NetBSD/sys/dev/rndpool.c

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/* $NetBSD: rndpool.c,v 1.12 2001/09/09 00:32:52 enami Exp $ */
/*-
* Copyright (c) 1997 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Michael Graff <explorer@flame.org>. This code uses ideas and
* algorithms from the Linux driver written by Ted Ts'o.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the NetBSD
* Foundation, Inc. and its contributors.
* 4. Neither the name of The NetBSD Foundation nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/param.h>
#include <sys/types.h>
#include <sys/systm.h>
#include <sys/sha1.h>
#include <sys/rnd.h>
/*
* The random pool "taps"
*/
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#define TAP1 99
#define TAP2 59
#define TAP3 31
#define TAP4 9
#define TAP5 7
static inline void rndpool_add_one_word(rndpool_t *, u_int32_t);
void
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rndpool_init(rndpool_t *rp)
{
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rp->cursor = 0;
rp->rotate = 0;
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memset(&rp->stats, 0, sizeof(rp->stats));
rp->stats.curentropy = 0;
rp->stats.poolsize = RND_POOLWORDS;
rp->stats.threshold = RND_ENTROPY_THRESHOLD;
rp->stats.maxentropy = RND_POOLBITS;
assert(RND_ENTROPY_THRESHOLD*2 <= 20); /* XXX sha knowledge */
}
u_int32_t
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rndpool_get_entropy_count(rndpool_t *rp)
{
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return (rp->stats.curentropy);
}
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void rndpool_get_stats(rndpool_t *rp, void *rsp, int size)
{
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memcpy(rsp, &rp->stats, size);
}
void
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rndpool_increment_entropy_count(rndpool_t *rp, u_int32_t entropy)
{
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rp->stats.curentropy += entropy;
rp->stats.added += entropy;
if (rp->stats.curentropy > RND_POOLBITS) {
rp->stats.discarded += (rp->stats.curentropy - RND_POOLBITS);
rp->stats.curentropy = RND_POOLBITS;
}
}
u_int32_t *
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rndpool_get_pool(rndpool_t *rp)
{
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return (rp->pool);
}
u_int32_t
rndpool_get_poolsize(void)
{
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return (RND_POOLWORDS);
}
/*
* Add one word to the pool, rotating the input as needed.
*/
static inline void
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rndpool_add_one_word(rndpool_t *rp, u_int32_t val)
{
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/*
* Steal some values out of the pool, and xor them into the
* word we were given.
*
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* Mix the new value into the pool using xor. This will
* prevent the actual values from being known to the caller
* since the previous values are assumed to be unknown as well.
*/
val ^= rp->pool[(rp->cursor + TAP1) & (RND_POOLWORDS - 1)];
val ^= rp->pool[(rp->cursor + TAP2) & (RND_POOLWORDS - 1)];
val ^= rp->pool[(rp->cursor + TAP3) & (RND_POOLWORDS - 1)];
val ^= rp->pool[(rp->cursor + TAP4) & (RND_POOLWORDS - 1)];
val ^= rp->pool[(rp->cursor + TAP5) & (RND_POOLWORDS - 1)];
if (rp->rotate != 0)
val = ((val << rp->rotate) | (val >> (32 - rp->rotate)));
rp->pool[rp->cursor++] ^= val;
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/*
* If we have looped around the pool, increment the rotate
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* variable so the next value will get xored in rotated to
* a different position.
* Increment by a value that is relativly prime to the word size
* to try to spread the bits throughout the pool quickly when the
* pool is empty.
*/
if (rp->cursor == RND_POOLWORDS) {
rp->cursor = 0;
rp->rotate = (rp->rotate + 7) & 31;
}
}
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#if 0
/*
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* Stir a 32-bit value (with possibly less entropy than that) into the pool.
* Update entropy estimate.
