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ACME                                                          Y. Sheffer
Internet-Draft                                                    Intuit
Intended status: Standards Track                                D. Lopez
Expires: December 31, 2018                           O. Gonzalez de Dios
                                                       A. Pastor Perales
                                                          Telefonica I+D
                                                              T. Fossati
                                                                   Nokia
                                                           June 29, 2018


 Generating Certificate Requests for Short-Term, Automatically-Renewed
                          (STAR) Certificates
                   draft-sheffer-acme-star-request-02

Abstract

   This memo proposes a protocol that allows a domain name owner to
   delegate to a third party (such as a CDN) control over a certificate
   that bears one or more names in that domain.  Specifically the third
   party creates a Certificate Signing Request for the domain, which can
   then be used by the domain owner to request a short term and
   automatically renewed (STAR) certificate.

   This is a component in a solution where a third-party such as a CDN
   can terminate TLS sessions on behalf of a domain name owner (e.g., a
   content provider), and the domain owner can cancel this delegation at
   any time without having to rely on certificate revocation mechanisms.

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 December 31, 2018.






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Copyright Notice

   Copyright (c) 2018 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 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Conventions used in this document . . . . . . . . . . . .   4
   2.  Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Preconditions . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Bootstrap . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Refresh . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.4.  Termination . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Protocol Details  . . . . . . . . . . . . . . . . . . . . . .   8
     3.1.  STAR API  . . . . . . . . . . . . . . . . . . . . . . . .   8
       3.1.1.  Creating a Delegation Request . . . . . . . . . . . .   8
       3.1.2.  Polling the Delegation Request  . . . . . . . . . . .  10
     3.2.  Transport Security for the STAR Protocol  . . . . . . . .  11
   4.  CDNI Use Cases  . . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  Multiple Parallel Delegates . . . . . . . . . . . . . . .  11
     4.2.  Chained Delegation  . . . . . . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
     5.1.  STAR Protocol Authentication  . . . . . . . . . . . . . .  12
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  14
     A.1.  draft-sheffer-acme-star-request-02  . . . . . . . . . . .  14
     A.2.  draft-sheffer-acme-star-request-01  . . . . . . . . . . .  14
     A.3.  draft-sheffer-acme-star-request-00  . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14







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1.  Introduction

   This document is a companion document to [I-D.ietf-acme-star].  To
   avoid duplication, we give here a bare-bones description of the
   motivation for this solution.  For more details and further use
   cases, please refer to the introductory sections of
   [I-D.ietf-acme-star].

   A content provider (referred to in this document as Domain Name
   Owner, DNO, or more generally as Identity Owner, IdO) has agreements
   in place with one or more Content Delivery Networks (CDNs) that are
   contracted to serve its content over HTTPS.  The CDN terminates the
   HTTPS connection at one of its edge cache servers and needs to
   present its clients (browsers, set-top-boxes) a certificate whose
   name matches the authority of the URL that is requested, i.e. that of
   the DNO.  However, many DNOs balk at sharing their long-term private
   keys with another organization and, equally, delegates (henceforth
   referred to as NDC, Name Delegation Consumer) would rather not have
   to handle other parties' long-term secrets.

   This document describes a protocol where the IdO and the NDC agree on
   a CSR template and the NDC generates a CSR for a private key that it
   holds.  The IdO then uses the ACME protocol (as extended in
   [I-D.ietf-acme-star]) to issue the STAR certificate.

   The generated short-term certificate is automatically renewed by an
   ACME Certification Authority (CA) [I-D.ietf-acme-acme] and
   periodically fetched into the NDC and used for HTTPS connections.
   The IdO can end the delegation at any time by simply instructing the
   CA to stop the automatic renewal and letting the certificate expire
   shortly thereafter.

