simplistic deterministic algorithm.
 .Pp
-For all the six generator routines described next, the first
-computational step is to perform a single iteration of the algorithm.
+If the standardized behavior is required then
+.Fn srand48_deterministic ,
+.Fn seed48_deterministic ,
+and
+.Fn lcong48_deterministic
+can be substituted for
+.Fn srand48 ,
+.Fn seed48 ,
+and
+.Fn lcong48 .
+That will cause subsequent
+calls to
+.Fn drand48 ,
+.Fn lrand48 ,
+and
+.Fn jrand48
+to return results using the deterministic algorithm.
 .Pp
 .Fn drand48
 and
@@ -91,6 +119,21 @@ return values of type long in the range
 [-2**31, 2**31-1].
 The high-order (32) bits of r(n+1) are loaded into the returned value.
 .Pp
+In the deterministic mode, the
+.Fn rand48
+family of functions generates numbers using a linear congruential
+algorithm working on integers 48 bits in size.
+The particular formula employed is
+r(n+1) = (a * r(n) + c) mod m
+where the default values are
+for the multiplicand a = 0xfdeece66d = 25214903917 and
+the addend c = 0xb = 11.
+The modulus is always fixed at m = 2 ** 48.
+r(n) is called the seed of the random number generator.
+.Pp
+For all the six generator routines described next, the first
+computational step is to perform a single iteration of the algorithm.
+.Pp
 .Fn drand48 ,
 .Fn lrand48 ,
 and
@@ -110,7 +153,7 @@ holds the least significant bits.
 .Pp
 All functions share the same multiplicand and addend.
 .Pp
-.Fn srand48
+.Fn srand48_deterministic
 is used to initialize the internal buffer r(n) of
 .Fn drand48 ,
 .Fn lrand48 ,
@@ -121,7 +164,7 @@ of r(n), with the lower 16 bits of r(n) arbitrarily being set to 0x330e.
 Additionally, the constant multiplicand and addend of the algorithm are
 reset to the default values given above.
 .Pp
-.Fn seed48
+.Fn seed48_deterministic
 also initializes the internal buffer r(n) of
 .Fn drand48 ,
 .Fn lrand48 ,
@@ -131,14 +174,14 @@ but here all 48 bits of the seed can be specified in an array of 3 shorts,
 where the zeroth member specifies the lowest bits.
 Again, the constant multiplicand and addend of the algorithm are
 reset to the default values given above.
-.Fn seed48
+.Fn seed48_deterministic
 returns a pointer to an array of 3 shorts which contains the old seed.
 This array is statically allocated, so its contents are lost after
 each new call to
-.Fn seed48 .
+.Fn seed48_deterministic .
 .Pp
 Finally,
-.Fn lcong48
+.Fn lcong48_deterministic
 allows full control over the multiplicand and addend used in
 .Fn drand48 ,
 .Fn erand48 ,
@@ -169,14 +212,27 @@ The
 .Fn drand48 ,
 .Fn erand48 ,
 .Fn jrand48 ,
-.Fn lcong48 ,
 .Fn lrand48 ,
 .Fn mrand48 ,
-.Fn nrand48 ,
-.Fn seed48 ,
 and
-.Fn srand48
+.Fn nrand48 ,
 functions conform to
 .St -p1003.1-2008 .
+.Pp
+The
+.Fn seed48 ,
+.Fn srand48 ,
+and
+.Fn lcong48
+function do not conform to
+.St -ansiC ,
+intentionally.
+.Pp
+The
+.Fn seed48_deterministic ,
+.Fn srand48_deterministic ,
+and
+.Fn lcong48_deterministic
+functions are OpenBSD extensions.
 .Sh AUTHORS
 .An Martin Birgmeier
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