Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2589 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-dnssec.c b/src/resolve/resolved-dns-dnssec.c
new file mode 100644
index 0000000..a192d82
--- /dev/null
+++ b/src/resolve/resolved-dns-dnssec.c
@@ -0,0 +1,2589 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "alloc-util.h"
+#include "dns-domain.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "gcrypt-util.h"
+#include "hexdecoct.h"
+#include "memory-util.h"
+#include "memstream-util.h"
+#include "openssl-util.h"
+#include "resolved-dns-dnssec.h"
+#include "resolved-dns-packet.h"
+#include "sort-util.h"
+#include "string-table.h"
+
+#if PREFER_OPENSSL && OPENSSL_VERSION_MAJOR >= 3
+#  pragma GCC diagnostic push
+#    pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+DEFINE_TRIVIAL_CLEANUP_FUNC_FULL(RSA*, RSA_free, NULL);
+DEFINE_TRIVIAL_CLEANUP_FUNC_FULL(EC_KEY*, EC_KEY_free, NULL);
+#  pragma GCC diagnostic pop
+#endif
+
+#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)
+
+/* Maximum number of NSEC3 iterations we'll do. RFC5155 says 2500 shall be the maximum useful value, but
+ * RFC9276 § 3.2 says that we should reduce the acceptable iteration count */
+#define NSEC3_ITERATIONS_MAX 100
+
+/*
+ * 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
+ */
+
+uint16_t dnssec_keytag(DnsResourceRecord *dnskey, bool mask_revoke) {
+        const uint8_t *p;
+        uint32_t sum, f;
+
+        /* The algorithm from RFC 4034, Appendix B. */
+
+        assert(dnskey);
+        assert(dnskey->key->type == DNS_TYPE_DNSKEY);
+
+        f = (uint32_t) dnskey->dnskey.flags;
+
+        if (mask_revoke)
+                f &= ~DNSKEY_FLAG_REVOKE;
+
+        sum = f + ((((uint32_t) dnskey->dnskey.protocol) << 8) + (uint32_t) dnskey->dnskey.algorithm);
+
+        p = dnskey->dnskey.key;
+
+        for (size_t 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);
+}
+
+#if HAVE_OPENSSL_OR_GCRYPT
+
+static int rr_compare(DnsResourceRecord * const *a, DnsResourceRecord * const *b) {
+        const DnsResourceRecord *x = *a, *y = *b;
+        size_t m;
+        int r;
+
+        /* Let's order the RRs according to RFC 4034, Section 6.3 */
+
+        assert(x);
+        assert(x->wire_format);
+        assert(y);
+        assert(y->wire_format);
+
+        m = MIN(DNS_RESOURCE_RECORD_RDATA_SIZE(x), DNS_RESOURCE_RECORD_RDATA_SIZE(y));
+
+        r = memcmp(DNS_RESOURCE_RECORD_RDATA(x), DNS_RESOURCE_RECORD_RDATA(y), m);
+        if (r != 0)
+                return r;
+
+        return CMP(DNS_RESOURCE_RECORD_RDATA_SIZE(x), DNS_RESOURCE_RECORD_RDATA_SIZE(y));
+}
+
+static int dnssec_rsa_verify_raw(
+                hash_algorithm_t 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) {
+        int r;
+
+#if PREFER_OPENSSL
+#  pragma GCC diagnostic push
+#    pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+        _cleanup_(RSA_freep) RSA *rpubkey = NULL;
+        _cleanup_(EVP_PKEY_freep) EVP_PKEY *epubkey = NULL;
+        _cleanup_(EVP_PKEY_CTX_freep) EVP_PKEY_CTX *ctx = NULL;
+        _cleanup_(BN_freep) BIGNUM *e = NULL, *m = NULL;
+
+        assert(hash_algorithm);
+
+        e = BN_bin2bn(exponent, exponent_size, NULL);
+        if (!e)
+                return -EIO;
+
+        m = BN_bin2bn(modulus, modulus_size, NULL);
+        if (!m)
+                return -EIO;
+
+        rpubkey = RSA_new();
+        if (!rpubkey)
+                return -ENOMEM;
+
+        if (RSA_set0_key(rpubkey, m, e, NULL) <= 0)
+                return -EIO;
+        e = m = NULL;
+
+        assert((size_t) RSA_size(rpubkey) == signature_size);
+
+        epubkey = EVP_PKEY_new();
+        if (!epubkey)
+                return -ENOMEM;
+
+        if (EVP_PKEY_assign_RSA(epubkey, RSAPublicKey_dup(rpubkey)) <= 0)
+                return -EIO;
+
+        ctx = EVP_PKEY_CTX_new(epubkey, NULL);
+        if (!ctx)
+                return -ENOMEM;
+
+        if (EVP_PKEY_verify_init(ctx) <= 0)
+                return -EIO;
+
+        if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
+                return -EIO;
+
+        if (EVP_PKEY_CTX_set_signature_md(ctx, hash_algorithm) <= 0)
+                return -EIO;
+
+        r = EVP_PKEY_verify(ctx, signature, signature_size, data, data_size);
+        if (r < 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO),
+                                       "Signature verification failed: 0x%lx", ERR_get_error());
+
+#  pragma GCC diagnostic pop
+#else
+        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;
+
+        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 (gpg_err_code(ge) == GPG_ERR_BAD_SIGNATURE)
+                r = 0;
+        else if (ge != 0)
+                r = log_debug_errno(SYNTHETIC_ERRNO(EIO),
+                                    "RSA signature check failed: %s", gpg_strerror(ge));
+        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);
+#endif
+        return r;
+}
+
+static int dnssec_rsa_verify(
+                hash_algorithm_t hash_algorithm,
+                const void *hash, size_t hash_size,
+                DnsResourceRecord *rrsig,
+                DnsResourceRecord *dnskey) {
+
+        size_t exponent_size, modulus_size;
+        void *exponent, *modulus;
+
+        assert(hash_algorithm);
+        assert(hash);
+        assert(hash_size > 0);
+        assert(rrsig);
+        assert(dnskey);
+
+        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)[1]) << 8) |
+                        ((size_t) ((uint8_t*) dnskey->dnskey.key)[2]);
+
+                if (exponent_size < 256)
+                        return -EINVAL;
+
+                if (3 + exponent_size >= dnskey->dnskey.key_size)
+                        return -EINVAL;
+
+                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)
+                        return -EINVAL;
+
+                if (1 + exponent_size >= dnskey->dnskey.key_size)
+                        return -EINVAL;
+
+                modulus = (uint8_t*) dnskey->dnskey.key + 1 + exponent_size;
+                modulus_size = dnskey->dnskey.key_size - 1 - exponent_size;
+        }
+
+        return dnssec_rsa_verify_raw(
+                        hash_algorithm,
+                        rrsig->rrsig.signature, rrsig->rrsig.signature_size,
+                        hash, hash_size,
+                        exponent, exponent_size,
+                        modulus, modulus_size);
+}
+
+static int dnssec_ecdsa_verify_raw(
+                hash_algorithm_t hash_algorithm,
+                elliptic_curve_t curve,
+                const void *signature_r, size_t signature_r_size,
+                const void *signature_s, size_t signature_s_size,
+                const void *data, size_t data_size,
+                const void *key, size_t key_size) {
+        int k;
+
+#if PREFER_OPENSSL
+#  pragma GCC diagnostic push
+#    pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+        _cleanup_(EC_GROUP_freep) EC_GROUP *ec_group = NULL;
+        _cleanup_(EC_POINT_freep) EC_POINT *p = NULL;
+        _cleanup_(EC_KEY_freep) EC_KEY *eckey = NULL;
+        _cleanup_(BN_CTX_freep) BN_CTX *bctx = NULL;
+        _cleanup_(BN_freep) BIGNUM *r = NULL, *s = NULL;
+        _cleanup_(ECDSA_SIG_freep) ECDSA_SIG *sig = NULL;
+
+        assert(hash_algorithm);
+
+        ec_group = EC_GROUP_new_by_curve_name(curve);
+        if (!ec_group)
+                return -ENOMEM;
+
+        p = EC_POINT_new(ec_group);
+        if (!p)
+                return -ENOMEM;
+
+        bctx = BN_CTX_new();
+        if (!bctx)
+                return -ENOMEM;
+
+        if (EC_POINT_oct2point(ec_group, p, key, key_size, bctx) <= 0)
+                return -EIO;
+
+        eckey = EC_KEY_new();
+        if (!eckey)
+                return -ENOMEM;
+
+        if (EC_KEY_set_group(eckey, ec_group) <= 0)
+                return -EIO;
+
+        if (EC_KEY_set_public_key(eckey, p) <= 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO),
+                                       "EC_POINT_bn2point failed: 0x%lx", ERR_get_error());
+
+        assert(EC_KEY_check_key(eckey) == 1);
+
+        r = BN_bin2bn(signature_r, signature_r_size, NULL);
+        if (!r)
+                return -EIO;
+
+        s = BN_bin2bn(signature_s, signature_s_size, NULL);
+        if (!s)
+                return -EIO;
+
+        /* TODO: We should eventually use the EVP API once it supports ECDSA signature verification */
+
+        sig = ECDSA_SIG_new();
+        if (!sig)
+                return -ENOMEM;
+
+        if (ECDSA_SIG_set0(sig, r, s) <= 0)
+                return -EIO;
+        r = s = NULL;
+
+        k = ECDSA_do_verify(data, data_size, sig, eckey);
+        if (k < 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO),
+                                       "Signature verification failed: 0x%lx", ERR_get_error());
+
+#  pragma GCC diagnostic pop
+#else
+        gcry_sexp_t public_key_sexp = NULL, data_sexp = NULL, signature_sexp = NULL;
+        gcry_mpi_t q = NULL, r = NULL, s = NULL;
+        gcry_error_t ge;
+
+        assert(hash_algorithm);
+
+        ge = gcry_mpi_scan(&r, GCRYMPI_FMT_USG, signature_r, signature_r_size, NULL);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_mpi_scan(&s, GCRYMPI_FMT_USG, signature_s, signature_s_size, NULL);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_mpi_scan(&q, GCRYMPI_FMT_USG, key, key_size, NULL);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_sexp_build(&signature_sexp,
+                             NULL,
+                             "(sig-val (ecdsa (r %m) (s %m)))",
+                             r,
+                             s);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_sexp_build(&data_sexp,
+                             NULL,
+                             "(data (flags rfc6979) (hash %s %b))",
+                             hash_algorithm,
+                             (int) data_size,
+                             data);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_sexp_build(&public_key_sexp,