1.1.  Terminology

   IdO  Identity Owner, the owner of an identity (e.g., a domain name)
      that needs to be delegated.
   DNO  Domain Name Owner, a specific kind of IdO whose identity is a
      domain name.
   NDC  Name Delegation Consumer, the entity to which the domain name is
      delegated for a limited time.  This is often a CDN (in fact,
      readers may note the similarity of the two acronyms).
   CDN  Content Delivery Network, a widely distributed network that
      serves the domain's web content to a wide audience at high
      performance.
   STAR  Short-Term, Automatically Renewed X.509 certificates.
   ACME  The IETF Automated Certificate Management Environment, a
      certificate management protocol.
   CA A Certificate Authority that implements the ACME protocol.



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1.2.  Conventions used in this document

   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
   [RFC2119].

2.  Protocol Flow

   This section presents the protocol flow.  For completeness, we
   include the STAR Interface proposed in this draft, as well as the
   extended ACME protocol as described in [I-D.ietf-acme-star].

2.1.  Preconditions

   The protocol assumes the following preconditions are met:

   o  A mutually authenticated channel between NDC and IdO pre-exists.
      This is called "STAR channel" and all STAR protocol exchanges
      between NDC and IdO are run over it.  It provides the guarantee
      that requests and responses are authentic.
   o  NDC and IdO have agreed on a "CSR template" to use, including at a
      minimum:

      -  Subject name (e.g., "somesite.example.com"),
      -  Requested algorithms,
      -  Key length,
      -  Key usage.

      The NDC is required to use this template for every CSR created
      under the same delegation.
   o  IdO has registered through the ACME interface exposed by the
      Certificate Authority (CA) using the usual ACME registration
      procedure.  In ACME terms, the IdO has an Account on the server
      and is ready to issue Orders.

2.2.  Bootstrap

   The NDC (STAR Client) generates a key-pair, wraps it into a
   Certificate Signing Request (CSR) according to the agreed upon CSR
   template, and sends it to the IdO (STAR Proxy) over the pre-
   established STAR channel.  The IdO uses the NDC identity provided on
   the STAR channel to look up the CSR template that applies to the
   requesting NDC and decides whether or not to accept the request.
   Assuming everything is in order, it then "forwards" the NDC request
   to the ACME CA by means of the usual ACME application procedure.
   Specifically, the IdO, in its role as an ACME client, requests the CA
   to issue a STAR certificate, i.e., one that:



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   o  Has a short validity (e.g., 24 to 72 hours);
   o  Is automatically renewed by the CA for a certain period of time;
   o  Is downloadable from a (highly available) public link without
      requiring any special authorization.

   Other than that, the ACME protocol flows as normal between IdO and
   CA, in particular IdO is responsible for satisfying the requested
   ACME challenges until the CA is willing to issue the requested
   certificate.  Per normal ACME processing, the IdO is given back an
   Order ID for the issued STAR certificate to be used in subsequent
   interaction with the CA (e.g., if the certificate needs to be
   terminated.)

   Concurrently, a response is sent back to the NDC with an endpoint to
   poll for completion of the certificate generation process.

   The bootstrap phase ends when the IdO obtains the OK from the ACME CA
   and posts the certificate's URL to the "completion endpoint" where
   the NDC can retrieve it.
































