Internet DRAFT - draft-huque-dane-client-cert
draft-huque-dane-client-cert
Internet Engineering Task Force S. Huque
Internet-Draft Salesforce
Updates: 6698, 7671 (if approved) V. Dukhovni
Intended status: Standards Track Two Sigma
Expires: 18 August 2022 A. Wilson
Valimail
14 February 2022
TLS Client Authentication via DANE TLSA records
draft-huque-dane-client-cert-08
Abstract
The DANE TLSA protocol [RFC6698] [RFC7671] describes how to publish
Transport Layer Security (TLS) server certificates or public keys in
the DNS. This document updates RFC 6698 and RFC 7671. It describes
how to additionally use the TLSA record to publish client
certificates or public keys, and also the rules and considerations
for using them with TLS.
Status of This Memo
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This Internet-Draft will expire on 18 August 2022.
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Table of Contents
1. Introduction and Motivation . . . . . . . . . . . . . . . . . 2
2. Associating Client Identities in TLSA Records . . . . . . . . 3
2.1. Format 1: Service specific client identity . . . . . . . 3
2.2. Format 2: DevId: IOT Device Identity . . . . . . . . . . 3
3. Authentication Model . . . . . . . . . . . . . . . . . . . . 3
4. Client Identifiers in X.509 certificates . . . . . . . . . . 4
5. Signaling the Client's DANE Identity in TLS . . . . . . . . . 4
6. Example TLSA records for clients . . . . . . . . . . . . . . 5
6.1. Format 1: Service Specific Client Identity . . . . . . . 5
6.2. Format 2: DevID . . . . . . . . . . . . . . . . . . . . . 5
7. Changes to Client and Server behavior . . . . . . . . . . . . 5
8. Raw Public Keys . . . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
11. Security Considerations . . . . . . . . . . . . . . . . . . . 7
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
12.1. Normative References . . . . . . . . . . . . . . . . . . 7
12.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction and Motivation
The Transport Layer Security (TLS) protocol [RFC5246] [RFC8446]
optionally supports the authentication of clients using X.509
certificates [RFC5280] or raw public keys [RFC7250]. TLS
applications that perform DANE authentication of servers using TLSA
records may also desire to authenticate clients using the same
mechanism, especially if the client identity is in the form of or can
be represented by a DNS domain name. Some design patterns from the
Internet of Things (IoT) plan to make use of this form of
authentication, where large networks of physical objects identified
by DNS names may authenticate themselves using TLS to centralized
device management and control platforms.
In this document, the term TLS is used generically to describe both
the TLS and DTLS (Datagram Transport Layer Security) [RFC6347]
protocols.
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2. Associating Client Identities in TLSA Records
Different applications may have quite different conventions for
naming clients via domain names. This document thus does not
proscribe a single format, but mentions a few that may have wide
applicability.
2.1. Format 1: Service specific client identity
In this format, the owner name of the client TLSA record has the
following structure:
_service.[client-domain-name]
The first label identifies the application service name. The
remaining labels are composed of the client domain name.
Encoding the application service name into the owner name allows the
same client domain name to have different authentication credentials
for different application services. There is no need to encode the
transport label - the same name form is usable with both TLS and
DTLS.
The _service label could be a custom string for an application, but
more commonly is expected to be a service name registered in the IANA
Service Name Registry [SRVREG].
The RDATA or data field portion of the TLSA record is formed exactly
as specified in RFC 6698 and RFC 7671, and carries the same meaning.
2.2. Format 2: DevId: IOT Device Identity
The DevID form of the TLSA record has the following structure:
[devicename]._device.[org-domain-name]
It is loosely based on the proposed PKI Certificate Identifier Format
for Devices [CERTDEVID], but is simpler in form. It makes no
distinction between manufacturer issued and locally issued
certificates, and does away with the "serial" and "type" labels. The
"_device" label that precedes the organization domain name allows all
the device identities to be delegated to a subzone or to another
party.