+                             NULL,
+                             "(public-key (ecc (curve %s) (q %m)))",
+                             curve,
+                             q);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_pk_verify(signature_sexp, data_sexp, public_key_sexp);
+        if (gpg_err_code(ge) == GPG_ERR_BAD_SIGNATURE)
+                k = 0;
+        else if (ge != 0) {
+                log_debug("ECDSA signature check failed: %s", gpg_strerror(ge));
+                k = -EIO;
+        } else
+                k = 1;
+finish:
+        if (r)
+                gcry_mpi_release(r);
+        if (s)
+                gcry_mpi_release(s);
+        if (q)
+                gcry_mpi_release(q);
+
+        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);
+#endif
+        return k;
+}
+
+static int dnssec_ecdsa_verify(
+                hash_algorithm_t hash_algorithm,
+                int algorithm,
+                const void *hash, size_t hash_size,
+                DnsResourceRecord *rrsig,
+                DnsResourceRecord *dnskey) {
+
+        elliptic_curve_t curve;
+        size_t key_size;
+        uint8_t *q;
+
+        assert(hash);
+        assert(hash_size);
+        assert(rrsig);
+        assert(dnskey);
+
+        if (algorithm == DNSSEC_ALGORITHM_ECDSAP256SHA256) {
+                curve = OPENSSL_OR_GCRYPT(NID_X9_62_prime256v1, "NIST P-256");  /* NIST P-256 */
+                key_size = 32;
+        } else if (algorithm == DNSSEC_ALGORITHM_ECDSAP384SHA384) {
+                curve = OPENSSL_OR_GCRYPT(NID_secp384r1, "NIST P-384");         /* NIST P-384 */
+                key_size = 48;
+        } else
+                return -EOPNOTSUPP;
+
+        if (dnskey->dnskey.key_size != key_size * 2)
+                return -EINVAL;
+
+        if (rrsig->rrsig.signature_size != key_size * 2)
+                return -EINVAL;
+
+        q = newa(uint8_t, key_size*2 + 1);
+        q[0] = 0x04; /* Prepend 0x04 to indicate an uncompressed key */
+        memcpy(q+1, dnskey->dnskey.key, key_size*2);
+
+        return dnssec_ecdsa_verify_raw(
+                        hash_algorithm,
+                        curve,
+                        rrsig->rrsig.signature, key_size,
+                        (uint8_t*) rrsig->rrsig.signature + key_size, key_size,
+                        hash, hash_size,
+                        q, key_size*2+1);
+}
+
+static int dnssec_eddsa_verify_raw(
+                elliptic_curve_t curve,
+                const uint8_t *signature, size_t signature_size,
+                const uint8_t *data, size_t data_size,
+                const uint8_t *key, size_t key_size) {
+
+#if PREFER_OPENSSL
+        _cleanup_(EVP_PKEY_freep) EVP_PKEY *evkey = NULL;
+        _cleanup_(EVP_PKEY_CTX_freep) EVP_PKEY_CTX *pctx = NULL;
+        _cleanup_(EVP_MD_CTX_freep) EVP_MD_CTX *ctx = NULL;
+        int r;
+
+        assert(curve == NID_ED25519);
+        assert(signature_size == key_size * 2);
+
+        uint8_t *q = newa(uint8_t, signature_size + 1);
+        q[0] = 0x04; /* Prepend 0x04 to indicate an uncompressed key */
+        memcpy(q+1, signature, signature_size);
+
+        evkey = EVP_PKEY_new_raw_public_key(EVP_PKEY_ED25519, NULL, key, key_size);
+        if (!evkey)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO),
+                                       "EVP_PKEY_new_raw_public_key failed: 0x%lx", ERR_get_error());
+
+        pctx = EVP_PKEY_CTX_new(evkey, NULL);
+        if (!pctx)
+                return -ENOMEM;
+
+        ctx = EVP_MD_CTX_new();
+        if (!ctx)
+                return -ENOMEM;
+
+        /* This prevents EVP_DigestVerifyInit from managing pctx and complicating our free logic. */
+        EVP_MD_CTX_set_pkey_ctx(ctx, pctx);
+
+        /* One might be tempted to use EVP_PKEY_verify_init, but see Ed25519(7ssl). */
+        if (EVP_DigestVerifyInit(ctx, &pctx, NULL, NULL, evkey) <= 0)
+                return -EIO;
+
+        r = EVP_DigestVerify(ctx, signature, signature_size, data, data_size);
+        if (r < 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EIO),
+                                       "Signature verification failed: 0x%lx", ERR_get_error());
+
+        return r;
+
+#elif GCRYPT_VERSION_NUMBER >= 0x010600
+        gcry_sexp_t public_key_sexp = NULL, data_sexp = NULL, signature_sexp = NULL;
+        gcry_error_t ge;
+        int k;
+
+        assert(signature_size == key_size * 2);
+
+        ge = gcry_sexp_build(&signature_sexp,
+                             NULL,
+                             "(sig-val (eddsa (r %b) (s %b)))",
+                             (int) key_size,
+                             signature,
+                             (int) key_size,
+                             signature + key_size);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_sexp_build(&data_sexp,
+                             NULL,
+                             "(data (flags eddsa) (hash-algo sha512) (value %b))",
+                             (int) data_size,
+                             data);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_sexp_build(&public_key_sexp,
+                             NULL,
+                             "(public-key (ecc (curve %s) (flags eddsa) (q %b)))",
+                             curve,
+                             (int) key_size,
+                             key);
+        if (ge != 0) {
+                k = -EIO;
+                goto finish;
+        }
+
+        ge = gcry_pk_verify(signature_sexp, data_sexp, public_key_sexp);
+        if (gpg_err_code(ge) == GPG_ERR_BAD_SIGNATURE)
+                k = 0;
+        else if (ge != 0)
+                k = log_debug_errno(SYNTHETIC_ERRNO(EIO),
+                                    "EdDSA signature check failed: %s", gpg_strerror(ge));
+        else
+                k = 1;
+finish:
+        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 k;
+#else
+        return -EOPNOTSUPP;
+#endif
+}
+
+static int dnssec_eddsa_verify(
+                int algorithm,
+                const void *data, size_t data_size,
+                DnsResourceRecord *rrsig,
+                DnsResourceRecord *dnskey) {
+        elliptic_curve_t curve;
+        size_t key_size;
+
+        if (algorithm == DNSSEC_ALGORITHM_ED25519) {
+                curve = OPENSSL_OR_GCRYPT(NID_ED25519, "Ed25519");
+                key_size = 32;
+        } else
+                return -EOPNOTSUPP;
+
+        if (dnskey->dnskey.key_size != key_size)
+                return -EINVAL;
+
+        if (rrsig->rrsig.signature_size != key_size * 2)
+                return -EINVAL;
+
+        return dnssec_eddsa_verify_raw(
+                        curve,
+                        rrsig->rrsig.signature, rrsig->rrsig.signature_size,
+                        data, data_size,
+                        dnskey->dnskey.key, key_size);
+}
+
+static int md_add_uint8(hash_context_t ctx, uint8_t v) {
+#if PREFER_OPENSSL
+        return EVP_DigestUpdate(ctx, &v, sizeof(v));
+#else
+        gcry_md_write(ctx, &v, sizeof(v));
+        return 0;
+#endif
+}
+
+static int md_add_uint16(hash_context_t ctx, uint16_t v) {
+        v = htobe16(v);
+#if PREFER_OPENSSL
+        return EVP_DigestUpdate(ctx, &v, sizeof(v));
+#else
+        gcry_md_write(ctx, &v, sizeof(v));
+        return 0;
+#endif
+}
+
+static void fwrite_uint8(FILE *fp, uint8_t v) {
+        fwrite(&v, sizeof(v), 1, fp);
+}
+
+static void fwrite_uint16(FILE *fp, uint16_t v) {
+        v = htobe16(v);
+        fwrite(&v, sizeof(v), 1, fp);
+}
+
+static void fwrite_uint32(FILE *fp, uint32_t v) {
+        v = htobe32(v);
+        fwrite(&v, sizeof(v), 1, fp);
+}
+
+static int dnssec_rrsig_prepare(DnsResourceRecord *rrsig) {
+        int n_key_labels, n_signer_labels;
+        const char *name;
+        int r;
+
+        /* Checks whether the specified RRSIG RR is somewhat valid, and initializes the .n_skip_labels_source
+         * and .n_skip_labels_signer fields so that we can use them later on. */
+
+        assert(rrsig);
+        assert(rrsig->key->type == DNS_TYPE_RRSIG);
+
+        /* Check if this RRSIG RR is already prepared */
+        if (rrsig->n_skip_labels_source != UINT8_MAX)
+                return 0;
+
+        if (rrsig->rrsig.inception > rrsig->rrsig.expiration)
+                return -EINVAL;
+
+        name = dns_resource_key_name(rrsig->key);
+
+        n_key_labels = dns_name_count_labels(name);
+        if (n_key_labels < 0)
+                return n_key_labels;
+        if (rrsig->rrsig.labels > n_key_labels)
+                return -EINVAL;
+
+        n_signer_labels = dns_name_count_labels(rrsig->rrsig.signer);
+        if (n_signer_labels < 0)
+                return n_signer_labels;
+        if (n_signer_labels > rrsig->rrsig.labels)
+                return -EINVAL;
+
+        r = dns_name_skip(name, n_key_labels - n_signer_labels, &name);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return -EINVAL;
+
+        /* Check if the signer is really a suffix of us */
+        r = dns_name_equal(name, rrsig->rrsig.signer);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return -EINVAL;
+
+        assert(n_key_labels < UINT8_MAX); /* UINT8_MAX/-1 means unsigned. */
+        rrsig->n_skip_labels_source = n_key_labels - rrsig->rrsig.labels;
+        rrsig->n_skip_labels_signer = n_key_labels - n_signer_labels;
+
+        return 0;
+}
+
+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;
+
+        /* Consider inverted validity intervals as expired */
+        if (inception > expiration)
+                return true;
+
+        /* 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;
+}
+
+static hash_md_t algorithm_to_implementation_id(uint8_t algorithm) {
+
+        /* Translates a DNSSEC signature algorithm into an openssl/gcrypt digest identifier.
+         *
+         * Note that we implement all algorithms listed as "Must implement" and "Recommended to Implement" in
+         * RFC6944. We don't implement any algorithms that are listed as "Optional" or "Must Not Implement".
