308 lines
7.7 KiB
C
308 lines
7.7 KiB
C
/* $OpenBSD: arc4random.c,v 1.19 2008/06/04 00:50:23 djm Exp $ */
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/*
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* Copyright (c) 1996, David Mazieres <dm@uun.org>
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* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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/*
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* Arc4 random number generator for OpenBSD.
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*
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* This code is derived from section 17.1 of Applied Cryptography,
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* second edition, which describes a stream cipher allegedly
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* compatible with RSA Labs "RC4" cipher (the actual description of
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* which is a trade secret). The same algorithm is used as a stream
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* cipher called "arcfour" in Tatu Ylonen's ssh package.
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*
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* Here the stream cipher has been modified always to include the time
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* when initializing the state. That makes it impossible to
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* regenerate the same random sequence twice, so this can't be used
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* for encryption, but will generate good random numbers.
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*
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* RC4 is a registered trademark of RSA Laboratories.
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*/
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#include <fcntl.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/param.h>
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#include <sys/time.h>
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#include "thread_private.h"
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/* BIONIC-BEGIN */
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/* this lock should protect the global variables in this file */
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static pthread_mutex_t _arc4_lock = PTHREAD_MUTEX_INITIALIZER;
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#define _ARC4_LOCK() pthread_mutex_lock(&_arc4_lock)
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#define _ARC4_UNLOCK() pthread_mutex_unlock(&_arc4_lock)
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/* BIONIC-END */
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#ifdef __GNUC__
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#define inline __inline
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#else /* !__GNUC__ */
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#define inline
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#endif /* !__GNUC__ */
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struct arc4_stream {
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u_int8_t i;
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u_int8_t j;
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u_int8_t s[256];
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};
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static int rs_initialized;
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static struct arc4_stream rs;
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static pid_t arc4_stir_pid;
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static int arc4_count;
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static inline u_int8_t arc4_getbyte(void);
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static inline void
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arc4_init(void)
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{
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int n;
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for (n = 0; n < 256; n++)
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rs.s[n] = n;
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rs.i = 0;
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rs.j = 0;
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}
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static inline void
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arc4_addrandom(u_char *dat, int datlen)
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{
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int n;
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u_int8_t si;
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rs.i--;
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for (n = 0; n < 256; n++) {
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rs.i = (rs.i + 1);
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si = rs.s[rs.i];
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rs.j = (rs.j + si + dat[n % datlen]);
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rs.s[rs.i] = rs.s[rs.j];
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rs.s[rs.j] = si;
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}
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rs.j = rs.i;
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}
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static void
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arc4_stir(void)
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{
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#if 1 /* BIONIC-BEGIN */
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int i, fd;
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union {
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struct timeval tv;
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u_int rnd[128 / sizeof(u_int)];
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} rdat;
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int n;
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if (!rs_initialized) {
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arc4_init();
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rs_initialized = 1;
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}
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fd = open("/dev/urandom", O_RDONLY);
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if (fd != -1) {
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read(fd, rdat.rnd, sizeof(rdat.rnd));
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close(fd);
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}
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else
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{
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/* fd < 0 ? Ah, what the heck. We'll just take
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* whatever was on the stack. just add a little more
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* time-based randomness though
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*/
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gettimeofday(&rdat.tv, NULL);
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}
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arc4_stir_pid = getpid();
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arc4_addrandom((void *) &rdat, sizeof(rdat));
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#else /* BIONIC-END */
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int i, mib[2];
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size_t len;
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u_char rnd[128];
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if (!rs_initialized) {
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arc4_init();
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rs_initialized = 1;
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}
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mib[0] = CTL_KERN;
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mib[1] = KERN_ARND;
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len = sizeof(rnd);
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sysctl(mib, 2, rnd, &len, NULL, 0);
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arc4_stir_pid = getpid();
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arc4_addrandom(rnd, sizeof(rnd));
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#endif
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/*
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* Discard early keystream, as per recommendations in:
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* http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
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*/
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for (i = 0; i < 256; i++)
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(void)arc4_getbyte();
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arc4_count = 1600000;
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}
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static inline u_int8_t
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arc4_getbyte(void)
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{
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u_int8_t si, sj;
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rs.i = (rs.i + 1);
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si = rs.s[rs.i];
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rs.j = (rs.j + si);
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sj = rs.s[rs.j];
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rs.s[rs.i] = sj;
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rs.s[rs.j] = si;
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return (rs.s[(si + sj) & 0xff]);
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}
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u_int8_t
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__arc4_getbyte(void)
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{
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u_int8_t val;
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_ARC4_LOCK();
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if (--arc4_count == 0 || !rs_initialized)
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arc4_stir();
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val = arc4_getbyte();
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_ARC4_UNLOCK();
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return val;
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}
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static inline u_int32_t
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arc4_getword(void)
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{
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u_int32_t val;
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val = arc4_getbyte() << 24;
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val |= arc4_getbyte() << 16;
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val |= arc4_getbyte() << 8;
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val |= arc4_getbyte();
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return val;
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}
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void
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arc4random_stir(void)
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{
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_ARC4_LOCK();
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arc4_stir();
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_ARC4_UNLOCK();
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}
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void
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arc4random_addrandom(u_char *dat, int datlen)
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{
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_ARC4_LOCK();
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if (!rs_initialized)
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arc4_stir();
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arc4_addrandom(dat, datlen);
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_ARC4_UNLOCK();
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}
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u_int32_t
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arc4random(void)
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{
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u_int32_t val;
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_ARC4_LOCK();
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arc4_count -= 4;
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if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != getpid())
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arc4_stir();
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val = arc4_getword();
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_ARC4_UNLOCK();
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return val;
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}
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void
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arc4random_buf(void *_buf, size_t n)
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{
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u_char *buf = (u_char *)_buf;
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_ARC4_LOCK();
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if (!rs_initialized || arc4_stir_pid != getpid())
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arc4_stir();
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while (n--) {
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if (--arc4_count <= 0)
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arc4_stir();
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buf[n] = arc4_getbyte();
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}
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_ARC4_UNLOCK();
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}
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/*
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* Calculate a uniformly distributed random number less than upper_bound
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* avoiding "modulo bias".
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*
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* Uniformity is achieved by generating new random numbers until the one
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* returned is outside the range [0, 2**32 % upper_bound). This
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* guarantees the selected random number will be inside
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* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
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* after reduction modulo upper_bound.
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*/
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u_int32_t
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arc4random_uniform(u_int32_t upper_bound)
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{
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u_int32_t r, min;
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if (upper_bound < 2)
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return 0;
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#if (ULONG_MAX > 0xffffffffUL)
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min = 0x100000000UL % upper_bound;
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#else
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/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
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if (upper_bound > 0x80000000)
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min = 1 + ~upper_bound; /* 2**32 - upper_bound */
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else {
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/* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
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min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
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}
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#endif
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/*
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* This could theoretically loop forever but each retry has
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* p > 0.5 (worst case, usually far better) of selecting a
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* number inside the range we need, so it should rarely need
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* to re-roll.
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*/
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for (;;) {
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r = arc4random();
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if (r >= min)
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break;
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}
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return r % upper_bound;
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}
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#if 0
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/*-------- Test code for i386 --------*/
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#include <stdio.h>
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#include <machine/pctr.h>
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int
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main(int argc, char **argv)
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{
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const int iter = 1000000;
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int i;
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pctrval v;
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v = rdtsc();
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for (i = 0; i < iter; i++)
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arc4random();
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v = rdtsc() - v;
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v /= iter;
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printf("%qd cycles\n", v);
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}
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#endif
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