postgresql/contrib/pgcrypto/fortuna.c
2005-10-15 02:49:52 +00:00

440 lines
8.9 KiB
C

/*
* fortuna.c
* Fortuna-like PRNG.
*
* Copyright (c) 2005 Marko Kreen
* All rights reserved.
*
* 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 AUTHOR 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 AUTHOR 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.
*
* $PostgreSQL: pgsql/contrib/pgcrypto/fortuna.c,v 1.5 2005/10/15 02:49:06 momjian Exp $
*/
#include "postgres.h"
#include <sys/time.h>
#include <time.h>
#include "rijndael.h"
#include "sha2.h"
#include "fortuna.h"
/*
* Why Fortuna-like: There does not seem to be any definitive reference
* on Fortuna in the net. Instead this implementation is based on
* following references:
*
* http://en.wikipedia.org/wiki/Fortuna_(PRNG)
* - Wikipedia article
* http://jlcooke.ca/random/
* - Jean-Luc Cooke Fortuna-based /dev/random driver for Linux.
*/
/*
* There is some confusion about whether and how to carry forward
* the state of the pools. Seems like original Fortuna does not
* do it, resetting hash after each request. I guess expecting
* feeding to happen more often that requesting. This is absolutely
* unsuitable for pgcrypto, as nothing asynchronous happens here.
*
* J.L. Cooke fixed this by feeding previous hash to new re-initialized
* hash context.
*
* Fortuna predecessor Yarrow requires ability to query intermediate
* 'final result' from hash, without affecting it.
*
* This implementation uses the Yarrow method - asking intermediate
* results, but continuing with old state.
*/
/*
* Algorithm parameters
*/
/*
* How many pools.
*
* Original Fortuna uses 32 pools, that means 32'th pool is
* used not earlier than in 13th year. This is a waste in
* pgcrypto, as we have very low-frequancy seeding. Here
* is preferable to have all entropy usable in reasonable time.
*
* With 23 pools, 23th pool is used after 9 days which seems
* more sane.
*
* In our case the minimal cycle time would be bit longer
* than the system-randomness feeding frequency.
*/
#define NUM_POOLS 23
/* in microseconds */
#define RESEED_INTERVAL 100000 /* 0.1 sec */
/* for one big request, reseed after this many bytes */
#define RESEED_BYTES (1024*1024)
/*
* Skip reseed if pool 0 has less than this many
* bytes added since last reseed.
*/
#define POOL0_FILL (256/8)
/*
* Algorithm constants
*/
/* Both cipher key size and hash result size */
#define BLOCK 32
/* cipher block size */
#define CIPH_BLOCK 16
/* for internal wrappers */
#define MD_CTX SHA256_CTX
#define CIPH_CTX rijndael_ctx
struct fortuna_state
{
uint8 counter[CIPH_BLOCK];
uint8 result[CIPH_BLOCK];
uint8 key[BLOCK];
MD_CTX pool[NUM_POOLS];
CIPH_CTX ciph;
unsigned reseed_count;
struct timeval last_reseed_time;
unsigned pool0_bytes;
unsigned rnd_pos;
int counter_init;
};
typedef struct fortuna_state FState;
/*
* Use our own wrappers here.
* - Need to get intermediate result from digest, without affecting it.
* - Need re-set key on a cipher context.
* - Algorithms are guaranteed to exist.
* - No memory allocations.
*/
static void
ciph_init(CIPH_CTX * ctx, const uint8 *key, int klen)
{
rijndael_set_key(ctx, (const uint32 *) key, klen, 1);
}
static void
ciph_encrypt(CIPH_CTX * ctx, const uint8 *in, uint8 *out)
{
rijndael_encrypt(ctx, (const uint32 *) in, (uint32 *) out);
}
static void
md_init(MD_CTX * ctx)
{
SHA256_Init(ctx);
}
static void
md_update(MD_CTX * ctx, const uint8 *data, int len)
{
SHA256_Update(ctx, data, len);
}
static void
md_result(MD_CTX * ctx, uint8 *dst)
{
SHA256_CTX tmp;
memcpy(&tmp, ctx, sizeof(*ctx));
SHA256_Final(dst, &tmp);
memset(&tmp, 0, sizeof(tmp));
}
/*
* initialize state
*/
static void
init_state(FState * st)
{
int i;
memset(st, 0, sizeof(*st));
for (i = 0; i < NUM_POOLS; i++)
md_init(&st->pool[i]);
}
/*
* Endianess does not matter.
* It just needs to change without repeating.
*/
static void
inc_counter(FState * st)
{
uint32 *val = (uint32 *) st->counter;
if (++val[0])
return;
if (++val[1])
return;
if (++val[2])
return;
++val[3];
}
/*
* This is called 'cipher in counter mode'.
