lib/dns/dnssec.c

	dnssec.c revision 81ab85fd39c3f6c781ecac725d830364a311479d
/*
 * Copyright (C) 1999, 2000  Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/*
 * $Id: dnssec.c,v 1.36 2000/05/17 22:48:00 bwelling Exp $
 * Principal Author: Brian Wellington
 */


#include <config.h>

#include <stdlib.h>

#include <isc/mem.h>
#include <isc/string.h>
#include <isc/util.h>

#include <dns/db.h>
#include <dns/dnssec.h>
#include <dns/keyvalues.h>
#include <dns/message.h>
#include <dns/rdata.h>
#include <dns/rdatalist.h>
#include <dns/rdataset.h>
#include <dns/result.h>
#include <dns/tsig.h>       /* for DNS_TSIG_FUDGE */

#include <dst/result.h>

#define is_response(msg) (msg->flags & DNS_MESSAGEFLAG_QR)

#define RETERR(x) do { \
    result = (x); \
    if (result != ISC_R_SUCCESS) \
        goto failure; \
    } while (0)


#define TYPE_SIGN 0
#define TYPE_VERIFY 1

typedef struct digestctx {
    dst_key_t *key;
    dst_context_t context;
    isc_uint8_t type;
} digestctx_t;

static isc_result_t
digest_callback(void *arg, isc_region_t *data);

static isc_result_t
keyname_to_name(char *keyname, isc_mem_t *mctx, dns_name_t *name);

static int
rdata_compare_wrapper(const void *rdata1, const void *rdata2);

static isc_result_t
rdataset_to_sortedarray(dns_rdataset_t *set, isc_mem_t *mctx,
            dns_rdata_t **rdata, int *nrdata);

static isc_result_t
digest_callback(void *arg, isc_region_t *data) {
    digestctx_t *ctx = arg;
    isc_result_t result;

    REQUIRE(ctx->type == TYPE_SIGN || ctx->type == TYPE_VERIFY);

    if (ctx->type == TYPE_SIGN)
        result = dst_key_sign(DST_SIGMODE_UPDATE, ctx->key,
                      &ctx->context, data, NULL);
    else
        result = dst_key_verify(DST_SIGMODE_UPDATE, ctx->key,
                    &ctx->context, data, NULL);
    return (result);
}

/*
 * Converts the name of a key into a canonical dns_name_t.
 */
static isc_result_t
keyname_to_name(char *keyname, isc_mem_t *mctx, dns_name_t *name) {
    isc_buffer_t src, dst;
    unsigned char data[1024];
    isc_result_t ret;
    dns_name_t tname;

    dns_name_init(name, NULL);
    dns_name_init(&tname, NULL);
    isc_buffer_init(&src, keyname, strlen(keyname));
    isc_buffer_add(&src, strlen(keyname));
    isc_buffer_init(&dst, data, sizeof(data));
    ret = dns_name_fromtext(&tname, &src, NULL, ISC_TRUE, &dst);
    if (ret != ISC_R_SUCCESS)
        return (ret);

    ret = dns_name_dup(&tname, mctx, name);
    dns_name_downcase(name, name, NULL);
    return (ret);
}

/*
 * Make qsort happy.
 */
static int
rdata_compare_wrapper(const void *rdata1, const void *rdata2) {
    return dns_rdata_compare((dns_rdata_t *)rdata1, (dns_rdata_t *)rdata2);
}

/*
 * Sort the rdataset into an array.
 */
static isc_result_t
rdataset_to_sortedarray(dns_rdataset_t *set, isc_mem_t *mctx,
            dns_rdata_t **rdata, int *nrdata)
{
    isc_result_t ret;
    int i = 0, n = 1;
    dns_rdata_t *data;

    ret = dns_rdataset_first(set);
    if (ret != ISC_R_SUCCESS)
        return (ret);
    /*
     * Count the records.
     */
    while (dns_rdataset_next(set) == ISC_R_SUCCESS)
        n++;

    data = isc_mem_get(mctx, n * sizeof(dns_rdata_t));
    if (data == NULL)
        return (ISC_R_NOMEMORY);

    ret = dns_rdataset_first(set);
    if (ret != ISC_R_SUCCESS)
        return (ret);

