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Versions: 00 01 02 03 04 05 06 07                                       
Internet Engineering Task Force                                 S. Huque
Internet-Draft                                                Salesforce
Updates: 6698, 7671 (if approved)                            V. Dukhovni
Intended status: Standards Track                               Two Sigma
Expires: 3 November 2021                                       A. Wilson
                                                                Valimail
                                                              2 May 2021


            TLS Client Authentication via DANE TLSA records
                    draft-huque-dane-client-cert-06

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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 3 November 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components



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   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

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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