+         * Specifically, we do not implement RSAMD5, DSASHA1, DH, DSA-NSEC3-SHA1, and GOST-ECC. */
+
+        switch (algorithm) {
+
+        case DNSSEC_ALGORITHM_RSASHA1:
+        case DNSSEC_ALGORITHM_RSASHA1_NSEC3_SHA1:
+                return OPENSSL_OR_GCRYPT(EVP_sha1(), GCRY_MD_SHA1);
+
+        case DNSSEC_ALGORITHM_RSASHA256:
+        case DNSSEC_ALGORITHM_ECDSAP256SHA256:
+                return OPENSSL_OR_GCRYPT(EVP_sha256(), GCRY_MD_SHA256);
+
+        case DNSSEC_ALGORITHM_ECDSAP384SHA384:
+                return OPENSSL_OR_GCRYPT(EVP_sha384(), GCRY_MD_SHA384);
+
+        case DNSSEC_ALGORITHM_RSASHA512:
+                return OPENSSL_OR_GCRYPT(EVP_sha512(), GCRY_MD_SHA512);
+
+        default:
+                return OPENSSL_OR_GCRYPT(NULL, -EOPNOTSUPP);
+        }
+}
+
+static void dnssec_fix_rrset_ttl(
+                DnsResourceRecord *list[],
+                unsigned n,
+                DnsResourceRecord *rrsig) {
+
+        assert(list);
+        assert(n > 0);
+        assert(rrsig);
+
+        for (unsigned k = 0; k < n; k++) {
+                DnsResourceRecord *rr = list[k];
+
+                /* Pick the TTL as the minimum of the RR's TTL, the
+                 * RR's original TTL according to the RRSIG and the
+                 * RRSIG's own TTL, see RFC 4035, Section 5.3.3 */
+                rr->ttl = MIN3(rr->ttl, rrsig->rrsig.original_ttl, rrsig->ttl);
+                rr->expiry = rrsig->rrsig.expiration * USEC_PER_SEC;
+
+                /* Copy over information about the signer and wildcard source of synthesis */
+                rr->n_skip_labels_source = rrsig->n_skip_labels_source;
+                rr->n_skip_labels_signer = rrsig->n_skip_labels_signer;
+        }
+
+        rrsig->expiry = rrsig->rrsig.expiration * USEC_PER_SEC;
+}
+
+static int dnssec_rrset_serialize_sig(
+                DnsResourceRecord *rrsig,
+                const char *source,
+                DnsResourceRecord **list,
+                size_t list_len,
+                bool wildcard,
+                char **ret_sig_data,
+                size_t *ret_sig_size) {
+
+        _cleanup_(memstream_done) MemStream m = {};
+        uint8_t wire_format_name[DNS_WIRE_FORMAT_HOSTNAME_MAX];
+        DnsResourceRecord *rr;
+        FILE *f;
+        int r;
+
+        assert(rrsig);
+        assert(source);
+        assert(list || list_len == 0);
+        assert(ret_sig_data);
+        assert(ret_sig_size);
+
+        f = memstream_init(&m);
+        if (!f)
+                return -ENOMEM;
+
+        fwrite_uint16(f, rrsig->rrsig.type_covered);
+        fwrite_uint8(f, rrsig->rrsig.algorithm);
+        fwrite_uint8(f, rrsig->rrsig.labels);
+        fwrite_uint32(f, rrsig->rrsig.original_ttl);
+        fwrite_uint32(f, rrsig->rrsig.expiration);
+        fwrite_uint32(f, rrsig->rrsig.inception);
+        fwrite_uint16(f, rrsig->rrsig.key_tag);
+
+        r = dns_name_to_wire_format(rrsig->rrsig.signer, wire_format_name, sizeof(wire_format_name), true);
+        if (r < 0)
+                return r;
+        fwrite(wire_format_name, 1, r, f);
+
+        /* Convert the source of synthesis into wire format */
+        r = dns_name_to_wire_format(source, wire_format_name, sizeof(wire_format_name), true);
+        if (r < 0)
+                return r;
+
+        for (size_t k = 0; k < list_len; k++) {
+                size_t l;
+
+                rr = list[k];
+
+                /* Hash the source of synthesis. If this is a wildcard, then prefix it with the *. label */
+                if (wildcard)
+                        fwrite((uint8_t[]) { 1, '*'}, sizeof(uint8_t), 2, f);
+                fwrite(wire_format_name, 1, r, f);
+
+                fwrite_uint16(f, rr->key->type);
+                fwrite_uint16(f, rr->key->class);
+                fwrite_uint32(f, rrsig->rrsig.original_ttl);
+
+                l = DNS_RESOURCE_RECORD_RDATA_SIZE(rr);
+                assert(l <= 0xFFFF);
+
+                fwrite_uint16(f, (uint16_t) l);
+                fwrite(DNS_RESOURCE_RECORD_RDATA(rr), 1, l, f);
+        }
+
+        return memstream_finalize(&m, ret_sig_data, ret_sig_size);
+}
+
+static int dnssec_rrset_verify_sig(
+                DnsResourceRecord *rrsig,
+                DnsResourceRecord *dnskey,
+                const char *sig_data,
+                size_t sig_size) {
+
+        assert(rrsig);
+        assert(dnskey);
+        assert(sig_data);
+        assert(sig_size > 0);
+
+        hash_md_t md_algorithm;
+
+#if PREFER_OPENSSL
+        uint8_t hash[EVP_MAX_MD_SIZE];
+        unsigned hash_size;
+#else
+        _cleanup_(gcry_md_closep) gcry_md_hd_t md = NULL;
+        void *hash;
+        size_t hash_size;
+
+        initialize_libgcrypt(false);
+#endif
+
+        switch (rrsig->rrsig.algorithm) {
+        case DNSSEC_ALGORITHM_ED25519:
+#if PREFER_OPENSSL || GCRYPT_VERSION_NUMBER >= 0x010600
+                return dnssec_eddsa_verify(
+                                rrsig->rrsig.algorithm,
+                                sig_data, sig_size,
+                                rrsig,
+                                dnskey);
+#endif
+        case DNSSEC_ALGORITHM_ED448:
+                return -EOPNOTSUPP;
+        default:
+                /* OK, the RRs are now in canonical order. Let's calculate the digest */
+                md_algorithm = algorithm_to_implementation_id(rrsig->rrsig.algorithm);
+#if PREFER_OPENSSL
+                if (!md_algorithm)
+                        return -EOPNOTSUPP;
+
+                _cleanup_(EVP_MD_CTX_freep) EVP_MD_CTX *ctx = EVP_MD_CTX_new();
+                if (!ctx)
+                        return -ENOMEM;
+
+                if (EVP_DigestInit_ex(ctx, md_algorithm, NULL) <= 0)
+                        return -EIO;
+
+                if (EVP_DigestUpdate(ctx, sig_data, sig_size) <= 0)
+                        return -EIO;
+
+                if (EVP_DigestFinal_ex(ctx, hash, &hash_size) <= 0)
+                        return -EIO;
+
+                assert(hash_size > 0);
+
+#else
+                if (md_algorithm < 0)
+                        return md_algorithm;
+
+                gcry_error_t err = gcry_md_open(&md, md_algorithm, 0);
+                if (gcry_err_code(err) != GPG_ERR_NO_ERROR || !md)
+                        return -EIO;
+
+                hash_size = gcry_md_get_algo_dlen(md_algorithm);
+                assert(hash_size > 0);
+
+                gcry_md_write(md, sig_data, sig_size);
+
+                hash = gcry_md_read(md, 0);
+                if (!hash)
+                        return -EIO;
+#endif
+        }
+
+        switch (rrsig->rrsig.algorithm) {
+
+        case DNSSEC_ALGORITHM_RSASHA1:
+        case DNSSEC_ALGORITHM_RSASHA1_NSEC3_SHA1:
+        case DNSSEC_ALGORITHM_RSASHA256:
+        case DNSSEC_ALGORITHM_RSASHA512:
+                return dnssec_rsa_verify(
+                                OPENSSL_OR_GCRYPT(md_algorithm, gcry_md_algo_name(md_algorithm)),
+                                hash, hash_size,
+                                rrsig,
+                                dnskey);
+
+        case DNSSEC_ALGORITHM_ECDSAP256SHA256:
+        case DNSSEC_ALGORITHM_ECDSAP384SHA384:
+                return dnssec_ecdsa_verify(
+                                OPENSSL_OR_GCRYPT(md_algorithm, gcry_md_algo_name(md_algorithm)),
+                                rrsig->rrsig.algorithm,
+                                hash, hash_size,
+                                rrsig,
+                                dnskey);
+
+        default:
+                assert_not_reached();
+        }
+}
+
+int dnssec_verify_rrset(
+                DnsAnswer *a,
+                const DnsResourceKey *key,
+                DnsResourceRecord *rrsig,
+                DnsResourceRecord *dnskey,
+                usec_t realtime,
+                DnssecResult *result) {
+
+        DnsResourceRecord **list, *rr;
+        const char *source, *name;
+        _cleanup_free_ char *sig_data = NULL;
+        size_t sig_size = 0; /* avoid false maybe-uninitialized warning */
+        size_t n = 0;
+        bool wildcard;
+        int r;
+
+        assert(key);
+        assert(rrsig);
+        assert(dnskey);
+        assert(result);
+        assert(rrsig->key->type == DNS_TYPE_RRSIG);
+        assert(dnskey->key->type == DNS_TYPE_DNSKEY);
+
+        /* Verifies that the RRSet matches the specified "key" in "a",
+         * using the signature "rrsig" and the key "dnskey". It's
+         * assumed that RRSIG and DNSKEY match. */
+
+        r = dnssec_rrsig_prepare(rrsig);
+        if (r == -EINVAL) {
+                *result = DNSSEC_INVALID;
+                return r;
+        }
+        if (r < 0)
+                return r;
+
+        r = dnssec_rrsig_expired(rrsig, realtime);
+        if (r < 0)
+                return r;
+        if (r > 0) {
+                *result = DNSSEC_SIGNATURE_EXPIRED;
+                return 0;
+        }
+
+        name = dns_resource_key_name(key);
+
+        /* Some keys may only appear signed in the zone apex, and are invalid anywhere else. (SOA, NS...) */
+        if (dns_type_apex_only(rrsig->rrsig.type_covered)) {
+                r = dns_name_equal(rrsig->rrsig.signer, name);
+                if (r < 0)
+                        return r;
+                if (r == 0) {
+                        *result = DNSSEC_INVALID;
+                        return 0;
+                }
+        }
+
+        /* OTOH DS RRs may not appear in the zone apex, but are valid everywhere else. */
+        if (rrsig->rrsig.type_covered == DNS_TYPE_DS) {
+                r = dns_name_equal(rrsig->rrsig.signer, name);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        *result = DNSSEC_INVALID;
+                        return 0;
+                }
+        }
+
+        /* Determine the "Source of Synthesis" and whether this is a wildcard RRSIG */
+        r = dns_name_suffix(name, rrsig->rrsig.labels, &source);
+        if (r < 0)
+                return r;
+        if (r > 0 && !dns_type_may_wildcard(rrsig->rrsig.type_covered)) {