    /*
     * Put them in the array.
     */
    do {
        dns_rdataset_current(set, &data[i++]);
    } while (dns_rdataset_next(set) == ISC_R_SUCCESS);

    /*
     * Sort the array.
     */
    qsort(data, n, sizeof(dns_rdata_t), rdata_compare_wrapper);
    *rdata = data;
    *nrdata = n;
    return (ISC_R_SUCCESS);
}

isc_result_t
dns_dnssec_keyfromrdata(dns_name_t *name, dns_rdata_t *rdata, isc_mem_t *mctx,
            dst_key_t **key)
{
    isc_buffer_t b, namebuf;
    isc_region_t r;
    isc_result_t ret;
    char namestr[1024];

    INSIST(name != NULL);
    INSIST(rdata != NULL);
    INSIST(mctx != NULL);
    INSIST(key != NULL);
    INSIST(*key == NULL);

    isc_buffer_init(&namebuf, namestr, sizeof(namestr) - 1);
    ret = dns_name_totext(name, ISC_FALSE, &namebuf);
    if (ret != ISC_R_SUCCESS)
        return ret;
    isc_buffer_usedregion(&namebuf, &r);
    namestr[r.length] = 0;
    dns_rdata_toregion(rdata, &r);
    isc_buffer_init(&b, r.base, r.length);
    isc_buffer_add(&b, r.length);
    return (dst_key_fromdns(namestr, &b, mctx, key));
}

isc_result_t
dns_dnssec_sign(dns_name_t *name, dns_rdataset_t *set, dst_key_t *key,
        isc_stdtime_t *inception, isc_stdtime_t *expire,
        isc_mem_t *mctx, isc_buffer_t *buffer, dns_rdata_t *sigrdata)
{
    dns_rdata_sig_t sig;
    dns_rdata_t *rdatas;
    int nrdatas, i;
    isc_buffer_t b, sigbuf, envbuf;
    isc_region_t r;
    dst_context_t ctx = NULL;
    isc_result_t ret;
    unsigned char data[300];
    digestctx_t dctx;
    isc_uint32_t flags;
    unsigned int sigsize;

    REQUIRE(name != NULL);
    REQUIRE(dns_name_depth(name) <= 255);
    REQUIRE(set != NULL);
    REQUIRE(key != NULL);
    REQUIRE(inception != NULL);
    REQUIRE(expire != NULL);
    REQUIRE(mctx != NULL);
    REQUIRE(sigrdata != NULL);

    if (*inception >= *expire)
        return (DNS_R_INVALIDTIME);

    /*
     * Is the key allowed to sign data?
     */
    flags = dst_key_flags(key);
    if (flags & DNS_KEYTYPE_NOAUTH)
        return (DNS_R_KEYUNAUTHORIZED);
    if ((flags & DNS_KEYFLAG_OWNERMASK) != DNS_KEYOWNER_ZONE)
        return (DNS_R_KEYUNAUTHORIZED);

    sig.mctx = mctx;
    sig.common.rdclass = set->rdclass;
    sig.common.rdtype = dns_rdatatype_sig;
    ISC_LINK_INIT(&sig.common, link);

    ret = keyname_to_name(dst_key_name(key), mctx, &sig.signer);
    if (ret != ISC_R_SUCCESS)
        return (ret);

    sig.covered = set->type;
    sig.algorithm = dst_key_alg(key);
    sig.labels = dns_name_depth(name) - 1;
    if (dns_name_iswildcard(name))
        sig.labels--;
    sig.originalttl = set->ttl;
    sig.timesigned = *inception;
    sig.timeexpire = *expire;
    sig.keyid = dst_key_id(key);
    ret = dst_key_sigsize(key, &sigsize);
    if (ret != ISC_R_SUCCESS)
        return (ret);
    sig.siglen = sigsize;
    sig.signature = isc_mem_get(mctx, sig.siglen);
    if (sig.signature == NULL)
        goto cleanup_name;

    isc_buffer_init(&b, data, sizeof(data));
    ret = dns_rdata_fromstruct(NULL, sig.common.rdclass,
                  sig.common.rdtype, &sig, &b);
    if (ret != ISC_R_SUCCESS)
        goto cleanup_signature;

    isc_buffer_usedregion(&b, &r);

