isc/win32/entropy.c

	entropy.c revision 2d67c2474475acf52c8251dc48bfb7565ee5f2ff
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson/*
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * Copyright (C) 2000, 2001  Internet Software Consortium.
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer *
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * Permission to use, copy, modify, and distribute this software for any
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * purpose with or without fee is hereby granted, provided that the above
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * copyright notice and this permission notice appear in all copies.
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer *
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * INTERNET SOFTWARE CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer */
d3498432822fb487e58f8f72bb5f880dd8307d7dMichael Sawyer
c51203011182577cbb53a6d16d496aa9697fff5cAndreas Gustafsson/* $Id: entropy.c,v 1.1 2001/06/21 14:19:20 tale Exp $ */
c51203011182577cbb53a6d16d496aa9697fff5cAndreas Gustafsson
c51203011182577cbb53a6d16d496aa9697fff5cAndreas Gustafsson/*
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson * This is the system depenedent part of the ISC entropy API.
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson */
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson#include <config.h>
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson
a2b565626ba9a98eecc7b82cb86c6d68c38d3d94Michael Sawyer#include <windows.h>
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson#include <wincrypt.h>
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson#include <process.h>
c51203011182577cbb53a6d16d496aa9697fff5cAndreas Gustafsson#include <io.h>
c51203011182577cbb53a6d16d496aa9697fff5cAndreas Gustafsson#include <share.h>
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson
c51203011182577cbb53a6d16d496aa9697fff5cAndreas Gustafsson/*
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson * There is only one variable in the entropy data structures that is not
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson * system independent, but pulling the structure that uses it into this file
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson * ultimately means pulling several other independent structures here also to
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson * resolve their interdependencies.  Thus only the problem variable's type
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson * is defined here.
5a3e08cbb2fc02f38edd784be8fc0549b92f02e8Michael Sawyer */
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson#define FILESOURCE_HANDLE_TYPE  HCRYPTPROV
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson
0e9dcd548051a8ec34744bfa18b4e09fea742a39Andreas Gustafsson#include "../entropy.c"

static unsigned int
get_from_filesource(isc_entropysource_t *source, isc_uint32_t desired) {
    isc_entropy_t *ent = source->ent;
    unsigned char buf[128];
    HCRYPTPROV hcryptprov = source->sources.file.handle;
    ssize_t ndesired;
    unsigned int added;

    if (source->bad)
        return (0);

    desired = desired / 8 + (((desired & 0x07) > 0) ? 1 : 0);

    added = 0;
    while (desired > 0) {
        ndesired = ISC_MIN(desired, sizeof(buf));
        if(!CryptGenRandom(hcryptprov, ndesired, buf)) {
            CryptReleaseContext(hcryptprov, 0);
            source->bad = ISC_TRUE;
            goto out;
        }

        entropypool_adddata(ent, buf, ndesired, ndesired * 8);
        added += ndesired * 8;
        desired -= ndesired;
    }

 out:
    return (added);
}

static unsigned int
get_from_callback(isc_entropysource_t *source, unsigned int desired,
          isc_boolean_t blocking)
{
    isc_entropy_t *ent = source->ent;
    isc_cbsource_t *cbs = &source->sources.callback;
    unsigned int added;
    unsigned int got;
    isc_result_t result;

    if (desired == 0)
        return (0);

    if (source->bad)
        return (0);

    if (!cbs->start_called && cbs->startfunc != NULL) {
        result = cbs->startfunc(source, cbs->arg, blocking);
        if (result != ISC_R_SUCCESS)
            return (0);
        cbs->start_called = ISC_TRUE;
    }

    added = 0;
    result = ISC_R_SUCCESS;
    while (desired > 0 && result == ISC_R_SUCCESS) {
        result = cbs->getfunc(source, cbs->arg, blocking);
        if (result == ISC_R_QUEUEFULL) {
            got = crunchsamples(ent, &cbs->samplequeue);
            added += got;
            desired -= ISC_MIN(got, desired);
            result = ISC_R_SUCCESS;
        } else if (result != ISC_R_SUCCESS &&
               result != ISC_R_NOTBLOCKING)
            source->bad = ISC_TRUE;

