--- /dev/null
+.\" $OpenBSD: arc4random.3,v 1.19 2005/07/17 08:50:55 jaredy Exp $
+.\"
+.\" Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\" notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\" notice, this list of conditions and the following disclaimer in the
+.\" documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\" must display the following acknowledgement:
+.\" This product includes software developed by Niels Provos.
+.\" 4. The name of the author may not be used to endorse or promote products
+.\" derived from this software without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\" Manual page, using -mandoc macros
+.\"
+.Dd April 15, 1997
+.Dt ARC4RANDOM 3
+.Os
+.Sh NAME
+.Nm arc4random ,
+.Nm arc4random_stir ,
+.Nm arc4random_addrandom
+.Nd arc4 random number generator
+.Sh SYNOPSIS
+.Fd #include <stdlib.h>
+.Ft uint32_t
+.Fn arc4random "void"
+.Ft void
+.Fn arc4random_stir "void"
+.Ft void
+.Fn arc4random_addrandom "u_char *dat" "int datlen"
+.Sh DESCRIPTION
+The
+.Fn arc4random
+function provides a high quality 32-bit pseudo-random
+number very quickly.
+.Fn arc4random
+seeds itself on a regular basis from the kernel strong random number
+subsystem described in
+.Xr random 4 .
+On each call, an ARC4 generator is used to generate a new result.
+The
+.Fn arc4random
+function uses the ARC4 cipher key stream generator,
+which uses 8*8 8-bit S-Boxes.
+The S-Boxes can be in about (2**1700) states.
+.Pp
+.Fn arc4random
+fits into a middle ground not covered by other subsystems such as
+the strong, slow, and resource expensive random
+devices described in
+.Xr random 4
+versus the fast but poor quality interfaces described in
+.Xr rand 3 ,
+.Xr random 3 ,
+and
+.Xr drand48 3 .
+.Pp
+The
+.Fn arc4random_stir
+function reads data from a pseudo-random device, usually
+.Pa /dev/urandom,
+and uses it to permute the S-Boxes via
+.Fn arc4random_addrandom .
+.Pp
+There is no need to call
+.Fn arc4random_stir
+before using
+.Fn arc4random ,
+since
+.Fn arc4random
+automatically initializes itself.
+.Sh SEE ALSO
+.Xr rand 3 ,
+.Xr rand48 3 ,
+.Xr random 3
+.Sh HISTORY
+An algorithm called
+.Pa RC4
+was designed by RSA Data Security, Inc.
+It was considered a trade secret.
+Because it was a trade secret, it obviously could not be patented.
+A clone of this was posted anonymously to USENET and confirmed to
+be equivalent by several sources who had access to the original cipher.
+Because of the trade secret situation, RSA Data Security, Inc. can do
+nothing about the release of the ARC4 algorithm.
+Since
+.Pa RC4
+used to be a trade secret, the cipher is now referred to as
+.Pa ARC4 .
+.Pp
+These functions first appeared in
+.Ox 2.1 .
-/* $$$: arc4random.c 2005/02/08 robert */
-/* $NetBSD: arc4random.c,v 1.5.2.1 2004/03/26 22:52:50 jmc Exp $ */
-/* $OpenBSD: arc4random.c,v 1.6 2001/06/05 05:05:38 pvalchev Exp $ */
-
/*
- * Arc4 random number generator for OpenBSD.
- * Copyright 1996 David Mazieres <dm@lcs.mit.edu>.
+ * Copyright (c) 1996, David Mazieres <dm@uun.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
*
- * Modification and redistribution in source and binary forms is
- * permitted provided that due credit is given to the author and the
- * OpenBSD project by leaving this copyright notice intact.
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
+ * Arc4 random number generator for OpenBSD.
+ *
* This code is derived from section 17.1 of Applied Cryptography,
* second edition, which describes a stream cipher allegedly
* compatible with RSA Labs "RC4" cipher (the actual description of
* which is a trade secret). The same algorithm is used as a stream
* cipher called "arcfour" in Tatu Ylonen's ssh package.
*
- * Here the stream cipher has been modified always to include the time
+ * Here the stream cipher has been modified always to include entropy
* when initializing the state. That makes it impossible to
* regenerate the same random sequence twice, so this can't be used
* for encryption, but will generate good random numbers.
* RC4 is a registered trademark of RSA Laboratories.