+                /* We refuse to validate NSEC3 or SOA RRs that are synthesized from wildcards */
+                *result = DNSSEC_INVALID;
+                return 0;
+        }
+        if (r == 1) {
+                /* If we stripped a single label, then let's see if that maybe was "*". If so, we are not really
+                 * synthesized from a wildcard, we are the wildcard itself. Treat that like a normal name. */
+                r = dns_name_startswith(name, "*");
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        source = name;
+
+                wildcard = r == 0;
+        } else
+                wildcard = r > 0;
+
+        /* Collect all relevant RRs in a single array, so that we can look at the RRset */
+        list = newa(DnsResourceRecord *, dns_answer_size(a));
+
+        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 > VERIFY_RRS_MAX)
+                        return -E2BIG;
+        }
+
+        if (n <= 0)
+                return -ENODATA;
+
+        /* Bring the RRs into canonical order */
+        typesafe_qsort(list, n, rr_compare);
+
+        r = dnssec_rrset_serialize_sig(rrsig, source, list, n, wildcard,
+                                       &sig_data, &sig_size);
+        if (r < 0)
+                return r;
+
+        r = dnssec_rrset_verify_sig(rrsig, dnskey, sig_data, sig_size);
+        if (r == -EOPNOTSUPP) {
+                *result = DNSSEC_UNSUPPORTED_ALGORITHM;
+                return 0;
+        }
+        if (r < 0)
+                return r;
+
+        /* Now, fix the ttl, expiry, and remember the synthesizing source and the signer */
+        if (r > 0)
+                dnssec_fix_rrset_ttl(list, n, rrsig);
+
+        if (r == 0)
+                *result = DNSSEC_INVALID;
+        else if (wildcard)
+                *result = DNSSEC_VALIDATED_WILDCARD;
+        else
+                *result = DNSSEC_VALIDATED;
+
+        return 0;
+}
+
+int dnssec_rrsig_match_dnskey(DnsResourceRecord *rrsig, DnsResourceRecord *dnskey, bool revoked_ok) {
+
+        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 (!revoked_ok && (dnskey->dnskey.flags & DNSKEY_FLAG_REVOKE))
+                return 0;
+        if (dnskey->dnskey.protocol != 3)
+                return 0;
+        if (dnskey->dnskey.algorithm != rrsig->rrsig.algorithm)
+                return 0;
+
+        if (dnssec_keytag(dnskey, false) != rrsig->rrsig.key_tag)
+                return 0;
+
+        return dns_name_equal(dns_resource_key_name(dnskey->key), rrsig->rrsig.signer);
+}
+
+int dnssec_key_match_rrsig(const 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,
+                const DnsResourceKey *key,
+                DnsAnswer *validated_dnskeys,
+                usec_t realtime,
+                DnssecResult *result,
+                DnsResourceRecord **ret_rrsig) {
+
+        bool found_rrsig = false, found_invalid = false, found_expired_rrsig = false, found_unsupported_algorithm = false;
+        unsigned nvalidations = 0;
+        DnsResourceRecord *rrsig;
+        int r;
+
+        assert(key);
+        assert(result);
+
+        /* Verifies all RRs from "a" that match the key "key" against DNSKEYs in "validated_dnskeys" */
+
+        if (dns_answer_isempty(a))
+                return -ENODATA;
+
+        /* Iterate through each RRSIG RR. */
+        DNS_ANSWER_FOREACH(rrsig, a) {
+                DnsResourceRecord *dnskey;
+                DnsAnswerFlags flags;
+
+                /* Is this an RRSIG RR that applies to RRs matching our key? */
+                r = dnssec_key_match_rrsig(key, rrsig);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                found_rrsig = true;
+
+                /* Look for a matching key */
+                DNS_ANSWER_FOREACH_FLAGS(dnskey, flags, validated_dnskeys) {
+                        DnssecResult one_result;
+
+                        if ((flags & DNS_ANSWER_AUTHENTICATED) == 0)
+                                continue;
+
+                        /* Is this a DNSKEY RR that matches they key of our RRSIG? */
+                        r = dnssec_rrsig_match_dnskey(rrsig, dnskey, false);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        /* 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);
+
+                        /* Have we seen an unreasonable number of invalid signaures? */
+                        if (nvalidations > DNSSEC_INVALID_MAX) {
+                                if (ret_rrsig)
+                                        *ret_rrsig = NULL;
+                                *result = DNSSEC_TOO_MANY_VALIDATIONS;
+                                return (int) nvalidations;
+                        }
+
+                        /* 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, &one_result);
+                        if (r < 0)
+                                return r;
+
+                        nvalidations++;
+
+                        switch (one_result) {
+
+                        case DNSSEC_VALIDATED:
+                        case DNSSEC_VALIDATED_WILDCARD:
+                                /* Yay, the RR has been validated,
+                                 * return immediately, but fix up the expiry */
+                                if (ret_rrsig)
+                                        *ret_rrsig = rrsig;
+
+                                *result = one_result;
+                                return (int) nvalidations;
+
+                        case DNSSEC_INVALID:
+                                /* If the signature is invalid, 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. */
+                                found_invalid = true;
+                                continue;
+
+                        case DNSSEC_UNSUPPORTED_ALGORITHM:
+                                /* If the key algorithm is
+                                   unsupported, try another
+                                   RRSIG/DNSKEY pair, but remember we
+                                   encountered this, so that we can
+                                   return a proper error when we
+                                   encounter nothing better. */
+                                found_unsupported_algorithm = true;
+                                continue;
+
+                        case DNSSEC_SIGNATURE_EXPIRED:
+                                /* If the signature is expired, try
+                                   another one, but remember it, so
+                                   that we can return this */
+                                found_expired_rrsig = true;
+                                continue;
+
+                        default:
+                                assert_not_reached();
+                        }
+                }
+        }
+
+        if (found_expired_rrsig)
+                *result = DNSSEC_SIGNATURE_EXPIRED;
+        else if (found_unsupported_algorithm)
+                *result = DNSSEC_UNSUPPORTED_ALGORITHM;
+        else if (found_invalid)
+                *result = DNSSEC_INVALID;
+        else if (found_rrsig)
+                *result = DNSSEC_MISSING_KEY;
+        else
+                *result = DNSSEC_NO_SIGNATURE;
+
+        if (ret_rrsig)
+                *ret_rrsig = NULL;
+
+        return (int) nvalidations;
+}
+
+int dnssec_has_rrsig(DnsAnswer *a, const DnsResourceKey *key) {
+        DnsResourceRecord *rr;
+        int r;
+
+        /* Checks whether there's at least one RRSIG in 'a' that protects RRs of the specified key */
+
+        DNS_ANSWER_FOREACH(rr, a) {
+                r = dnssec_key_match_rrsig(key, rr);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        return 1;
+        }
+
+        return 0;
+}
+
+static hash_md_t digest_to_hash_md(uint8_t algorithm) {
+
+        /* Translates a DNSSEC digest algorithm into an openssl/gcrypt digest identifier */
+
+        switch (algorithm) {
+
+        case DNSSEC_DIGEST_SHA1:
+                return OPENSSL_OR_GCRYPT(EVP_sha1(), GCRY_MD_SHA1);
+
+        case DNSSEC_DIGEST_SHA256:
+                return OPENSSL_OR_GCRYPT(EVP_sha256(), GCRY_MD_SHA256);
+
+        case DNSSEC_DIGEST_SHA384:
+                return OPENSSL_OR_GCRYPT(EVP_sha384(), GCRY_MD_SHA384);
+
+        default:
+                return OPENSSL_OR_GCRYPT(NULL, -EOPNOTSUPP);
+        }
+}
+
+int dnssec_verify_dnskey_by_ds(DnsResourceRecord *dnskey, DnsResourceRecord *ds, bool mask_revoke) {
+        uint8_t wire_format[DNS_WIRE_FORMAT_HOSTNAME_MAX];
+        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 (!mask_revoke && (dnskey->dnskey.flags & DNSKEY_FLAG_REVOKE))
+                return -EKEYREJECTED;
+        if (dnskey->dnskey.protocol != 3)
+                return -EKEYREJECTED;
+
+        if (dnskey->dnskey.algorithm != ds->ds.algorithm)
+                return 0;
+        if (dnssec_keytag(dnskey, mask_revoke) != ds->ds.key_tag)
+                return 0;
+
+        r = dns_name_to_wire_format(dns_resource_key_name(dnskey->key), wire_format, sizeof wire_format, true);
+        if (r < 0)
+                return r;
+
+        hash_md_t md_algorithm = digest_to_hash_md(ds->ds.digest_type);
+
+#if PREFER_OPENSSL
+        if (!md_algorithm)
+                return -EOPNOTSUPP;
+
+        _cleanup_(EVP_MD_CTX_freep) EVP_MD_CTX *ctx = NULL;
+        uint8_t result[EVP_MAX_MD_SIZE];
+
+        unsigned hash_size = EVP_MD_size(md_algorithm);
+        assert(hash_size > 0);
+
+        if (ds->ds.digest_size != hash_size)
+                return 0;
+
+        ctx = EVP_MD_CTX_new();
+        if (!ctx)
+                return -ENOMEM;
+
+        if (EVP_DigestInit_ex(ctx, md_algorithm, NULL) <= 0)
+                return -EIO;
+
+        if (EVP_DigestUpdate(ctx, wire_format, r) <= 0)
+                return -EIO;
+
+        if (mask_revoke)
+                md_add_uint16(ctx, dnskey->dnskey.flags & ~DNSKEY_FLAG_REVOKE);
+        else
+                md_add_uint16(ctx, dnskey->dnskey.flags);
+
+        r = md_add_uint8(ctx, dnskey->dnskey.protocol);
+        if (r <= 0)
+                return r;
+        r = md_add_uint8(ctx, dnskey->dnskey.algorithm);
+        if (r <= 0)
