summaryrefslogtreecommitdiff
path: root/src/resolve/resolved-dns-dnssec.c
blob: a82265ad82119ae95768a92cc1c3dcb736634bf2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2015 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include <gcrypt.h>

#include "alloc-util.h"
#include "dns-domain.h"
#include "resolved-dns-dnssec.h"
#include "resolved-dns-packet.h"
#include "string-table.h"

/* Open question:
 *
 * How does the DNSSEC canonical form of a hostname with a label
 * containing a dot look like, the way DNS-SD does it?
 *
 * TODO:
 *
 *   - Iterative validation
 *   - NSEC proof of non-existance
 *   - NSEC3 proof of non-existance
 *   - Trust anchor store
 *   - wildcard zones
 *   - multi-label zones
 *   - cname support
 *   - DNSSEC bus API extensions
 *   - global + per-interface DNSSEC setting
 *   - DSA support
 *   - EC support?
 *
 * */

#define VERIFY_RRS_MAX 256
#define MAX_KEY_SIZE (32*1024)

/* Permit a maximum clock skew of 1h 10min. This should be enough to deal with DST confusion */
#define SKEW_MAX (1*USEC_PER_HOUR + 10*USEC_PER_MINUTE)

/*
 * The DNSSEC Chain of trust:
 *
 *            Normal RRs are protected via RRSIG RRs in combination with DNSKEY RRs, all in the same zone
 *            DNSKEY RRs are either protected like normal RRs, or via a DS from a zone "higher" up the tree
 *            DS RRs are protected like normal RRs
 *
 * Example chain:
 *            Normal RR → RRSIG/DNSKEY+ → DS → RRSIG/DNSKEY+ → DS → ... → DS → RRSIG/DNSKEY+ → DS
 */

static bool dnssec_algorithm_supported(int algorithm) {
        return IN_SET(algorithm,
                      DNSSEC_ALGORITHM_RSASHA1,
                      DNSSEC_ALGORITHM_RSASHA1_NSEC3_SHA1,
                      DNSSEC_ALGORITHM_RSASHA256,
                      DNSSEC_ALGORITHM_RSASHA512);
}

static bool dnssec_digest_supported(int digest) {
        return IN_SET(digest,
                      DNSSEC_DIGEST_SHA1,
                      DNSSEC_DIGEST_SHA256);
}

uint16_t dnssec_keytag(DnsResourceRecord *dnskey) {
        const uint8_t *p;
        uint32_t sum;
        size_t i;

        /* The algorithm from RFC 4034, Appendix B. */

        assert(dnskey);
        assert(dnskey->key->type == DNS_TYPE_DNSKEY);

        sum = (uint32_t) dnskey->dnskey.flags +
                ((((uint32_t) dnskey->dnskey.protocol) << 8) + (uint32_t) dnskey->dnskey.algorithm);

        p = dnskey->dnskey.key;

        for (i = 0; i < dnskey->dnskey.key_size; i++)
                sum += (i & 1) == 0 ? (uint32_t) p[i] << 8 : (uint32_t) p[i];

        sum += (sum >> 16) & UINT32_C(0xFFFF);

        return sum & UINT32_C(0xFFFF);
}

static int rr_compare(const void *a, const void *b) {
        DnsResourceRecord **x = (DnsResourceRecord**) a, **y = (DnsResourceRecord**) b;
        size_t m;
        int r;

        /* Let's order the RRs according to RFC 4034, Section 6.3 */

        assert(x);
        assert(*x);
        assert((*x)->wire_format);
        assert(y);
        assert(*y);
        assert((*y)->wire_format);

        m = MIN((*x)->wire_format_size, (*y)->wire_format_size);

        r = memcmp((*x)->wire_format, (*y)->wire_format, m);
        if (r != 0)
                return r;

        if ((*x)->wire_format_size < (*y)->wire_format_size)
                return -1;
        else if ((*x)->wire_format_size > (*y)->wire_format_size)
                return 1;

        return 0;
}

static int dnssec_rsa_verify(
                const char *hash_algorithm,
                const void *signature, size_t signature_size,
                const void *data, size_t data_size,
                const void *exponent, size_t exponent_size,
                const void *modulus, size_t modulus_size) {

        gcry_sexp_t public_key_sexp = NULL, data_sexp = NULL, signature_sexp = NULL;
        gcry_mpi_t n = NULL, e = NULL, s = NULL;
        gcry_error_t ge;
        int r;

        assert(hash_algorithm);

