Internet DRAFT - draft-dnsop-dnssec-extension-pkix
draft-dnsop-dnssec-extension-pkix
Internet Engineering Task Force H. Lee
Internet-Draft T. Kwon
Intended status: Standards Track Seoul National University
Expires: 9 September 2023 8 March 2023
DNSSEC Extension by Using PKIX Certificates
draft-dnsop-dnssec-extension-pkix-01
Abstract
The Domain Name System Security Extensions (DNSSEC) were standardized
a couple of decades ago but it has not been widely deployed. Thus, a
vast majority of DNS messages in the real world are still vulnerable
to various kinds of integrity attacks like cache poisoning attacks.
This document describes a mechanism that extends the current DNSSEC
protocol in such a way that guarantees the integrity of DNS messages
using PKIX certificates without any dependencies on other entities in
the DNS infrastructure.
Status of This Memo
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This Internet-Draft will expire on 9 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. DNSSEC-PKI Overview . . . . . . . . . . . . . . . . . . . . . 3
2.1. Design Requirements . . . . . . . . . . . . . . . . . . . 3
2.2. The Operations of DNSSEC-PKI . . . . . . . . . . . . . . 4
3. Authoritative DNS Server-side Deployment . . . . . . . . . . 5
3.1. Generating Signatures of RRsets . . . . . . . . . . . . . 5
3.1.1. PKIX Certificates . . . . . . . . . . . . . . . . . . 6
3.1.2. RRSIG Records . . . . . . . . . . . . . . . . . . . . 6
3.2. Publishing Public Keys and Certificate Chains . . . . . . 6
3.2.1. DNSKEY Records . . . . . . . . . . . . . . . . . . . 6
3.2.2. CERT Records . . . . . . . . . . . . . . . . . . . . 7
4. Validator's Behavior . . . . . . . . . . . . . . . . . . . . 7
4.1. Verifying DNS RR . . . . . . . . . . . . . . . . . . . . 7
4.2. Determine Verification Results . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6.1. Authenticated Denial of Existence . . . . . . . . . . . . 9
6.2. Leveraging Certificate Authorities . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The DNSSEC [RFC4033] was standardized to provide integrity and
authentication of DNS records. After twenty years of its
introduction, DNSSEC is widely deployed for top-level domains.
However, its deployment rates in second-level domains are low and
most DNS messages in the real world are still vulnerable to tampering
like cache poisoning attacks.
In addition, to support DNSSEC, it is necessary that a domain
publishes DS records to its upper zone (i.e., parent zone) to
establish a chain of trust. Usually, this process requires manual
intervention of domain owners which often results in errors. Thus,
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it is reported that a large number of domains do not have their
corresponding DS records in their upper zones [DNSSEC-Deployment],
which results in DNSSEC validation failures. Thus, we need a more
practical and deployable mechanism to guarantee the integrity and
authenticity of DNS records.
This document specifies DNSSEC-PKI to provide the integrity and
authentication of DNS Resource Record sets (RRsets) by leveraging
PKIX [RFC5280] certificates. DNSSEC-PKI offers domain owners another
option to provide the DNS integrity without requiring the cooperation
(or dependencies) of other entities in the DNS infrastructure (e.g.,
establishing a chain of trust across zones). For this purpose,
DNSSEC-PKI exploits PKIX certificates widely used by most domains.
Thus, DNSSEC-PKI allows a domain (or a zone) to use a public/private
key pair from its certificate rather than generating a distinct key
for DNS. This document defines the requirements and operations of
domains and validators (e.g., resolvers) to support DNSSEC-PKI.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. DNSSEC-PKI Overview
DNSSEC-PKI is designed to provide a practical and deployable way that
guarantees the integrity and authenticity of DNSSEC RRsets. To
achieve this, we need a mechanism that does not have dependencies on
other entities in the DNS infrastructure.
2.1. Design Requirements
We consider two requirements when designing DNSSEC-PKI.
1. Minimum or no changes of other entities in the DNS
infrastructure:
* Requiring changes (or cooperations) from other entities causes
dependency on those entities in the DNSSEC operations. Thus,
DNSSEC-PKI should minimally require a change of other entities
in the DNS infrastructure (e.g. parent zones and DNS
registrars).
2. Maximum reuse of the current DNSSEC standards and DNS
infrastructure:
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* DNSSEC-PKI should work with the existing DNS in a way that
maximally reuses the current infrastructure. That is, DNSSEC-
PKI seeks to achieve compatibility with the current DNSSEC
standards.
