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openssh/openbsd-compat/arc4random.c

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/* OPENBSD ORIGINAL: lib/libc/crypto/arc4random.c */
/* $OpenBSD: arc4random.c,v 1.25 2013/10/01 18:34:57 markus Exp $ */
/*
* Copyright (c) 1996, David Mazieres <dm@uun.org>
* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
* Copyright (c) 2013, Markus Friedl <markus@openbsd.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.
*
* 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.
*/
/*
* ChaCha based random number generator for OpenBSD.
*/
#include "includes.h"
#include <sys/types.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#ifdef HAVE_SYS_RANDOM_H
# include <sys/random.h>
#endif
#ifndef HAVE_ARC4RANDOM
#ifdef WITH_OPENSSL
#include <openssl/rand.h>
#include <openssl/err.h>
#endif
#include "log.h"
#define KEYSTREAM_ONLY
#include "chacha_private.h"
#ifdef __GNUC__
#define inline __inline
#else /* !__GNUC__ */
#define inline
#endif /* !__GNUC__ */
/* OpenSSH isn't multithreaded */
#define _ARC4_LOCK()
#define _ARC4_UNLOCK()
#define KEYSZ 32
#define IVSZ 8
#define BLOCKSZ 64
#define RSBUFSZ (16*BLOCKSZ)
static int rs_initialized;
static pid_t rs_stir_pid;
static chacha_ctx rs; /* chacha context for random keystream */
static u_char rs_buf[RSBUFSZ]; /* keystream blocks */
static size_t rs_have; /* valid bytes at end of rs_buf */
static size_t rs_count; /* bytes till reseed */
static inline void _rs_rekey(u_char *dat, size_t datlen);
static inline void
_rs_init(u_char *buf, size_t n)
{
if (n < KEYSZ + IVSZ)
return;
chacha_keysetup(&rs, buf, KEYSZ * 8, 0);
chacha_ivsetup(&rs, buf + KEYSZ);
}
#ifndef WITH_OPENSSL
# ifndef SSH_RANDOM_DEV
# define SSH_RANDOM_DEV "/dev/urandom"
# endif /* SSH_RANDOM_DEV */
static void
getrnd(u_char *s, size_t len)
{
int fd;
ssize_t r;
size_t o = 0;
#ifdef HAVE_GETRANDOM
if ((r = getrandom(s, len, 0)) > 0 && (size_t)r == len)
return;
#endif /* HAVE_GETRANDOM */
if ((fd = open(SSH_RANDOM_DEV, O_RDONLY)) == -1)
fatal("Couldn't open %s: %s", SSH_RANDOM_DEV, strerror(errno));
while (o < len) {
r = read(fd, s + o, len - o);
if (r < 0) {
if (errno == EAGAIN || errno == EINTR ||
errno == EWOULDBLOCK)
continue;
fatal("read %s: %s", SSH_RANDOM_DEV, strerror(errno));
}
o += r;
}
close(fd);
}
#endif /* WITH_OPENSSL */
static void
_rs_stir(void)
{
u_char rnd[KEYSZ + IVSZ];
#ifdef WITH_OPENSSL
if (RAND_bytes(rnd, sizeof(rnd)) <= 0)
fatal("Couldn't obtain random bytes (error 0x%lx)",
(unsigned long)ERR_get_error());
#else
getrnd(rnd, sizeof(rnd));
#endif
if (!rs_initialized) {
rs_initialized = 1;
_rs_init(rnd, sizeof(rnd));
} else
_rs_rekey(rnd, sizeof(rnd));
explicit_bzero(rnd, sizeof(rnd));
/* invalidate rs_buf */
rs_have = 0;
memset(rs_buf, 0, RSBUFSZ);
rs_count = 1600000;
}
static inline void
_rs_stir_if_needed(size_t len)
{
pid_t pid = getpid();
if (rs_count <= len || !rs_initialized || rs_stir_pid != pid) {
rs_stir_pid = pid;
_rs_stir();
} else
rs_count -= len;
}
static inline void
_rs_rekey(u_char *dat, size_t datlen)
{
#ifndef KEYSTREAM_ONLY
memset(rs_buf, 0,RSBUFSZ);
#endif
/* fill rs_buf with the keystream */
