Network Working Group M. Bretelle
Internet-Draft Facebook
Intended status: Standards Track March 11, 2019
Expires: September 12, 2019
DNS-over-TLS for insecure delegations
draft-bretelle-dprive-dot-for-insecure-delegations-01
Abstract
This document describes an alternative mechanism to DANE ([RFC6698])
in order to authenticate a DNS-over-TLS (DoT [RFC7858]) authoritative
server by not making DNSSEC a hard requirement, making DoT server
authentication available for insecure delegations.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Authenticating an insecure delegation . . . . . . . . . . . . 3
3.1. Public Key Infrastructure (PKIX) . . . . . . . . . . . . 3
3.2. Subject Public Key Info (SPKI) . . . . . . . . . . . . . 3
3.3. Authenticating from the parent . . . . . . . . . . . . . 4
3.3.1. Example . . . . . . . . . . . . . . . . . . . . . . . 4
4. DSPKI Resource Record . . . . . . . . . . . . . . . . . . . . 4
4.1. The DSPKI Resource Record . . . . . . . . . . . . . . . . 5
4.1.1. DSPKI RDATA Wire Format . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This document describes an alternative mechanism to DANE ([RFC6698])
as described in [I-D.bortzmeyer-dprive-resolver-to-auth] Section 2
extending the authentication of DNS over Transport Layer Security
(DoT) [RFC7858] to insecure delegations and therefore enabling the
onboarding of DoT authoritative servers without the requirement for
the authorities to support DNSSEC ([RFC4033], [RFC4034], and
[RFC4035]). To do so, this document introduce the Delegation Subject
Public Key Info (DSPKI) resource record, its purpose, usage and
format.
2. Terminology
A server that supports DNS-over-TLS is called a "DoT server" to
differentiate it from a "DNS Server" (one that provides DNS service
over any other protocol), likewise, a client that supports this
protocol is called a "DoT client"
A secure delegation ([RFC4956] Section 2) is a signed name containing
a delegation (NS RRset), and a signed DS RRset, signifying a
delegation to a signed zone.
An insecure delegation ([RFC4956] Section 2) is a signed name
containing a delegation (NS RRset), but lacking a DS RRset,
signifying a delegation to an unsigned subzone.
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
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Authenticating an insecure delegation
To authenticate a DoT server of a secure delegation, it is possible
to use the TLSA resource record [RFC6698] of the nameserver as
decribed in [I-D.bortzmeyer-dprive-resolver-to-auth] Section 2, while
this method is valid, the absence of support of DNSSEC for such
delegations precludes the onboarding and discovery of nameservers
serving those zones as DoT servers.
Without the use of DNSSEC, a delegation is not able to authenticate
itself as the chain of trust cannot be followed, however other
mechanisms exist to have a server authenticate itself, such as Public
Key Infrastructure (PKIX [RFC6125]) , SPKI, which have their own pros
and cons.
3.1. Public Key Infrastructure (PKIX)
It would be possible to authenticate the name servers of the insecure
delegation using PKIX, relying on an existing trust model and trust
anchors.
While simple, a single trusted Certificate Authority (CA) that breaks
said trust (voluntarily or involuntarily), can issue certificate for
any domains, allowing an attacker to potentially impersonate both the
application and the DoT server.
Another issue that rises is that the DoT servers may use an identity
which belong to the same origin as application servers, which could
permit personal information (such as cookies) to be leaked to the DoT
servers.
3.2. Subject Public Key Info (SPKI)
The zone owner generates his own certificate and distribute the SPKI
fingerprint into the DNS.
This is in essence what, amongst other things, TLSA records solve but
with the requirement for DNSSEC to be enabled and functional for the
queried zone. For insecure delegations, simply advertising the SPKI
fingerprint would be trivial to intercept, disable, and modify.