2.2. The Operations of DNSSEC-PKI
+---------------+
| Certificate |
| Authority |
| (CA) |
+---------------+
|
| Certificate
v
+----------+ +---------------+
| | RRSIG, DNSKEY, CERT | |
| Client |<--------------------------| Authoritative |
| | | Name Server |
| | | |
+----------+ +---------------+
Figure 1: Entities in DNSSEC-PKI
To satisfy the design requirements, we leverage PKIX certificates
issued by CAs. A domain generates a private/public key pair. Also,
it asks a CA to issue a certificate that contains its domain name and
the public key. It then uses the private key to generate the
signatures of its DNS RRsets. Each signature (for each RRset) is
published as a DNS record. Here, we reuse an RRSIG record [RFC4034],
which is used to store the signature of an RRset. The domain
publishes the public key in the certificate as a DNSKEY record
[RFC4034]. Also the certificates in the certificate chain are
published as CERT records [RFC4398]. The signature (i.e., RRSIG
record) guarantees the integrity and authenticity of the
corresponding DNS RRset and the certificate guarantees that the
signature is generated by the domain owner’s private key.
A validator (e.g., a client or a resolver) can check the integrity of
a given RRset by fetching the corresponding signature (RRSIG), a
public key (DNSKEY), and a certificate chain (CERTs) and verifying
them.
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Validator Authoritative Certificate
(e.g., Resolver) Name Server Authority
| | (CA)
| | Issue a certificate |
| |<---------------------------|
| | |
| |
| |
| + Generate signatures of RRsets
| |
| + Publish RRSIG, DNSKEY, CERT records
| |
| Fetch a target DNS record |
| (i.e., A record) |
|<-----------------------------|
| |
| Fetch RRSIG, DNSKEY, CERT |
|<-----------------------------|
| |
| |
+ Verify the target record |
| using RRSIG, DNSKEY, CERT |
| |
Figure 2: The operations of DNSSEC-PKI
3. Authoritative DNS Server-side Deployment
Deploying DNSSEC-PKI on the authoritative DNS server (i.e., a domain
or a zone) requires the following steps:
1. A domain is issued a PKIX certificate (from a CA).
2. The domain generates the signatures of its DNS RRsets using its
private key in the certificate.
3. The domain publishes the signatures as RRSIG records.
4. The domain publishes the corresponding public key as a DNSKEY
record.
5. Finally, the domain publishes the certificates (of its
certificate chain) as CERT records.
3.1. Generating Signatures of RRsets
For each RRset, the domain generates its signature and publishes it
as an RRSIG record.
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3.1.1. PKIX Certificates
ost domains use PKIX [RFC5280] certificates for HTTPS (or TLS).
Thus, they are familiar with how to handle such certificates
(issuance, storage, and so on). We also rely on PKIX certificates
issued by CAs for DNSSEC-PKI.
3.1.2. RRSIG Records
We use RRSIG records for digital signatures of RRsets, which are
generated by a private key in a PKIX certificate. The description of
the RRSIG RR format is specified in Section 3 of [RFC4034]. The Key
Tag field should be calculated as explained in Appendix B of
[RFC4034].
A validator can fetch and validate RRSIG records to check the
integrity and authenticity of DNS RRs.
3.2. Publishing Public Keys and Certificate Chains
Like DNSSEC, DNSSEC-PKI uses the public key cryptography to generate
signatures of DNS RRsets. Thus, a domain should publish the public
key as a DNS record. Also, the domain should publish a certificate
that contains the public key and its certificate chain to allow a DNS
client to validate the certificate and the signature. For this
purpose, we use two existing DNS resource record (RR) types in
DNSSEC.
3.2.1. DNSKEY Records
A domain (or zone) generates the signatures of DNS RRsets using its
private key. The corresponding public key is stored in a DNSKEY RR
which is described in Section 2 of [RFC4034]. As specified in
Section 2 of [RFC4034], a DNSKEY RR MUST have a signature algorithm
and a public key.
Other fields except the Flags field have the same meaning as those
specified in Section 2 of [RFC4034].
3.2.1.1. The Flags Field extension
[RFC4034] specifies the use of two bits in the Flags field. Bit 7 is
used to specify the Zone Key flag. If bit 7 is set to 1, the DNSKEY
RR contains a DNS zone key. Otherwise, the DNSKEY MUST NOT be used
to verify RRSIGs. Thus, to use DNSSEC-PKI, bit 7 MUST be set to 1.
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Bit 15 is used to specify the Secure Entry Point flag which is
described in [RFC3757]. If bit 7 is set to 1, the DNSKEY RR contains
a key-signing key (KSK). Otherwise, the DNSKEY RR contains a zone-
signing key (ZSK). In DNSSEC-PKI, a private key corresponding to the
public key in the DNSKEY RR is used to sign a zone’s RRsets, and
hence its role is similar to that of a ZSK. Thus, for DNSSEC-PKI,
bit 7 MUST be set to 0.
We propose to use bit 3 to specify whether the DNSSEC-PKI extension
is supported flag (P). If bit 3 is set to 1, the public key in
DNSKEY RR MUST be validated using the certificates in CERT RRs
(specified in Section 3.2.2).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |P| flags | protocol | algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
/ public key /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: DNSSEC-PKI (P) Flag
3.2.2. CERT Records
A CERT RR [RFC4398] contains a PKIX certificate. The certificate
includes a public key which is also included in a DNSKEY RR.
A Key Tag should be calculated using the public key in the
certificate as specified in Appendix B of [RFC4034].