+                return r;
+        if (EVP_DigestUpdate(ctx, dnskey->dnskey.key, dnskey->dnskey.key_size) <= 0)
+                return -EIO;
+
+        if (EVP_DigestFinal_ex(ctx, result, NULL) <= 0)
+                return -EIO;
+
+#else
+        if (md_algorithm < 0)
+                return -EOPNOTSUPP;
+
+        initialize_libgcrypt(false);
+
+        _cleanup_(gcry_md_closep) gcry_md_hd_t md = NULL;
+
+        size_t hash_size = gcry_md_get_algo_dlen(md_algorithm);
+        assert(hash_size > 0);
+
+        if (ds->ds.digest_size != hash_size)
+                return 0;
+
+        gcry_error_t err = gcry_md_open(&md, md_algorithm, 0);
+        if (gcry_err_code(err) != GPG_ERR_NO_ERROR || !md)
+                return -EIO;
+
+        gcry_md_write(md, wire_format, r);
+        if (mask_revoke)
+                md_add_uint16(md, dnskey->dnskey.flags & ~DNSKEY_FLAG_REVOKE);
+        else
+                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);
+
+        void *result = gcry_md_read(md, 0);
+        if (!result)
+                return -EIO;
+#endif
+
+        return memcmp(result, ds->ds.digest, ds->ds.digest_size) == 0;
+}
+
+int dnssec_verify_dnskey_by_ds_search(DnsResourceRecord *dnskey, DnsAnswer *validated_ds) {
+        DnsResourceRecord *ds;
+        DnsAnswerFlags flags;
+        int r;
+
+        assert(dnskey);
+
+        if (dnskey->key->type != DNS_TYPE_DNSKEY)
+                return 0;
+
+        DNS_ANSWER_FOREACH_FLAGS(ds, flags, validated_ds) {
+
+                if ((flags & DNS_ANSWER_AUTHENTICATED) == 0)
+                        continue;
+
+                if (ds->key->type != DNS_TYPE_DS)
+                        continue;
+                if (ds->key->class != dnskey->key->class)
+                        continue;
+
+                r = dns_name_equal(dns_resource_key_name(dnskey->key), dns_resource_key_name(ds->key));
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                r = dnssec_verify_dnskey_by_ds(dnskey, ds, false);
+                if (IN_SET(r, -EKEYREJECTED, -EOPNOTSUPP))
+                        return 0; /* The DNSKEY is revoked or otherwise invalid, or we don't support the digest algorithm */
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        return 1;
+        }
+
+        return 0;
+}
+
+static hash_md_t nsec3_hash_to_hash_md(uint8_t algorithm) {
+
+        /* Translates a DNSSEC NSEC3 hash algorithm into an openssl/gcrypt digest identifier */
+
+        switch (algorithm) {
+
+        case NSEC3_ALGORITHM_SHA1:
+                return OPENSSL_OR_GCRYPT(EVP_sha1(), GCRY_MD_SHA1);
+
+        default:
+                return OPENSSL_OR_GCRYPT(NULL, -EOPNOTSUPP);
+        }
+}
+
+int dnssec_nsec3_hash(DnsResourceRecord *nsec3, const char *name, void *ret) {
+        uint8_t wire_format[DNS_WIRE_FORMAT_HOSTNAME_MAX];
+        int r;
+
+        assert(nsec3);
+        assert(name);
+        assert(ret);
+
+        if (nsec3->key->type != DNS_TYPE_NSEC3)
+                return -EINVAL;
+
+        if (nsec3->nsec3.iterations > NSEC3_ITERATIONS_MAX)
+                return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
+                                       "Ignoring NSEC3 RR %s with excessive number of iterations.",
+                                       dns_resource_record_to_string(nsec3));
+
+        hash_md_t algorithm = nsec3_hash_to_hash_md(nsec3->nsec3.algorithm);
+#if PREFER_OPENSSL
+        if (!algorithm)
+                return -EOPNOTSUPP;
+
+        size_t hash_size = EVP_MD_size(algorithm);
+        assert(hash_size > 0);
+
+        if (nsec3->nsec3.next_hashed_name_size != hash_size)
+                return -EINVAL;
+
+        _cleanup_(EVP_MD_CTX_freep) EVP_MD_CTX *ctx = EVP_MD_CTX_new();
+        if (!ctx)
+                return -ENOMEM;
+
+        if (EVP_DigestInit_ex(ctx, algorithm, NULL) <= 0)
+                return -EIO;
+
+        r = dns_name_to_wire_format(name, wire_format, sizeof(wire_format), true);
+        if (r < 0)
+                return r;
+
+        if (EVP_DigestUpdate(ctx, wire_format, r) <= 0)
+                return -EIO;
+        if (EVP_DigestUpdate(ctx, nsec3->nsec3.salt, nsec3->nsec3.salt_size) <= 0)
+                return -EIO;
+
+        uint8_t result[EVP_MAX_MD_SIZE];
+        if (EVP_DigestFinal_ex(ctx, result, NULL) <= 0)
+                return -EIO;
+
+        for (unsigned k = 0; k < nsec3->nsec3.iterations; k++) {
+                if (EVP_DigestInit_ex(ctx, algorithm, NULL) <= 0)
+                        return -EIO;
+                if (EVP_DigestUpdate(ctx, result, hash_size) <= 0)
+                        return -EIO;
+                if (EVP_DigestUpdate(ctx, nsec3->nsec3.salt, nsec3->nsec3.salt_size) <= 0)
+                        return -EIO;
+
+                if (EVP_DigestFinal_ex(ctx, result, NULL) <= 0)
+                        return -EIO;
+        }
+#else
+        if (algorithm < 0)
+                return algorithm;
+
+        initialize_libgcrypt(false);
+
+        unsigned hash_size = gcry_md_get_algo_dlen(algorithm);
+        assert(hash_size > 0);
+
+        if (nsec3->nsec3.next_hashed_name_size != hash_size)
+                return -EINVAL;
+
+        r = dns_name_to_wire_format(name, wire_format, sizeof(wire_format), true);
+        if (r < 0)
+                return r;
+
+        _cleanup_(gcry_md_closep) gcry_md_hd_t md = NULL;
+        gcry_error_t err = gcry_md_open(&md, algorithm, 0);
+        if (gcry_err_code(err) != GPG_ERR_NO_ERROR || !md)
+                return -EIO;
+
+        gcry_md_write(md, wire_format, r);
+        gcry_md_write(md, nsec3->nsec3.salt, nsec3->nsec3.salt_size);
+
+        void *result = gcry_md_read(md, 0);
+        if (!result)
+                return -EIO;
+
+        for (unsigned k = 0; k < nsec3->nsec3.iterations; k++) {
+                uint8_t tmp[hash_size];
+                memcpy(tmp, result, hash_size);
+
+                gcry_md_reset(md);
+                gcry_md_write(md, tmp, hash_size);
+                gcry_md_write(md, nsec3->nsec3.salt, nsec3->nsec3.salt_size);
+
+                result = gcry_md_read(md, 0);
+                if (!result)
+                        return -EIO;
+        }
+#endif
+
+        memcpy(ret, result, hash_size);
+        return (int) hash_size;
+}
+
+static int nsec3_is_good(DnsResourceRecord *rr, DnsResourceRecord *nsec3) {
+        const char *a, *b;
+        int r;
+
+        assert(rr);
+
+        if (rr->key->type != DNS_TYPE_NSEC3)
+                return 0;
+
+        /* RFC 5155, Section 8.2 says we MUST ignore NSEC3 RRs with flags != 0 or 1 */
+        if (!IN_SET(rr->nsec3.flags, 0, 1))
+                return 0;
+
+        /* Ignore NSEC3 RRs whose algorithm we don't know */
+#if PREFER_OPENSSL
+        if (!nsec3_hash_to_hash_md(rr->nsec3.algorithm))
+                return 0;
+#else
+        if (nsec3_hash_to_hash_md(rr->nsec3.algorithm) < 0)
+                return 0;
+#endif
+
+        /* Ignore NSEC3 RRs with an excessive number of required iterations */
+        if (rr->nsec3.iterations > NSEC3_ITERATIONS_MAX)
+                return 0;
+
+        /* Ignore NSEC3 RRs generated from wildcards. If these NSEC3 RRs weren't correctly signed we can't make this
+         * check (since rr->n_skip_labels_source is -1), but that's OK, as we won't trust them anyway in that case. */
+        if (!IN_SET(rr->n_skip_labels_source, 0, UINT8_MAX))
+                return 0;
+        /* Ignore NSEC3 RRs that are located anywhere else than one label below the zone */
+        if (!IN_SET(rr->n_skip_labels_signer, 1, UINT8_MAX))
+                return 0;
+
+        if (!nsec3)
+                return 1;
+
+        /* If a second NSEC3 RR is specified, also check if they are from the same zone. */
+
+        if (nsec3 == rr) /* Shortcut */
+                return 1;
+
+        if (rr->key->class != nsec3->key->class)
+                return 0;
+        if (rr->nsec3.algorithm != nsec3->nsec3.algorithm)
+                return 0;
+        if (rr->nsec3.iterations != nsec3->nsec3.iterations)
+                return 0;
+        if (rr->nsec3.salt_size != nsec3->nsec3.salt_size)
+                return 0;
+        if (memcmp_safe(rr->nsec3.salt, nsec3->nsec3.salt, rr->nsec3.salt_size) != 0)
+                return 0;
+
+        a = dns_resource_key_name(rr->key);
+        r = dns_name_parent(&a); /* strip off hash */
+        if (r <= 0)
+                return r;
+
+        b = dns_resource_key_name(nsec3->key);
+        r = dns_name_parent(&b); /* strip off hash */
+        if (r <= 0)
+                return r;
+
+        /* Make sure both have the same parent */
+        return dns_name_equal(a, b);
+}
+
+static int nsec3_hashed_domain_format(const uint8_t *hashed, size_t hashed_size, const char *zone, char **ret) {
+        _cleanup_free_ char *l = NULL;
+        char *j;
+
+        assert(hashed);
+        assert(hashed_size > 0);
+        assert(zone);
+        assert(ret);
+
+        l = base32hexmem(hashed, hashed_size, false);
+        if (!l)
+                return -ENOMEM;
+
+        j = strjoin(l, ".", zone);
+        if (!j)
+                return -ENOMEM;
+
+        *ret = j;
+        return (int) hashed_size;
+}
+
+static int nsec3_hashed_domain_make(DnsResourceRecord *nsec3, const char *domain, const char *zone, char **ret) {
+        uint8_t hashed[DNSSEC_HASH_SIZE_MAX];
+        int hashed_size;
+
+        assert(nsec3);
+        assert(domain);
+        assert(zone);
+        assert(ret);
+
+        hashed_size = dnssec_nsec3_hash(nsec3, domain, hashed);
+        if (hashed_size < 0)
+                return hashed_size;
+
+        return nsec3_hashed_domain_format(hashed, (size_t) hashed_size, zone, ret);
+}
+
+/* See RFC 5155, Section 8
+ * First try to find a NSEC3 record that matches our query precisely, if that fails, find the closest
+ * enclosure. Secondly, find a proof that there is no closer enclosure and either a proof that there
+ * is no wildcard domain as a direct descendant of the closest enclosure, or find an NSEC3 record that
+ * matches the wildcard domain.
