547 lines
12 KiB
C
547 lines
12 KiB
C
/* Portable arc4random.c based on arc4random.c from OpenBSD.
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* Portable version by Chris Davis, adapted for Libevent by Nick Mathewson
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* Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson
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* Copyright (c) 2010-2012 Niels Provos and Nick Mathewson
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*
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* Note that in Libevent, this file isn't compiled directly. Instead,
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* it's included from evutil_rand.c
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*/
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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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#ifndef ARC4RANDOM_EXPORT
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#define ARC4RANDOM_EXPORT
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#endif
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#ifndef ARC4RANDOM_UINT32
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#define ARC4RANDOM_UINT32 uint32_t
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#endif
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#ifndef ARC4RANDOM_NO_INCLUDES
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#include "evconfig-private.h"
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#ifdef _WIN32
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#include <wincrypt.h>
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#include <process.h>
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#include <winerror.h>
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#else
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#include <fcntl.h>
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#include <unistd.h>
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#include <sys/param.h>
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#include <sys/time.h>
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#ifdef EVENT__HAVE_SYS_SYSCTL_H
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#include <sys/sysctl.h>
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#endif
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#ifdef EVENT__HAVE_SYS_RANDOM_H
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#include <sys/random.h>
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#endif
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#endif
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#include <limits.h>
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#include <stdlib.h>
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#include <string.h>
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#endif
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/* Add platform entropy 32 bytes (256 bits) at a time. */
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#define ADD_ENTROPY 32
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/* Re-seed from the platform RNG after generating this many bytes. */
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#define BYTES_BEFORE_RESEED 1600000
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struct arc4_stream {
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unsigned char i;
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unsigned char j;
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unsigned char s[256];
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};
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#ifdef _WIN32
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#define getpid _getpid
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#define pid_t int
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#endif
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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 unsigned char 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(const unsigned char *dat, int datlen)
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{
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int n;
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unsigned char 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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#ifndef _WIN32
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static ssize_t
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read_all(int fd, unsigned char *buf, size_t count)
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{
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size_t numread = 0;
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ssize_t result;
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while (numread < count) {
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result = read(fd, buf+numread, count-numread);
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if (result<0)
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return -1;
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else if (result == 0)
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break;
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numread += result;
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}
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return (ssize_t)numread;
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}
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#endif
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#ifdef _WIN32
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#define TRY_SEED_WIN32
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static int
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arc4_seed_win32(void)
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{
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/* This is adapted from Tor's crypto_seed_rng() */
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static int provider_set = 0;
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static HCRYPTPROV provider;
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unsigned char buf[ADD_ENTROPY];
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if (!provider_set) {
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if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
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CRYPT_VERIFYCONTEXT)) {
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if (GetLastError() != (DWORD)NTE_BAD_KEYSET)
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return -1;
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}
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provider_set = 1;
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}
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if (!CryptGenRandom(provider, sizeof(buf), buf))
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return -1;
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arc4_addrandom(buf, sizeof(buf));
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evutil_memclear_(buf, sizeof(buf));
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return 0;
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}
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#endif
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#if defined(EVENT__HAVE_GETRANDOM)
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#define TRY_SEED_GETRANDOM
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static int
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arc4_seed_getrandom(void)
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{
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unsigned char buf[ADD_ENTROPY];
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size_t len, n;
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unsigned i;
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int any_set;
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memset(buf, 0, sizeof(buf));
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for (len = 0; len < sizeof(buf); len += n) {
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n = sizeof(buf) - len;
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if (0 == getrandom(&buf[len], n, 0))
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return -1;
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}
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/* make sure that the buffer actually got set. */
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for (i=0,any_set=0; i<sizeof(buf); ++i) {
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any_set |= buf[i];
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}
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if (!any_set)
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return -1;
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arc4_addrandom(buf, sizeof(buf));
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evutil_memclear_(buf, sizeof(buf));
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return 0;
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}
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#endif /* EVENT__HAVE_GETRANDOM */
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#if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL)
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#if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND
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#define TRY_SEED_SYSCTL_BSD
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static int
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arc4_seed_sysctl_bsd(void)
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{
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/* Based on code from William Ahern and from OpenBSD, this function
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* tries to use the KERN_ARND syscall to get entropy from the kernel.
