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/*
* cryptographic random number generator for PuTTY's ssh client
*/

#include "putty.h"
#include "ssh.h"
#include <assert.h>

/* Collect environmental noise every 5 minutes */
#define NOISE_REGULAR_INTERVAL (5*60*TICKSPERSEC)

void noise_get_heavy(void (*func) (void *, int));
void noise_get_light(void (*func) (void *, int));

/*
* `pool' itself is a pool of random data which we actually use: we
* return bytes from `pool', at position `poolpos', until `poolpos'
* reaches the end of the pool. At this point we generate more
* random data, by adding noise, stirring well, and resetting
* `poolpos' to point to just past the beginning of the pool (not
* _the_ beginning, since otherwise we'd give away the whole
* contents of our pool, and attackers would just have to guess the
* next lot of noise).
*
* `incomingb' buffers acquired noise data, until it gets full, at
* which point the acquired noise is SHA'ed into `incoming' and
* `incomingb' is cleared. The noise in `incoming' is used as part
* of the noise for each stirring of the pool, in addition to local
* time, process listings, and other such stuff.
*/

#define HASHINPUT 64 /* 64 bytes SHA input */
#define HASHSIZE 20 /* 160 bits SHA output */
#define POOLSIZE 1200 /* size of random pool */

struct RandPool {
    unsigned char pool[POOLSIZE];
    int poolpos;

    unsigned char incoming[HASHSIZE];

    unsigned char incomingb[HASHINPUT];
    int incomingpos;

    int stir_pending;
};

static struct RandPool pool;
int random_active = 0;
long next_noise_collection;

static void random_stir(void)
{
    word32 block[HASHINPUT / sizeof(word32)];
    word32 digest[HASHSIZE / sizeof(word32)];
    int i, j, k;

    /*
* noise_get_light will call random_add_noise, which may call
* back to here. Prevent recursive stirs.
*/
    if (pool.stir_pending)
return;
    pool.stir_pending = TRUE;

    noise_get_light(random_add_noise);

    SHATransform((word32 *) pool.incoming, (word32 *) pool.incomingb);
    pool.incomingpos = 0;

    /*
* Chunks of this code are blatantly endianness-dependent, but
* as it's all random bits anyway, WHO CARES?
*/
    memcpy(digest, pool.incoming, sizeof(digest));

    /*
* Make two passes over the pool.
*/
    for (i = 0; i < 2; i++) {

/*
* We operate SHA in CFB mode, repeatedly adding the same
* block of data to the digest. But we're also fiddling
* with the digest-so-far, so this shouldn't be Bad or
* anything.
*/
memcpy(block, pool.pool, sizeof(block));

/*
* Each pass processes the pool backwards in blocks of
* HASHSIZE, just so that in general we get the output of
* SHA before the corresponding input, in the hope that
* things will be that much less predictable that way
* round, when we subsequently return bytes ...
*/
for (j = POOLSIZE; (j -= HASHSIZE) >= 0;) {
/*
* XOR the bit of the pool we're processing into the
* digest.
*/

for (k = 0; k < sizeof(digest) / sizeof(*digest); k++)
digest[k] ^= ((word32 *) (pool.pool + j))[k];

/*
* Munge our unrevealed first block of the pool into
* it.
*/
SHATransform(digest, block);

/*
* Stick the result back into the pool.
*/

for (k = 0; k < sizeof(digest) / sizeof(*digest); k++)
((word32 *) (pool.pool + j))[k] = digest[k];
}
    }

    /*
* Might as well save this value back into `incoming', just so
* there'll be some extra bizarreness there.
*/
    SHATransform(digest, block);
    memcpy(pool.incoming, digest, sizeof(digest));

    pool.poolpos = sizeof(pool.incoming);

    pool.stir_pending = FALSE;
}

void random_add_noise(void *noise, int length)
{
    unsigned char *p = noise;
    int i;

    if (!random_active)
return;

    /*
* This function processes HASHINPUT bytes into only HASHSIZE
* bytes, so _if_ we were getting incredibly high entropy
* sources then we would be throwing away valuable stuff.
*/
    while (length >= (HASHINPUT - pool.incomingpos)) {
memcpy(pool.incomingb + pool.incomingpos, p,
HASHINPUT - pool.incomingpos);
p += HASHINPUT - pool.incomingpos;
length -= HASHINPUT - pool.incomingpos;
SHATransform((word32 *) pool.incoming, (word32 *) pool.incomingb);
for (i = 0; i < HASHSIZE; i++) {
pool.pool[pool.poolpos++] ^= pool.incomingb[i];
if (pool.poolpos >= POOLSIZE)
pool.poolpos = 0;
}
if (pool.poolpos < HASHSIZE)
random_stir();

pool.incomingpos = 0;
    }

    memcpy(pool.incomingb + pool.incomingpos, p, length);
    pool.incomingpos += length;
}

void random_add_heavynoise(void *noise, int length)
{
    unsigned char *p = noise;
    int i;

    while (length >= POOLSIZE) {
for (i = 0; i < POOLSIZE; i++)
pool.pool[i] ^= *p++;
random_stir();
length -= POOLSIZE;
    }

    for (i = 0; i < length; i++)
pool.pool[i] ^= *p++;
    random_stir();
}

static void random_add_heavynoise_bitbybit(void *noise, int length)
{
    unsigned char *p = noise;
    int i;

    while (length >= POOLSIZE - pool.poolpos) {
for (i = 0; i < POOLSIZE - pool.poolpos; i++)
pool.pool[pool.poolpos + i] ^= *p++;
random_stir();
length -= POOLSIZE - pool.poolpos;
pool.poolpos = 0;
    }

    for (i = 0; i < length; i++)
pool.pool[i] ^= *p++;
    pool.poolpos = i;
}

static void random_timer(void *ctx, long now)
{
    if (random_active > 0 && now - next_noise_collection >= 0) {
noise_regular();
next_noise_collection =
schedule_timer(NOISE_REGULAR_INTERVAL, random_timer, &pool);
    }
}

void random_ref(void)
{
    if (!random_active) {
memset(&pool, 0, sizeof(pool)); /* just to start with */

noise_get_heavy(random_add_heavynoise_bitbybit);
random_stir();

next_noise_collection =
schedule_timer(NOISE_REGULAR_INTERVAL, random_timer, &pool);
    }

    random_active++;
}

void random_unref(void)
{
    random_active--;
    assert(random_active >= 0);
    if (random_active) return;

    expire_timer_context(&pool);
}

int random_byte(void)
{
    if (pool.poolpos >= POOLSIZE)
random_stir();

    return pool.pool[pool.poolpos++];
}

void random_get_savedata(void **data, int *len)
{
    void *buf = snewn(POOLSIZE / 2, char);
    random_stir();
    memcpy(buf, pool.pool + pool.poolpos, POOLSIZE / 2);
    *len = POOLSIZE / 2;
    *data = buf;
    random_stir();
}
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