    }

    return (added);
}

/*
 * Poll each source, trying to get data from it to stuff into the entropy
 * pool.
 */
static void
fillpool(isc_entropy_t *ent, unsigned int desired, isc_boolean_t blocking) {
    unsigned int added;
    unsigned int remaining;
    unsigned int needed;
    unsigned int nsource;
    isc_entropysource_t *source;
    isc_entropysource_t *firstsource;

    REQUIRE(VALID_ENTROPY(ent));

    needed = desired;

    /*
     * This logic is a little strange, so an explanation is in order.
     *
     * If needed is 0, it means we are being asked to "fill to whatever
     * we think is best."  This means that if we have at least a
     * partially full pool (say, > 1/4th of the pool) we probably don't
     * need to add anything.
     *
     * Also, we will check to see if the "pseudo" count is too high.
     * If it is, try to mix in better data.  Too high is currently
     * defined as 1/4th of the pool.
     *
     * Next, if we are asked to add a specific bit of entropy, make
     * certain that we will do so.  Clamp how much we try to add to
     * (DIGEST_SIZE * 8 < needed < POOLBITS - entropy).
     *
     * Note that if we are in a blocking mode, we will only try to
     * get as much data as we need, not as much as we might want
     * to build up.
     */
    if (needed == 0) {
        REQUIRE(!blocking);

        if ((ent->pool.entropy >= RND_POOLBITS / 4)
            && (ent->pool.pseudo <= RND_POOLBITS / 4))
            return;

        needed = THRESHOLD_BITS * 4;
    } else {
        needed = ISC_MAX(needed, THRESHOLD_BITS);
        needed = ISC_MIN(needed, RND_POOLBITS);
    }

    /*
     * In any case, clamp how much we need to how much we can add.
     */
    needed = ISC_MIN(needed, RND_POOLBITS - ent->pool.entropy);

    /*
     * But wait!  If we're not yet initialized, we need at least
     *  THRESHOLD_BITS
     * of randomness.
     */
    if (ent->initialized < THRESHOLD_BITS)
        needed = ISC_MAX(needed, THRESHOLD_BITS - ent->initialized);

    /*
     * Poll each file source to see if we can read anything useful from
     * it.  XXXMLG When where are multiple sources, we should keep a
     * record of which one we last used so we can start from it (or the
     * next one) to avoid letting some sources build up entropy while
     * others are always drained.
     */

    added = 0;
    remaining = needed;
    if (ent->nextsource == NULL) {
        ent->nextsource = ISC_LIST_HEAD(ent->sources);
        if (ent->nextsource == NULL)
            return;
    }
    source = ent->nextsource;
    /*
     * Remember the first source so we can break if we have looped back to
     * the beginning and still have nothing
     */
    firstsource = source;
 again_file:
    for (nsource = 0 ; nsource < ent->nsources ; nsource++) {
        unsigned int got;

        if (remaining == 0)
            break;

        got = 0;

        if (source->type == ENTROPY_SOURCETYPE_FILE)
            got = get_from_filesource(source, remaining);

        added += got;

        remaining -= ISC_MIN(remaining, got);

        source = ISC_LIST_NEXT(source, link);
        if (source == NULL)
            source = ISC_LIST_HEAD(ent->sources);
    }
    ent->nextsource = source;

    /*
     * Go again only if there's been progress and we've not
     * gone back to the beginning
     */
    if (!(ent->nextsource == firstsource && added == 0)) {
        if (blocking && remaining != 0) {
                goto again_file;
        }
    }

    /*
     * Here, if there are bits remaining to be had and we can block,
     * check to see if we have a callback source.  If so, call them.
     */
    source = ISC_LIST_HEAD(ent->sources);
    while ((remaining != 0) && (source != NULL)) {
        unsigned int got;

        got = 0;

        if (source->type == ENTROPY_SOURCETYPE_CALLBACK)
            got = get_from_callback(source, remaining, blocking);

        added += got;
        remaining -= ISC_MIN(remaining, got);

        if (added >= needed)
            break;

        source = ISC_LIST_NEXT(source, link);
    }

    /*
     * Mark as initialized if we've added enough data.
     */
    if (ent->initialized < THRESHOLD_BITS)
        ent->initialized += added;
}

