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Niels Möller authored
(yarrow_iterate): New function. (yarrow_fast_reseed): Call yarrow_iterate. Rev: src/nettle/yarrow256.c:1.9
Niels Möller authored(yarrow_iterate): New function. (yarrow_fast_reseed): Call yarrow_iterate. Rev: src/nettle/yarrow256.c:1.9
yarrow256.c 8.23 KiB
/* yarrow256.c
*
* The yarrow pseudo-randomness generator.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2001 Niels Mller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA.
*/
#include "yarrow.h"
#include "macros.h"
#include <assert.h>
#include <string.h>
/* #define YARROW_DEBUG */
#ifdef YARROW_DEBUG
#include <stdio.h>
#endif
/* Parameters */
/* An upper limit on the entropy (in bits) in one octet of sample
* data. */
#define YARROW_MULTIPLIER 4
/* Entropy threshold for reseeding from the fast pool */
#define YARROW_FAST_THRESHOLD 100
/* Entropy threshold for reseeding from the fast pool */
#define YARROW_SLOW_THRESHOLD 160
/* Number of sources that must exceed the threshold for slow reseed */
#define YARROW_SLOW_K 2
/* The number of iterations when reseeding, P_t in the yarrow paper.
* Should be chosen so that reseeding takes on the order of 0.1-1
* seconds. */
#define YARROW_RESEED_ITERATIONS 1500
/* Entropy estimates sticks to this value, it is treated as infinity
* in calculations. It should fit comfortably in an uint32_t, to avoid
* overflows. */
#define YARROW_MAX_ENTROPY 0x100000
void
yarrow256_init(struct yarrow256_ctx *ctx,
unsigned n,
struct yarrow_source *s)
{
sha256_init(&ctx->pools[0]);
sha256_init(&ctx->pools[1]);
unsigned i;
ctx->seeded = 0;
ctx->nsources = n;
ctx->sources = s;
for (i = 0; i<n; i++)
{
ctx->sources[i].estimate[YARROW_FAST] = 0;
ctx->sources[i].estimate[YARROW_SLOW] = 0;
ctx->sources[i].next = YARROW_FAST;
}
}
static void
yarrow_generate_block(struct yarrow256_ctx *ctx,
uint8_t *block)
{
unsigned i;
aes_encrypt(&ctx->key, sizeof(ctx->counter), block, ctx->counter);
/* Increment counter, treating it as a big-endian number. This is
* machine independent, and follows appendix B of the NIST
* specification of cipher modes of operation.
*
* We could keep a representation of thy counter as 4 32-bit values,
* and write entire words (in big-endian byteorder) into the counter
* block, whenever they change. */
for (i = sizeof(ctx->counter); i--; )
{
if (++ctx->counter[i])
break;
}
}
static void
yarrow_iterate(uint8_t *digest)
{
uint8_t v0[SHA256_DIGEST_SIZE];
unsigned i;
memcpy(v0, digest, SHA256_DIGEST_SIZE);
/* When hashed inside the loop, i should run from 1 to
* YARROW_RESEED_ITERATIONS */
for (i = 0; ++i < YARROW_RESEED_ITERATIONS; )
{
uint8_t count[4];
struct sha256_ctx hash;
sha256_init(&hash);
/* Hash v_i | v_0 | i */
WRITE_UINT32(count, i);
sha256_update(&hash, SHA256_DIGEST_SIZE, digest);
sha256_update(&hash, sizeof(v0), v0);
sha256_update(&hash, sizeof(count), count);
sha256_final(&hash);
sha256_digest(&hash, SHA256_DIGEST_SIZE, digest);
}
}
/* NOTE: The SHA-256 digest size equals the AES key size, so we need
* no "size adaptor". */
static void
yarrow_fast_reseed(struct yarrow256_ctx *ctx)
{ uint8_t digest[SHA256_DIGEST_SIZE];
unsigned i;
#ifdef YARROW_DEBUG
fprintf(stderr, "yarrow_fast_reseed\n");
#endif
/* We feed two block of output using the current key into the pool
* before emptying it. */
if (ctx->seeded)
{
uint8_t blocks[AES_BLOCK_SIZE * 2];
yarrow_generate_block(ctx, blocks);
yarrow_generate_block(ctx, blocks + AES_BLOCK_SIZE);
sha256_update(&ctx->pools[YARROW_FAST], sizeof(blocks), blocks);
}
sha256_final(&ctx->pools[YARROW_FAST]);
