draft-ietf-dnsext-delegation-signer-00.txt   draft-ietf-dnsext-delegation-signer-01.txt 
DNSEXT Working Group Olafur Gudmundsson DNSEXT Working Group Olafur Gudmundsson
<draft-ietf-dnsext-delegation-signer-00.txt> <draft-ietf-dnsext-delegation-signer-01.txt>
Updates: RFC 1035, RFC 2535, RFC 3008. Updates: RFC 1035, RFC 2535, RFC 3008.
Delegation Signer record in parent. Delegation Signer record in parent.
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. provisions of Section 10 of RFC2026.
skipping to change at page 1, line 32 skipping to change at page 1, line 33
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html http://www.ietf.org/shadow.html
Comments should be sent to the authors or the DNSEXT WG mailing list Comments should be sent to the authors or the DNSEXT WG mailing list
namedroppers@ops.ietf.org namedroppers@ops.ietf.org
This draft expires on November 30, 2001. This draft expires on January 15, 2002.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2001). All rights reserved. Copyright (C) The Internet Society (2001). All rights reserved.
Abstract Abstract
One of the biggest problems in DNS occur when records of the same type One of the biggest problems in DNS occur when records of the same type
can appear on both sides of an delegation. If the contents of these can appear on both sides of an delegation. If the contents of these
sets differs clients can get confused. RFC2535 KEY records follows sets differs clients can get confused. RFC2535 KEY records follows
the same model as for NS records, parent is responsible for the the same model as for NS records, parent is responsible for the
records but the child is responsible for the contents. This document records but the child is responsible for the contents. This document
proposes to store a different record in the parent that specifies proposes to store a different record in the parent that specifies
which one of the child's keys can sign the child's KEY set. This which one of the child's keys are authorized to sign the child's KEY
change is not backwards compatible with RFC2535 but simplifies DNSSEC set. This change is not backwards compatible with RFC2535 but
operation. simplifies DNSSEC operation.
1 - Introduction 1 - Introduction
Familiarity with the DNS system [RFC1035], DNS security extensions Familiarity with the DNS system [RFC1035], DNS security extensions
[RFC2535] and DNSSEC terminology [RFC3090] is important. [RFC2535] and DNSSEC terminology [RFC3090] is important.
When the same data can reside in two administratively different DNS When the same data can reside in two administratively different DNS
zones sources it is common that the data gets out of sync. NS record zones sources it is common that the data gets out of sync. NS record
in a zone indicates that there is a delegation at this name and the NS in a zone indicates that there is a delegation at this name and the NS
record lists the authorative servers for the real zone. Based on record lists the authorative servers for the real zone. Based on
actual measurements 10-30% of all delegations in the Internet have actual measurements 10-30% of all delegations in the Internet have
differing NS sets at parent and child. There are number of reasons for differing NS sets at parent and child. There are number of reasons for
this including lack of communication between parent and child, and this, including lack of communication between parent and child and
bogus nameservers are listed to meet registrar requirements. bogus name-servers being listed to meet registrar requirements.
DNSSEC [RFC2535,RFC3008,RFC3090] specifies that child must have its DNSSEC [RFC2535,RFC3008,RFC3090] specifies that child must have its
KEY set signed by the parent to create a verifiable chain of KEYs. KEY set signed by the parent to create a verifiable chain of KEYs.
There is some debate, where the signed KEY set should reside, There is some debate, where the signed KEY set should reside,
parent[Parent] or child[RFC2535]. If the KEY set resides at the child, parent[Parent] or child[RFC2535]. If the KEY set resides at the child,
frequent communication is needed between the two to transmit keysets frequent communication is needed between the two parties, to transmit
up to parent and signatures down to child. If the KEY set resides at key sets up to parent and then the signed set or signatures down to
the parent[Parent] the communication is reduced having only child send child. If the KEY set resides at the parent[Parent] the communication
updated key sets to parent. DNSSEC requires that the parent store NULL is reduced having only child send updated key sets to parent.
key set for unsecure children, this complicates resolution process as DNSSEC[RFC2535] requires that the parent store NULL key set for
in many cases as servers for both parent and child need to be queried unsecure children, this complicates resolution process as in many
for KEY set. cases as servers for both parent and child need to be queried for KEY
set the [Parent] proposal simplifies this.