3. Authentication Model
The authentication model assumed in this document is the following:
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The client is assigned an identity corresponding to a DNS domain
name. This domain name doesn't necessarily have any relation to its
network layer addresses. Clients often have dynamic or unpredictable
addresses, and may move around the network, so tying their identity
to network addresses is not feasible or wise in the general case.
The client generates (or has generated for it) a private and public
key pair. Where client certificates are being used, the client also
has a certificate binding the name to its public key. The
certificate or public key has a corresponding TLSA record published
in the DNS, which allows it to be authenticated directly via the DNS
(using the DANE-TA or DANE-EE certificate usage modes) or via a PKIX
public CA system constraint if the client's certificate was issued by
a public CA (using the PKIX-TA or PKIX-EE DANE usage modes).
4. Client Identifiers in X.509 certificates
If the TLS DANE Client Identity extension (see Section 5) is not
being used, the client certificate MUST have have the client's DNS
name specified in the Subject Alternative Name extension's dNSName
type.
If the TLS DANE Client Identity extension is in use, then with DANE-
EE(3), the subject name need not be present in the certificate.
5. Signaling the Client's DANE Identity in TLS
The client SHOULD explicitly signal that it has a DANE identity. The
most important reason is that the server may want an explicit
indication from the client that it has a DANE record, so as to avoid
unnecessary DNS queries in-band with the TLS handshake.
The DANE Client Identity TLS extension [TLSCLIENTID] is used for this
purpose. This extension can also be used to convey the actual DANE
client identity (i.e. domain name) that the TLS server should attempt
to authenticate. This is required when using TLS raw public key
authentication, since there is no client certificate from which to
extract the client's DNS identity. It is also helpful when the
client certificate contains multiple identities, and only a specific
one has a DANE record.
An additional case where such client signaling is helpful, is one
where DANE client authentication is optional, and there is a
population of buggy client software that does not react gracefully to
receipt of a Certificate Request message from the TLS server. This
extension allows TLS servers to deal with this situation by
selectively sending a Certificate Request message only to clients
that have sent this extension.
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6. Example TLSA records for clients
The following examples are provided in the textual presentation
format of the TLSA record.
6.1. Format 1: Service Specific Client Identity
An example TLSA record for the client "device1.example.com." and the
application "smtp-client". This record specifies the SHA-256 hash of
the subject public key component of the end-entity certificate
corresponding to the client. The certificate usage for this record
is 3 (DANE-EE) and thus is validated in accordance with section 5.1
of RFC 7671.
_smtp-client.device1.example.com. IN TLSA (
3 1 1 d2abde240d7cd3ee6b4b28c54df034b9
7983a1d16e8a410e4561cb106618e971 )
6.2. Format 2: DevID
An example TLSA record for the device named "sensor7" managed by the
organization "example.com" This record specifies the SHA-512 hash of
the subject public key component of an EE certificate corresponding
to the client.
sensor7._device.example.com. IN TLSA (
3 1 2 0f8b48ff5fd94117f21b6550aaee89c8
d8adbc3f433c8e587a85a14e54667b25
f4dcd8c4ae6162121ea9166984831b57
b408534451fd1b9702f8de0532ecd03c )
7. Changes to Client and Server behavior
A TLS Client conforming to this specification MUST have a signed DNS
TLSA record published corresponding to its DNS name and X.509
certificate or public key. The client presents this certificate or
public key in the TLS handshake with the server. The client should
not offer ciphersuites that are incompatible with its certificate or
public key. If the client's certificate has a DANE record with a
certificate usage other than DANE-EE, then the presented client
certificate MUST have have the client's DNS name specified in the
Subject Alternative Name extension's dNSName type.
Additionally, when using raw public key authentication, the client
MUST send the TLS DANE Client Identity extension [TLSCLIENTID] in its
Client Hello message. When using X.509 certificate authentication,
it SHOULD send this extension.
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A TLS Server implementing this specification performs the following
steps:
* Request a client certificate in the TLS handshake (the "Client
Certificate Request" message). This could be done
unconditionally, or only when it receives the TLS DANE Client
Identity extension from the client.