        ge = gcry_mpi_scan(&s, GCRYMPI_FMT_USG, signature, signature_size, NULL);
        if (ge != 0) {
                r = -EIO;
                goto finish;
        }

        ge = gcry_mpi_scan(&e, GCRYMPI_FMT_USG, exponent, exponent_size, NULL);
        if (ge != 0) {
                r = -EIO;
                goto finish;
        }

        ge = gcry_mpi_scan(&n, GCRYMPI_FMT_USG, modulus, modulus_size, NULL);
        if (ge != 0) {
                r = -EIO;
                goto finish;
        }

        ge = gcry_sexp_build(&signature_sexp,
                             NULL,
                             "(sig-val (rsa (s %m)))",
                             s);

        if (ge != 0) {
                r = -EIO;
                goto finish;
        }

        ge = gcry_sexp_build(&data_sexp,
                             NULL,
                             "(data (flags pkcs1) (hash %s %b))",
                             hash_algorithm,
                             (int) data_size,
                             data);
        if (ge != 0) {
                r = -EIO;
                goto finish;
        }

        ge = gcry_sexp_build(&public_key_sexp,
                             NULL,
                             "(public-key (rsa (n %m) (e %m)))",
                             n,
                             e);
        if (ge != 0) {
                r = -EIO;
                goto finish;
        }

        ge = gcry_pk_verify(signature_sexp, data_sexp, public_key_sexp);
        if (ge == GPG_ERR_BAD_SIGNATURE)
                r = 0;
        else if (ge != 0)
                r = -EIO;
        else
                r = 1;

finish:
        if (e)
                gcry_mpi_release(e);
        if (n)
                gcry_mpi_release(n);
        if (s)
                gcry_mpi_release(s);

        if (public_key_sexp)
                gcry_sexp_release(public_key_sexp);
        if (signature_sexp)
                gcry_sexp_release(signature_sexp);
        if (data_sexp)
                gcry_sexp_release(data_sexp);

        return r;
}

static void md_add_uint8(gcry_md_hd_t md, uint8_t v) {
        gcry_md_write(md, &v, sizeof(v));
}

static void md_add_uint16(gcry_md_hd_t md, uint16_t v) {
        v = htobe16(v);
        gcry_md_write(md, &v, sizeof(v));
}

static void md_add_uint32(gcry_md_hd_t md, uint32_t v) {
        v = htobe32(v);
        gcry_md_write(md, &v, sizeof(v));
}

static int dnssec_rrsig_expired(DnsResourceRecord *rrsig, usec_t realtime) {
        usec_t expiration, inception, skew;

        assert(rrsig);
        assert(rrsig->key->type == DNS_TYPE_RRSIG);

        if (realtime == USEC_INFINITY)
                realtime = now(CLOCK_REALTIME);

        expiration = rrsig->rrsig.expiration * USEC_PER_SEC;
        inception = rrsig->rrsig.inception * USEC_PER_SEC;

        if (inception > expiration)
                return -EKEYREJECTED;

        /* Permit a certain amount of clock skew of 10% of the valid
         * time range. This takes inspiration from unbound's
         * resolver. */
        skew = (expiration - inception) / 10;
        if (skew > SKEW_MAX)
                skew = SKEW_MAX;

        if (inception < skew)
                inception = 0;
        else
                inception -= skew;

        if (expiration + skew < expiration)
                expiration = USEC_INFINITY;
        else
                expiration += skew;

        return realtime < inception || realtime > expiration;
}

int dnssec_verify_rrset(
                DnsAnswer *a,
                DnsResourceKey *key,
                DnsResourceRecord *rrsig,
                DnsResourceRecord *dnskey,
                usec_t realtime) {

        uint8_t wire_format_name[DNS_WIRE_FOMAT_HOSTNAME_MAX];
        size_t exponent_size, modulus_size, hash_size;
        void *exponent, *modulus, *hash;
        DnsResourceRecord **list, *rr;
        gcry_md_hd_t md = NULL;
        size_t k, n = 0;
        int r;

        assert(key);
        assert(rrsig);
        assert(dnskey);
        assert(rrsig->key->type == DNS_TYPE_RRSIG);
        assert(dnskey->key->type == DNS_TYPE_DNSKEY);

        /* Verifies the the RRSet matching the specified "key" in "a",
         * using the signature "rrsig" and the key "dnskey". It's
         * assumed the RRSIG and DNSKEY match. */

        if (!dnssec_algorithm_supported(rrsig->rrsig.algorithm))
                return -EOPNOTSUPP;

        if (a->n_rrs > VERIFY_RRS_MAX)
                return -E2BIG;

        r = dnssec_rrsig_expired(rrsig, realtime);
        if (r < 0)
                return r;
        if (r > 0)
                return DNSSEC_SIGNATURE_EXPIRED;