/*
 * Extract some number of bytes from the random pool, decreasing the
 * estimate of randomness as each byte is extracted.
 *
 * Do this by stiring the pool and returning a part of hash as randomness.
 * Note that no secrets are given away here since parts of the hash are
 * xored together before returned.
 *
 * Honor the request from the caller to only return good data, any data,
 * etc.
 */
isc_result_t
isc_entropy_getdata(isc_entropy_t *ent, void *data, unsigned int length,
            unsigned int *returned, unsigned int flags)
{
    unsigned int i;
    isc_sha1_t hash;
    unsigned char digest[ISC_SHA1_DIGESTLENGTH];
    isc_uint32_t remain, deltae, count, total;
    isc_uint8_t *buf;
    isc_boolean_t goodonly, partial, blocking;

    REQUIRE(VALID_ENTROPY(ent));
    REQUIRE(data != NULL);
    REQUIRE(length > 0);

    goodonly = ISC_TF((flags & ISC_ENTROPY_GOODONLY) != 0);
    partial = ISC_TF((flags & ISC_ENTROPY_PARTIAL) != 0);
    blocking = ISC_TF((flags & ISC_ENTROPY_BLOCKING) != 0);

    REQUIRE(!partial || returned != NULL);

    LOCK(&ent->lock);

    remain = length;
    buf = data;
    total = 0;
    while (remain != 0) {
        count = ISC_MIN(remain, RND_ENTROPY_THRESHOLD);

        /*
         * If we are extracting good data only, make certain we
         * have enough data in our pool for this pass.  If we don't,
         * get some, and fail if we can't, and partial returns
         * are not ok.
         */
        if (goodonly) {
            unsigned int fillcount;

            fillcount = ISC_MAX(remain * 8, count * 8);

            /*
             * If, however, we have at least THRESHOLD_BITS
             * of entropy in the pool, don't block here.  It is
             * better to drain the pool once in a while and
             * then refill it than it is to constantly keep the
             * pool full.
             */
            if (ent->pool.entropy >= THRESHOLD_BITS)
                fillpool(ent, fillcount, ISC_FALSE);
            else
                fillpool(ent, fillcount, blocking);

            /*
             * Verify that we got enough entropy to do one
             * extraction.  If we didn't, bail.
             */
            if (ent->pool.entropy < THRESHOLD_BITS) {
                if (!partial)
                    goto zeroize;
                else
                    goto partial_output;
            }
        } else {
            /*
             * If we've extracted half our pool size in bits
             * since the last refresh, try to refresh here.
             */
            if (ent->initialized < THRESHOLD_BITS)
                fillpool(ent, THRESHOLD_BITS, blocking);
            else
                fillpool(ent, 0, ISC_FALSE);

            /*
             * If we've not initialized with enough good random
             * data, seed with our crappy code.
             */
            if (ent->initialized < THRESHOLD_BITS)
                reseed(ent);
        }

        isc_sha1_init(&hash);
        isc_sha1_update(&hash, (void *)(ent->pool.pool),
                RND_POOLBYTES);
        isc_sha1_final(&hash, digest);

        /*
         * Stir the extracted data (all of it) back into the pool.
         */
        entropypool_adddata(ent, digest, ISC_SHA1_DIGESTLENGTH, 0);

        for (i = 0; i < count; i++)
            buf[i] = digest[i] ^ digest[i + RND_ENTROPY_THRESHOLD];

        buf += count;
        remain -= count;

        deltae = count * 8;
        deltae = ISC_MIN(deltae, ent->pool.entropy);
        total += deltae;
        subtract_entropy(ent, deltae);
        add_pseudo(ent, count * 8);
    }

 partial_output:
    memset(digest, 0, sizeof(digest));

    if (returned != NULL)
        *returned = (length - remain);

    UNLOCK(&ent->lock);

    return (ISC_R_SUCCESS);

 zeroize:
    /* put the entropy we almost extracted back */
    add_entropy(ent, total);
    memset(data, 0, length);
    memset(digest, 0, sizeof(digest));
    if (returned != NULL)
        *returned = 0;

