md_rand.c

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			 * than necessary given that conflicts occur only
			 * when the total seeding is longer than the random
			 * state. */
			state[st_idx++]^=local_md[k];
			if (st_idx >= STATE_SIZE)
				st_idx=0;
			}
		}
	EVP_MD_CTX_cleanup(&m);

	if (!do_not_lock) CRYPTO_w_lock(CRYPTO_LOCK_RAND);
	/* Don't just copy back local_md into md -- this could mean that
	 * other thread's seeding remains without effect (except for
	 * the incremented counter).  By XORing it we keep at least as
	 * much entropy as fits into md. */
	for (k = 0; k < (int)sizeof(md); k++)
		{
		md[k] ^= local_md[k];
		}
	if (entropy < ENTROPY_NEEDED) /* stop counting when we have enough */
	    entropy += add;
	if (!do_not_lock) CRYPTO_w_unlock(CRYPTO_LOCK_RAND);
	
#if !defined(OPENSSL_THREADS) && !defined(OPENSSL_SYS_WIN32)
	assert(md_c[1] == md_count[1]);
#endif
	}

static void ssleay_rand_seed(const void *buf, int num)
	{
	ssleay_rand_add(buf, num, (double)num);
	}

static int ssleay_rand_bytes(unsigned char *buf, int num)
	{
	static volatile int stirred_pool = 0;
	int i,j,k,st_num,st_idx;
	int num_ceil;
	int ok;
	long md_c[2];
	unsigned char local_md[MD_DIGEST_LENGTH];
	EVP_MD_CTX m;
#ifndef GETPID_IS_MEANINGLESS
	pid_t curr_pid = getpid();
#endif
	int do_stir_pool = 0;

#ifdef PREDICT
	if (rand_predictable)
		{
		static unsigned char val=0;

		for (i=0; i<num; i++)
			buf[i]=val++;
		return(1);
		}
#endif

	if (num <= 0)
		return 1;

	EVP_MD_CTX_init(&m);
	/* round upwards to multiple of MD_DIGEST_LENGTH/2 */
	num_ceil = (1 + (num-1)/(MD_DIGEST_LENGTH/2)) * (MD_DIGEST_LENGTH/2);

	/*
	 * (Based on the rand(3) manpage:)
	 *
	 * For each group of 10 bytes (or less), we do the following:
	 *
	 * Input into the hash function the local 'md' (which is initialized from
	 * the global 'md' before any bytes are generated), the bytes that are to
	 * be overwritten by the random bytes, and bytes from the 'state'
	 * (incrementing looping index). From this digest output (which is kept
	 * in 'md'), the top (up to) 10 bytes are returned to the caller and the
	 * bottom 10 bytes are xored into the 'state'.
	 * 
	 * Finally, after we have finished 'num' random bytes for the
	 * caller, 'count' (which is incremented) and the local and global 'md'
	 * are fed into the hash function and the results are kept in the
	 * global 'md'.
	 */

	CRYPTO_w_lock(CRYPTO_LOCK_RAND);

	/* prevent ssleay_rand_bytes() from trying to obtain the lock again */
	CRYPTO_w_lock(CRYPTO_LOCK_RAND2);
	locking_thread = CRYPTO_thread_id();
	CRYPTO_w_unlock(CRYPTO_LOCK_RAND2);
	crypto_lock_rand = 1;

	if (!initialized)
		{
		RAND_poll();
		initialized = 1;
		}
	
	if (!stirred_pool)
		do_stir_pool = 1;
	
	ok = (entropy >= ENTROPY_NEEDED);
	if (!ok)
		{
		/* If the PRNG state is not yet unpredictable, then seeing
		 * the PRNG output may help attackers to determine the new
		 * state; thus we have to decrease the entropy estimate.
		 * Once we've had enough initial seeding we don't bother to
		 * adjust the entropy count, though, because we're not ambitious
		 * to provide *information-theoretic* randomness.
		 *
		 * NOTE: This approach fails if the program forks before
		 * we have enough entropy. Entropy should be collected
		 * in a separate input pool and be transferred to the
		 * output pool only when the entropy limit has been reached.
		 */
		entropy -= num;
		if (entropy < 0)
			entropy = 0;
		}

	if (do_stir_pool)
		{
		/* In the output function only half of 'md' remains secret,
		 * so we better make sure that the required entropy gets
		 * 'evenly distributed' through 'state', our randomness pool.
		 * The input function (ssleay_rand_add) chains all of 'md',
		 * which makes it more suitable for this purpose.
		 */

		int n = STATE_SIZE; /* so that the complete pool gets accessed */
		while (n > 0)
			{
#if MD_DIGEST_LENGTH > 20
# error "Please adjust DUMMY_SEED."
#endif
#define DUMMY_SEED "...................." /* at least MD_DIGEST_LENGTH */
			/* Note that the seed does not matter, it's just that
			 * ssleay_rand_add expects to have something to hash. */
			ssleay_rand_add(DUMMY_SEED, MD_DIGEST_LENGTH, 0.0);
			n -= MD_DIGEST_LENGTH;
			}
		if (ok)
			stirred_pool = 1;
		}

	st_idx=state_index;
	st_num=state_num;
	md_c[0] = md_count[0];
	md_c[1] = md_count[1];
	memcpy(local_md, md, sizeof md);

	state_index+=num_ceil;
	if (state_index > state_num)
		state_index %= state_num;

