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// Copyright (C) 2019-2023 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package dnssec
import (
"context"
"fmt"
"strings"
"time"
"github.com/miekg/dns"
)
type trustedZone struct {
name string
zsk map[uint16]dns.DNSKEY // zone signing keys
ksk map[uint16]dns.DNSKEY // key signing keys
rrSig map[uint16]dns.RRSIG // DNSKEY RR signature(s), used for validity
dss []dns.DS // DS or root anchor authenticating this zone in DS format
}
func (tz *trustedZone) isExpired(t time.Time) bool {
for _, sig := range tz.rrSig {
if !sig.ValidityPeriod(t) {
return true
}
}
return false
}
// ensure at least one of the keytags in ZSK of this zone
func (tz *trustedZone) checkKeys(keytags []uint16) bool {
for _, kt := range keytags {
if _, ok := tz.zsk[kt]; ok {
return true
}
}
return false
}
// verifyDS checks DS RRSIG using this zone ZSK
// cacheOutdated indicates no ZSK in this zone to verify the provided RRSIG
func (tz *trustedZone) verifyDS(rrSet []dns.RR, rrSig []dns.RRSIG, t time.Time) (cacheOutdated bool, err error) {
// parent zone's DNSKEY RRSET is cached but DS is just came from the network
// and might be signed by newer key
kt := make([]uint16, len(rrSig))
for i, sig := range rrSig {
kt[i] = sig.KeyTag
}
// so if no such keys in a cache return cache outdated that must force this zone update
if !tz.checkKeys(kt) {
cacheOutdated = true
return
}
// at least one signature must be valid
verifiedSig := verifyRRSig(rrSet, rrSig, t, tz.zsk)
if len(verifiedSig) == 0 {
requestedZone := (rrSig)[0].Hdr.Name
err = fmt.Errorf("DS signature verification failed for '%s'", requestedZone)
}
return
}
func getParentDS(ctx context.Context, fqZoneName string, c Querier, parent trustedZone, t time.Time) (dss []dns.DS, cacheOutdated bool, err error) {
var rrSet []dns.RR
var rrSig []dns.RRSIG
rrSet, rrSig, err = c.QueryRRSet(ctx, fqZoneName, dns.TypeDS) // physically stored in parent zone of fqZoneName zone
if err != nil {
return
}
// since a new zone is being created its DS is always fetched from the network
// but parent zone is cached and cache outdated error possbile
cacheOutdated, err = parent.verifyDS(rrSet, rrSig, t)
if err != nil || cacheOutdated {
return
}
for _, rr := range rrSet {
switch obj := rr.(type) {
case *dns.DS:
dss = append(dss, *obj)
}
}
return
}
// makeTrustedZone creates a new trustedZone for **fqZoneName**.
// it uses **client** for emitting DNSKEY and DS queries and
// **parent** for DS verification using cached keys.
// returns:
// 1. newly created trustedZone in case of success
// 2. cacheOutdated if cached parent does not have ZSK for DS validation
// 3. error in all other cases
//
// Note 1: the function should never return cacheOutdated for the root zone
// otherwise it might cause infinity loop in the caller.
//
// Note2: the function requests both DNSKEY (from child) and DS (from parent)
// and this allows to tolerate KSK rotation: if child zone refreshed KSK
// then its digest is propagated to parent DS and used to sign child's DNSKEY
func makeTrustedZone(ctx context.Context, fqZoneName string, parent trustedZone, c TrustQuerier, t time.Time) (tz trustedZone, cacheOutdated bool, err error) {
rrSet, rrSig, err := c.QueryRRSet(ctx, fqZoneName, dns.TypeDNSKEY)
if err != nil {
return
}
var dss []dns.DS
if fqZoneName == "." {
if dss, err = c.GetRootAnchorDS(); err != nil {
return
}
} else {
dss, cacheOutdated, err = getParentDS(ctx, fqZoneName, c, parent, t)
if err != nil || cacheOutdated {
return
}
}
zsk := make(map[uint16]dns.DNSKEY)
ksk := make(map[uint16]dns.DNSKEY)
for _, rr := range rrSet {
switch obj := rr.(type) {
case *dns.DNSKEY:
if obj.Flags&dns.ZONE != 0 { // 256
if obj.Flags&dns.SEP != 0 { // 257
ksk[obj.KeyTag()] = *obj
} else {
zsk[obj.KeyTag()] = *obj
}
}
default:
}
}
// find DNSKEY matched to RS retrieved from parent zone or from a trust anchor
matchedDS, verifiedKSK := matchKSKDigest(dss, ksk)
if len(verifiedKSK) == 0 {
err = fmt.Errorf("failed to verify %s KSK against digest in parent DS", fqZoneName)
return
}
// validate DNSKEY RRSIG using matched (verified) keys
// DNSKEY RRSET is self-signed so makes sense to check this signature at the very end with authenticated via parent DS
verifiedSig := verifyRRSig(rrSet, rrSig, t, verifiedKSK)
if len(verifiedSig) == 0 {
err = fmt.Errorf("no KSK to verify DNSKEY RRSet of %s", fqZoneName)
return
}
// zone and keys are authenticated, create a new zone
tz = trustedZone{
name: fqZoneName,
zsk: zsk,
ksk: verifiedKSK,
rrSig: verifiedSig,
dss: matchedDS,
}
return
}
// verifyRRSig takes RRSET, array of RRSIG, time and ZSKs in form of map
// and returns a map of matched signatures by keytag
func verifyRRSig(rrSet []dns.RR, rrSig []dns.RRSIG, t time.Time, keys map[uint16]dns.DNSKEY) map[uint16]dns.RRSIG {
verifiedSig := make(map[uint16]dns.RRSIG)
for _, sig := range rrSig {
if !sig.ValidityPeriod(t) {
continue
}
ksk := keys[sig.KeyTag]
if err := sig.Verify(&ksk, rrSet); err == nil {
verifiedSig[sig.KeyTag] = sig
}
}
return verifiedSig
}
// matchKSKDigest takes array of DS and KSKs in form of map
// and returns an array of matched DS records and verified keys
func matchKSKDigest(dss []dns.DS, ksk map[uint16]dns.DNSKEY) ([]dns.DS, map[uint16]dns.DNSKEY) {
verifiedKSK := make(map[uint16]dns.DNSKEY)
matchedDS := make([]dns.DS, 0, len(dss))
for _, ds := range dss {
if key, ok := ksk[ds.KeyTag]; ok {
keyDigest := strings.ToLower(key.ToDS(ds.DigestType).Digest)
if keyDigest == strings.ToLower(ds.Digest) {
verifiedKSK[ds.KeyTag] = key
matchedDS = append(matchedDS, ds)
}
}
}
return matchedDS, verifiedKSK
}
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