Further complication of the DNSSEC KEY model is that KEY record is Further complication of the DNSSEC KEY model is that KEY record is
used to store DNS zone keys and public keys for other protocols. This used to store DNS zone keys and public keys for other protocols. This
can lead to large key sets at delegation points. There are number of can lead to large key sets at delegation points. There are number of
potential problems with this. potential problems with this including:
1. KEY set may become quite large if many applications/protocols store 1. KEY set may become quite large if many applications/protocols store
their keys at the zone apex. Example of protocols are IPSEC, HTTP, their keys at the zone apex. Example of protocols are IPSEC, HTTP,
SMTP, SSH etc. SMTP, SSH etc.
2. Key set may require frequent updates, 2. Key set may require frequent updates.
3. Probability of compromised/lost keys increases and triggers 3. Probability of compromised/lost keys increases and triggers
emergency key rollover. emergency key rollover.
4. Parent may refuse sign key sets with NON DNS zone keys. 4. Parent may refuse sign key sets with NON DNS zone keys.
5. Parent may not have QoS on key changes that meets child's 5. Parent may not have QoS on key changes that meets child's
expectations. expectations.
Given these and other reasons there is good reason to explore Given these and other reasons there is good reason to explore
alternatives to using only KEY records to create chain of trust. alternatives to using only KEY records to create chain of trust.
Some of these problems can be reduced or eliminated by operational Some of these problems can be reduced or eliminated by operational
rules or protocol changes. To reduce the number of keys at apex, rule rules or protocol changes. To reduce the number of keys at apex, rule
to require applications to store their KEY records at the SRV name for to require applications to store their KEY records at the SRV name for
that application is one possibility. Another is to restrict KEY record that application is one possibility. Another is to restrict KEY record
to DNS keys only and create a new type for all non DNS keys. Third to DNS keys only and create a new type for all non DNS keys. Third
possible solution is to ban the storage of non DNS related keys at possible solution is to ban the storage of non DNS related keys at
zone apex. There are other possible solutions but they are outside the zone apex. There are other possible solutions but they are outside the
scope of this draft. scope of this document.
1.1 - Delegation Signer Record model 1.1 - Delegation Signer Record model
This draft proposes an alternative to the KEY record chain of trust, This document proposes an alternative to the KEY record chain of
that uses a special record that can only reside at the parent. This trust, that uses a special record that can only reside at the parent.
record will identify the key(s) that child will use to self sign its This record will identify the key(s) that child will use to self sign
KEY set. its own KEY set.
The chain of trust is now established by verifying the parent KEY set, The chain of trust is now established by verifying the parent KEY set,
the DK set from the parent and then the KEY set at the child. This is the DS set from the parent and then the KEY set at the child. This is
cryptographically equivalent to just using KEY records. cryptographically equivalent to just using KEY records.
Communication between the parent and child is reduced as the parent Communication between the parent and child is reduced as the parent
only needs to know of changes in DNS zone KEY records used to sign the only needs to know of changes in DNS zone KEY(s) used to sign the apex
apex KEY set. If other KEY records are stored at the zone apex, the KEY set. If other KEY records are stored at the zone apex, the parent
parent does not to be aware of them. does not need to be aware of them.
If child wants to have frequent key rollover for its DNS keys it is This approach has the advantage that it minimizes the communication
possible to do that without communicating to the parent, in this case between the parent and child and the child is the authority for the
the child uses on strong key to sign its apex KEY set and other KEY set with full control over the contents. This enables each to
smaller keys to sign the zone for a short time. operate and maintain each zone independent of each other. Thus if
child wants to have frequent key rollover for its DNS keys parent does
not need to be aware of it as the child can use one key to only sign
its apex KEY set and other keys to sign the other record sets in the
zone. The child can just as well use the same key to sign all records
in its zone.