    UNLOCK(&ent->lock);

    return (ISC_R_NOENTROPY);
}

static void
isc_entropypool_init(isc_entropypool_t *pool) {
    pool->cursor = RND_POOLWORDS - 1;
    pool->entropy = 0;
    pool->pseudo = 0;
    pool->rotate = 0;
    memset(pool->pool, 0, RND_POOLBYTES);
}

static void
isc_entropypool_invalidate(isc_entropypool_t *pool) {
    pool->cursor = 0;
    pool->entropy = 0;
    pool->pseudo = 0;
    pool->rotate = 0;
    memset(pool->pool, 0, RND_POOLBYTES);
}

isc_result_t
isc_entropy_create(isc_mem_t *mctx, isc_entropy_t **entp) {
    isc_result_t ret;
    isc_entropy_t *ent;

    REQUIRE(mctx != NULL);
    REQUIRE(entp != NULL && *entp == NULL);

    ent = isc_mem_get(mctx, sizeof(isc_entropy_t));
    if (ent == NULL)
        return (ISC_R_NOMEMORY);

    /*
     * We need a lock.
     */
    if (isc_mutex_init(&ent->lock) != ISC_R_SUCCESS) {
        ret = ISC_R_UNEXPECTED;
        goto errout;
    }

    /*
     * From here down, no failures will/can occur.
     */
    ISC_LIST_INIT(ent->sources);
    ent->nextsource = NULL;
    ent->nsources = 0;
    ent->mctx = NULL;
    isc_mem_attach(mctx, &ent->mctx);
    ent->refcnt = 1;
    ent->initialized = 0;
    ent->initcount = 0;
    ent->magic = ENTROPY_MAGIC;

    isc_entropypool_init(&ent->pool);

    *entp = ent;
    return (ISC_R_SUCCESS);

 errout:
    isc_mem_put(mctx, ent, sizeof(isc_entropy_t));

    return (ret);
}

/*
 * Requires "ent" be locked.
 */
static void
destroyfilesource(isc_entropyfilesource_t *source) {
    CryptReleaseContext(source->handle, 0);
}

static inline isc_boolean_t
destroy_check(isc_entropy_t *ent) {
    isc_entropysource_t *source;

    if (ent->refcnt > 0)
        return (ISC_FALSE);

    source = ISC_LIST_HEAD(ent->sources);
    while (source != NULL) {
        switch (source->type) {
        case ENTROPY_SOURCETYPE_FILE:
            break;
        default:
            return (ISC_FALSE);
        }
        source = ISC_LIST_NEXT(source, link);
    }

    return (ISC_TRUE);
}

static void
destroy(isc_entropy_t **entp) {
    isc_entropy_t *ent;
    isc_entropysource_t *source;
    isc_mem_t *mctx;

    REQUIRE(entp != NULL && *entp != NULL);
    ent = *entp;
    *entp = NULL;

    LOCK(&ent->lock);

    REQUIRE(ent->refcnt == 0);

    /*
     * Here, detach non-sample sources.
     */
    source = ISC_LIST_HEAD(ent->sources);
    while (source != NULL) {
        switch(source->type) {
        case ENTROPY_SOURCETYPE_FILE:
            destroysource(&source);
            break;
        }
        source = ISC_LIST_HEAD(ent->sources);
    }

    /*
     * If there are other types of sources, we've found a bug.
     */
    REQUIRE(ISC_LIST_EMPTY(ent->sources));

    mctx = ent->mctx;

    isc_entropypool_invalidate(&ent->pool);

    UNLOCK(&ent->lock);

    DESTROYLOCK(&ent->lock);

    memset(ent, 0, sizeof(isc_entropy_t));
    isc_mem_put(mctx, ent, sizeof(isc_entropy_t));
    isc_mem_detach(&mctx);
}


isc_result_t
isc_entropy_createfilesource(isc_entropy_t *ent, const char *fname) {
    isc_result_t ret;
    isc_entropysource_t *source;
    HCRYPTPROV hcryptprov;
    DWORD errval;
    BOOL err;

    REQUIRE(VALID_ENTROPY(ent));
    REQUIRE(fname != NULL);

    LOCK(&ent->lock);

    source = NULL;