    /*
     * Digest the SIG rdata.
     */
    r.length -= sig.siglen;
    ret = dst_key_sign(DST_SIGMODE_INIT | DST_SIGMODE_UPDATE,
               key, &ctx, &r, NULL);

    if (ret != ISC_R_SUCCESS)
        goto cleanup_signature;

    dns_name_toregion(name, &r);

    /*
     * Create an envelope for each rdata: <name|type|class|ttl>.
     */
    isc_buffer_init(&envbuf, data, sizeof(data));
    memcpy(data, r.base, r.length);
    isc_buffer_add(&envbuf, r.length);
    isc_buffer_putuint16(&envbuf, set->type);
    isc_buffer_putuint16(&envbuf, set->rdclass);
    isc_buffer_putuint32(&envbuf, set->ttl);

    memset(&dctx, 0, sizeof(dctx));
    dctx.key = key;
    dctx.context = ctx;
    dctx.type = TYPE_SIGN;

    ret = rdataset_to_sortedarray(set, mctx, &rdatas, &nrdatas);
    if (ret != ISC_R_SUCCESS)
        goto cleanup_signature;
    isc_buffer_usedregion(&envbuf, &r);

    for (i = 0; i < nrdatas; i++) {
        isc_uint16_t len;
        isc_buffer_t lenbuf;
        isc_region_t lenr;

        /*
         * Digest the envelope.
         */
        ret = dst_key_sign(DST_SIGMODE_UPDATE, key, &ctx, &r, NULL);
        if (ret != ISC_R_SUCCESS)
            goto cleanup_array;

        /*
         * Digest the length of the rdata.
         */
        isc_buffer_init(&lenbuf, &len, sizeof(len));
        INSIST(rdatas[i].length < 65536);
        isc_buffer_putuint16(&lenbuf, (isc_uint16_t)rdatas[i].length);
        isc_buffer_usedregion(&lenbuf, &lenr);
        ret = dst_key_sign(DST_SIGMODE_UPDATE, key, &ctx, &lenr, NULL);
        if (ret != ISC_R_SUCCESS)
            goto cleanup_array;

        /*
         * Digest the rdata.
         */
        ret = dns_rdata_digest(&rdatas[i], digest_callback, &dctx);
        if (ret != ISC_R_SUCCESS)
            goto cleanup_array;
    }

    isc_buffer_init(&sigbuf, sig.signature, sig.siglen);
    ret = dst_key_sign(DST_SIGMODE_FINAL, key, &ctx, NULL, &sigbuf);
    if (ret != ISC_R_SUCCESS)
        goto cleanup_array;
    isc_buffer_usedregion(&sigbuf, &r);
    if (r.length != sig.siglen) {
        ret = ISC_R_NOSPACE;
        goto cleanup_array;
    }
    memcpy(sig.signature, r.base, sig.siglen);

    ret = dns_rdata_fromstruct(sigrdata, sig.common.rdclass,
                  sig.common.rdtype, &sig, buffer);

cleanup_array:
    isc_mem_put(mctx, rdatas, nrdatas * sizeof(dns_rdata_t));
cleanup_signature:
    isc_mem_put(mctx, sig.signature, sig.siglen);
cleanup_name:
    dns_name_free(&sig.signer, mctx);

    return (ret);
}

isc_result_t
dns_dnssec_verify(dns_name_t *name, dns_rdataset_t *set, dst_key_t *key,
          isc_boolean_t ignoretime, isc_mem_t *mctx,
          dns_rdata_t *sigrdata)
{
    dns_rdata_sig_t sig;
    dns_fixedname_t fnewname;
    isc_region_t r;
    isc_buffer_t envbuf;
    dns_rdata_t *rdatas;
    int nrdatas, i;
    isc_stdtime_t now;
    isc_result_t ret;
    unsigned char data[300];
    dst_context_t ctx;
    digestctx_t dctx;
    int labels;
    isc_uint32_t flags;