+ *
+ * Based on this we can prove either the existence of the record in @key, or NXDOMAIN or NODATA, or
+ * that there is no proof either way. The latter is the case if a proof of non-existence of a given
+ * name uses an NSEC3 record with the opt-out bit set. Lastly, if we are given insufficient NSEC3 records
+ * to conclude anything we indicate this by returning NO_RR. */
+static int dnssec_test_nsec3(DnsAnswer *answer, DnsResourceKey *key, DnssecNsecResult *result, bool *authenticated, uint32_t *ttl) {
+        _cleanup_free_ char *next_closer_domain = NULL, *wildcard_domain = NULL;
+        const char *zone, *p, *pp = NULL, *wildcard;
+        DnsResourceRecord *rr, *enclosure_rr, *zone_rr, *wildcard_rr = NULL;
+        DnsAnswerFlags flags;
+        int hashed_size, r;
+        bool a, no_closer = false, no_wildcard = false, optout = false;
+
+        assert(key);
+        assert(result);
+
+        /* First step, find the zone name and the NSEC3 parameters of the zone.
+         * it is sufficient to look for the longest common suffix we find with
+         * any NSEC3 RR in the response. Any NSEC3 record will do as all NSEC3
+         * records from a given zone in a response must use the same
+         * parameters. */
+        zone = dns_resource_key_name(key);
+        for (;;) {
+                DNS_ANSWER_FOREACH_FLAGS(zone_rr, flags, answer) {
+                        r = nsec3_is_good(zone_rr, NULL);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        r = dns_name_equal_skip(dns_resource_key_name(zone_rr->key), 1, zone);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                goto found_zone;
+                }
+
+                /* Strip one label from the front */
+                r = dns_name_parent(&zone);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+        }
+
+        *result = DNSSEC_NSEC_NO_RR;
+        return 0;
+
+found_zone:
+        /* Second step, find the closest encloser NSEC3 RR in 'answer' that matches 'key' */
+        p = dns_resource_key_name(key);
+        for (;;) {
+                _cleanup_free_ char *hashed_domain = NULL;
+
+                hashed_size = nsec3_hashed_domain_make(zone_rr, p, zone, &hashed_domain);
+                if (hashed_size == -EOPNOTSUPP) {
+                        *result = DNSSEC_NSEC_UNSUPPORTED_ALGORITHM;
+                        return 0;
+                }
+                if (hashed_size < 0)
+                        return hashed_size;
+
+                DNS_ANSWER_FOREACH_FLAGS(enclosure_rr, flags, answer) {
+
+                        r = nsec3_is_good(enclosure_rr, zone_rr);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        if (enclosure_rr->nsec3.next_hashed_name_size != (size_t) hashed_size)
+                                continue;
+
+                        r = dns_name_equal(dns_resource_key_name(enclosure_rr->key), hashed_domain);
+                        if (r < 0)
+                                return r;
+                        if (r > 0) {
+                                a = flags & DNS_ANSWER_AUTHENTICATED;
+                                goto found_closest_encloser;
+                        }
+                }
+
+                /* We didn't find the closest encloser with this name,
+                 * but let's remember this domain name, it might be
+                 * the next closer name */
+
+                pp = p;
+
+                /* Strip one label from the front */
+                r = dns_name_parent(&p);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+        }
+
+        *result = DNSSEC_NSEC_NO_RR;
+        return 0;
+
+found_closest_encloser:
+        /* We found a closest encloser in 'p'; next closer is 'pp' */
+
+        if (!pp) {
+                /* We have an exact match! If we area looking for a DS RR, then we must insist that we got the NSEC3 RR
+                 * from the parent. Otherwise the one from the child. Do so, by checking whether SOA and NS are
+                 * appropriately set. */
+
+                if (key->type == DNS_TYPE_DS) {
+                        if (bitmap_isset(enclosure_rr->nsec3.types, DNS_TYPE_SOA))
+                                return -EBADMSG;
+                } else {
+                        if (bitmap_isset(enclosure_rr->nsec3.types, DNS_TYPE_NS) &&
+                            !bitmap_isset(enclosure_rr->nsec3.types, DNS_TYPE_SOA))
+                                return -EBADMSG;
+                }
+
+                /* No next closer NSEC3 RR. That means there's a direct NSEC3 RR for our key. */
+                if (bitmap_isset(enclosure_rr->nsec3.types, key->type))
+                        *result = DNSSEC_NSEC_FOUND;
+                else if (bitmap_isset(enclosure_rr->nsec3.types, DNS_TYPE_CNAME))
+                        *result = DNSSEC_NSEC_CNAME;
+                else
+                        *result = DNSSEC_NSEC_NODATA;
+
+                if (authenticated)
+                        *authenticated = a;
+                if (ttl)
+                        *ttl = enclosure_rr->ttl;
+
+                return 0;
+        }
+
+        /* Ensure this is not a DNAME domain, see RFC5155, section 8.3. */
+        if (bitmap_isset(enclosure_rr->nsec3.types, DNS_TYPE_DNAME))
+                return -EBADMSG;
+
+        /* Ensure that this data is from the delegated domain
+         * (i.e. originates from the "lower" DNS server), and isn't
+         * just glue records (i.e. doesn't originate from the "upper"
+         * DNS server). */
+        if (bitmap_isset(enclosure_rr->nsec3.types, DNS_TYPE_NS) &&
+            !bitmap_isset(enclosure_rr->nsec3.types, DNS_TYPE_SOA))
+                return -EBADMSG;
+
+        /* Prove that there is no next closer and whether or not there is a wildcard domain. */
+
+        wildcard = strjoina("*.", p);
+        r = nsec3_hashed_domain_make(enclosure_rr, wildcard, zone, &wildcard_domain);
+        if (r < 0)
+                return r;
+        if (r != hashed_size)
+                return -EBADMSG;
+
+        r = nsec3_hashed_domain_make(enclosure_rr, pp, zone, &next_closer_domain);
+        if (r < 0)
+                return r;
+        if (r != hashed_size)
+                return -EBADMSG;
+
+        DNS_ANSWER_FOREACH_FLAGS(rr, flags, answer) {
+                _cleanup_free_ char *next_hashed_domain = NULL;
+
+                r = nsec3_is_good(rr, zone_rr);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                r = nsec3_hashed_domain_format(rr->nsec3.next_hashed_name, rr->nsec3.next_hashed_name_size, zone, &next_hashed_domain);
+                if (r < 0)
+                        return r;
+
+                r = dns_name_between(dns_resource_key_name(rr->key), next_closer_domain, next_hashed_domain);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        if (rr->nsec3.flags & 1)
+                                optout = true;
+
+                        a = a && (flags & DNS_ANSWER_AUTHENTICATED);
+
+                        no_closer = true;
+                }
+
+                r = dns_name_equal(dns_resource_key_name(rr->key), wildcard_domain);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        a = a && (flags & DNS_ANSWER_AUTHENTICATED);
+
+                        wildcard_rr = rr;
+                }
+
+                r = dns_name_between(dns_resource_key_name(rr->key), wildcard_domain, next_hashed_domain);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        if (rr->nsec3.flags & 1)
+                                /* This only makes sense if we have a wildcard delegation, which is
+                                 * very unlikely, see RFC 4592, Section 4.2, but we cannot rely on
+                                 * this not happening, so hence cannot simply conclude NXDOMAIN as
+                                 * we would wish */
+                                optout = true;
+
+                        a = a && (flags & DNS_ANSWER_AUTHENTICATED);
+
+                        no_wildcard = true;
+                }
+        }
+
+        if (wildcard_rr && no_wildcard)
+                return -EBADMSG;
+
+        if (!no_closer) {
+                *result = DNSSEC_NSEC_NO_RR;
+                return 0;
+        }
+
+        if (wildcard_rr) {
+                /* A wildcard exists that matches our query. */
+                if (optout)
+                        /* This is not specified in any RFC to the best of my knowledge, but
+                         * if the next closer enclosure is covered by an opt-out NSEC3 RR
+                         * it means that we cannot prove that the source of synthesis is
+                         * correct, as there may be a closer match. */
+                        *result = DNSSEC_NSEC_OPTOUT;
+                else if (bitmap_isset(wildcard_rr->nsec3.types, key->type))
+                        *result = DNSSEC_NSEC_FOUND;
+                else if (bitmap_isset(wildcard_rr->nsec3.types, DNS_TYPE_CNAME))
+                        *result = DNSSEC_NSEC_CNAME;
+                else
+                        *result = DNSSEC_NSEC_NODATA;
+        } else {
+                if (optout)
+                        /* The RFC only specifies that we have to care for optout for NODATA for
+                         * DS records. However, children of an insecure opt-out delegation should
+                         * also be considered opt-out, rather than verified NXDOMAIN.
