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/* $OpenBSD: arc4random.c,v 1.31 2014/05/31 10:32:12 jca 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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* Copyright (c) 2013, Markus Friedl <markus@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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* ChaCha based random number generator for OpenBSD.
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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 <string.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 <sys/sysctl.h>
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#include <sys/mman.h>
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#include "thread_private.h"
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#define KEYSTREAM_ONLY
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#include "chacha_private.h"
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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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#define KEYSZ 32
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#define IVSZ 8
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#define BLOCKSZ 64
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#define RSBUFSZ (16*BLOCKSZ)
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static int rs_initialized;
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static pid_t rs_stir_pid;
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static chacha_ctx *rs; /* chacha context for random keystream */
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static u_char *rs_buf; /* keystream blocks */
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static size_t rs_have; /* valid bytes at end of rs_buf */
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static size_t rs_count; /* bytes till reseed */
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static inline void _rs_rekey(u_char *dat, size_t datlen);
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static inline void
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_rs_init(u_char *buf, size_t n)
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{
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if (n < KEYSZ + IVSZ)
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return;
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if (rs == NULL && (rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE,
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MAP_ANON, -1, 0)) == MAP_FAILED)
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abort();
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if (rs_buf == NULL && (rs_buf = mmap(NULL, RSBUFSZ, PROT_READ|PROT_WRITE,
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MAP_ANON, -1, 0)) == MAP_FAILED)
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abort();
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chacha_keysetup(rs, buf, KEYSZ * 8, 0);
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chacha_ivsetup(rs, buf + KEYSZ);
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}
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static void
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_rs_stir(void)
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{
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int mib[2];
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size_t len;
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u_char rnd[KEYSZ + IVSZ];
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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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if (!rs_initialized) {
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rs_initialized = 1;
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_rs_init(rnd, sizeof(rnd));
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} else
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_rs_rekey(rnd, sizeof(rnd));
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explicit_bzero(rnd, sizeof(rnd));
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/* invalidate rs_buf */
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rs_have = 0;
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memset(rs_buf, 0, RSBUFSZ);
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rs_count = 1600000;
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}
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static inline void
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_rs_stir_if_needed(size_t len)
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{
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pid_t pid = getpid();
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if (rs_count <= len || !rs_initialized || rs_stir_pid != pid) {
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rs_stir_pid = pid;
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_rs_stir();
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} else
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rs_count -= len;
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}
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static inline void
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_rs_rekey(u_char *dat, size_t datlen)
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{
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#ifndef KEYSTREAM_ONLY
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memset(rs_buf, 0,RSBUFSZ);
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#endif
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/* fill rs_buf with the keystream */
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chacha_encrypt_bytes(rs, rs_buf, rs_buf, RSBUFSZ);
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/* mix in optional user provided data */
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if (dat) {
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size_t i, m;
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m = MIN(datlen, KEYSZ + IVSZ);
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for (i = 0; i < m; i++)
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rs_buf[i] ^= dat[i];
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}
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/* immediately reinit for backtracking resistance */
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_rs_init(rs_buf, KEYSZ + IVSZ);
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memset(rs_buf, 0, KEYSZ + IVSZ);
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rs_have = RSBUFSZ - KEYSZ - IVSZ;
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}
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static inline void
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_rs_random_buf(void *_buf, size_t n)
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{
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u_char *buf = (u_char *)_buf;
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size_t m;
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_rs_stir_if_needed(n);
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while (n > 0) {
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if (rs_have > 0) {
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m = MIN(n, rs_have);
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memcpy(buf, rs_buf + RSBUFSZ - rs_have, m);
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memset(rs_buf + RSBUFSZ - rs_have, 0, m);
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buf += m;
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n -= m;
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rs_have -= m;
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}
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if (rs_have == 0)
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_rs_rekey(NULL, 0);
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}
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}
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static inline void
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_rs_random_u32(u_int32_t *val)
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{
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_rs_stir_if_needed(sizeof(*val));
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if (rs_have < sizeof(*val))
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_rs_rekey(NULL, 0);
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memcpy(val, rs_buf + RSBUFSZ - rs_have, sizeof(*val));
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memset(rs_buf + RSBUFSZ - rs_have, 0, sizeof(*val));
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rs_have -= sizeof(*val);
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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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_rs_random_u32(&val);
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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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_ARC4_LOCK();
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_rs_random_buf(buf, n);
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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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/* 2**32 % x == (2**32 - x) % x */
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min = -upper_bound % upper_bound;
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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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