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3.3. Authenticating from the parent
While a delegation is not secured, the DNS core infrastructure
already support, for the most part, DNSSEC, meaning that if the owner
of an insecure delegation could set the SPKI fingerprint in a
resource record (RR) at the parent, such fingerprint could be signed
and validated by the DoT client. The DoT client can then establish a
TLS connection to the zone name servers and authenticate the DoT
server against the fingerprint acquired earlier from the parent zone.
3.3.1. Example
example.com is an insecure delegation from .com which has set the
DSPKI RRset.
A DoT client looking for records under example.com will learn from
.com that example.com is delegated to
example.com IN 172800 NS ns1.example.com
example.com IN 172800 NS ns2.example.com
# sha256
example.com IN DSPKI (
1 4e44f900cdeb8c769f4df97e23f8fc81
4ac4bf45a3d9dc265a2ed925171f0b71 )
# sha512
example.com IN DSPKI (
2 ab40ed300fd220d8c72a600069f9ceb1
f9fd7c003117e4ef34b228da1c9d76a0
500be99e82a0c01e7f80930a46ad28b8
ed3d5ed2df34d822b5f56c99f45889ef
)
ns1.example.com IN 172800 AAAA 2001:db8:abcd:12:1:2:3:4
ns2.example.com IN 172800 AAAA 2001:db8:abcd:ab:1:2:3:4
with the accompanying signature.
The DSPKI RRset signals that the nameservers are able to support DNS-
over-TLS. The DoT client can then establish a TLS connection to the
DoT server and authenticate them by ensuring that the SPKI matches
the one learned from the parent zone.
4. DSPKI Resource Record
There may be 0 or more DSPKI served by the parent of the delegation.
0 means that DSPKI is not supported, therefore the DoT client could
try other alternatives. 1 or multiple public keys can be distributed
to let the DoT client validate multiple public keys, which can be
useful while doing certificate rotation or when willing to provide
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different secret keys to different providers that may serve the
delegated zone.
4.1. The DSPKI Resource Record
The DSPKI resource record (RR) is used to associate a DoT server
public key (SPKI) with the zone it is serving.
4.1.1. DSPKI RDATA Wire Format
The RDATA of the DSPKI RR consists of a one-octet matching type
field, and the DER-encoded binary structure of the
SubjectPublicKeyInfo field as defined in [RFC5280].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| matching type | DER-encoded SPKI field /
+-+-+-+-+-+-+-+-+ /
/ /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.1.1.1. The Matching Type Field
A one-octet value, called "matching type", specifies how the SPKI is
presented. The types defined in this document are:
o 0 - Exact match on SPKI
o 1 - SHA-256 hash of SPKI
o 2 - SHA-512 hash of SPKI
Where the SPKI can be extracted as follow:
openssl x509 -in cert.pem -pubkey -noout | openssl pkey -pubin -outform der
and the SHA-256 as:
openssl x509 -in cert.pem -pubkey -noout | openssl pkey -pubin -outform der | \
openssl dgst -sha256 -binary
*FIXME*: consider
o alternate URI to support DoT (host, port, spki), DoH (host, port,
URL template), DNS-over-QUIC... would rather be an ALTNS type of
record
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o CDSPKI a la CDS, CDNSKEY
5. Security Considerations
TODO Security
6. IANA Considerations
TODO: This document requires IANA actions (new RR type).
7. Normative References
[I-D.bortzmeyer-dprive-resolver-to-auth]
Bortzmeyer, S., "Encryption and authentication of the DNS
resolver-to-authoritative communication", draft-
bortzmeyer-dprive-resolver-to-auth-01 (work in progress),
March 2018.
[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>.
[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>.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<https://www.rfc-editor.org/info/rfc4035>.
[RFC4956] Arends, R., Kosters, M., and D. Blacka, "DNS Security
(DNSSEC) Opt-In", RFC 4956, DOI 10.17487/RFC4956, July
2007, <https://www.rfc-editor.org/info/rfc4956>.
[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>.
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[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/info/rfc6698>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[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>.
Acknowledgments
TODO acknowledge.
Author's Address
Emmanuel Bretelle
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Email: chantra@fb.com
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