+                         * Note that we do not require a proof of wildcard non-existence if the
+                         * next closer domain is covered by an opt-out, as that would not provide
+                         * any additional information. */
+                        *result = DNSSEC_NSEC_OPTOUT;
+                else if (no_wildcard)
+                        *result = DNSSEC_NSEC_NXDOMAIN;
+                else {
+                        *result = DNSSEC_NSEC_NO_RR;
+
+                        return 0;
+                }
+        }
+
+        if (authenticated)
+                *authenticated = a;
+
+        if (ttl)
+                *ttl = enclosure_rr->ttl;
+
+        return 0;
+}
+
+static int dnssec_nsec_wildcard_equal(DnsResourceRecord *rr, const char *name) {
+        char label[DNS_LABEL_MAX];
+        const char *n;
+        int r;
+
+        assert(rr);
+        assert(rr->key->type == DNS_TYPE_NSEC);
+
+        /* Checks whether the specified RR has a name beginning in "*.", and if the rest is a suffix of our name */
+
+        if (rr->n_skip_labels_source != 1)
+                return 0;
+
+        n = dns_resource_key_name(rr->key);
+        r = dns_label_unescape(&n, label, sizeof label, 0);
+        if (r <= 0)
+                return r;
+        if (r != 1 || label[0] != '*')
+                return 0;
+
+        return dns_name_endswith(name, n);
+}
+
+static int dnssec_nsec_in_path(DnsResourceRecord *rr, const char *name) {
+        const char *nn, *common_suffix;
+        int r;
+
+        assert(rr);
+        assert(rr->key->type == DNS_TYPE_NSEC);
+
+        /* Checks whether the specified nsec RR indicates that name is an empty non-terminal (ENT)
+         *
+         * A couple of examples:
+         *
+         *      NSEC             bar →   waldo.foo.bar: indicates that foo.bar exists and is an ENT
+         *      NSEC   waldo.foo.bar → yyy.zzz.xoo.bar: indicates that xoo.bar and zzz.xoo.bar exist and are ENTs
+         *      NSEC yyy.zzz.xoo.bar →             bar: indicates pretty much nothing about ENTs
+         */
+
+        /* First, determine parent of next domain. */
+        nn = rr->nsec.next_domain_name;
+        r = dns_name_parent(&nn);
+        if (r <= 0)
+                return r;
+
+        /* If the name we just determined is not equal or child of the name we are interested in, then we can't say
+         * anything at all. */
+        r = dns_name_endswith(nn, name);
+        if (r <= 0)
+                return r;
+
+        /* If the name we are interested in is not a prefix of the common suffix of the NSEC RR's owner and next domain names, then we can't say anything either. */
+        r = dns_name_common_suffix(dns_resource_key_name(rr->key), rr->nsec.next_domain_name, &common_suffix);
+        if (r < 0)
+                return r;
+
+        return dns_name_endswith(name, common_suffix);
+}
+
+static int dnssec_nsec_from_parent_zone(DnsResourceRecord *rr, const char *name) {
+        int r;
+
+        assert(rr);
+        assert(rr->key->type == DNS_TYPE_NSEC);
+
+        /* Checks whether this NSEC originates to the parent zone or the child zone. */
+
+        r = dns_name_parent(&name);
+        if (r <= 0)
+                return r;
+
+        r = dns_name_equal(name, dns_resource_key_name(rr->key));
+        if (r <= 0)
+                return r;
+
+        /* DNAME, and NS without SOA is an indication for a delegation. */
+        if (bitmap_isset(rr->nsec.types, DNS_TYPE_DNAME))
+                return 1;
+
+        if (bitmap_isset(rr->nsec.types, DNS_TYPE_NS) && !bitmap_isset(rr->nsec.types, DNS_TYPE_SOA))
+                return 1;
+
+        return 0;
+}
+
+static int dnssec_nsec_covers(DnsResourceRecord *rr, const char *name) {
+        const char *signer;
+        int r;
+
+        assert(rr);
+        assert(rr->key->type == DNS_TYPE_NSEC);
+
+        /* Checks whether the name is covered by this NSEC RR. This means, that the name is somewhere below the NSEC's
+         * signer name, and between the NSEC's two names. */
+
+        r = dns_resource_record_signer(rr, &signer);
+        if (r < 0)
+                return r;
+
+        r = dns_name_endswith(name, signer); /* this NSEC isn't suitable the name is not in the signer's domain */
+        if (r <= 0)
+                return r;
+
+        return dns_name_between(dns_resource_key_name(rr->key), name, rr->nsec.next_domain_name);
+}
+
+static int dnssec_nsec_generate_wildcard(DnsResourceRecord *rr, const char *name, char **wc) {
+        const char *common_suffix1, *common_suffix2, *signer;
+        int r, labels1, labels2;
+
+        assert(rr);
+        assert(rr->key->type == DNS_TYPE_NSEC);
+
+        /* Generates "Wildcard at the Closest Encloser" for the given name and NSEC RR. */
+
+        r = dns_resource_record_signer(rr, &signer);
+        if (r < 0)
+                return r;
+
+        r = dns_name_endswith(name, signer); /* this NSEC isn't suitable the name is not in the signer's domain */
+        if (r <= 0)
+                return r;
+
+        r = dns_name_common_suffix(name, dns_resource_key_name(rr->key), &common_suffix1);
+        if (r < 0)
+                return r;
+
+        r = dns_name_common_suffix(name, rr->nsec.next_domain_name, &common_suffix2);
+        if (r < 0)
+                return r;
+
+        labels1 = dns_name_count_labels(common_suffix1);
+        if (labels1 < 0)
+            return labels1;
+
+        labels2 = dns_name_count_labels(common_suffix2);
+        if (labels2 < 0)
+            return labels2;
+
+        if (labels1 > labels2)
+                r = dns_name_concat("*", common_suffix1, 0, wc);
+        else
+                r = dns_name_concat("*", common_suffix2, 0, wc);
+
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
+int dnssec_nsec_test(DnsAnswer *answer, DnsResourceKey *key, DnssecNsecResult *result, bool *authenticated, uint32_t *ttl) {
+        bool have_nsec3 = false, covering_rr_authenticated = false, wildcard_rr_authenticated = false;
+        DnsResourceRecord *rr, *covering_rr = NULL, *wildcard_rr = NULL;
+        DnsAnswerFlags flags;
+        const char *name;
+        int r;
+
+        assert(key);
+        assert(result);
+
+        /* Look for any NSEC/NSEC3 RRs that say something about the specified key. */
+
+        name = dns_resource_key_name(key);
+
+        DNS_ANSWER_FOREACH_FLAGS(rr, flags, answer) {
+
+                if (rr->key->class != key->class)
+                        continue;
+
+                have_nsec3 = have_nsec3 || (rr->key->type == DNS_TYPE_NSEC3);
+
+                if (rr->key->type != DNS_TYPE_NSEC)
+                        continue;
+
+                /* The following checks only make sense for NSEC RRs that are not expanded from a wildcard */
+                r = dns_resource_record_is_synthetic(rr);
+                if (r == -ENODATA) /* No signing RR known. */
+                        continue;
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        continue;
+
+                /* Check if this is a direct match. If so, we have encountered a NODATA case */
+                r = dns_name_equal(dns_resource_key_name(rr->key), name);
+                if (r < 0)
+                        return r;
+                if (r == 0) {
+                        /* If it's not a direct match, maybe it's a wild card match? */
+                        r = dnssec_nsec_wildcard_equal(rr, name);
+                        if (r < 0)
+                                return r;
+                }
+                if (r > 0) {
+                        if (key->type == DNS_TYPE_DS) {
+                                /* If we look for a DS RR and the server sent us the NSEC RR of the child zone
+                                 * we have a problem. For DS RRs we want the NSEC RR from the parent */
+                                if (bitmap_isset(rr->nsec.types, DNS_TYPE_SOA))
+                                        continue;
+                        } else {
+                                /* For all RR types, ensure that if NS is set SOA is set too, so that we know
+                                 * we got the child's NSEC. */
+                                if (bitmap_isset(rr->nsec.types, DNS_TYPE_NS) &&
+                                    !bitmap_isset(rr->nsec.types, DNS_TYPE_SOA))
+                                        continue;
+                        }
+
+                        if (bitmap_isset(rr->nsec.types, key->type))
+                                *result = DNSSEC_NSEC_FOUND;
+                        else if (bitmap_isset(rr->nsec.types, DNS_TYPE_CNAME))
+                                *result = DNSSEC_NSEC_CNAME;
+                        else
+                                *result = DNSSEC_NSEC_NODATA;
+
+                        if (authenticated)
+                                *authenticated = flags & DNS_ANSWER_AUTHENTICATED;
+                        if (ttl)
+                                *ttl = rr->ttl;
+
+                        return 0;
+                }
+
+                /* Check if the name we are looking for is an empty non-terminal within the owner or next name
+                 * of the NSEC RR. */
+                r = dnssec_nsec_in_path(rr, name);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        *result = DNSSEC_NSEC_NODATA;
+
+                        if (authenticated)
+                                *authenticated = flags & DNS_ANSWER_AUTHENTICATED;
+                        if (ttl)
+                                *ttl = rr->ttl;
+
+                        return 0;
+                }
+
+                /* The following two "covering" checks, are not useful if the NSEC is from the parent */
+                r = dnssec_nsec_from_parent_zone(rr, name);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        continue;
+
+                /* Check if this NSEC RR proves the absence of an explicit RR under this name */
+                r = dnssec_nsec_covers(rr, name);
+                if (r < 0)
+                        return r;
+                if (r > 0 && (!covering_rr || !covering_rr_authenticated)) {
+                        covering_rr = rr;
+                        covering_rr_authenticated = flags & DNS_ANSWER_AUTHENTICATED;
+                }
+        }
+
+        if (covering_rr) {
+                _cleanup_free_ char *wc = NULL;
+                r = dnssec_nsec_generate_wildcard(covering_rr, name, &wc);
+                if (r < 0)
+                        return r;
+
+                DNS_ANSWER_FOREACH_FLAGS(rr, flags, answer) {
+
+                        if (rr->key->class != key->class)
+                                continue;
+
+                        if (rr->key->type != DNS_TYPE_NSEC)
+                                continue;
+
+                        /* Check if this NSEC RR proves the nonexistence of the wildcard */
+                        r = dnssec_nsec_covers(rr, wc);
+                        if (r < 0)
+                                return r;
+                        if (r > 0 && (!wildcard_rr || !wildcard_rr_authenticated)) {
+                                wildcard_rr = rr;
+                                wildcard_rr_authenticated = flags & DNS_ANSWER_AUTHENTICATED;
+                        }
+                }
+        }
+
+        if (covering_rr && wildcard_rr) {
+                /* If we could prove that neither the name itself, nor the wildcard at the closest encloser exists, we
+                 * proved the NXDOMAIN case. */
+                *result = DNSSEC_NSEC_NXDOMAIN;
+