    REQUIRE(name != NULL);
    REQUIRE(set != NULL);
    REQUIRE(key != NULL);
    REQUIRE(mctx != NULL);
    REQUIRE(sigrdata != NULL && sigrdata->type == dns_rdatatype_sig);

    ret = dns_rdata_tostruct(sigrdata, &sig, mctx);
    if (ret != ISC_R_SUCCESS)
        return (ret);

    if (!ignoretime) {
        isc_stdtime_get(&now);

        /*
         * Is SIG temporally valid?
         */
        if (sig.timesigned > now)
            return (DNS_R_SIGFUTURE);
        else if (sig.timeexpire < now)
            return (DNS_R_SIGEXPIRED);
    }

    /*
     * Is the key allowed to sign data?
     */
    flags = dst_key_flags(key);
    if (flags & DNS_KEYTYPE_NOAUTH)
        return (DNS_R_KEYUNAUTHORIZED);
    if ((flags & DNS_KEYFLAG_OWNERMASK) != DNS_KEYOWNER_ZONE)
        return (DNS_R_KEYUNAUTHORIZED);

    /*
     * Digest the SIG rdata (not including the signature).
     */
    dns_rdata_toregion(sigrdata, &r);
    r.length -= sig.siglen;
    RUNTIME_CHECK(r.length >= 19);

    ret = dst_key_verify(DST_SIGMODE_INIT | DST_SIGMODE_UPDATE,
                 key, &ctx, &r, NULL);

    /*
     * If the name is an expanded wildcard, use the wildcard name.
     */
    labels = dns_name_depth(name) - 1;
    if (labels - sig.labels > 0) {
        dns_fixedname_init(&fnewname);
        dns_name_splitatdepth(name, sig.labels + 1, NULL,
                      dns_fixedname_name(&fnewname));
        dns_name_toregion(dns_fixedname_name(&fnewname), &r);
    }
    else
        dns_name_toregion(name, &r);

    /*
     * Create an envelope for each rdata: <name|type|class|ttl>.
     */
    isc_buffer_init(&envbuf, data, sizeof(data));
    if (labels - sig.labels > 0) {
        isc_buffer_putuint8(&envbuf, 1);
        isc_buffer_putuint8(&envbuf, '*');
        memcpy(data + 2, r.base, r.length);
    }
    else
        memcpy(data, r.base, r.length);
    isc_buffer_add(&envbuf, r.length);
    isc_buffer_putuint16(&envbuf, set->type);
    isc_buffer_putuint16(&envbuf, set->rdclass);
    isc_buffer_putuint32(&envbuf, sig.originalttl);

    memset(&dctx, 0, sizeof(dctx));
    dctx.key = key;
    dctx.context = ctx;
    dctx.type = TYPE_VERIFY;

    ret = rdataset_to_sortedarray(set, mctx, &rdatas, &nrdatas);
    if (ret != ISC_R_SUCCESS)
        goto cleanup_struct;
    isc_buffer_usedregion(&envbuf, &r);

    for (i = 0; i < nrdatas; i++) {
        isc_uint16_t len;
        isc_buffer_t lenbuf;
        isc_region_t lenr;

        /*
         * Digest the envelope.
         */
        ret = dst_key_verify(DST_SIGMODE_UPDATE, key, &ctx, &r, NULL);
        if (ret != ISC_R_SUCCESS)
            goto cleanup_array;

        /*
         * Digest the rdata length.
         */
        isc_buffer_init(&lenbuf, &len, sizeof(len));
        INSIST(rdatas[i].length < 65536);
        isc_buffer_putuint16(&lenbuf, (isc_uint16_t)rdatas[i].length);
        isc_buffer_usedregion(&lenbuf, &lenr);