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                      ...........................
 STAR                 :  STAR Proxy /           :              ACME/STAR
 Client               :           ACME Client   :               Server
   |                  :    |               |    :                  |
   |                  :    |               |   ACME registration   |
   +-------.          :    |               |<--------------------->|
   |       |          :    |               |   STAR capabilities   |
   |   generate CSR   :    |               |    :                  |
   |       |          :    |               |    :                  |
   |<------'          :    |               |    :                  |
   |                  :    |               |    :                  |
   |     Request new  :    |               |    :                  |
   +---------------------->|               |    :                  |
   |     cert for CSR :    |               |    :                  |
   |                  :    +-------.       |    :                  |
   |                  :    |       |       |    :                  |
   |                  :    |   Verify CSR  |    :                  |
   |                  :    |       |       |    :                  |
   |                  :    +<------'       |    :                  |
   |   Accepted, poll at   |               |    :                  |
   |<----------------------+               |    :                  |
   |    "completion URL"   |- - - - - - - >|    Application for    |
   |                  :    |               +---------------------->|
   |                  :    |               |    STAR certificate   |
   |                  :    |               |    :                  |
   |  GET "completion URL" |               |    :  Challenge       |
   |<--------------------->|               |<--------------------->|
   |   in progress    :    |               |    :  Response        |
   |                  :    |               |    :                  |
   |                  :    |               |  Finalize/Certificate |
   |                  :    |               |<----------------------+
   |  GET "completion URL" |< - - - - - - -|    : + Order Id       |
   +---------------------->|               |    :                  |
   |                  :    |               |    :                  |
   |  200, certificate URL |               |    :                  |
   |<----------------------+               |    :                  |
   |   and other metadata  |               |    :                  |
   |                  :    |               |    :                  |
                      `.........................'

                            Figure 1: Bootstrap

2.3.  Refresh

   The CA automatically re-issues the certificate (using the same CSR)
   before it expires and publishes it to the URL that the NDC has come
   to know at the end of the bootstrap phase.  The NDC downloads and
   installs it.  This process goes on until either:



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   o  IdO terminates the delegation, or
   o  Automatic renewal expires.

           STAR                    ACME/STAR
           Client                  Server
             |     Retrieve cert     |                     [...]
             |<--------------------->|                      |
             |                       +------.              /
             |                       |      |             /
             |                       | Automatic renewal :
             |                       |      |             \
             |                       |<-----'              \
             |     Retrieve cert     |                      |
             |<--------------------->|                   72 hours
             |                       |                      |
             |                       +------.              /
             |                       |      |             /
             |                       | Automatic renewal :
             |                       |      |             \
             |                       |<-----'              \
             |     Retrieve cert     |                      |
             |<--------------------->|                   72 hours
             |                       |                      |
             |                       +------.              /
             |                       |      |             /
             |                       | Automatic renewal :
             |                       |      |             \
             |                       |<-----'              \
             |                       |                      |
             |         [...]         |                    [...]

                          Figure 2: Auto renewal

2.4.  Termination

   The IdO may request early termination of the STAR certificate by
   including the Order ID in a certificate termination request to the
   ACME interface, defined below.  After the CA receives and verifies
   the request, it shall:

   o  Cancel the automatic renewal process for the STAR certificate;
   o  Change the certificate publication resource to return an error
      indicating the termination of the delegation to external clients,
      including the NDC.

   Note that it is not necessary to explicitly revoke the short-term
   certificate.




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   STAR                    STAR                   ACME/STAR
   Client                  Proxy                  Server
     |                       |                       |
     |                       |  Terminate Order ID   |
     |                       +---------------------->|
     |                       |                       +-------.
     |                       |                       |       |
     |                       |                       |  End auto renewal
     |                       |                       |  Remove cert link
     |                       |                       |  etc.
     |                       |                       |       |
     |                       |         Done          |<------'
     |                       |<----------------------+
     |                       |                       |
     |                                               |
     |                 Retrieve cert                 |
     +---------------------------------------------->|
     |                 Error: terminated             |
     |<----------------------------------------------+
     |                                               |

                           Figure 3: Termination

   No facility is provided for the NDC to directly initiate the
   termination of a STAR certificate.

3.  Protocol Details

   This section describes the STAR API between the STAR Client and the
   STAR Proxy.

3.1.  STAR API

   This API allows an IdO (STAR Proxy) to control the long-term
   delegation of one of its names to an authorized third-party (STAR
   Client).

3.1.1.  Creating a Delegation Request

   To create a new delegation request, the client wraps the following
   parameters in a POST to the '/star/delegation' path:

   o  csr (required, string): A CSR encoding the parameters for the
      certificate being requested [RFC2986].  The CSR is sent in the
      base64url-encoded version of the DER format.  (Note: Because this
      field uses base64url, and does not include headers, it is
      different from PEM.)