	/* state[st_idx], ..., state[(st_idx + num_ceil - 1) % st_num]
	 * are now ours (but other threads may use them too) */

	md_count[0] += 1;

	/* before unlocking, we must clear 'crypto_lock_rand' */
	crypto_lock_rand = 0;
	CRYPTO_w_unlock(CRYPTO_LOCK_RAND);

	while (num > 0)
		{
		/* num_ceil -= MD_DIGEST_LENGTH/2 */
		j=(num >= MD_DIGEST_LENGTH/2)?MD_DIGEST_LENGTH/2:num;
		num-=j;
		MD_Init(&m);
#ifndef GETPID_IS_MEANINGLESS
		if (curr_pid) /* just in the first iteration to save time */
			{
			MD_Update(&m,(unsigned char*)&curr_pid,sizeof curr_pid);
			curr_pid = 0;
			}
#endif
		MD_Update(&m,local_md,MD_DIGEST_LENGTH);
		MD_Update(&m,(unsigned char *)&(md_c[0]),sizeof(md_c));
#ifndef PURIFY
		MD_Update(&m,buf,j); /* purify complains */
#endif
		k=(st_idx+MD_DIGEST_LENGTH/2)-st_num;
		if (k > 0)
			{
			MD_Update(&m,&(state[st_idx]),MD_DIGEST_LENGTH/2-k);
			MD_Update(&m,&(state[0]),k);
			}
		else
			MD_Update(&m,&(state[st_idx]),MD_DIGEST_LENGTH/2);
		MD_Final(&m,local_md);

		for (i=0; i<MD_DIGEST_LENGTH/2; i++)
			{
			state[st_idx++]^=local_md[i]; /* may compete with other threads */
			if (st_idx >= st_num)
				st_idx=0;
			if (i < j)
				*(buf++)=local_md[i+MD_DIGEST_LENGTH/2];
			}
		}

	MD_Init(&m);
	MD_Update(&m,(unsigned char *)&(md_c[0]),sizeof(md_c));
	MD_Update(&m,local_md,MD_DIGEST_LENGTH);
	CRYPTO_w_lock(CRYPTO_LOCK_RAND);
	MD_Update(&m,md,MD_DIGEST_LENGTH);
	MD_Final(&m,md);
	CRYPTO_w_unlock(CRYPTO_LOCK_RAND);

	EVP_MD_CTX_cleanup(&m);
	if (ok)
		return(1);
	else
		{
		RANDerr(RAND_F_SSLEAY_RAND_BYTES,RAND_R_PRNG_NOT_SEEDED);
		ERR_add_error_data(1, "You need to read the OpenSSL FAQ, "
			"http://www.openssl.org/support/faq.html");
		return(0);
		}
	}

/* pseudo-random bytes that are guaranteed to be unique but not
   unpredictable */
static int ssleay_rand_pseudo_bytes(unsigned char *buf, int num) 
	{
	int ret;
	unsigned long err;

	ret = RAND_bytes(buf, num);
	if (ret == 0)
		{
		err = ERR_peek_error();
		if (ERR_GET_LIB(err) == ERR_LIB_RAND &&
		    ERR_GET_REASON(err) == RAND_R_PRNG_NOT_SEEDED)
			ERR_clear_error();
		}
	return (ret);
	}

static int ssleay_rand_status(void)
	{
	int ret;
	int do_not_lock;

	/* check if we already have the lock
	 * (could happen if a RAND_poll() implementation calls RAND_status()) */
	if (crypto_lock_rand)
		{
		CRYPTO_r_lock(CRYPTO_LOCK_RAND2);
		do_not_lock = (locking_thread == CRYPTO_thread_id());
		CRYPTO_r_unlock(CRYPTO_LOCK_RAND2);
		}
	else
		do_not_lock = 0;
	
	if (!do_not_lock)
		{
		CRYPTO_w_lock(CRYPTO_LOCK_RAND);
		
		/* prevent ssleay_rand_bytes() from trying to obtain the lock again */
		CRYPTO_w_lock(CRYPTO_LOCK_RAND2);
		locking_thread = CRYPTO_thread_id();
		CRYPTO_w_unlock(CRYPTO_LOCK_RAND2);
		crypto_lock_rand = 1;
		}
	
	if (!initialized)
		{
		RAND_poll();
		initialized = 1;
		}

	ret = entropy >= ENTROPY_NEEDED;

	if (!do_not_lock)
		{
		/* before unlocking, we must clear 'crypto_lock_rand' */
		crypto_lock_rand = 0;
		
		CRYPTO_w_unlock(CRYPTO_LOCK_RAND);
		}
	
	return ret;
	}