    /*
     * The first time we just try to acquire the context
     */
    err = CryptAcquireContext(&hcryptprov, NULL, NULL, PROV_RSA_FULL,
                  CRYPT_VERIFYCONTEXT);
    if(!err){
        errval = GetLastError();
            ret = ISC_R_IOERROR;
            goto errout;
        }

    source = isc_mem_get(ent->mctx, sizeof(isc_entropysource_t));
    if (source == NULL) {
        ret = ISC_R_NOMEMORY;
        goto closecontext;
    }

    /*
     * From here down, no failures can occur.
     */
    source->magic = SOURCE_MAGIC;
    source->type = ENTROPY_SOURCETYPE_FILE;
    source->ent = ent;
    source->total = 0;
    source->bad = ISC_FALSE;
    memset(source->name, 0, sizeof(source->name));
    ISC_LINK_INIT(source, link);
    source->sources.file.handle = hcryptprov;

    /*
     * Hook it into the entropy system.
     */
    ISC_LIST_APPEND(ent->sources, source, link);
    ent->nsources++;

    UNLOCK(&ent->lock);
    return (ISC_R_SUCCESS);

 closecontext:
    CryptReleaseContext(hcryptprov, 0);

 errout:
    if (source != NULL)
        isc_mem_put(ent->mctx, source, sizeof(isc_entropysource_t));

    UNLOCK(&ent->lock);

    return (ret);
}

void
isc_entropy_destroysource(isc_entropysource_t **sourcep) {
    isc_entropysource_t *source;
    isc_entropy_t *ent;
    isc_boolean_t killit;

    REQUIRE(sourcep != NULL);
    REQUIRE(VALID_SOURCE(*sourcep));

    source = *sourcep;
    *sourcep = NULL;

    ent = source->ent;
    REQUIRE(VALID_ENTROPY(ent));

    LOCK(&ent->lock);

    destroysource(&source);

    killit = destroy_check(ent);

    UNLOCK(&ent->lock);

    if (killit)
        destroy(&ent);
}

isc_result_t
isc_entropy_createcallbacksource(isc_entropy_t *ent,
                 isc_entropystart_t start,
                 isc_entropyget_t get,
                 isc_entropystop_t stop,
                 void *arg,
                 isc_entropysource_t **sourcep)
{
    isc_result_t ret;
    isc_entropysource_t *source;
    isc_cbsource_t *cbs;

    REQUIRE(VALID_ENTROPY(ent));
    REQUIRE(get != NULL);
    REQUIRE(sourcep != NULL && *sourcep == NULL);

    LOCK(&ent->lock);

    source = isc_mem_get(ent->mctx, sizeof(isc_entropysource_t));
    if (source == NULL) {
        ret = ISC_R_NOMEMORY;
        goto errout;
    }
    source->bad = ISC_FALSE;

    cbs = &source->sources.callback;

    ret = samplesource_allocate(ent, &cbs->samplequeue);
    if (ret != ISC_R_SUCCESS)
        goto errout;

    cbs->start_called = ISC_FALSE;
    cbs->startfunc = start;
    cbs->getfunc = get;
    cbs->stopfunc = stop;
    cbs->arg = arg;

    /*
     * From here down, no failures can occur.
     */
    source->magic = SOURCE_MAGIC;
    source->type = ENTROPY_SOURCETYPE_CALLBACK;
    source->ent = ent;
    source->total = 0;
    memset(source->name, 0, sizeof(source->name));
    ISC_LINK_INIT(source, link);

    /*
     * Hook it into the entropy system.
     */
    ISC_LIST_APPEND(ent->sources, source, link);
    ent->nsources++;

    *sourcep = source;

    UNLOCK(&ent->lock);
    return (ISC_R_SUCCESS);

 errout:
    if (source != NULL)
        isc_mem_put(ent->mctx, source, sizeof(isc_entropysource_t));

    UNLOCK(&ent->lock);

    return (ret);
}

void
isc_entropy_stopcallbacksources(isc_entropy_t *ent) {
    isc_entropysource_t *source;
    isc_cbsource_t *cbs;

    REQUIRE(VALID_ENTROPY(ent));