*/
void
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rndpool_add_uint32(rndpool_t *rp, u_int32_t val, u_int32_t entropy)
{
rndpool_add_one_word(rp, val);
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rp->entropy += entropy;
rp->stats.added += entropy;
if (rp->entropy > RND_POOLBITS) {
rp->stats.discarded += (rp->entropy - RND_POOLBITS);
rp->entropy = RND_POOLBITS;
}
}
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#endif
/*
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* Add a buffer's worth of data to the pool.
*/
void
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rndpool_add_data(rndpool_t *rp, void *p, u_int32_t len, u_int32_t entropy)
{
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u_int32_t val;
u_int8_t *buf;
buf = p;
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for (; len > 3; len -= 4) {
val = *((u_int32_t *)buf);
rndpool_add_one_word(rp, val);
buf += 4;
}
if (len != 0) {
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val = 0;
switch (len) {
case 3:
val = *buf++;
case 2:
val = val << 8 | *buf++;
case 1:
val = val << 8 | *buf++;
}
rndpool_add_one_word(rp, val);
}
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rp->stats.curentropy += entropy;
rp->stats.added += entropy;
if (rp->stats.curentropy > RND_POOLBITS) {
rp->stats.discarded += (rp->stats.curentropy - RND_POOLBITS);
rp->stats.curentropy = RND_POOLBITS;
}
}
/*
* Extract some number of bytes from the random pool, decreasing the
* estimate of randomness as each byte is extracted.
*
* Do this by stiring the pool and returning a part of hash as randomness.
* Note that no secrets are given away here since parts of the hash are
* xored together before returned.
*
* Honor the request from the caller to only return good data, any data,
* etc. Note that we must have at least 64 bits of entropy in the pool
* before we return anything in the high-quality modes.
*/
int
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rndpool_extract_data(rndpool_t *rp, void *p, u_int32_t len, u_int32_t mode)
{
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u_int i;
SHA1_CTX hash;
u_char digest[20]; /* XXX SHA knowledge */
u_int32_t remain, deltae, count;
u_int8_t *buf;
int good;
buf = p;
remain = len;
if (mode == RND_EXTRACT_ANY)
good = 1;
else
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good = (rp->stats.curentropy >= (8 * RND_ENTROPY_THRESHOLD));
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assert(RND_ENTROPY_THRESHOLD*2 <= 20); /* XXX SHA knowledge */
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while (good && (remain != 0)) {
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/*
* While bytes are requested, compute the hash of the pool,
* and then "fold" the hash in half with XOR, keeping the
* exact hash value secret, as it will be stirred back into
* the pool.
*
* XXX this approach needs examination by competant
* cryptographers! It's rather expensive per bit but
* also involves every bit of the pool in the
* computation of every output bit..
*/
SHA1Init(&hash);
SHA1Update(&hash, (u_int8_t *)rp->pool, RND_POOLWORDS * 4);
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SHA1Final(digest, &hash);
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/*
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* Stir the hash back into the pool. This guarantees
* that the next hash will generate a different value
* if no new values were added to the pool.
*/
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for (i = 0; i < 5; i++) {
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u_int32_t word;
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memcpy(&word, &digest[i * 4], 4);
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rndpool_add_one_word(rp, word);
}
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count = min(remain, RND_ENTROPY_THRESHOLD);
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for (i = 0; i < count; i++)
buf[i] = digest[i] ^ digest[i + RND_ENTROPY_THRESHOLD];
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buf += count;
deltae = count * 8;
remain -= count;
deltae = min(deltae, rp->stats.curentropy);
rp->stats.removed += deltae;
rp->stats.curentropy -= deltae;
if (rp->stats.curentropy == 0)
rp->stats.generated += (count * 8) - deltae;
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if (mode == RND_EXTRACT_GOOD)
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good = (rp->stats.curentropy >=
(8 * RND_ENTROPY_THRESHOLD));
}
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memset(&hash, 0, sizeof(hash));
memset(digest, 0, sizeof(digest));
return (len - remain);
}