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* This can work even if /dev/urandom is inaccessible for some reason
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* (e.g., we're running in a chroot). */
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int mib[] = { CTL_KERN, KERN_ARND };
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unsigned char buf[ADD_ENTROPY];
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size_t len, n;
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int i, any_set;
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memset(buf, 0, sizeof(buf));
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len = sizeof(buf);
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if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) {
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for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) {
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n = sizeof(unsigned);
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if (n + len > sizeof(buf))
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n = len - sizeof(buf);
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if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1)
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return -1;
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}
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}
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/* make sure that the buffer actually got set. */
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for (i=any_set=0; i<sizeof(buf); ++i) {
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any_set |= buf[i];
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}
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if (!any_set)
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return -1;
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arc4_addrandom(buf, sizeof(buf));
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evutil_memclear_(buf, sizeof(buf));
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return 0;
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}
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#endif
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#endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */
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#ifdef __linux__
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#define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
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static int
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arc4_seed_proc_sys_kernel_random_uuid(void)
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{
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/* Occasionally, somebody will make /proc/sys accessible in a chroot,
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* but not /dev/urandom. Let's try /proc/sys/kernel/random/uuid.
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* Its format is stupid, so we need to decode it from hex.
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*/
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int fd;
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char buf[128];
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unsigned char entropy[64];
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int bytes, n, i, nybbles;
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for (bytes = 0; bytes<ADD_ENTROPY; ) {
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fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0);
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if (fd < 0)
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return -1;
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n = read(fd, buf, sizeof(buf));
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close(fd);
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if (n<=0)
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return -1;
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memset(entropy, 0, sizeof(entropy));
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for (i=nybbles=0; i<n; ++i) {
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if (EVUTIL_ISXDIGIT_(buf[i])) {
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int nyb = evutil_hex_char_to_int_(buf[i]);
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if (nybbles & 1) {
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entropy[nybbles/2] |= nyb;
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} else {
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entropy[nybbles/2] |= nyb<<4;
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}
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++nybbles;
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}
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}
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if (nybbles < 2)
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return -1;
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arc4_addrandom(entropy, nybbles/2);
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bytes += nybbles/2;
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}
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evutil_memclear_(entropy, sizeof(entropy));
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evutil_memclear_(buf, sizeof(buf));
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return 0;
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}
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#endif
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#ifndef _WIN32
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#define TRY_SEED_URANDOM
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static char *arc4random_urandom_filename = NULL;
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static int arc4_seed_urandom_helper_(const char *fname)
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{
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unsigned char buf[ADD_ENTROPY];
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int fd;
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size_t n;
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fd = evutil_open_closeonexec_(fname, O_RDONLY, 0);
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if (fd<0)
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return -1;
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n = read_all(fd, buf, sizeof(buf));
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close(fd);
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if (n != sizeof(buf))
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return -1;
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arc4_addrandom(buf, sizeof(buf));
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evutil_memclear_(buf, sizeof(buf));
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return 0;
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}
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static int
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arc4_seed_urandom(void)
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{
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/* This is adapted from Tor's crypto_seed_rng() */
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static const char *filenames[] = {
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"/dev/srandom", "/dev/urandom", "/dev/random", NULL
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};
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int i;
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if (arc4random_urandom_filename)
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return arc4_seed_urandom_helper_(arc4random_urandom_filename);
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for (i = 0; filenames[i]; ++i) {
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if (arc4_seed_urandom_helper_(filenames[i]) == 0) {
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return 0;
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}
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}
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return -1;
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}
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#endif
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static int
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arc4_seed(void)
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{
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int ok = 0;
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/* We try every method that might work, and don't give up even if one
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* does seem to work. There's no real harm in over-seeding, and if
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* one of these sources turns out to be broken, that would be bad. */
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#ifdef TRY_SEED_WIN32
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if (0 == arc4_seed_win32())
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ok = 1;
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#endif
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#ifdef TRY_SEED_GETRANDOM
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if (0 == arc4_seed_getrandom())
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ok = 1;
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#endif
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#ifdef TRY_SEED_URANDOM
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if (0 == arc4_seed_urandom())
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ok = 1;
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#endif
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#ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID
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if (arc4random_urandom_filename == NULL &&
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0 == arc4_seed_proc_sys_kernel_random_uuid())
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ok = 1;
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#endif
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#ifdef TRY_SEED_SYSCTL_BSD
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if (0 == arc4_seed_sysctl_bsd())
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ok = 1;
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#endif
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return ok ? 0 : -1;
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}
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static int
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arc4_stir(void)
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{
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int i;
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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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if (0 != arc4_seed())
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return -1;
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/*
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* Discard early keystream, as per recommendations in
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* "Weaknesses in the Key Scheduling Algorithm of RC4" by
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* Scott Fluhrer, Itsik Mantin, and Adi Shamir.