*/
+/* $OpenBSD: arc4random.c,v 1.16 2007/02/12 19:58:47 otto Exp $ */
+
#include <features.h>
+
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
-#include <sys/param.h>
#include <sys/time.h>
-#ifdef __ARC4RANDOM_USE_ERANDOM__
-#include <sys/sysctl.h>
-#endif
-
struct arc4_stream {
u_int8_t i;
static smallint rs_initialized;
static struct arc4_stream rs;
+static pid_t arc4_stir_pid;
+static int arc4_count;
static __inline__ void
arc4_init(struct arc4_stream *as)
static void
arc4_stir(struct arc4_stream *as)
{
- int fd;
- struct {
- struct timeval tv;
- uint rnd[(128 - sizeof(struct timeval)) / sizeof(uint)];
- } rdat;
int n;
+ u_char rnd[128];
+ struct timeval tv;
+
+#ifndef __ARC4RANDOM_USES_NODEV__
+ int fd;
- gettimeofday(&rdat.tv, NULL);
fd = open("/dev/urandom", O_RDONLY);
if (fd != -1) {
- read(fd, rdat.rnd, sizeof(rdat.rnd));
+ read(fd, rnd, sizeof(rnd));
close(fd);
}
-#ifdef __ARC4RANDOM_USE_ERANDOM__
+ /* Did the pseudo-random device fail? Use gettimeofday(). */
+ else
+#endif
+ if (gettimeofday(&tv, NULL) != (-1)) {
+
+ /* Initialize the first element so it's hopefully not '0',
+ * to help out the next loop. Tossing in some prime numbers
+ * probably can't hurt. */
+ rnd[0] = (tv.tv_sec % 10000) * 3 + tv.tv_usec * 7 + \
+ (getpid() % 1000) * 13;
+
+ for (n = 1; n < 127 ; n++) {
+
+ /* Take advantage of the stack space. Only initialize
+ * elements equal to '0'. This will make the rnd[]
+ * array much less vulnerable to timing attacks. Here
+ * we'll stir getpid() into the value of the previous
+ * element. Approximately 1 in 128 elements will still
+ * become '0'. */
+
+ if (rnd[n] == 0) {
+ rnd[n] = ((rnd[n - 1] + n) ^ \
+ ((getpid() % 1000) * 17));
+ }
+ }
+ }
else {
- int mib[3];
- uint i;
- size_t len;
-
- /* Device could not be opened, we might be chrooted, take
- * randomness from sysctl. */
-
- mib[0] = CTL_KERN;
- mib[1] = KERN_RANDOM;
- mib[2] = RANDOM_ERANDOM;
-
- for (i = 0; i < sizeof(rdat.rnd) / sizeof(uint); i++) {
- len = sizeof(uint);
- if (sysctl(mib, 3, &rdat.rnd[i], &len, NULL, 0) == -1)
- break;
+ /* gettimeofday() failed? Do the same thing as above, but only
+ * with getpid(). */
+
+ rnd[0] = (getpid() % 1000) * 19;
+ for (n = 1; n < 127 ; n++) {
+ if (rnd[n] == 0) {
+ rnd[n] = ((rnd[n - 1] + n) ^ \
+ ((getpid() % 1000) * 23));
+ }
}
}
-#endif
- arc4_addrandom(as, (void *) &rdat, sizeof(rdat));
+ arc4_stir_pid = getpid();
+ arc4_addrandom(as, rnd, sizeof(rnd));
/*
- * Throw away the first N words of output, as suggested in the
- * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
- * by Fluher, Mantin, and Shamir. N = 1024 is based on
- * suggestions in the paper "(Not So) Random Shuffles of RC4"
- * by Ilya Mironov.
+ * Discard early keystream, as per recommendations in:
+ * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
*/
- for (n = 0; n < 1024; n++)
- arc4_getbyte(as);
+ for (n = 0; n < 256; n++)
+ (void)arc4_getbyte(as);
+ arc4_count = 1600000;
+}
+
+#if 0
+static void __arc4random_stir(void);
+/*
+ * __arc4_getbyte() is a libc private function intended for use
+ * with malloc.
+ */
+u_int8_t
+__arc4_getbyte(void)
+{
+ if (--arc4_count == 0 || !rs_initialized)
+ __arc4random_stir();
+ return arc4_getbyte(&rs);
}
+#endif
static __inline__ u_int32_t
arc4_getword(struct arc4_stream *as)
u_int32_t
arc4random(void)
{
- if (!rs_initialized)
+ arc4_count -= 4;
+ if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != getpid())
__arc4random_stir();
return arc4_getword(&rs);
}
-
-#if 0
-/*-------- Test code --------*/
-#include <stdlib.h>
-#include <stdio.h>
-
-int main(void) {
- int random_number;
- random_number = arc4random() % 65536;
- printf("%d\n", random_number);
- return 0;
-}
-#endif
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