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/*
* Cryptographically Secure Randomness.
*
* Copyright (c) 2014 Marko Kreen
*
* Permission to use, copy, modify, and/or 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.
*/
#include <usual/crypto/csrandom.h>
#include <usual/crypto/entropy.h>
#include <usual/err.h>
#include <usual/string.h>
#include <usual/pthread.h>
#include <usual/crypto/keccak_prng.h>
#include <usual/crypto/chacha.h>
#ifdef HAVE_ARC4RANDOM_BUF
/*
* Simply wrap arc4random_buf() API.
*/
uint32_t csrandom(void)
{
return arc4random();
}
void csrandom_bytes(void *buf, size_t nbytes)
{
arc4random_buf(buf, nbytes);
}
uint32_t csrandom_range(upper_bound)
{
return arc4random_uniform(upper_bound);
}
#else /* !HAVE_ARC4RANDOM_BUF */
#define USE_KECCAK
#ifdef USE_KECCAK
/*
* Keccak-based PRNG.
*/
static struct KeccakPRNG prng_keccak;
static void impl_init(void)
{
char buf[32];
if (getentropy(buf, sizeof(buf)) != 0)
errx(1, "Cannot get system entropy");
if (!keccak_prng_init(&prng_keccak, 576))
errx(1, "Cannot initialize PRNG");
keccak_prng_add_data(&prng_keccak, buf, sizeof(buf));
explicit_bzero(buf, sizeof(buf));
}
static void impl_extract(void *buf, size_t nbytes)
{
keccak_prng_extract(&prng_keccak, buf, nbytes);
}
#else
/*
* ChaCha-based PRNG.
*/
static struct ChaCha prng_chacha;
static void impl_init(void)
{
uint8_t buf[CHACHA_KEY_SIZE + CHACHA_IV_SIZE];
if (getentropy(buf, sizeof(buf)) != 0)
errx(1, "Cannot get system entropy");
chacha_set_key_256(&prng_chacha, buf);
chacha_set_nonce(&prng_chacha, 0, 0, buf + CHACHA_KEY_SIZE);
explicit_bzero(buf, sizeof(buf));
}
static void impl_extract(void *buf, size_t nbytes)
{
chacha_keystream(&prng_chacha, buf, nbytes);
}
#endif
/*
* Locking
*/
static pthread_once_t once_init = PTHREAD_ONCE_INIT;
static pthread_mutex_t prng_mutex;
static pid_t last_pid;
static int first_init_done;
#ifdef HAVE_PTHREAD_ATFORK
static void atfork_child(void)
{
pthread_once_t tmp = PTHREAD_ONCE_INIT;
memcpy(&once_init, &tmp, sizeof(tmp));
last_pid = -1;
}
#endif
static void setup_locking(void)
{
int err;
char buf[128];
last_pid = -1;
/* reset lock */
memset(&prng_mutex, 0, sizeof(prng_mutex));
err = pthread_mutex_init(&prng_mutex, NULL);
if (err != 0)
errx(1, "csrandom lock init failed: %s", strerror_r(err, buf, sizeof(buf)));
/* do the rest really only once */
if (first_init_done)
return;
first_init_done = true;
#ifdef HAVE_PTHREAD_ATFORK
pthread_atfork(NULL, NULL, atfork_child);
#endif
}
static void prng_lock(void)
{
int err;
char buf[128];
err = pthread_mutex_lock(&prng_mutex);
if (err != 0)
errx(1, "csrandom lock failed: %s", strerror_r(err, buf, sizeof(buf)));
}
static void prng_unlock(void)
{
int err;
char buf[128];
err = pthread_mutex_unlock(&prng_mutex);
if (err != 0)
errx(1, "csrandom unlock failed: %s", strerror_r(err, buf, sizeof(buf)));
}
/*
* Make sure state is initialized.
*/
static void prng_check_and_lock(void)
{
bool reseed = false;
pid_t new_pid;
pthread_once(&once_init, setup_locking);
prng_lock();
new_pid = getpid();
if (new_pid != last_pid) {
reseed = true;
last_pid = new_pid;
}
if (reseed)
impl_init();
}
/*
* Public API follows
*/
void csrandom_bytes(void *buf, size_t nbytes)
{
prng_check_and_lock();
impl_extract(buf, nbytes);
prng_unlock();
}
uint32_t csrandom(void)
{
uint32_t val;
csrandom_bytes(&val, sizeof(val));
return val;
}
uint32_t csrandom_range(uint32_t upper_bound)
{
uint32_t mod, lim, val;
if (upper_bound <= 1)
return 0;
/* 2**32 % x == (2**32 - x) % x */
mod = -upper_bound % upper_bound;
/* wait for value in range [0 .. 2**32-mod) */
lim = -mod;
/* loop until good value appears */
while (1) {
val = csrandom();
if (val < lim || lim == 0)
return val % upper_bound;
}
}
#endif /* !HAVE_ARC4RANDOM_BUF */
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