We assume that a DNS client already stores the certificate of a root
CA. Thus, CERT RRs include the certificates of the domain, issuing
CA and intermediate CAs (excluding the root CA).
4. Validator's Behavior
4.1. Verifying DNS RR
DNSSEC-PKI guarantees the integrity and authenticity of DNS RRs based
on public key cryptography. Validators should verify the signatures
of DNS RRsets generated by domains.
To check the integrity and authenticity of DNS RRs, a validator:
1. Fetches a target DNS RRset and its RRSIG, DNSKEY, and CERT RRs.
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* If there are cached DNS records whose TTLs are valid, the
validator can use them directly.
* The fetched DNS records can be cached.
2. Extracts a public key from the DNSKEY RR and another from a leaf
certificate in the CERT RR.
* If the extracted public keys are not matched, the verification
of the signature fails.
* Otherwise, it proceeds to the next step.
3. Validates the chain of certificates in the CERT RRs.
* A certificate chain can be verified according to Section 6 of
[RFC5280].
* If the certificate chain verification fails, the verification
of the signature fails.
4. Verifies the signature in the RRSIG RR using the public key.
4.2. Determine Verification Results
The signature verification will result in one of the following:
* Mismatch of public keys in DNSKEY and Certificate: A public key in
a DNSKEY RR and another in a certificate are different.
* Certificate chain validation failure: The public keys in a DNSKEY
RR and a certificate are matched but a certificate chain
validation failed. (e.g., a certificate of a CA is expired).
* Signature validation failure: A chain of certificates is validated
but the validation of RRSIGs fails (e.g., missing signatures or
incorrect signatures).
* Authenticated: the signature is verified.
If a client trusts a (local or public) resolver, the resolver should
validate the signature of DNS RRs and return the result to the
client. A resolver sets the Authenticated Data (AD) bit in the
message header of the DNS response message if and only if the queried
RRset is authenticated.
If a client does not trust the resolver, it should verify the
signature (RRSIG) by itself.
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5. IANA Considerations
We ask to update the “DNSKEY FLAGS” registry [RFC3755][RFC4034] to
assign 3rd bit in the DNSKEY Flags as the DNSSEC-PKI (P) bit.
+========+================+==================================+
| Number | Description | Reference |
+========+================+==================================+
| 3 | DNSSEC-PKI (P) | Section 3.2.1.1 of this document |
+--------+----------------+----------------------------------+
Table 1: DNSSEC-PKI (P) bit
6. Security Considerations
6.1. Authenticated Denial of Existence
We recommend using the NSEC [RFC4034] or NSEC3 [RFC5155] mechanism to
provide the authenticated denial of existence.
6.2. Leveraging Certificate Authorities
DNSSEC-PKI leverages PKIX certificates issued by CAs. However,
Certificate Authorities (CAs) have been criticized since there are no
limits in a namespace in terms of certificate issuance. Protocols
such as DNS CAA [RFC8659] and Certificates Transparency [RFC9162] can
mitigate the problem.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation
Signer (DS)", RFC 3755, DOI 10.17487/RFC3755, May 2004,
<https://www.rfc-editor.org/info/rfc3755>.
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[RFC3757] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name
System KEY (DNSKEY) Resource Record (RR) Secure Entry
Point (SEP) Flag", RFC 3757, DOI 10.17487/RFC3757, April
2004, <https://www.rfc-editor.org/info/rfc3757>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
<https://www.rfc-editor.org/info/rfc4034>.
[RFC4398] Josefsson, S., "Storing Certificates in the Domain Name
System (DNS)", RFC 4398, DOI 10.17487/RFC4398, March 2006,
<https://www.rfc-editor.org/info/rfc4398>.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
<https://www.rfc-editor.org/info/rfc5155>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC8659] Hallam-Baker, P., Stradling, R., and J. Hoffman-Andrews,
"DNS Certification Authority Authorization (CAA) Resource
Record", RFC 8659, DOI 10.17487/RFC8659, November 2019,
<https://www.rfc-editor.org/info/rfc8659>.
[RFC9162] Laurie, B., Messeri, E., and R. Stradling, "Certificate
Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162,
December 2021, <https://www.rfc-editor.org/info/rfc9162>.
7.2. Informative References
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[DNSSEC-Deployment]
Chung, T., van Rijswijk-Deij, R., Chandrasekaran, B.,
Choffnes, D., Levin, D., Maggs, B. M., Misloven, A., and
C. Wilson, "A Longitudinal, End-to-End View of the DNSSEC
Ecosystem", Proceedings of the 26th USENIX Security
Symposium, Vancouver, August 2017,
<https://www.usenix.org/system/files/conference/
usenixsecurity17/sec17-chung.pdf>.
Authors' Addresses
Hyeonmin Lee
Seoul National University
Korea, Republic of
Email: min0921110@snu.ac.kr
Taekyoung Kwon
Seoul National University
Korea, Republic of
Email: tkkwon@snu.ac.kr
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