This approach has the advantage that communication between the parent Another advantage is that this model fits well with slow rollout of
and child is kept to a minimum and the child is the authority for the DNSSEC and islands of security model. In the islands of security model
KEY set with full control over the contents. The load on the parent someone that trusts "good.example." preconfigures a key from
is reduced and it can maintain its zone as it sees fit. "good.example." as a trusted keys and from then on trusts any data
that is signed by that key or has a chain of trust to that key. If
"example." starts advertising DS records "good.example." does not have
to change operations, by suspending self-signing. If DS records can
also be used to identify trusted keys instead of KEY records.
The main disadvantage of this approach is to double the number of The main disadvantage of this approach is double the number of
signatures that need to be verified for the each KEY set. The signatures that need to be verified for the each delegation KEY set.
advantage on the other hand is that child only needs to update data in There is no impact on verifying other record sets.
parent when it changes DNS signing key.
1.2 - Reserved words 1.2 - Reserved words
The key words "CAN", "MUST", "MUST NOT", "SHOULD", "DOES NOT" and The key words "MUST", "MUST NOT", "SHOULD", and "MAY" in this document
"MAY" in this document are to be interpreted as described in RFC2119. are to be interpreted as described in RFC2119.
2 - DK (Delegation KEY signer) record: 2 - DS (Delegation KEY signer) record:
2.1 Protocol change 2.1 Protocol change
DK record MUST only appear at a delegation in the parent zone. The DS record MUST only appear at secure delegations in the parent zone.
record lists the child's keys that CAN sign the child's key set. The record lists the child's keys that SHOULD sign the child's key
Insecure delegation MUST NOT have a DK record, the presence of DK set. Insecure delegation MUST NOT have a DS record, the presence of
record SHOULD be considered a hint that the child might be secure. DS record SHOULD be considered a hint that the child might be secure.
Resolver MUST only trust KEY records that match a DK record. Resolver MUST only trust KEY records that match a DS record.
NOTE: It has been suggested that NULL DK record for insecure children NOTE: It has been suggested that NULL DS record for insecure children
is better than no record. The advantage is to have authenticated is better than no record. The advantage is to have authenticated
denial of child's security status, the drawback is for large denial of child's security status, the drawback is for large
delegating zones there will be many NULL DK records. delegating zones there will be many NULL DS records. If parent uses
NXT records adding NXT record to the authority section in the cases
when no DS record exists at delegation will give the same result as
NULL DS record.
WG please comment on which approach is better. WG please comment on which approach is better.
Updates RFC2535 sections 2.3.4 and 3.4, as well as RFC3008 section Updates RFC2535 sections 2.3.4 and 3.4, as well as RFC3008 section
2.7: Delegating zones MUST NOT store KEY records for delegations. The 2.7: Delegating zones MUST NOT store KEY records for delegations. The
only records that can appear at delegation in parent are NS, SIG, NXT only records that can appear at delegation in parent are NS, SIG, NXT
and DK. and DS.
Zone MUST self sign its apex KEY set, it SHOULD sign it with a key Zone MUST self sign its apex KEY set, it SHOULD sign it with a key
that corresponds to a DK record in the parent. that corresponds to a DS record in the parent. The KEY used to sign
the apex KEY RRset CAN sign other RRsets in the zone.
If child apex KEY RRset is not signed with one of the keys specified If child apex KEY RRset is not signed with one of the keys specified
in the DK record the child is locally secure[RFC3090] and SHOULD only in the DS record the child is locally secure[RFC3090] and SHOULD only
be considered secure the resolver has been instructed to trust the key be considered secure the resolver has been instructed to trust the key
used, via preconfiguration. used, via preconfiguration.
Authorative server answering a query, that has the OK bit set[OKbit], Authorative server answering a query, that has the OK bit set[OKbit],
MUST include the DK set in the additional section if the answer is a MUST include the DS set in the additional section if the answer is a
referral and there is space. Caching servers MAY return the DK record referral and there is space. Caching servers SHOULD return the DS
in the additional section under the same condition. record in the additional section under the same condition.
2.1.1 - Comments on protocol change 2.1.1 - Comments on protocol change
DK record is the first DNS record to be only stored at the upper side
of a delegation. NS records appear at both sides as do SIG and NXT.