chacha_encrypt_bytes(&rs, rs_buf, rs_buf, RSBUFSZ);
/* mix in optional user provided data */
if (dat) {
size_t i, m;
m = MIN(datlen, KEYSZ + IVSZ);
for (i = 0; i < m; i++)
rs_buf[i] ^= dat[i];
}
/* immediately reinit for backtracking resistance */
_rs_init(rs_buf, KEYSZ + IVSZ);
memset(rs_buf, 0, KEYSZ + IVSZ);
rs_have = RSBUFSZ - KEYSZ - IVSZ;
}
static inline void
_rs_random_buf(void *_buf, size_t n)
{
u_char *buf = (u_char *)_buf;
size_t m;
_rs_stir_if_needed(n);
while (n > 0) {
if (rs_have > 0) {
m = MIN(n, rs_have);
memcpy(buf, rs_buf + RSBUFSZ - rs_have, m);
memset(rs_buf + RSBUFSZ - rs_have, 0, m);
buf += m;
n -= m;
rs_have -= m;
}
if (rs_have == 0)
_rs_rekey(NULL, 0);
}
}
static inline void
_rs_random_u32(u_int32_t *val)
{
_rs_stir_if_needed(sizeof(*val));
if (rs_have < sizeof(*val))
_rs_rekey(NULL, 0);
memcpy(val, rs_buf + RSBUFSZ - rs_have, sizeof(*val));
memset(rs_buf + RSBUFSZ - rs_have, 0, sizeof(*val));
rs_have -= sizeof(*val);
return;
}
void
arc4random_stir(void)
{
_ARC4_LOCK();
_rs_stir();
_ARC4_UNLOCK();
}
void
arc4random_addrandom(u_char *dat, int datlen)
{
int m;
_ARC4_LOCK();
if (!rs_initialized)
_rs_stir();
while (datlen > 0) {
m = MIN(datlen, KEYSZ + IVSZ);
_rs_rekey(dat, m);
dat += m;
datlen -= m;
}
_ARC4_UNLOCK();
}
u_int32_t
arc4random(void)
{
u_int32_t val;
_ARC4_LOCK();
_rs_random_u32(&val);
_ARC4_UNLOCK();
return val;
}
/*
* If we are providing arc4random, then we can provide a more efficient
* arc4random_buf().
*/
# ifndef HAVE_ARC4RANDOM_BUF
void
arc4random_buf(void *buf, size_t n)
{
_ARC4_LOCK();
_rs_random_buf(buf, n);
_ARC4_UNLOCK();
}
# endif /* !HAVE_ARC4RANDOM_BUF */
#endif /* !HAVE_ARC4RANDOM */
/* arc4random_buf() that uses platform arc4random() */
#if !defined(HAVE_ARC4RANDOM_BUF) && defined(HAVE_ARC4RANDOM)
void
arc4random_buf(void *_buf, size_t n)
{
size_t i;
u_int32_t r = 0;
char *buf = (char *)_buf;
for (i = 0; i < n; i++) {
if (i % 4 == 0)
r = arc4random();
buf[i] = r & 0xff;
r >>= 8;
}
explicit_bzero(&r, sizeof(r));
}
#endif /* !defined(HAVE_ARC4RANDOM_BUF) && defined(HAVE_ARC4RANDOM) */
#ifndef HAVE_ARC4RANDOM_UNIFORM
/*
* Calculate a uniformly distributed random number less than upper_bound
* avoiding "modulo bias".
*
* Uniformity is achieved by generating new random numbers until the one
* returned is outside the range [0, 2**32 % upper_bound). This
* guarantees the selected random number will be inside
* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
* after reduction modulo upper_bound.
*/
u_int32_t
arc4random_uniform(u_int32_t upper_bound)
{
u_int32_t r, min;
if (upper_bound < 2)
return 0;
/* 2**32 % x == (2**32 - x) % x */
min = -upper_bound % upper_bound;
/*
* This could theoretically loop forever but each retry has
* 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 /* !HAVE_ARC4RANDOM_UNIFORM */
#if 0
/*-------- Test code for i386 --------*/
#include <stdio.h>
#include <machine/pctr.h>
int
main(int argc, char **argv)
{
const int iter = 1000000;
int i;
pctrval v;
v = rdtsc();
for (i = 0; i < iter; i++)
arc4random();
v = rdtsc() - v;
v /= iter;
printf("%qd cycles\n", v);
exit(0);
}
#endif
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