/* $NetBSD: kern_rndpool.c,v 1.16 2015/04/21 04:41:36 riastradh 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 . 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.
*
* 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
__KERNEL_RCSID(0, "$NetBSD: kern_rndpool.c,v 1.16 2015/04/21 04:41:36 riastradh Exp $");
#include
#include
#include
#include
#include
/*
* The random pool "taps"
*/
#define TAP1 99
#define TAP2 59
#define TAP3 31
#define TAP4 9
#define TAP5 7
void
rndpool_init(rndpool_t *rp)
{
rp->cursor = 0;
rp->rotate = 1;
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;
}
u_int32_t
rndpool_get_entropy_count(rndpool_t *rp)
{
return (rp->stats.curentropy);
}
void
rndpool_set_entropy_count(rndpool_t *rp, u_int32_t count)
{
int32_t difference = count - rp->stats.curentropy;
if (__predict_true(difference > 0)) {
rp->stats.added += difference;
}
rp->stats.curentropy = count;
if (rp->stats.curentropy > RND_POOLBITS) {
rp->stats.discarded += (rp->stats.curentropy - RND_POOLBITS);
rp->stats.curentropy = RND_POOLBITS;
}
}
void rndpool_get_stats(rndpool_t *rp, void *rsp, int size)
{
memcpy(rsp, &rp->stats, size);
}
/*
* The input function treats the contents of the pool as an array of
* 32 LFSR's of length RND_POOLWORDS, one per bit-plane. The LFSR's
* are clocked once in parallel, using 32-bit xor operations, for each
* word to be added.
*
* Each word to be added is xor'd with the output word of the LFSR
* array (one tap at a time).
*
* In order to facilitate distribution of entropy between the
* bit-planes, a 32-bit rotate of this result is performed prior to
* feedback. The rotation distance is incremented every RND_POOLWORDS
* clocks, 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.
*
* Each LFSR thus takes its feedback from another LFSR, and is
* effectively re-keyed by both that LFSR and the new data. Feedback
* occurs with another XOR into the new LFSR, rather than assignment,
* to avoid destroying any entropy in the destination.
*
* Even with zeros as input, the LFSR output data are never visible;
* the contents of the pool are never divulged except via a hash of
* the entire pool, so there is no information for correlation
* attacks. With rotation-based rekeying, each LFSR runs at most a few
* cycles before being permuted. However, beware of initial
* conditions when no entropy has been added.
*
* The output function also stirs the generated hash back into the
* pool, further permuting the LFSRs and spreading entropy through the
* pool. Any unknown bits anywhere in the pool are thus reflected
* across all the LFSRs after output.
*
* (The final XOR assignment into the pool for feedback is equivalent
* to an additional LFSR tap of the MSB before shifting, in the case
* where no rotation is done, once every 32 cycles. This LFSR runs for
* at most one length.)
*/
static inline void
rndpool_add_one_word(rndpool_t *rp, u_int32_t val)
{
/*
* Shifting is implemented using a cursor and taps as offsets,
* added mod the size of the pool. For this reason,
* RND_POOLWORDS must be a power of two.
*/
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;
/*
* If we have looped around the pool, increment the rotate
* variable so the next value will get xored in rotated to
* a different position.
*/
if (rp->cursor == RND_POOLWORDS) {
rp->cursor = 0;
rp->rotate = (rp->rotate + 7) & 31;
}
}
/*
* Add a buffer's worth of data to the pool.
*/
void
rndpool_add_data(rndpool_t *rp,
const void * const p, u_int32_t len, u_int32_t entropy)
{
u_int32_t val;
const u_int8_t * buf;
buf = p;
for (; len > 3; len -= 4) {
(void)memcpy(&val, buf, 4);
rndpool_add_one_word(rp, val);
buf += 4;
}
if (len != 0) {
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);
}
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 hashing the pool and returning a part of the hash as
* randomness. Stir the hash back into the pool. Note that no
* secrets going back into the pool are given away here since parts of
* the hash are xored together before being returned.
*
* Honor the request from the caller to only return good data, any data,
* etc.
*
* For the "high-quality" mode, we must have as much data as the caller
* requests, and at some point we must have had at least the "threshold"
* amount of entropy in the pool.
*/
u_int32_t
rndpool_extract_data(rndpool_t *rp, void *p, u_int32_t len, u_int32_t mode)
{
u_int i;
SHA1_CTX hash;
u_char digest[SHA1_DIGEST_LENGTH];
u_int32_t remain, deltae, count;
u_int8_t *buf;
buf = p;
remain = len;
KASSERT(RND_ENTROPY_THRESHOLD * 2 <= sizeof(digest));
while (remain != 0 && ! (mode == RND_EXTRACT_GOOD &&
remain > rp->stats.curentropy * 8)) {
/*
* 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);
SHA1Final(digest, &hash);
/*
* 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.
*/
CTASSERT(RND_ENTROPY_THRESHOLD * 2 == SHA1_DIGEST_LENGTH);
for (i = 0; i < SHA1_DIGEST_LENGTH/4; i++) {
u_int32_t word;
memcpy(&word, &digest[i * 4], 4);
rndpool_add_one_word(rp, word);
}
/* XXX careful, here the THRESHOLD just controls folding */
count = min(remain, RND_ENTROPY_THRESHOLD);
for (i = 0; i < count; i++)
buf[i] = digest[i] ^ digest[i + RND_ENTROPY_THRESHOLD];
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;
}
explicit_memset(&hash, 0, sizeof(hash));
explicit_memset(digest, 0, sizeof(digest));
return (len - remain);
}