All other records can only appear at the lower side. This will cause
some problems as servers authorative for parent may reject DK record
even if the server understands unknown types. Similarly a nameserver
acting as a authorative for child and as a caching recursive server
may never return the DK record. A caching server does not care from
which side DK record comes from and thus should not have to be changed
if it supports unknown types.
Secure resolvers need to know about the DK record and how to interpret
it. In the worst case, introducing the DK record, doubles the
signatures that need to be checked to validate a KEY set, this is a
small price to pay to have a cleaner delegations structure.
Over the years there has been various discussions on that the Over the years there has been various discussions on that the
delegation model in DNS is broken as there is no real good way to delegation model in DNS is broken as there is no real good way to
assert if delegation exists. In RFC2535 version of DNSSEC the assert if delegation exists. In RFC2535 version of DNSSEC the
authentication of a delegation is the NS bit in the NXT bitmap at the authentication of a delegation is the NS bit in the NXT bitmap at the
delegation point. Something more explicit is needed and the DK record delegation point. Something more explicit is needed and the DS record
addresses this for secure delegations. addresses this for secure delegations.
2.2 Wire format of DK record DS record is the first DNS record to be only stored at the upper side
of a delegation. NS records appear at both sides as do SIG and NXT.
All other records can only appear at the lower side. This will cause
some problems as servers authorative for parent may reject DS record
even if the server understands unknown types, or not hand them out
unless explicitly asked. Similarly a nameserver acting as a
authorative for child and as a caching recursive server may never
return the DS record. A caching server does not care from which side
DS record comes from and thus should not have to be changed if it
supports unknown types. Different TTL values on the childs NS set and
parents DS set may cause the DS set to expire before the NS set. In
this case an non-DS aware server would ask the child server for the DS
set and get NXDOMAIN answer. DS aware server will know to ask the
parent for the DS record.
There are two possible ways to represent the DK record at the parent Secure resolvers need to know about the DS record and how to interpret
and this draft presents both for discussion, the WG is expected to it. In the worst case, introducing the DS record, doubles the
select one and only one. The two formats is either to reuse the RDATA signatures that need to be checked to validate a KEY set.
definition of the KEY record and the other one is to store an Note: The working group must determine if the tradeoff between more
identifier of the key. work in resolvers is justified by the operational simplification of
this model. The author think this is a small price to pay to have a
cleaner delegations structure. One argument put forward is that DNS
should be optimized for read when ever possible, and on the face of it
adding the DS record makes reading data from DNS more expensive. The
operational complexities and legal hurdles that KEY records in parents
or children make prevent DNSSEC to ever get deployed.
2.2.1 Compact DK format 2.2 Wire format of DS record
The DK record consists of algorithm, size, key tag and SHA-1 digest of The DS record consists of algorithm, size, key tag and SHA-1 digest of
the public key KEY record allowed to sign the child's delegation. the public key KEY record allowed to sign the child's delegation.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| key tag | size | | key tag | size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| algorithm | SHA-1 digest | | algorithm | SHA-1 digest |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (20 bytes) | | (20 bytes) |
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| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| | | |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
The key tag is calculated as specified in RFC2535, the size is the The key tag is calculated as specified in RFC2535, the size is the
size of the public key in bits as specified in the document specifying size of the public key in bits as specified in the document specifying
the algorithm. Algorithm MUST be an algorithm number assigned in the the algorithm. Algorithm MUST be an algorithm number assigned in the
range 1..251. The SHA-1 digest is calculated over the canonical name range 1..251. The SHA-1 digest is calculated over the canonical name
of the delegation followed by the RDATA of the KEY record. of the delegation followed by the RDATA of the KEY record.
The size of the DS RDATA is 25 bytes, regardless of the key size.
NOTE: if 160 bits is to large the SHA-1 digest can be shortened but
that weakens the overall security of the system.