*/
static void
encrypt_counter(FState * st, uint8 *dst)
{
ciph_encrypt(&st->ciph, st->counter, dst);
inc_counter(st);
}
/*
* The time between reseed must be at least RESEED_INTERVAL
* microseconds.
*/
static int
too_often(FState * st)
{
int ok;
struct timeval tv;
struct timeval *last = &st->last_reseed_time;
gettimeofday(&tv, NULL);
ok = 0;
if (tv.tv_sec != last->tv_sec)
ok = 1;
else if (tv.tv_usec - last->tv_usec >= RESEED_INTERVAL)
ok = 1;
memcpy(last, &tv, sizeof(tv));
memset(&tv, 0, sizeof(tv));
return ok;
}
/*
* generate new key from all the pools
*/
static void
reseed(FState * st)
{
unsigned k;
unsigned n;
MD_CTX key_md;
uint8 buf[BLOCK];
/* set pool as empty */
st->pool0_bytes = 0;
/*
* Both #0 and #1 reseed would use only pool 0. Just skip #0 then.
*/
n = ++st->reseed_count;
/*
* The goal: use k-th pool only 1/(2^k) of the time.
*/
md_init(&key_md);
for (k = 0; k < NUM_POOLS; k++)
{
md_result(&st->pool[k], buf);
md_update(&key_md, buf, BLOCK);
if (n & 1 || !n)
break;
n >>= 1;
}
/* add old key into mix too */
md_update(&key_md, st->key, BLOCK);
/* now we have new key */
md_result(&key_md, st->key);
/* use new key */
ciph_init(&st->ciph, st->key, BLOCK);
memset(&key_md, 0, sizeof(key_md));
memset(buf, 0, BLOCK);
}
/*
* Pick a random pool. This uses key bytes as random source.
*/
static unsigned
get_rand_pool(FState * st)
{
unsigned rnd;
/*
* This slightly prefers lower pools - thats OK.
*/
rnd = st->key[st->rnd_pos] % NUM_POOLS;
st->rnd_pos++;
if (st->rnd_pos >= BLOCK)
st->rnd_pos = 0;
return rnd;
}
/*
* update pools
*/
static void
add_entropy(FState * st, const uint8 *data, unsigned len)
{
unsigned pos;
uint8 hash[BLOCK];
MD_CTX md;
/* hash given data */
md_init(&md);
md_update(&md, data, len);
md_result(&md, hash);
/*
* Make sure the pool 0 is initialized, then update randomly.
*/
if (st->reseed_count == 0 && st->pool0_bytes < POOL0_FILL)
pos = 0;
else
pos = get_rand_pool(st);
md_update(&st->pool[pos], hash, BLOCK);
if (pos == 0)
st->pool0_bytes += len;
memset(hash, 0, BLOCK);
memset(&md, 0, sizeof(md));
}
/*
* Just take 2 next blocks as new key
*/
static void
rekey(FState * st)
{
encrypt_counter(st, st->key);
encrypt_counter(st, st->key + CIPH_BLOCK);
ciph_init(&st->ciph, st->key, BLOCK);
}
/*
* Fortuna relies on AES standing known-plaintext attack.
* In case it does not, slow down the attacker by initialising
* the couter to random value.
*/
static void
init_counter(FState * st)
{
/* Use next block as counter. */
encrypt_counter(st, st->counter);
/* Hide the key. */
rekey(st);
/* The counter can be shuffled only once. */
st->counter_init = 1;
}
static void
extract_data(FState * st, unsigned count, uint8 *dst)
{
unsigned n;
unsigned block_nr = 0;
/* Can we reseed? */
if (st->pool0_bytes >= POOL0_FILL && !too_often(st))
reseed(st);
/* Is counter initialized? */
if (!st->counter_init)
init_counter(st);
while (count > 0)
{
/* produce bytes */
encrypt_counter(st, st->result);
/* copy result */
if (count > CIPH_BLOCK)
n = CIPH_BLOCK;
else
n = count;
memcpy(dst, st->result, n);
dst += n;
count -= n;
/* must not give out too many bytes with one key */
block_nr++;
if (block_nr > (RESEED_BYTES / CIPH_BLOCK))
{
rekey(st);
block_nr = 0;
}
}
/* Set new key for next request. */
rekey(st);
}
/*
* public interface
*/
static FState main_state;
static int init_done = 0;
void
fortuna_add_entropy(const uint8 *data, unsigned len)
{
if (!init_done)
{
init_state(&main_state);
init_done = 1;
}
if (!data || !len)
return;
add_entropy(&main_state, data, len);
}
void
fortuna_get_bytes(unsigned len, uint8 *dst)
{
if (!init_done)
{
init_state(&main_state);
init_done = 1;
}
if (!dst || !len)
return;
extract_data(&main_state, len, dst);
}