* If the client has sent a non-empty DANE Client Identity extension,
then extract the client's domain name from the extension.
Otherwise, extract the client identity from the Subject
Alternative Name extension's dNSName type.
* Construct the DNS query name for the corresponding TLSA record.
If the TLS DANE client identity extension was present, then this
name should be used. Otherwise, identities from the client
certificate are used.
* Look up the TLSA record set in the DNS. The response MUST be
cryptographically validated using DNSSEC. The server could
perform the DNSSEC validation itself. It could also be configured
to trust responses obtained via a validating resolver to which it
has a secure connection.
* Extract the RDATA of the TLSA records and match them to the
presented client certificate according to the rules specified in
the DANE TLS protocol [RFC6698] [RFC7671]. If successfully
matched, the client is authenticated and the TLS session proceeds.
If unsuccessful, the server MUST treat the client as
unauthenticated (e.g. it could terminate the session, or proceed
with the session giving the client access to resources as a
generic unauthenticated user).
* If there are multiple records in the TLSA record set, then the
client is authenticated as long as at least one of the TLSA
records matches, subject to RFC7671 digest agility, which SHOULD
be implemented.
If the DANE Client Identity extension is not present, and the
presented client certificate has multiple distinct reference
identifier types (e.g. a dNSName, and an rfc822Name) then TLS servers
configured to perform DANE authentication according to this
specification should only examine and authenticate the dNSName.
If the presented client certificate has multiple dNSName identities,
then the client MUST use the TLS DANE client identity extension to
unambiguously indicate its intended name to the server.
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Specific applications may be designed to require additional
validation steps. For example, a server might want to verify the
client's IP address is associated with the certificate in some
manner, e.g. by confirming that a secure reverse DNS lookup of that
address ties it back to the same domain name, or by requiring an
iPAddress component to be included in the certificate. Such details
are outside the scope of this document, and should be outlined in
other documents specific to the applications that require this
behavior.
Servers may have their own whitelisting and authorization rules for
which certificates they accept. For example a TLS server may be
configured to only allow TLS sessions from clients with certificate
identities within a specific domain or set of domains.
8. Raw Public Keys
When using raw public keys in TLS [RFC7250], this specification
requires the use of the TLS DANE Client Identity extension. The
associated DANE TLSA records employ only certificate usage 3 (DANE-
EE) and a selector value of 1 (SPKI), as described in [RFC7671].
9. Acknowledgements
TBD.
10. IANA Considerations
This document includes no request to IANA.
11. Security Considerations
This document updates RFC 6698 by defining the use of the TLSA record
for client TLS certificates. There are no security considerations
for this document beyond those described in RFC 6698 and RFC 7671 and
in the specifications for TLS and DTLS [RFC8446], [RFC5246],
[RFC6347].
12. References
12.1. Normative References
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
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[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>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[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>.
[RFC7671] Dukhovni, V. and W. Hardaker, "The DNS-Based
Authentication of Named Entities (DANE) Protocol: Updates
and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
October 2015, <https://www.rfc-editor.org/info/rfc7671>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[TLSCLIENTID]
Huque, S. and V. Dukhovni, "TLS Extension for DANE Client
Identity", <https://tools.ietf.org/html/draft-huque-tls-
dane-clientid>.
12.2. Informative References
[CERTDEVID]
Friel, O. and R. Barnes, "PKI Certificate Identifier
Format for Devices", <https://tools.ietf.org/id/draft-
friel-pki-for-devices-00.html>.
[SRVREG] IANA, "Service Name and Transport Protocol Port Number
Registry", <https://www.iana.org/assignments/service-
names-port-numbers/service-names-port-numbers.txt>.
Authors' Addresses
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Shumon Huque
Salesforce
Email: shuque@gmail.com
Viktor Dukhovni
Two Sigma
Email: ietf-dane@dukhovni.org
Ash Wilson
Valimail
Email: ash.wilson@valimail.com
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