    LOCK(&ent->lock);

    source = ISC_LIST_HEAD(ent->sources);
    while (source != NULL) {
        if (source->type == ENTROPY_SOURCETYPE_CALLBACK) {
            cbs = &source->sources.callback;
            if (cbs->start_called && cbs->stopfunc != NULL) {
                cbs->stopfunc(source, cbs->arg);
                cbs->start_called = ISC_FALSE;
            }
        }

        source = ISC_LIST_NEXT(source, link);
    }

    UNLOCK(&ent->lock);
}

isc_result_t
isc_entropy_createsamplesource(isc_entropy_t *ent,
                   isc_entropysource_t **sourcep)
{
    isc_result_t ret;
    isc_entropysource_t *source;
    sample_queue_t *sq;

    REQUIRE(VALID_ENTROPY(ent));
    REQUIRE(sourcep != NULL && *sourcep == NULL);

    LOCK(&ent->lock);

    source = isc_mem_get(ent->mctx, sizeof(isc_entropysource_t));
    if (source == NULL) {
        ret = ISC_R_NOMEMORY;
        goto errout;
    }

    sq = &source->sources.sample.samplequeue;
    ret = samplesource_allocate(ent, sq);
    if (ret != ISC_R_SUCCESS)
        goto errout;

    /*
     * From here down, no failures can occur.
     */
    source->magic = SOURCE_MAGIC;
    source->type = ENTROPY_SOURCETYPE_SAMPLE;
    source->ent = ent;
    source->total = 0;
    memset(source->name, 0, sizeof(source->name));
    ISC_LINK_INIT(source, link);

    /*
     * Hook it into the entropy system.
     */
    ISC_LIST_APPEND(ent->sources, source, link);
    ent->nsources++;

    *sourcep = source;

    UNLOCK(&ent->lock);
    return (ISC_R_SUCCESS);

 errout:
    if (source != NULL)
        isc_mem_put(ent->mctx, source, sizeof(isc_entropysource_t));

    UNLOCK(&ent->lock);

    return (ret);
}

static inline unsigned int
estimate_entropy(sample_queue_t *sq, isc_uint32_t t)
{
    isc_int32_t     delta;
    isc_int32_t     delta2;
    isc_int32_t     delta3;

    /*
     * If the time counter has overflowed, calculate the real difference.
     * If it has not, it is simplier.
     */
    if (t < sq->last_time)
        delta = UINT_MAX - sq->last_time + t;
    else
        delta = sq->last_time - t;

    if (delta < 0)
        delta = -delta;

    /*
     * Calculate the second and third order differentials
     */
    delta2 = sq->last_delta - delta;
    if (delta2 < 0)
        delta2 = -delta2;

    delta3 = sq->last_delta2 - delta2;
    if (delta3 < 0)
        delta3 = -delta3;

    sq->last_time = t;
    sq->last_delta = delta;
    sq->last_delta2 = delta2;

    /*
     * If any delta is 0, we got no entropy.  If all are non-zero, we
     * might have something.
     */
    if (delta == 0 || delta2 == 0 || delta3 == 0)
        return 0;

    /*
     * We could find the smallest delta and claim we got log2(delta)
     * bits, but for now return that we found 1 bit.
     */
    return 1;
}

static unsigned int
crunchsamples(isc_entropy_t *ent, sample_queue_t *sq) {
    unsigned int ns;
    unsigned int added;

    if (sq->nsamples < 6)
        return (0);

    added = 0;
    sq->last_time = sq->samples[0];
    sq->last_delta = 0;
    sq->last_delta2 = 0;

    /*
     * Prime the values by adding in the first 4 samples in.  This
     * should completely initialize the delta calculations.
     */
    for (ns = 0 ; ns < 4 ; ns++)
        (void)estimate_entropy(sq, sq->samples[ns]);

    for (ns = 4 ; ns < sq->nsamples ; ns++)
        added += estimate_entropy(sq, sq->samples[ns]);

    entropypool_adddata(ent, sq->samples, sq->nsamples * 4, added);
    entropypool_adddata(ent, sq->extra, sq->nsamples * 4, 0);