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   o  duration (optional, integer): How long the delegation should last
      (in seconds).  If not specified, a local default applies.
   o  certificate-lifetime (optional, integer): How long each short-term
      certificate should last (in seconds).  If not specified, a local
      default applies.

   Note that the STAR Proxy MAY treat both "duration" and "certificate-
   lifetime" as hints, and MAY update any of them due to local policy
   decisions or as a result of the interaction with the ACME server.

       POST /star/delegation
       Host: star-proxy.example.net
       Content-Type: application/json

       {
           "csr": "jcRf4uXra7FGYW5ZMewvV...rhlnznwy8YbpMGqwidEXfE",
           "duration": 31536000,
           "certificate-lifetime": 604800
       }

   On success, the service returns a 201 Created status with the URL of
   the newly generated delegation order in the Location header field.
   The current state of the delegation order is returned in the body of
   the response in JSON format:

       HTTP/1.1 201 Created
       Content-Type: application/json
       Location: http://example.net/star/delegation/567

       {
           "id": "567",
           "certificate-lifetime": 604800,
           "duration": 31536000,
           "status": "new"
       }

   If an error occurs, an error response (4XX or 5XX) is generated with
   an appropriate problem detail [RFC7807] body, e.g.:













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       HTTP/1.1 400 Bad Request
       Content-Type: application/problem+json

       {
          "type": "https://example.net/validation-error",
          "title": "Your request parameters didn't validate.",
          "invalid-params": [ {
                                "name": "csr",
                                "reason": "missing mandatory parameter"
                              } ]
       }

3.1.2.  Polling the Delegation Request

   The returned delegation order URL can be polled until the dialog
   between the STAR Proxy and the ACME server is complete (i.e., the
   "status" attribute changes from "new" or "pending" to one of "failed"
   or "success"):

       GET /star/delegation/567
       Host: star-proxy.example.net

   In responding to poll requests while the validation is still in
   progress, the server MUST return a 200 (OK) response and MAY include
   a Retry-After header field to suggest a polling interval to the
   client.  The Retry-After value MUST be expressed in seconds.  If the
   Retry-After header is present, in order to avoid surprising
   interactions with heuristic expiration times, a max-age Cache-Control
   SHOULD also be present and set to a value slightly smaller than the
   Retry-After value:

       HTTP/1.1 200 OK
       Content-Type: application/json
       Retry-After: 10
       Cache-Control: max-age=9

       {
           "id": "5",
           "certificate-lifetime": 604800,
           "creation-date": "2017-11-12T01:38:09Z",
           "duration": 31536000,
           "status": "pending"
       }

   When the operation is successfully completed, the ACME Proxy returns:






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       HTTP/1.1 200 OK

       {
           "status": "success", // or "failed"
           "lifetime": 365,     // lifetime of the registration in days,
                                // possibly less than requested
           "certificates": "https://ca.example.org/certificates/A51A3"
       }

   The "certificates" attribute contains a URL of the certificate pull
   endpoint, received from the ACME Server.

   If the registration fails for any reason, the server returns a "200
   OK" response, with the status as "failed" and a "reason" attribute
   containing a human readable error message.

3.2.  Transport Security for the STAR Protocol

   Traffic between the STAR Client and the STAR Proxy MUST be protected
   with HTTPS.  For interoperability, all implementations MUST support
   HTTP Basic Authentication [RFC7617].  However some deployments MAY
   prefer mutually-authenticated HTTPS or two-legged OAUTH.

4.  CDNI Use Cases

   Members of the IETF CDNI (Content Delivery Network Interconnection)
   working group are interested in delegating authority over web content
   to CDNs.  Their requirements are described in a draft
   [I-D.fieau-cdni-https-delegation] that compares several solutions.
   This section discusses two particular requirements in the context of
   the STAR protocol.