        /*
         * Digest the rdata.
         */
        ret = dst_key_verify(DST_SIGMODE_UPDATE, key, &ctx, &lenr,
                     NULL);
        if (ret != ISC_R_SUCCESS)
            goto cleanup_array;
        ret = dns_rdata_digest(&rdatas[i], digest_callback, &dctx);
        if (ret != ISC_R_SUCCESS)
            goto cleanup_array;
    }

    r.base = sig.signature;
    r.length = sig.siglen;
    ret = dst_key_verify(DST_SIGMODE_FINAL, key, &ctx, NULL, &r);
    if (ret == DST_R_VERIFYFINALFAILURE)
        ret = DNS_R_SIGINVALID;

cleanup_array:
    isc_mem_put(mctx, rdatas, nrdatas * sizeof(dns_rdata_t));
cleanup_struct:
    dns_rdata_freestruct(&sig);

    return (ret);
}

#define is_zone_key(key) ((dst_key_flags(key) & DNS_KEYFLAG_OWNERMASK) \
              == DNS_KEYOWNER_ZONE)

isc_result_t
dns_dnssec_findzonekeys(dns_db_t *db, dns_dbversion_t *ver,
            dns_dbnode_t *node, dns_name_t *name, isc_mem_t *mctx,
            unsigned int maxkeys, dst_key_t **keys,
            unsigned int *nkeys)
{
    dns_rdataset_t rdataset;
    dns_rdata_t rdata;
    isc_result_t result;
    dst_key_t *pubkey = NULL;
    unsigned int count = 0;

    *nkeys = 0;
    dns_rdataset_init(&rdataset);
    RETERR(dns_db_findrdataset(db, node, ver, dns_rdatatype_key, 0, 0,
                   &rdataset, NULL));
    RETERR(dns_rdataset_first(&rdataset));
    while (result == ISC_R_SUCCESS && count < maxkeys) {
        pubkey = NULL;
        dns_rdataset_current(&rdataset, &rdata);
        RETERR(dns_dnssec_keyfromrdata(name, &rdata, mctx, &pubkey));
        if (!is_zone_key(pubkey))
            goto next;
        result = dst_key_fromfile(dst_key_name(pubkey),
                      dst_key_id(pubkey),
                      dst_key_alg(pubkey),
                      DST_TYPE_PRIVATE,
                      mctx, &keys[count]);
        if (result == DST_R_INVALIDPRIVATEKEY)
            goto next;
        if (result != ISC_R_SUCCESS)
            goto failure;
        if ((dst_key_flags(keys[count]) & DNS_KEYTYPE_NOAUTH) != 0) {
            dst_key_free(keys[count]);
            keys[count] = NULL;
            goto next;
        }
        count++;
 next:
        dst_key_free(pubkey);
        pubkey = NULL;
        result = dns_rdataset_next(&rdataset);
    }
    if (result != ISC_R_NOMORE)
        goto failure;
    if (count == 0)
        result = ISC_R_NOTFOUND;
    else
        result = ISC_R_SUCCESS;

 failure:
    if (dns_rdataset_isassociated(&rdataset))
        dns_rdataset_disassociate(&rdataset);
    if (pubkey != NULL)
        dst_key_free(pubkey);
    *nkeys = count;
    return (result);
}

isc_result_t
dns_dnssec_signmessage(dns_message_t *msg, dst_key_t *key) {
    dns_rdata_sig_t sig;
    unsigned char data[512];
    unsigned char header[DNS_MESSAGE_HEADERLEN];
    isc_buffer_t headerbuf, databuf, sigbuf;
    unsigned int sigsize;
    isc_buffer_t *dynbuf;
    dns_name_t signer;
    dns_rdata_t *rdata;
    dns_rdatalist_t *datalist;
    dns_rdataset_t *dataset;
    isc_region_t r;
    isc_stdtime_t now;
    dst_context_t ctx;
    isc_mem_t *mctx;
    isc_result_t result;
    isc_boolean_t signeedsfree = ISC_TRUE;