        /* Collect all relevant RRs in a single array, so that we can look at the RRset */
        list = newa(DnsResourceRecord *, a->n_rrs);

        DNS_ANSWER_FOREACH(rr, a) {
                r = dns_resource_key_equal(key, rr->key);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                /* We need the wire format for ordering, and digest calculation */
                r = dns_resource_record_to_wire_format(rr, true);
                if (r < 0)
                        return r;

                list[n++] = rr;
        }

        if (n <= 0)
                return -ENODATA;

        /* Bring the RRs into canonical order */
        qsort_safe(list, n, sizeof(DnsResourceRecord), rr_compare);

        /* OK, the RRs are now in canonical order. Let's calculate the digest */
        switch (rrsig->rrsig.algorithm) {

        case DNSSEC_ALGORITHM_RSASHA1:
        case DNSSEC_ALGORITHM_RSASHA1_NSEC3_SHA1:
                gcry_md_open(&md, GCRY_MD_SHA1, 0);
                hash_size = 20;
                break;

        case DNSSEC_ALGORITHM_RSASHA256:
                gcry_md_open(&md, GCRY_MD_SHA256, 0);
                hash_size = 32;
                break;

        case DNSSEC_ALGORITHM_RSASHA512:
                gcry_md_open(&md, GCRY_MD_SHA512, 0);
                hash_size = 64;
                break;

        default:
                assert_not_reached("Unknown digest");
        }

        if (!md)
                return -EIO;

        md_add_uint16(md, rrsig->rrsig.type_covered);
        md_add_uint8(md, rrsig->rrsig.algorithm);
        md_add_uint8(md, rrsig->rrsig.labels);
        md_add_uint32(md, rrsig->rrsig.original_ttl);
        md_add_uint32(md, rrsig->rrsig.expiration);
        md_add_uint32(md, rrsig->rrsig.inception);
        md_add_uint16(md, rrsig->rrsig.key_tag);

        r = dns_name_to_wire_format(rrsig->rrsig.signer, wire_format_name, sizeof(wire_format_name), true);
        if (r < 0)
                goto finish;
        gcry_md_write(md, wire_format_name, r);

        for (k = 0; k < n; k++) {
                size_t l;
                rr = list[k];

                r = dns_name_to_wire_format(DNS_RESOURCE_KEY_NAME(rr->key), wire_format_name, sizeof(wire_format_name), true);
                if (r < 0)
                        goto finish;
                gcry_md_write(md, wire_format_name, r);

                md_add_uint16(md, rr->key->type);
                md_add_uint16(md, rr->key->class);
                md_add_uint32(md, rrsig->rrsig.original_ttl);

                assert(rr->wire_format_rdata_offset <= rr->wire_format_size);
                l = rr->wire_format_size - rr->wire_format_rdata_offset;
                assert(l <= 0xFFFF);

                md_add_uint16(md, (uint16_t) l);
                gcry_md_write(md, (uint8_t*) rr->wire_format + rr->wire_format_rdata_offset, l);
        }

        hash = gcry_md_read(md, 0);
        if (!hash) {
                r = -EIO;
                goto finish;
        }

        if (*(uint8_t*) dnskey->dnskey.key == 0) {
                /* exponent is > 255 bytes long */

                exponent = (uint8_t*) dnskey->dnskey.key + 3;
                exponent_size =
                        ((size_t) (((uint8_t*) dnskey->dnskey.key)[0]) << 8) |
                        ((size_t) ((uint8_t*) dnskey->dnskey.key)[1]);

                if (exponent_size < 256) {
                        r = -EINVAL;
                        goto finish;
                }

                if (3 + exponent_size >= dnskey->dnskey.key_size) {
                        r = -EINVAL;
                        goto finish;
                }

                modulus = (uint8_t*) dnskey->dnskey.key + 3 + exponent_size;
                modulus_size = dnskey->dnskey.key_size - 3 - exponent_size;