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* http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
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*
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* Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that
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* we drop at least 2*256 bytes, with 12*256 as a conservative
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* value.
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*
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* RFC4345 says to drop 6*256.
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*
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* At least some versions of this code drop 4*256, in a mistaken
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* belief that "words" in the Fluhrer/Mantin/Shamir paper refers
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* to processor words.
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*
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* We add another sect to the cargo cult, and choose 12*256.
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*/
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for (i = 0; i < 12*256; i++)
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(void)arc4_getbyte();
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arc4_count = BYTES_BEFORE_RESEED;
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return 0;
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}
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static void
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arc4_stir_if_needed(void)
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{
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pid_t pid = getpid();
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if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid)
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{
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arc4_stir_pid = pid;
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arc4_stir();
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}
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}
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static inline unsigned char
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arc4_getbyte(void)
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{
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unsigned char 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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static inline unsigned int
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arc4_getword(void)
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{
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unsigned int 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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#ifndef ARC4RANDOM_NOSTIR
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ARC4RANDOM_EXPORT int
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arc4random_stir(void)
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{
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int val;
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ARC4_LOCK_();
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val = arc4_stir();
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ARC4_UNLOCK_();
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return val;
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}
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#endif
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#ifndef ARC4RANDOM_NOADDRANDOM
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ARC4RANDOM_EXPORT void
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arc4random_addrandom(const unsigned char *dat, int datlen)
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{
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int j;
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ARC4_LOCK_();
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if (!rs_initialized)
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arc4_stir();
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for (j = 0; j < datlen; j += 256) {
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/* arc4_addrandom() ignores all but the first 256 bytes of
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* its input. We want to make sure to look at ALL the
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* data in 'dat', just in case the user is doing something
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* crazy like passing us all the files in /var/log. */
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arc4_addrandom(dat + j, datlen - j);
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}
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ARC4_UNLOCK_();
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}
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#endif
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#ifndef ARC4RANDOM_NORANDOM
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ARC4RANDOM_EXPORT ARC4RANDOM_UINT32
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arc4random(void)
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{
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ARC4RANDOM_UINT32 val;
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ARC4_LOCK_();
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arc4_count -= 4;
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arc4_stir_if_needed();
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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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#endif
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ARC4RANDOM_EXPORT void
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arc4random_buf(void *buf_, size_t n)
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{
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unsigned char *buf = buf_;
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ARC4_LOCK_();
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arc4_stir_if_needed();
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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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#ifndef ARC4RANDOM_NOUNIFORM
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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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ARC4RANDOM_EXPORT unsigned int
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arc4random_uniform(unsigned int upper_bound)
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{
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ARC4RANDOM_UINT32 r, min;
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if (upper_bound < 2)
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return 0;
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#if (UINT_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
|
|
* number inside the range we need, so it should rarely need
|
|
* to re-roll.
|
|
*/
|
|
for (;;) {
|
|
r = arc4random();
|
|
if (r >= min)
|
|
break;
|
|
}
|
|
|
|
return r % upper_bound;
|
|
}
|
|
#endif
|