2.2.1.1 Justifications for fields 2.2.1 Justifications for fields
The algorithm and size fields are here to allow resolvers to quickly The algorithm and size fields are here to allow resolvers to quickly
identify the candidate KEY records to examine. Key Tag is to allow identify the candidate KEY records to examine. Key Tag is to allow
quick check if this is a good candidate. The key tag is redundant but quick check if this is a good candidate. The key tag is redundant but
provides some greater assurance than SHA-1 digest on its own. SHA-1 is provides some greater assurance than SHA-1 digest on its own. SHA-1 is
a strong cryptographic checksum, it is hard for attacker to generate a a strong cryptographic checksum, it is hard for attacker to generate a
KEY record that has the same SHA-1 digest. Making sure that the KEY KEY record that has the same SHA-1 digest. Making sure that the KEY
record is a valid public key is much harder. Combining the SHA-1 all record is a valid public key is much harder. Combining the name of the
the checks, the task of the attacker is as hard breaking the public key and the key data as input to the digest provides stronger
key. Even if someone creates a database of all SHA-1 key hashes seen assurance of the binding. Combining the SHA-1 with the other fields
so far, the addition of the name renders that database useless for makes the task of the attacker is as hard breaking the public key.
attacks. Even if someone creates a database of all SHA-1 key hashes seen so
far, the addition of the name renders that database useless for
2.2.2 Verbose DK format attacks against random zones.
The RDATA of the DK record is identical to the KEY record as specified
in RFC2535 sections 3.1, 3.1.2, 3.1.3 and 3.2.
2.3 Presentation format of DK record
Only one of these subsections will be used in RFC.
2.3.1 Presentation format for the compact DK record 2.3 Presentation format of DS record
The presentation format of DK record consists of 2 numbers, followed The presentation format of DS record consists of 2 numbers, followed
by either the name of the signature algorithm or the algorithm number. by either the name of the signature algorithm or the algorithm number.
The digest is to be presented in hex. The digest is to be presented in hex.
2.3.2 Presentation format for the verbose DK record 2.4 Justifications for compact format
Identical to KEY record.
2.4 Justifications for each format
2.4.1 Justification for compact format
This format allows concise representation of the keys that child will This format allows concise representation of the keys that child will
use, thus keeping down the size of the answer for the delegation, use, thus keeping down the size of the answer for the delegation,
reducing the probability of packet overflow. The SHA-1 hash is strong reducing the probability of packet overflow. The SHA-1 hash is strong
enough to uniquely identify the key. This is similar to PGP footprint. enough to uniquely identify the key. This is similar to the PGP
footprint.
Each DK record has RDATA size of 25, regardless of the size of the Each DS record has RDATA size of 25, regardless of the size of the
keys, keeping the answers from the parent smaller than if public key keys, keeping the answers from the parent smaller than if public key
was used. The smallest currently defined KEY record RDATA is 70 bytes. was used. The smallest currently defined KEY record RDATA is 70 bytes.
Compact DK format is also better suited to list trusted keys for Compact DS format is also better suited to list trusted keys for
islands of security in configuration files. islands of security in configuration files.
2.4.2 Justifications for verbose format 2.5 Transition issues for installed base
Even though this format results in larger DK set the effect on RFC2535 compliant resolver will assume that all DS secured delegations
implementations is smaller. Supporting I/O for DK record type is a are locally secure. This is a bad thing, thus it might be necessary
matter of reusing the code for reading/writing KEY records. For for a transition period to support both DS and SIG@Child. The cost is
finding DK to KEY matches simple compare will do, instead of digesting one more signatures in the answer and that early adopters have to
the public KEYS. cumbersome communications that DS is supposed to solve.
3 Resolver Example Resolvers will not get confused as they will select signatures with
the KEY they trust and ignore the other one.
This example uses compact notation for both DK and KEY for clarity. 3 Resolver Example
To create a chain of trust resolver goes from trusted KEY to DK to To create a chain of trust resolver goes from trusted KEY to DS to
KEY. KEY.
Assume the key for domain example. is trusted. In zone example we Assume the key for domain example. is trusted. In zone "example." we
have have
example. KEY <stuff> example. KEY <stuff>
secure.example. DK tag=12345 size=1024 alg=dsa <foofoo> secure.example. DS tag=12345 size=1024 alg=dsa <foofoo>
secure.example. NS ns1.secure.example. secure.example. NS ns1.secure.example.