sha256_digest(&ctx->pools[YARROW_FAST], sizeof(digest), digest);
sha256_init(&ctx->pools[YARROW_FAST]);
/* Iterate */
yarrow_iterate(digest);
aes_set_key(&ctx->key, sizeof(digest), digest);
/* Derive new counter value */
memset(ctx->counter, 0, sizeof(ctx->counter));
aes_encrypt(&ctx->key, sizeof(ctx->counter), ctx->counter, ctx->counter);
/* Reset estimates. */
for (i = 0; i<ctx->nsources; i++)
ctx->sources[i].estimate[YARROW_FAST] = 0;
}
static void
yarrow_slow_reseed(struct yarrow256_ctx *ctx)
{
uint8_t digest[SHA256_DIGEST_SIZE];
unsigned i;
#ifdef YARROW_DEBUG
fprintf(stderr, "yarrow_slow_reseed\n");
#endif
/* Get digest of the slow pool*/
sha256_final(&ctx->pools[YARROW_SLOW]);
sha256_digest(&ctx->pools[YARROW_SLOW], sizeof(digest), digest);
sha256_init(&ctx->pools[YARROW_SLOW]);
/* Feed it into the fast pool */
sha256_update(&ctx->pools[YARROW_SLOW], sizeof(digest), digest);
yarrow_fast_reseed(ctx);
/* Reset estimates. */
for (i = 0; i<ctx->nsources; i++)
ctx->sources[i].estimate[YARROW_SLOW] = 0;
}
void
yarrow256_update(struct yarrow256_ctx *ctx,
unsigned source_index, unsigned entropy,
unsigned length, const uint8_t *data)
{
enum yarrow_pool_id current;
struct yarrow_source *source;
assert(source_index < ctx->nsources);
if (!length)
/* Nothing happens */
return;
source = &ctx->sources[source_index];
if (!ctx->seeded)
/* While seeding, use the slow pool */
current = YARROW_SLOW;
else
{
current = source->next;
source->next = !source->next;
}
sha256_update(&ctx->pools[current], length, data);
/* NOTE: We should be careful to avoid overflows in the estimates. */
if (source->estimate[current] < YARROW_MAX_ENTROPY)
{
if (entropy > YARROW_MAX_ENTROPY)
entropy = YARROW_MAX_ENTROPY;
if ( (length < (YARROW_MAX_ENTROPY / YARROW_MULTIPLIER))
&& (entropy > YARROW_MULTIPLIER * length) )
entropy = YARROW_MULTIPLIER * length;
/* FIXME: Calling a more sophisticated estimater should be done
* here. */
entropy += source->estimate[current];
if (entropy > YARROW_MAX_ENTROPY)
entropy = YARROW_MAX_ENTROPY;
source->estimate[current] = entropy;
}
/* Check for seed/reseed */
switch(current)
{
case YARROW_FAST:
if (source->estimate[YARROW_FAST] >= YARROW_FAST_THRESHOLD)
yarrow_fast_reseed(ctx);
#ifdef YARROW_DEBUG
fprintf(stderr,
"yarrow256_update: source_index = %d,\n"
" fast pool estimate = %d\n",
source_index, source->estimate[YARROW_FAST]);
#endif
break;
case YARROW_SLOW:
{
/* FIXME: This is somewhat inefficient. It would be better to
* either maintain the count, or do this loop only if the
* current source just crossed the threshold. */
unsigned k, i;
for (i = k = 0; i < ctx->nsources; i++)
if (ctx->sources[i].estimate[YARROW_SLOW] >= YARROW_SLOW_THRESHOLD)
k++;
#ifdef YARROW_DEBUG
fprintf(stderr,
"yarrow256_update: source_index = %d,\n"
" slow pool estimate = %d,\n"
" number of sources above threshold = %d\n",
source_index, source->estimate[YARROW_SLOW], k);
#endif
if (k >= YARROW_SLOW_K)
{
yarrow_slow_reseed(ctx);
ctx->seeded = 1;
}
}
}
}
static void
yarrow_gate(struct yarrow256_ctx *ctx)
{
uint8_t key[AES_MAX_KEY_SIZE];
unsigned i;
for (i = 0; i < sizeof(key); i+= AES_BLOCK_SIZE)
yarrow_generate_block(ctx, key + i);
aes_set_key(&ctx->key, sizeof(key), key);
}
void
yarrow256_random(struct yarrow256_ctx *ctx, unsigned length, uint8_t *dst)
{
assert(ctx->seeded);
while (length >= AES_BLOCK_SIZE)
{
yarrow_generate_block(ctx, dst);
dst += AES_BLOCK_SIZE;
length -= AES_BLOCK_SIZE;
}
if (length)
{
uint8_t buffer[AES_BLOCK_SIZE];
assert(length < AES_BLOCK_SIZE);
yarrow_generate_block(ctx, buffer);
memcpy(dst, buffer, length);
}
yarrow_gate(ctx);
}