    REQUIRE(msg != NULL);
    REQUIRE(key != NULL);

    if (is_response(msg))
        REQUIRE(msg->query != NULL);

    mctx = msg->mctx;

    memset(&sig, 0, sizeof(dns_rdata_sig_t));

    sig.mctx = mctx;
    sig.common.rdclass = dns_rdataclass_any;
    sig.common.rdtype = dns_rdatatype_sig;
    ISC_LINK_INIT(&sig.common, link);

    sig.covered = 0;
    sig.algorithm = dst_key_alg(key);
    sig.labels = 0; /* the root name */
    sig.originalttl = 0;

    isc_stdtime_get(&now);
    sig.timesigned = now - DNS_TSIG_FUDGE;
    sig.timeexpire = now + DNS_TSIG_FUDGE;

    sig.keyid = dst_key_id(key);

    dns_name_init(&signer, NULL);
    RETERR(keyname_to_name(dst_key_name(key), mctx, &sig.signer));

    sig.siglen = 0;
    sig.signature = NULL;

    isc_buffer_init(&databuf, data, sizeof(data));

    RETERR(dst_key_sign(DST_SIGMODE_INIT, key, &ctx, NULL, NULL));

    if (is_response(msg))
        RETERR(dst_key_sign(DST_SIGMODE_UPDATE, key, &ctx, msg->query,
                    NULL));

    /*
     * Digest the header.
     */
    isc_buffer_init(&headerbuf, header, sizeof(header));
    dns_message_renderheader(msg, &headerbuf);
    isc_buffer_usedregion(&headerbuf, &r);
    RETERR(dst_key_sign(DST_SIGMODE_UPDATE, key, &ctx, &r, NULL));

    /*
     * Digest the remainder of the message.
     */
    isc_buffer_usedregion(msg->buffer, &r);
    isc_region_consume(&r, DNS_MESSAGE_HEADERLEN);
    RETERR(dst_key_sign(DST_SIGMODE_UPDATE, key, &ctx, &r, NULL));

    /*
     * Digest the fields of the SIG - we can cheat and use
     * dns_rdata_fromstruct.  Since siglen is 0, the digested data
     * is identical to dns format with the last 2 bytes removed.
     */
    RETERR(dns_rdata_fromstruct(NULL, dns_rdataclass_any,
                    dns_rdatatype_sig, &sig, &databuf));
    isc_buffer_usedregion(&databuf, &r);
    r.length -= 2;
    RETERR(dst_key_sign(DST_SIGMODE_UPDATE, key, &ctx, &r, NULL));

    RETERR(dst_key_sigsize(key, &sigsize));
    sig.siglen = sigsize;
    sig.signature = (unsigned char *) isc_mem_get(mctx, sig.siglen);
    if (sig.signature == NULL) {
        result = ISC_R_NOMEMORY;
        goto failure;
    }

    isc_buffer_init(&sigbuf, sig.signature, sig.siglen);
    RETERR(dst_key_sign(DST_SIGMODE_FINAL, key, &ctx, NULL, &sigbuf));

    rdata = NULL;
    RETERR(dns_message_gettemprdata(msg, &rdata));
    dynbuf = NULL;
    RETERR(isc_buffer_allocate(msg->mctx, &dynbuf, 1024));
    RETERR(dns_rdata_fromstruct(rdata, dns_rdataclass_any,
                    dns_rdatatype_sig, &sig, dynbuf));

    dns_rdata_freestruct(&sig);
    signeedsfree = ISC_FALSE;

    dns_message_takebuffer(msg, &dynbuf);

    datalist = NULL;
    RETERR(dns_message_gettemprdatalist(msg, &datalist));
    datalist->rdclass = dns_rdataclass_any;
    datalist->type = dns_rdatatype_sig;
    datalist->covers = 0;
    datalist->ttl = 0;
    ISC_LIST_INIT(datalist->rdata);
    ISC_LIST_APPEND(datalist->rdata, rdata, link);
    dataset = NULL;
    RETERR(dns_message_gettemprdataset(msg, &dataset));
    dns_rdataset_init(dataset);
    dns_rdatalist_tordataset(datalist, dataset);
    msg->sig0 = dataset;

    return (ISC_R_SUCCESS);

failure:
    if (dynbuf != NULL)
        isc_buffer_free(&dynbuf);
    if (signeedsfree)
        dns_rdata_freestruct(&sig);

    return (result);
}

isc_result_t
dns_dnssec_verifymessage(isc_buffer_t *source, dns_message_t *msg,
             dst_key_t *key)
{
    dns_rdata_sig_t sig;
    unsigned char header[DNS_MESSAGE_HEADERLEN];
    dns_rdata_t rdata;
    dns_name_t tname;
    isc_region_t r, r2, source_r, sig_r, header_r;
    isc_stdtime_t now;
    dst_context_t ctx;
    isc_mem_t *mctx;
    isc_result_t result;
    isc_uint16_t addcount;
    isc_boolean_t signeedsfree = ISC_FALSE;

