openssh/openbsd-compat/arc4random.c

/* 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>

#ifndef HAVE_ARC4RANDOM

/*
 * If we're not using a native getentropy, use the one from bsd-getentropy.c
 * under a different name, so that if in future these binaries are run on
 * a system that has a native getentropy OpenSSL cannot call the wrong one.
 */
#ifndef HAVE_GETENTROPY
# define getentropy(x, y) (_ssh_compat_getentropy((x), (y)))
#endif

#define MINIMUM(a, b)    (((a) < (b)) ? (a) : (b))

#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);
	chacha_ivsetup(&rs, buf + KEYSZ);
}

static void
_rs_stir(void)
{
	u_char rnd[KEYSZ + IVSZ];

	if (getentropy(rnd, sizeof rnd) == -1)
		fatal("getentropy failed");

	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 = MINIMUM(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 = MINIMUM(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 = MINIMUM(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) */

#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