--- /dev/null
+/*
+ * 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.
+ *
+ * $PostgreSQL$
+ */
+
+#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
+enough_time_passed(FState * st)
+{
+ int ok;
+ struct timeval tv;
+ struct timeval *last = &st->last_reseed_time;
+
+ gettimeofday(&tv, NULL);
+
+ /* check how much time has passed */
+ ok = 0;
+ if (tv.tv_sec > last->tv_sec + 1)
+ ok = 1;
+ else if (tv.tv_sec == last->tv_sec + 1)
+ {
+ if (1000000 + tv.tv_usec - last->tv_usec >= RESEED_INTERVAL)
+ ok = 1;
+ }
+ else if (tv.tv_usec - last->tv_usec >= RESEED_INTERVAL)
+ ok = 1;
+
+ /* reseed will happen, update last_reseed_time */
+ if (ok)
+ 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 && enough_time_passed(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);
+}
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