4.1.  Multiple Parallel Delegates

   In some cases the DNO would like to delegate authority over a web
   site to multiple CDNs.  This could happen if the DNO has agreements
   in place with different regional CDNs for different geographical
   regions.  STAR enables this use case naturally, since each CDN can
   authenticate separately to the DNO specifying its CSR, and the DNO is
   free to allow or deny each certificate request according to its own
   policy.

4.2.  Chained Delegation

   In other cases, a content owner (DNO) delegates some domains to a
   large CDN (CDN1), which in turn delegates to a smaller regional CDN,
   CDN2.  The DNO has a contractual relationship with CDN1, and CDN1 has




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   a similar relationship with CDN2.  However DNO may not even know
   about CDN2.

   The STAR protocol does not prevent this use case, although there is
   no special support for it.  CDN1 can forward requests from CDN2 to
   DNO, and forward responses back to CDN2.  Whether such proxying is
   allowed is governed by policy and contracts between the parties.

5.  Security Considerations

5.1.  STAR Protocol Authentication

   The STAR protocol allows its client to obtain certificates bearing
   the IdO's identity.  Therefore strong client authentication is
   mandatory.

   When multiple NDCs may connect to the same IdO, the STAR protocol's
   authentication MUST allow the IdO to distinguish between different
   NDCs, and the IdO MUST associate different Registration objects to
   different clients.  Among other benefits, this allows the IdO to
   cancel a STAR registration for one of its clients instead of all of
   them.

6.  Acknowledgments

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement no. 688421 Measurement and Architecture
   for a Middleboxed Internet (MAMI).  This support does not imply
   endorsement.

7.  References

7.1.  Normative References

   [I-D.ietf-acme-acme]
              Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
              Kasten, "Automatic Certificate Management Environment
              (ACME)", draft-ietf-acme-acme-12 (work in progress), April
              2018.

   [I-D.ietf-acme-star]
              Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T.
              Fossati, "Support for Short-Term, Automatically-Renewed
              (STAR) Certificates in Automated Certificate Management
              Environment (ACME)", draft-ietf-acme-star-03 (work in
              progress), March 2018.





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   [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>.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <https://www.rfc-editor.org/info/rfc2986>.

   [RFC7617]  Reschke, J., "The 'Basic' HTTP Authentication Scheme",
              RFC 7617, DOI 10.17487/RFC7617, September 2015,
              <https://www.rfc-editor.org/info/rfc7617>.

   [RFC7807]  Nottingham, M. and E. Wilde, "Problem Details for HTTP
              APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
              <https://www.rfc-editor.org/info/rfc7807>.

7.2.  Informative References

   [I-D.fieau-cdni-https-delegation]
              Fieau, F., Emile, S., and S. Mishra, "HTTPS delegation in
              CDNI", draft-fieau-cdni-https-delegation-02 (work in
              progress), July 2017.



























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Appendix A.  Document History

   [[Note to RFC Editor: please remove before publication.]]

A.1.  draft-sheffer-acme-star-request-02

   o  Clarifications and minor changes based on implementation
      experience.
   o  More detail on error cases.

A.2.  draft-sheffer-acme-star-request-01

   o  Correct reference to WG draft.

A.3.  draft-sheffer-acme-star-request-00

   o  Initial version, the STAR API extracted from draft-sheffer-acme-
      star-02.

Authors' Addresses

   Yaron Sheffer
   Intuit

   EMail: yaronf.ietf@gmail.com


   Diego Lopez
   Telefonica I+D

   EMail: diego.r.lopez@telefonica.com


   Oscar Gonzalez de Dios
   Telefonica I+D

   EMail: oscar.gonzalezdedios@telefonica.com


   Antonio Agustin Pastor Perales
   Telefonica I+D

   EMail: antonio.pastorperales@telefonica.com








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   Thomas Fossati
   Nokia

   EMail: thomas.fossati@nokia.com















































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