NS ns1.secure.example. NS ns1.secure.example. s
secure.example. NXT NS SIG NXT DK tail.example. secure.example. NXT NS SIG NXT DS tail.example.
secure.example. SIG(NXT) secure.example. SIG(NXT)
secure.example. SIG(DK) secure.example. SIG(DS)
In zone "secure.example." we have
In zone secure.example. we have
secure.example. SOA <soa stuff> secure.example. SOA <soa stuff>
secure.example. NS ns1.secure.example. secure.example. NS ns1.secure.example.
NS ns1.secure.example. NS ns1.secure.example.
secure.example. KEY <tag=12345 size=1024 alg=dsa> secure.example. KEY <tag=12345 size=1024 alg=dsa>
KEY <tag=54321 size=512 alg=rsa/sha1> KEY <tag=54321 size=512 alg=rsa/sha1>
KEY <tag=32145 size=1024 alg=dsa> KEY <tag=32145 size=1024 alg=dsa>
secure.example. SIG(KEY) <by key-tag=12345 size=1024 alg=dsa> secure.example. SIG(KEY) <key-tag=12345 size=1024 alg=dsa>
secure.example. SIG(SOA) <by key-tag=54321 size=512 alg=rsa/sha1> secure.example. SIG(SOA) <key-tag=54321 size=512 alg=rsa/sha1>
secure.example. SIG(NS) <by key-tag=54321 size=512 alg=rsa/sha1> secure.example. SIG(NS) <key-tag=54321 size=512 alg=rsa/sha1>
In this example the trusted key for example signs the DK record for In this example the trusted key for example signs the DS record for
secure.example, making that a trusted record. The DK record states "secure.example.", making that a trusted record. The DS record states
what key is supposed to sign the KEY record at secure.example. In what key is supposed to sign the KEY record at secure.example. In
this example secure.example. has three KEY records and the correct one this example "secure.example." has three different KEY records and the
signs the KEY set, thus the key set is validated and trusted. One of one corresponding to the KEY identified in the DS record signs the KEY
the other keys in the keyset actually signs the zone data, and set, thus the key set is validated and trusted. Note that one of the
resolvers will trust the signatures as the key appears in the KEY set other keys in the keyset actually signs the zone data, and resolvers
that was correctly signed. will trust the signatures as the key appears in the KEY set.
This example has only one DK record for the child but there no reason This example has only one DS record for the child but there no reason
to outlaw multiple DK records. More than one DK record is needed to outlaw multiple DS records. More than one DS record is needed
during signing key rollover. during signing key rollover. It is strongly recommended that the DS
set be kept small.
3.1 Resolver cost estimates for DS records
From a RFC2535 resolver point of view for each delegation followed to
chase down an answer one KEY record has to be verified and possibly
some other records based on policy, for example the contents of the NS
set. Once the resolver gets to the appropriate delegation validating
the answer may require verifying one or more signatures. For a simple
A record lookup requires at least N delegations to be verified and 1
RRset. For a DS enabled resolver the cost is 2N+1. For MX record the
cost where the target of the MX record is in the same zone as the MX
record the costs are N+2 and 2N+2. In the case of negative answer the
same holds ratios hold true.
Resolver may require an extra query to get the DS record but and this
may add to the overall cost of the query, but this is never worse than
chasing down NULL KEY records from the parent in RFC2535 DNSSEC.
DS adds processing overhead on resolvers, increases the size of
delegation answers. DS requires much less storage in large delegation
zones than SIG@Parent.
4 Acknowledgments 4 Acknowledgments
Number of people have over the last few years contributed number of Number of people have over the last few years contributed number of
ideas that are captured in this document. ideas that are captured in this document. The core idea of using one
key to that has only the role of signing a key set, comes from
discussions with Bill Manning and Perry Metzger on how to put in a
single root key in all resolver that lives for a long time. Brian
Wellington, Dan Massey, Edward Lewis, Havard Eidnes, Jakob Schlyter,
Mark Kosters, Miek Gieben, Roy Arens, Scott Rosen have provided
usefull comments.