        } else {
                /* exponent is <= 255 bytes long */

                exponent = (uint8_t*) dnskey->dnskey.key + 1;
                exponent_size = (size_t) ((uint8_t*) dnskey->dnskey.key)[0];

                if (exponent_size <= 0) {
                        r = -EINVAL;
                        goto finish;
                }

                if (1 + exponent_size >= dnskey->dnskey.key_size) {
                        r = -EINVAL;
                        goto finish;
                }

                modulus = (uint8_t*) dnskey->dnskey.key + 1 + exponent_size;
                modulus_size = dnskey->dnskey.key_size - 1 - exponent_size;
        }

        r = dnssec_rsa_verify(
                        gcry_md_algo_name(gcry_md_get_algo(md)),
                        rrsig->rrsig.signature, rrsig->rrsig.signature_size,
                        hash, hash_size,
                        exponent, exponent_size,
                        modulus, modulus_size);
        if (r < 0)
                goto finish;

        r = r ? DNSSEC_VERIFIED : DNSSEC_INVALID;

finish:
        gcry_md_close(md);
        return r;
}

int dnssec_rrsig_match_dnskey(DnsResourceRecord *rrsig, DnsResourceRecord *dnskey) {

        assert(rrsig);
        assert(dnskey);

        /* Checks if the specified DNSKEY RR matches the key used for
         * the signature in the specified RRSIG RR */

        if (rrsig->key->type != DNS_TYPE_RRSIG)
                return -EINVAL;

        if (dnskey->key->type != DNS_TYPE_DNSKEY)
                return 0;
        if (dnskey->key->class != rrsig->key->class)
                return 0;
        if ((dnskey->dnskey.flags & DNSKEY_FLAG_ZONE_KEY) == 0)
                return 0;
        if (dnskey->dnskey.protocol != 3)
                return 0;
        if (dnskey->dnskey.algorithm != rrsig->rrsig.algorithm)
                return 0;

        if (dnssec_keytag(dnskey) != rrsig->rrsig.key_tag)
                return 0;

        return dns_name_equal(DNS_RESOURCE_KEY_NAME(dnskey->key), DNS_RESOURCE_KEY_NAME(rrsig->key));
}

int dnssec_key_match_rrsig(DnsResourceKey *key, DnsResourceRecord *rrsig) {
        assert(key);
        assert(rrsig);

        /* Checks if the specified RRSIG RR protects the RRSet of the specified RR key. */

        if (rrsig->key->type != DNS_TYPE_RRSIG)
                return 0;
        if (rrsig->key->class != key->class)
                return 0;
        if (rrsig->rrsig.type_covered != key->type)
                return 0;

        return dns_name_equal(DNS_RESOURCE_KEY_NAME(rrsig->key), DNS_RESOURCE_KEY_NAME(key));
}

int dnssec_verify_rrset_search(
                DnsAnswer *a,
                DnsResourceKey *key,
                DnsAnswer *validated_dnskeys,
                usec_t realtime) {

        bool found_rrsig = false, found_dnskey = false;
        DnsResourceRecord *rrsig;
        int r;

        assert(key);

        /* Verifies all RRs from "a" that match the key "key", against DNSKEY RRs in "validated_dnskeys" */

        if (!a || a->n_rrs <= 0)
                return -ENODATA;

        /* Iterate through each RRSIG RR. */
        DNS_ANSWER_FOREACH(rrsig, a) {
                DnsResourceRecord *dnskey;

                r = dnssec_key_match_rrsig(key, rrsig);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                found_rrsig = true;

                DNS_ANSWER_FOREACH(dnskey, validated_dnskeys) {

                        r = dnssec_rrsig_match_dnskey(rrsig, dnskey);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                continue;

                        found_dnskey = true;

                        /* Take the time here, if it isn't set yet, so
                         * that we do all validations with the same
                         * time. */
                        if (realtime == USEC_INFINITY)
                                realtime = now(CLOCK_REALTIME);

                        /* Yay, we found a matching RRSIG with a matching
                         * DNSKEY, awesome. Now let's verify all entries of
                         * the RRSet against the RRSIG and DNSKEY
                         * combination. */

                        r = dnssec_verify_rrset(a, key, rrsig, dnskey, realtime);
                        if (r < 0 && r != EOPNOTSUPP)
                                return r;
                        if (r == DNSSEC_VERIFIED)
                                return DNSSEC_VERIFIED;

                        /* If the signature is invalid, or done using
                           an unsupported algorithm, let's try another
                           key and/or signature. After all they
                           key_tags and stuff are not unique, and
                           might be shared by multiple keys. */
                }
        }

        if (found_dnskey)
                return DNSSEC_INVALID;

        if (found_rrsig)
                return DNSSEC_MISSING_KEY;

        return DNSSEC_NO_SIGNATURE;
}

int dnssec_canonicalize(const char *n, char *buffer, size_t buffer_max) {
        _cleanup_free_ char *s = NULL;
        size_t c = 0;
        int r;

