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/* randomness machinery
* Copyright (C) 1997 Angelos D. Keromytis.
* Copyright (C) 1998-2001 D. Hugh Redelmeier.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* RCSID $Id: rnd.c,v 1.3 2005/09/08 16:26:30 as Exp $
*/
/* A true random number generator (we hope)
*
* Under LINUX ("linux" predefined), use /dev/urandom.
* Under OpenBSD ("__OpenBSD__" predefined), use arc4random().
* Otherwise use our own random number generator based on clock skew.
* I (ADK) first heard of the idea from John Ioannidis, who heard it
* from Matt Blaze and/or Jack Lacy.
* ??? Why is mixing need for linux but not OpenBSD?
*/
/* Pluto's uses of randomness:
*
* - Setting up the "secret_of_the_day". This changes every hour! 20
* bytes a shot. It is used in building responder cookies.
*
* - generating initiator cookies (8 bytes, once per Phase 1 initiation).
*
* - 32 bytes per DH local secret. Once per Main Mode exchange and once
* per Quick Mode Exchange with PFS. (Size is our choice, with
* tradeoffs.)
*
* - 16 bytes per nonce we generate. Once per Main Mode exchange and
* once per Quick Mode exchange. (Again, we choose the size.)
*
* - 4 bytes per SPI number that we generate. We choose the SPIs for all
* inbound SPIs, one to three per IPSEC SA (one for AH (rare, probably)
* one for ESP (almost always), and one for tunnel (very common)).
* I don't actually know how the kernel would generate these numbers --
* currently Pluto generates them; this isn't the way things will be
* done in the future.
*
* - 4 bytes per Message ID we need to generate. One per Quick Mode
* exchange. Eventually, one per informational exchange.
*/
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <sys/time.h>
#include <fcntl.h>
#include <freeswan.h>
#include "sha1.h"
#include "constants.h"
#include "defs.h"
#include "rnd.h"
#include "log.h"
#include "timer.h"
#ifdef linux
# define USE_DEV_RANDOM 1
# define RANDOM_PATH "/dev/urandom"
#else
# ifdef __OpenBSD__
# define USE_ARC4RANDOM
# else
# define USE_CLOCK_SLEW
# endif
#endif
#ifdef USE_ARC4RANDOM
#define get_rnd_byte() (arc4random() % 256)
#else /**** start of large #else ****/
#ifdef USE_DEV_RANDOM
static int random_fd = NULL_FD;
#endif
#define RANDOM_POOL_SIZE SHA1_DIGEST_SIZE
static u_char random_pool[RANDOM_POOL_SIZE];
#ifdef USE_DEV_RANDOM
/* Generate (what we hope is) a true random byte using /dev/urandom */
static u_char
generate_rnd_byte(void)
{
u_char c;
if (read(random_fd, &c, sizeof(c)) == -1)
exit_log_errno((e, "read() failed in get_rnd_byte()"));
return c;
}
#else /* !USE_DEV_RANDOM */
/* Generate (what we hope is) a true random byte using the clock skew trick.
* Note: this code is not maintained! In particular, LINUX signal(2)
* semantics changed with glibc2 (and not for the better). It isn't clear
* that this code will work. We keep the code because someday it might
* come in handy.
*/
# error "This code is not maintained. Please define USE_DEV_RANDOM."
static volatile sig_atomic_t i, j, k;
/* timer signal handler */
static void
rnd_handler(int ignore_me UNUSED)
{
k <<= 1; /* Shift left by 1 */
j++;
k |= (i & 0x1); /* Get lsbit of counter */
if (j != 8)
signal(SIGVTALRM, rnd_handler);
}
static u_char
generate_rnd_byte(void)
{
struct itimerval tmval, ntmval;
# ifdef NEVER /* ??? */
# ifdef linux
int mask = siggetmask();
mask |= SIGVTALRM;
sigsetmask(mask);
# endif
# endif
i = 0;
j = 0;
ntmval.it_interval.tv_sec = 0;
ntmval.it_interval.tv_usec = 1;
ntmval.it_value.tv_sec = 0;
ntmval.it_value.tv_usec = 1;
signal(SIGVTALRM, rnd_handler);
setitimer(ITIMER_VIRTUAL, &ntmval, &tmval);
while (j != 8)
i++;
setitimer(ITIMER_VIRTUAL, &tmval, &ntmval);
signal(SIGVTALRM, SIG_IGN);
# ifdef NEVER /* ??? */
# ifdef linux
mask ^= SIGVTALRM;
sigsetmask(mask);
# endif
# endif
return k;
}
#endif /* !USE_DEV_RANDOM */
static void
mix_pool(void)
{
SHA1_CTX ctx;
SHA1Init(&ctx);
SHA1Update(&ctx, random_pool, RANDOM_POOL_SIZE);
SHA1Final(random_pool, &ctx);
}
/*
* Get a single random byte.
*/
static u_char
get_rnd_byte(void)
{
random_pool[RANDOM_POOL_SIZE - 1] = generate_rnd_byte();
random_pool[0] = generate_rnd_byte();
mix_pool();
return random_pool[0];
}
#endif /* !USE_ARC4RANDOM */ /**** end of large #else ****/
void
get_rnd_bytes(u_char *buffer, int length)
{
int i;
for (i = 0; i < length; i++)
buffer[i] = get_rnd_byte();
}
/*
* Initialize the random pool.
*/
void
init_rnd_pool(void)
{
#ifndef USE_ARC4RANDOM
# ifdef USE_DEV_RANDOM
DBG(DBG_KLIPS, DBG_log("opening %s", RANDOM_PATH));
random_fd = open(RANDOM_PATH, O_RDONLY);
if (random_fd == -1)
exit_log_errno((e, "open of %s failed in init_rnd_pool()", RANDOM_PATH));
fcntl(random_fd, F_SETFD, FD_CLOEXEC);
# endif
get_rnd_bytes(random_pool, RANDOM_POOL_SIZE);
mix_pool();
#endif /* !USE_ARC4RANDOM */
/* start of rand(3) on the right foot */
{
unsigned int seed;
get_rnd_bytes((void *)&seed, sizeof(seed));
srand(seed);
}
}
u_char secret_of_the_day[SHA1_DIGEST_SIZE];
#ifndef NO_PLUTO
void
init_secret(void)
{
/*
* Generate the secret value for responder cookies, and
* schedule an event for refresh.
*/
get_rnd_bytes(secret_of_the_day, sizeof(secret_of_the_day));
event_schedule(EVENT_REINIT_SECRET, EVENT_REINIT_SECRET_DELAY, NULL);
}
#endif /* NO_PLUTO */
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