    REQUIRE(source != NULL);
    REQUIRE(msg != NULL);
    REQUIRE(key != NULL);

    if (is_response(msg))
        REQUIRE(msg->query != NULL);

    mctx = msg->mctx;

    msg->verify_attempted = 1;

    isc_buffer_usedregion(source, &source_r);

    RETERR(dns_rdataset_first(msg->sig0));
    dns_rdataset_current(msg->sig0, &rdata);

    RETERR(dns_rdata_tostruct(&rdata, &sig, mctx));
    signeedsfree = ISC_TRUE;

    if (sig.labels != 0) {
        result = DNS_R_SIGINVALID;
        goto failure;
    }

    isc_stdtime_get(&now);
    if (sig.timesigned > now) {
        result = DNS_R_SIGFUTURE;
        msg->sig0status = dns_tsigerror_badtime;
        goto failure;
    }
    else if (sig.timeexpire < now) {
        result = DNS_R_SIGEXPIRED;
        msg->sig0status = dns_tsigerror_badtime;
        goto failure;
    }

    /* XXXBEW ensure that sig.signer refers to this key */

    RETERR(dst_key_verify(DST_SIGMODE_INIT, key, &ctx, NULL, NULL));

    /*
     * If this is a response, digest the query.
     */
    if (is_response(msg))
        RETERR(dst_key_verify(DST_SIGMODE_UPDATE, key, &ctx,
                      msg->query, NULL));

    /*
     * Extract the header.
     */
    memcpy(header, source_r.base, DNS_MESSAGE_HEADERLEN);

    /*
     * Decrement the additional field counter.
     */
    memcpy(&addcount, &header[DNS_MESSAGE_HEADERLEN - 2], 2);
    addcount = htons(ntohs(addcount) - 1);
    memcpy(&header[DNS_MESSAGE_HEADERLEN - 2], &addcount, 2);

    /*
     * Digest the modified header.
     */
    header_r.base = (unsigned char *) header;
    header_r.length = DNS_MESSAGE_HEADERLEN;
    RETERR(dst_key_verify(DST_SIGMODE_UPDATE, key, &ctx, &header_r, NULL));

    /*
     * Digest all non-SIG(0) records.
     */
    r.base = source_r.base + DNS_MESSAGE_HEADERLEN;
    r.length = msg->sigstart - DNS_MESSAGE_HEADERLEN;
    RETERR(dst_key_verify(DST_SIGMODE_UPDATE, key, &ctx, &r, NULL));

    /*
     * Digest the SIG(0) record .  Find the start of the record, skip
     * the name and 10 bytes for class, type, ttl, length to get to
     * the start of the rdata.
     */
    r.base = source_r.base + msg->sigstart;
    r.length = source_r.length - msg->sigstart;
    dns_name_init(&tname, NULL);
    dns_name_fromregion(&tname, &r);
    dns_name_toregion(&tname, &r2);
    isc_region_consume(&r, r2.length + 10);
    r.length -= (sig.siglen + 2);
    RETERR(dst_key_verify(DST_SIGMODE_UPDATE, key, &ctx, &r, NULL));

    sig_r.base = sig.signature;
    sig_r.length = sig.siglen;
    result = dst_key_verify(DST_SIGMODE_FINAL, key, &ctx, NULL, &sig_r);
    if (result != ISC_R_SUCCESS) {
        msg->sig0status = dns_tsigerror_badsig;
        goto failure;
    }

    msg->verified_sig = 1;

    dns_rdata_freestruct(&sig);

    return (ISC_R_SUCCESS);

failure:
    if (signeedsfree)
        dns_rdata_freestruct(&sig);

    return (result);
}