        /* Converts the specified hostname into DNSSEC canonicalized
         * form. */

        if (buffer_max < 2)
                return -ENOBUFS;

        for (;;) {
                size_t i;

                r = dns_label_unescape(&n, buffer, buffer_max);
                if (r < 0)
                        return r;
                if (r == 0)
                        break;
                if (r > 0) {
                        int k;

                        /* DNSSEC validation is always done on the ASCII version of the label */
                        k = dns_label_apply_idna(buffer, r, buffer, buffer_max);
                        if (k < 0)
                                return k;
                        if (k > 0)
                                r = k;
                }

                if (buffer_max < (size_t) r + 2)
                        return -ENOBUFS;

                /* The DNSSEC canonical form is not clear on what to
                 * do with dots appearing in labels, the way DNS-SD
                 * does it. Refuse it for now. */

                if (memchr(buffer, '.', r))
                        return -EINVAL;

                for (i = 0; i < (size_t) r; i ++) {
                        if (buffer[i] >= 'A' && buffer[i] <= 'Z')
                                buffer[i] = buffer[i] - 'A' + 'a';
                }

                buffer[r] = '.';

                buffer += r + 1;
                c += r + 1;

                buffer_max -= r + 1;
        }

        if (c <= 0) {
                /* Not even a single label: this is the root domain name */

                assert(buffer_max > 2);
                buffer[0] = '.';
                buffer[1] = 0;

                return 1;
        }

        return (int) c;
}

int dnssec_verify_dnskey(DnsResourceRecord *dnskey, DnsResourceRecord *ds) {
        gcry_md_hd_t md = NULL;
        char owner_name[DNSSEC_CANONICAL_HOSTNAME_MAX];
        void *result;
        int r;

        assert(dnskey);
        assert(ds);

        /* Implements DNSKEY verification by a DS, according to RFC 4035, section 5.2 */

        if (dnskey->key->type != DNS_TYPE_DNSKEY)
                return -EINVAL;
        if (ds->key->type != DNS_TYPE_DS)
                return -EINVAL;
        if ((dnskey->dnskey.flags & DNSKEY_FLAG_ZONE_KEY) == 0)
                return -EKEYREJECTED;
        if (dnskey->dnskey.protocol != 3)
                return -EKEYREJECTED;

        if (!dnssec_algorithm_supported(dnskey->dnskey.algorithm))
                return -EOPNOTSUPP;
        if (!dnssec_digest_supported(ds->ds.digest_type))
                return -EOPNOTSUPP;

        if (dnskey->dnskey.algorithm != ds->ds.algorithm)
                return 0;
        if (dnssec_keytag(dnskey) != ds->ds.key_tag)
                return 0;

        switch (ds->ds.digest_type) {

        case DNSSEC_DIGEST_SHA1:

                if (ds->ds.digest_size != 20)
                        return 0;

                gcry_md_open(&md, GCRY_MD_SHA1, 0);
                break;

        case DNSSEC_DIGEST_SHA256:

                if (ds->ds.digest_size != 32)
                        return 0;

                gcry_md_open(&md, GCRY_MD_SHA256, 0);
                break;

        default:
                assert_not_reached("Unknown digest");
        }

        if (!md)
                return -EIO;

        r = dnssec_canonicalize(DNS_RESOURCE_KEY_NAME(dnskey->key), owner_name, sizeof(owner_name));
        if (r < 0)
                goto finish;

        gcry_md_write(md, owner_name, r);
        md_add_uint16(md, dnskey->dnskey.flags);
        md_add_uint8(md, dnskey->dnskey.protocol);
        md_add_uint8(md, dnskey->dnskey.algorithm);
        gcry_md_write(md, dnskey->dnskey.key, dnskey->dnskey.key_size);

        result = gcry_md_read(md, 0);
        if (!result) {
                r = -EIO;
                goto finish;
        }

        r = memcmp(result, ds->ds.digest, ds->ds.digest_size) != 0;

finish:
        gcry_md_close(md);
        return r;
}

static const char* const dnssec_mode_table[_DNSSEC_MODE_MAX] = {
        [DNSSEC_NO] = "no",
        [DNSSEC_TRUST] = "trust",
        [DNSSEC_YES] = "yes",
};
DEFINE_STRING_TABLE_LOOKUP(dnssec_mode, DnssecMode);