    /*
     * Move the last 4 samples into the first 4 positions, and start
     * adding new samples from that point.
     */
    for (ns = 0 ; ns < 4 ; ns++) {
        sq->samples[ns] = sq->samples[sq->nsamples - 4 + ns];
        sq->extra[ns] = sq->extra[sq->nsamples - 4 + ns];
    }

    sq->nsamples = 4;

    return (added);
}

/*
 * Add a sample, and return ISC_R_SUCCESS if the queue has become full,
 * ISC_R_NOENTROPY if it has space remaining, and ISC_R_NOMORE if the
 * queue was full when this function was called.
 */
static isc_result_t
addsample(sample_queue_t *sq, isc_uint32_t sample, isc_uint32_t extra) {
    if (sq->nsamples >= RND_EVENTQSIZE)
        return (ISC_R_NOMORE);

    sq->samples[sq->nsamples] = sample;
    sq->extra[sq->nsamples] = extra;
    sq->nsamples++;

    if (sq->nsamples >= RND_EVENTQSIZE)
        return (ISC_R_QUEUEFULL);

    return (ISC_R_SUCCESS);
}

isc_result_t
isc_entropy_addsample(isc_entropysource_t *source, isc_uint32_t sample,
              isc_uint32_t extra)
{
    isc_entropy_t *ent;
    sample_queue_t *sq;
    unsigned int entropy;
    isc_result_t result;

    REQUIRE(VALID_SOURCE(source));

    ent = source->ent;

    LOCK(&ent->lock);

    sq = &source->sources.sample.samplequeue;
    result = addsample(sq, sample, extra);
    if (result == ISC_R_QUEUEFULL) {
        entropy = crunchsamples(ent, sq);
        add_entropy(ent, entropy);
    }

    UNLOCK(&ent->lock);

    return (result);
}

isc_result_t
isc_entropy_addcallbacksample(isc_entropysource_t *source, isc_uint32_t sample,
                  isc_uint32_t extra)
{
    sample_queue_t *sq;
    isc_result_t result;

    REQUIRE(VALID_SOURCE(source));
    REQUIRE(source->type == ENTROPY_SOURCETYPE_CALLBACK);

    sq = &source->sources.callback.samplequeue;
    result = addsample(sq, sample, extra);

    return (result);
}

void
isc_entropy_putdata(isc_entropy_t *ent, void *data, unsigned int length,
            isc_uint32_t entropy)
{
    REQUIRE(VALID_ENTROPY(ent));

    LOCK(&ent->lock);

    entropypool_adddata(ent, data, length, entropy);

    if (ent->initialized < THRESHOLD_BITS)
        ent->initialized = THRESHOLD_BITS;

    UNLOCK(&ent->lock);
}

static void
dumpstats(isc_entropy_t *ent, FILE *out) {
    fprintf(out,
        isc_msgcat_get(isc_msgcat, ISC_MSGSET_ENTROPY,
                   ISC_MSG_ENTROPYSTATS,
                   "Entropy pool %p:  refcnt %u cursor %u,"
                   " rotate %u entropy %u pseudo %u nsources %u"
                   " nextsource %p initialized %u initcount %u\n"),
        ent, ent->refcnt,
        ent->pool.cursor, ent->pool.rotate,
        ent->pool.entropy, ent->pool.pseudo,
        ent->nsources, ent->nextsource, ent->initialized,
        ent->initcount);
}

/*
 * This function ignores locking.  Use at your own risk.
 */
void
isc_entropy_stats(isc_entropy_t *ent, FILE *out) {
    REQUIRE(VALID_ENTROPY(ent));

    LOCK(&ent->lock);
    dumpstats(ent, out);
    UNLOCK(&ent->lock);
}

void
isc_entropy_attach(isc_entropy_t *ent, isc_entropy_t **entp) {
    REQUIRE(VALID_ENTROPY(ent));
    REQUIRE(entp != NULL && *entp == NULL);

    LOCK(&ent->lock);

    ent->refcnt++;
    *entp = ent;

    UNLOCK(&ent->lock);
}

void
isc_entropy_detach(isc_entropy_t **entp) {
    isc_entropy_t *ent;
    isc_boolean_t killit;

    REQUIRE(entp != NULL && VALID_ENTROPY(*entp));
    ent = *entp;
    *entp = NULL;

    LOCK(&ent->lock);

    REQUIRE(ent->refcnt > 0);
    ent->refcnt--;

    killit = destroy_check(ent);

    UNLOCK(&ent->lock);

    if (killit)
        destroy(&ent);
}