Internet DRAFT - draft-bretelle-dprive-dot-spki-in-ns-name
draft-bretelle-dprive-dot-spki-in-ns-name
Network Working Group M. Bretelle
Internet-Draft Facebook
Intended status: Standards Track March 11, 2019
Expires: September 12, 2019
Encoding DNS-over-TLS (DoT) Subject Public Key Info (SPKI) in Name
Server name
draft-bretelle-dprive-dot-spki-in-ns-name-00
Abstract
This document describes a mechanism to exchange the Subject Public
Key Info (SPKI) ([RFC5280] Section 4.1.2.7) fingerprint associated
with a DNS-over-TLS (DoT [RFC7858]) authoritative server by encoding
it as part of its name. The fingerprint can thereafter be used to
validate the certificate received from the DoT server as well as
being able to discover support for DoT on the server.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 12, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Validating a remote DoT server . . . . . . . . . . . . . . . 3
4. Encoding data in a domain name label . . . . . . . . . . . . 3
4.1. Formatting DoT SPKI in name server name. . . . . . . . . 4
4.1.1. Example . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Handling by the recursive servers . . . . . . . . . . . . 4
4.2.1. Servers supporting this specification . . . . . . . . 4
4.2.2. Servers not supporting this specification . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This document describes a mechanism to exchange the Subject Public
Key Info (SPKI) ([RFC5280] Section 4.1.2.7) fingerprint associated
with a DNS-over-TLS (DoT [RFC7858]) authoritative server by encoding
it as part of its name. The fingerprint can thereafter be used to
validate the certificate received from the DoT server as well as
being able to discover support for DoT on the server.
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"
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.
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3. Validating a remote DoT server
While DoT provides protection against eavesdropping and on-path
tampering of the DNS queries exchanged with an authoritative server,
a recursive server that is talking to a remote DoT server needs a
mechanism to authenticate that the name server it is communicating
with is indeed the one that the authority of the zone manages or has
delegated responsibility to.
A common mechanism is to have TLS certificates issued by
"Certification Authorities" (CAs), those CA public keys are used as
trust anchors, and through a chain of trust, a leaf TLS certificate
can be validated. Any CA is able to issue a certificate for any
domain, which can have its drawbacks ([RFC6698] Section 1.1).
Another method is to leverage DANE/TLSA ([RFC6698]), in which case a
recursive resolver would be provided the certificate or SPKI hash
over DNS and validate it using DNSSEC ([RFC4033], [RFC4034], and
[RFC4035]).
This document describes a mechanism to signal to a recursive resolver
that DoT is supported by the authoritative name server as well as
providing a fingerprint of the SPKI to expect from the name server,
this is done by formatting a special first label for the name
servers. Recursive servers that understand the naming convention
detailed in this document will be able to upgrade their connection to
the authoritative server to TLS, while the ones that don't will
transparently use the name servers as a standard UDP/53 and TCP/53
servers. This format is heavily inspired from [dnscurve].
4. Encoding data in a domain name label
A label is limited to a maximum of 63 octets ([RFC1035]
Section 2.3.4) and has a limited set of characters that can be used
([RFC1035] Section 2.3.1), limiting both the amount of data that can
be embedded in a label as well as the encoding format.
The set of character used by Base32 encoding ([RFC4648] Section 6),
without padding character, is suitable to be used in a label. Base32
encodes a 5-bit group into 1 byte which allows to encode up to 39
bytes within the 63 bytes space of a label.
floor(63 * 5 / 8)
While this limits what can be encoded in a label, there is enough
space to store the hash produced by sha256 which requires 32 bytes,
leaving 7 bytes to spare.
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4.1. Formatting DoT SPKI in name server name.
The formatting of a name server is defined as follow:
<label> ::= <dot-header> <b32-spki-fingerprint>
<dot-header> ::= "dot-"
<b32-spki-fingerprint> ::= base32encode(<spki-fingerprint>)
<spki-fingerprint> ::= sha256(<spki>)
<spki> ::= der-encoded binary structure of SubjectPublicKeyInfo
4.1.1. Example
For the zone example.com, having 2 name servers, one at IPv4
192.0.2.1 and one at IPv6 2001:DB8::1, both of them providing DoT
support and using certificate cert.pem, the "<b32-spki-fingerprint>"
can be generated using the following command line:
openssl x509 -in /path/to/cert.pem -pubkey -noout | \
openssl pkey -pubin -outform der | \
openssl dgst -sha256 -binary | \
base32 | tr -d '=' | tr '[:upper:]' '[:lower:]'
tpwxmgqdaurcqxqsckxvdq5sty3opxlgcbjj43kumdq62kpqr72a
To generate the full label, "dot-" get prefixed to the base32 encoded
fingerprint.
...
...
;; QUESTION SECTION:
;example.com. IN NS
;; AUTHORITY SECTION:
example.com. 3600 IN NS dot-tpwxmgqdaurcqxqsckxvdq5sty3opxlgcbjj43kumdq62kpqr72a.a.example.com.
example.com. 3600 IN NS dot-tpwxmgqdaurcqxqsckxvdq5sty3opxlgcbjj43kumdq62kpqr72a.b.example.com.
;; ADDITIONAL SECTION:
dot-tpwxmgqdaurcqxqsckxvdq5sty3opxlgcbjj43kumdq62kpqr72a.a.example.com. 3600 IN A 192.0.2.1
dot-tpwxmgqdaurcqxqsckxvdq5sty3opxlgcbjj43kumdq62kpqr72a.b.example.com. 3600 IN AAAA 2001:DB8::1
...
...
4.2. Handling by the recursive servers
4.2.1. Servers supporting this specification
When a recursive server gets the list of authoritative servers
serving a specific zone, it gets a list of name of hosts.
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If:
o the first label is 56 bytes long
o AND the first 4 bytes matches "dot-"
o AND the remaining 52 bytes can be base32-decoded
the recursive server will attempt to connect to the name server using
TLS over port 853 and validate that the SHA256 hash of the SPKI in
the certificate provided by the name server matches what was
previously decoded.
If the TLS session fail to establish, either unavailability of the
service on port 853, TLS authentication failure, the behaviour of the
recursive server depends on whether it is operating in strict or
opportunistic mode ([I-D.ietf-dprive-dtls-and-tls-profiles]).
In strict mode, the resolver MUST stop using this authoritative name
server, and MUST try other servers of the DNS zone. In opportunistic
mode, the resolver MUST use the authoritative name server despite the
failure. It MAY try other name servers of the zone before, in the
hope they will accept TLS and be authenticated.
4.2.2. Servers not supporting this specification
A server not supporting this specification will be unaware of
anything special with this name server and consider it like any other
name servers.
5. Security Considerations
TODO Security
6. IANA Considerations
TODO: This document requires IANA actions (new RR type).
7. References
7.1. Normative References
[I-D.ietf-dprive-dtls-and-tls-profiles]
Dickinson, S., Gillmor, D., and T. Reddy, "Usage and
(D)TLS Profiles for DNS-over-(D)TLS", draft-ietf-dprive-
dtls-and-tls-profiles-11 (work in progress), September
2017.
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[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[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>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[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>.
[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>.
[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>.
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7.2. Informative References
[dnscurve]
"DNSCurve", n.d., <https://dnscurve.org/>.
Acknowledgments
TODO acknowledge.
Author's Address
Emmanuel Bretelle
Facebook
Email: chantra@fb.com
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