4 - Security Considerations: 4 - Security Considerations:
This document proposes a change to the validation chain of KEY records This document proposes a change to the validation chain of KEY records
in DNS. The change in is not believed to reduce security in the in DNS. The change in is not believed to reduce security in the
overall system, in RFC2535 DNSSEC child must communicate keys to overall system, in RFC2535 DNSSEC child must communicate keys to
parent and prudent parents will require some authentication on that parent and prudent parents will require some authentication on that
handshake. The modified protocol will require same authentication but handshake. The modified protocol will require same authentication but
allows the child to exert more local control over its own KEY set. allows the child to exert more local control over its own KEY set.
In the compact representation of DK record, there is a possibility In the representation of DS record, there is a possibility that an
that an attacker can generate an valid KEY that matches all the checks attacker can generate an valid KEY that matches all the checks thus
thus starting to forge data from the child. This is considered starting to forge data from the child. This is considered impractical
impractical as on average more than 2**80 keys must be generated as on average more than 2**80 keys must be generated before one is
before one is found that will match. found that will match.
DK record is a change to DNSSEC protocol and there is some installed DS record is a change to DNSSEC protocol and there is some installed
base of implementations, as well as text books on how to set up base of implementations, as well as text books on how to set up
secured delegations. Implementations that do not understand DK record secured delegations. Implementations that do not understand DS record
will not be able to follow the KEY to DK to KEY chain and consider all will not be able to follow the KEY to DS to KEY chain and consider all
zone secured that way insecure. zone secured that way insecure.
5 - IANA Considerations: 5 - IANA Considerations:
IANA needs to allocate RR type code for DK from the standard RR type IANA needs to allocate RR type code for DS from the standard RR type
space. space.
References: References:
[RFC1035] P. Mockapetris, ``Domain Names - Implementation and [RFC1035] P. Mockapetris, ``Domain Names - Implementation and
Specification'', STD 13, RFC 1035, November 1987. Specification'', STD 13, RFC 1035, November 1987.
[RFC2535] D. Eastlake, ``Domain Name System Security Extensions'', RFC [RFC2535] D. Eastlake, ``Domain Name System Security Extensions'', RFC
2535, March 1999. 2535, March 1999.
[RFC3008] B. Wellington, ``Domain Name System Security (DNSSEC) Signing [RFC3008] B. Wellington, ``Domain Name System Security (DNSSEC) Signing
Authority'', RFC 3008, November 2000. Authority'', RFC 3008, November 2000.
[RFC3090] E. Lewis `` DNS Security Extension Clarification on Zone [RFC3090] E. Lewis `` DNS Security Extension Clarification on Zone
Status'', RFC 3090, March 2001. Status'', RFC 3090, March 2001.
[IDbit] D. Conrad, ``Indicating Resolver Support of DNSSEC'', work in [OKbit] D. Conrad, ``Indicating Resolver Support of DNSSEC'', work in
progress <draft-ietf-dnsext-dnssec-okbit-02.txt>, April 2001. progress <draft-ietf-dnsext-dnssec-okbit-02.txt>, April 2001.
[Parent] R. Gieben, T. Lindgreen, ``Parent stores the child's zone [Parent] R. Gieben, T. Lindgreen, ``Parent stores the child's zone
KEYs'', work in progress <draft-ietf-dnsext-parent-stores- KEYs'', work in progress <draft-ietf-dnsext-parent-stores-
zones-keys-01.txt>, May 2001. zones-keys-01.txt>, May 2001.
Author Address Author Address
Olafur Gudmundsson Olafur Gudmundsson
3826 Legation Street, NW 3826 Legation Street, NW
Washington, DC, 20015 Washington, DC, 20015
USA USA
<ogud@ogud.com> <ogud@ogud.com>
Appendix A: Changes from Prior versions
Changes from version 00
Changed name from DK to DS based on working group comments.
Dropped verbose format based on WG comments.
Added text about TTL issue/problem in caching servers.
Added text about islands of security and clarified the cost impact.
Major editing of arguments and some reordering of text for clarity.
Added section on transition issues.
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published and or assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind, distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are provided that the above copyright notice and this paragraph are
 End of changes. 

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