+                if (authenticated)
+                        *authenticated = covering_rr_authenticated && wildcard_rr_authenticated;
+                if (ttl)
+                        *ttl = MIN(covering_rr->ttl, wildcard_rr->ttl);
+
+                return 0;
+        }
+
+        /* OK, this was not sufficient. Let's see if NSEC3 can help. */
+        if (have_nsec3)
+                return dnssec_test_nsec3(answer, key, result, authenticated, ttl);
+
+        /* No appropriate NSEC RR found, report this. */
+        *result = DNSSEC_NSEC_NO_RR;
+        return 0;
+}
+
+static int dnssec_nsec_test_enclosed(DnsAnswer *answer, uint16_t type, const char *name, const char *zone, bool *authenticated) {
+        DnsResourceRecord *rr;
+        DnsAnswerFlags flags;
+        int r;
+
+        assert(name);
+        assert(zone);
+
+        /* Checks whether there's an NSEC/NSEC3 that proves that the specified 'name' is non-existing in the specified
+         * 'zone'. The 'zone' must be a suffix of the 'name'. */
+
+        DNS_ANSWER_FOREACH_FLAGS(rr, flags, answer) {
+                bool found = false;
+
+                if (rr->key->type != type && type != DNS_TYPE_ANY)
+                        continue;
+
+                switch (rr->key->type) {
+
+                case DNS_TYPE_NSEC:
+
+                        /* We only care for NSEC RRs from the indicated zone */
+                        r = dns_resource_record_is_signer(rr, zone);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        r = dns_name_between(dns_resource_key_name(rr->key), name, rr->nsec.next_domain_name);
+                        if (r < 0)
+                                return r;
+
+                        found = r > 0;
+                        break;
+
+                case DNS_TYPE_NSEC3: {
+                        _cleanup_free_ char *hashed_domain = NULL, *next_hashed_domain = NULL;
+
+                        /* We only care for NSEC3 RRs from the indicated zone */
+                        r = dns_resource_record_is_signer(rr, zone);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        r = nsec3_is_good(rr, NULL);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                break;
+
+                        /* Format the domain we are testing with the NSEC3 RR's hash function */
+                        r = nsec3_hashed_domain_make(
+                                        rr,
+                                        name,
+                                        zone,
+                                        &hashed_domain);
+                        if (r < 0)
+                                return r;
+                        if ((size_t) r != rr->nsec3.next_hashed_name_size)
+                                break;
+
+                        /* Format the NSEC3's next hashed name as proper domain name */
+                        r = nsec3_hashed_domain_format(
+                                        rr->nsec3.next_hashed_name,
+                                        rr->nsec3.next_hashed_name_size,
+                                        zone,
+                                        &next_hashed_domain);
+                        if (r < 0)
+                                return r;
+
+                        r = dns_name_between(dns_resource_key_name(rr->key), hashed_domain, next_hashed_domain);
+                        if (r < 0)
+                                return r;
+
+                        found = r > 0;
+                        break;
+                }
+
+                default:
+                        continue;
+                }
+
+                if (found) {
+                        if (authenticated)
+                                *authenticated = flags & DNS_ANSWER_AUTHENTICATED;
+                        return 1;
+                }
+        }
+
+        return 0;
+}
+
+static int dnssec_test_positive_wildcard_nsec3(
+                DnsAnswer *answer,
+                const char *name,
+                const char *source,
+                const char *zone,
+                bool *authenticated) {
+
+        const char *next_closer = NULL;
+        int r;
+
+        /* Run a positive NSEC3 wildcard proof. Specifically:
+         *
+         * A proof that the "next closer" of the generating wildcard does not exist.
+         *
+         * Note a key difference between the NSEC3 and NSEC versions of the proof. NSEC RRs don't have to exist for
+         * empty non-transients. NSEC3 RRs however have to. This means it's sufficient to check if the next closer name
+         * exists for the NSEC3 RR and we are done.
+         *
+         * To prove that a.b.c.d.e.f is rightfully synthesized from a wildcard *.d.e.f all we have to check is that
+         * c.d.e.f does not exist. */
+
+        for (;;) {
+                next_closer = name;
+                r = dns_name_parent(&name);
+                if (r <= 0)
+                        return r;
+
+                r = dns_name_equal(name, source);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        break;
+        }
+
+        return dnssec_nsec_test_enclosed(answer, DNS_TYPE_NSEC3, next_closer, zone, authenticated);
+}
+
+static int dnssec_test_positive_wildcard_nsec(
+                DnsAnswer *answer,
+                const char *name,
+                const char *source,
+                const char *zone,
+                bool *_authenticated) {
+
+        bool authenticated = true;
+        int r;
+
+        /* Run a positive NSEC wildcard proof. Specifically:
+         *
+         * A proof that there's neither a wildcard name nor a non-wildcard name that is a suffix of the name "name" and
+         * a prefix of the synthesizing source "source" in the zone "zone".
+         *
+         * See RFC 5155, Section 8.8 and RFC 4035, Section 5.3.4
+         *
+         * Note that if we want to prove that a.b.c.d.e.f is rightfully synthesized from a wildcard *.d.e.f, then we
+         * have to prove that none of the following exist:
+         *
+         *      1) a.b.c.d.e.f
+         *      2) *.b.c.d.e.f
+         *      3)   b.c.d.e.f
+         *      4)   *.c.d.e.f
+         *      5)     c.d.e.f
+         */
+
+        for (;;) {
+                _cleanup_free_ char *wc = NULL;
+                bool a = false;
+
+                /* Check if there's an NSEC or NSEC3 RR that proves that the mame we determined is really non-existing,
+                 * i.e between the owner name and the next name of an NSEC RR. */
+                r = dnssec_nsec_test_enclosed(answer, DNS_TYPE_NSEC, name, zone, &a);
+                if (r <= 0)
+                        return r;
+
+                authenticated = authenticated && a;
+
+                /* Strip one label off */
+                r = dns_name_parent(&name);
+                if (r <= 0)
+                        return r;
+
+                /* Did we reach the source of synthesis? */
+                r = dns_name_equal(name, source);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        /* Successful exit */
+                        *_authenticated = authenticated;
+                        return 1;
+                }
+
+                /* Safety check, that the source of synthesis is still our suffix */
+                r = dns_name_endswith(name, source);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        return -EBADMSG;
+
+                /* Replace the label we stripped off with an asterisk */
+                wc = strjoin("*.", name);
+                if (!wc)
+                        return -ENOMEM;
+
+                /* And check if the proof holds for the asterisk name, too */
+                r = dnssec_nsec_test_enclosed(answer, DNS_TYPE_NSEC, wc, zone, &a);
+                if (r <= 0)
+                        return r;
+
+                authenticated = authenticated && a;
+                /* In the next iteration we'll check the non-asterisk-prefixed version */
+        }
+}
+
+int dnssec_test_positive_wildcard(
+                DnsAnswer *answer,
+                const char *name,
+                const char *source,
+                const char *zone,
+                bool *authenticated) {
+
+        int r;
+
+        assert(name);
+        assert(source);
+        assert(zone);
+        assert(authenticated);
+
+        r = dns_answer_contains_zone_nsec3(answer, zone);
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return dnssec_test_positive_wildcard_nsec3(answer, name, source, zone, authenticated);
+        else
+                return dnssec_test_positive_wildcard_nsec(answer, name, source, zone, authenticated);
+}
+
+#else
+
+int dnssec_verify_rrset(
+                DnsAnswer *a,
+                const DnsResourceKey *key,
+                DnsResourceRecord *rrsig,
+                DnsResourceRecord *dnskey,
+                usec_t realtime,
+                DnssecResult *result) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_rrsig_match_dnskey(DnsResourceRecord *rrsig, DnsResourceRecord *dnskey, bool revoked_ok) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_key_match_rrsig(const DnsResourceKey *key, DnsResourceRecord *rrsig) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_verify_rrset_search(
+                DnsAnswer *a,
+                const DnsResourceKey *key,
+                DnsAnswer *validated_dnskeys,
+                usec_t realtime,
+                DnssecResult *result,
+                DnsResourceRecord **ret_rrsig) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_has_rrsig(DnsAnswer *a, const DnsResourceKey *key) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_verify_dnskey_by_ds(DnsResourceRecord *dnskey, DnsResourceRecord *ds, bool mask_revoke) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_verify_dnskey_by_ds_search(DnsResourceRecord *dnskey, DnsAnswer *validated_ds) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_nsec3_hash(DnsResourceRecord *nsec3, const char *name, void *ret) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_nsec_test(DnsAnswer *answer, DnsResourceKey *key, DnssecNsecResult *result, bool *authenticated, uint32_t *ttl) {
+
+        return -EOPNOTSUPP;
+}
+
+int dnssec_test_positive_wildcard(
+                DnsAnswer *answer,
+                const char *name,
+                const char *source,
+                const char *zone,
+                bool *authenticated) {
+
+        return -EOPNOTSUPP;
+}
+
+#endif
+
+static const char* const dnssec_result_table[_DNSSEC_RESULT_MAX] = {
+        [DNSSEC_VALIDATED]             = "validated",
+        [DNSSEC_VALIDATED_WILDCARD]    = "validated-wildcard",
+        [DNSSEC_INVALID]               = "invalid",
+        [DNSSEC_SIGNATURE_EXPIRED]     = "signature-expired",
+        [DNSSEC_UNSUPPORTED_ALGORITHM] = "unsupported-algorithm",
+        [DNSSEC_NO_SIGNATURE]          = "no-signature",
+        [DNSSEC_MISSING_KEY]           = "missing-key",
+        [DNSSEC_UNSIGNED]              = "unsigned",
+        [DNSSEC_FAILED_AUXILIARY]      = "failed-auxiliary",
+        [DNSSEC_NSEC_MISMATCH]         = "nsec-mismatch",
+        [DNSSEC_INCOMPATIBLE_SERVER]   = "incompatible-server",
+        [DNSSEC_TOO_MANY_VALIDATIONS]  = "too-many-validations",
+};
+DEFINE_STRING_TABLE_LOOKUP(dnssec_result, DnssecResult);
+
+static const char* const dnssec_verdict_table[_DNSSEC_VERDICT_MAX] = {
+        [DNSSEC_SECURE]        = "secure",
+        [DNSSEC_INSECURE]      = "insecure",
+        [DNSSEC_BOGUS]         = "bogus",
+        [DNSSEC_INDETERMINATE] = "indeterminate",
+};
+DEFINE_STRING_TABLE_LOOKUP(dnssec_verdict, DnssecVerdict);