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ACME                                                          Y. Sheffer
Internet-Draft                                                    Intuit
Intended status: Standards Track                                D. Lopez
Expires: December 18, 2017                           O. Gonzalez de Dios
                                                       A. Pastor Perales
                                                          Telefonica I+D
                                                              T. Fossati
                                                                   Nokia
                                                           June 16, 2017


 Generating Certificate Requests for Short-Term, Automatically-Renewed
                          (STAR) Certificates
                   draft-sheffer-acme-star-request-01

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 http://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 18, 2017.






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Copyright Notice

   Copyright (c) 2017 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
   (http://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 Registration . . . . . . . . . . . . . . .   8
       3.1.2.  Polling the Registration  . . . . . . . . . . . . . .   9
     3.2.  Transport Security for the STAR Protocol  . . . . . . . .  10
   4.  CDNI Use Cases  . . . . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Multiple Parallel Delegates . . . . . . . . . . . . . . .  10
     4.2.  Chained Delegation  . . . . . . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
     5.1.  STAR Protocol Authentication  . . . . . . . . . . . . . .  11
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  13
     A.1.  draft-sheffer-acme-star-request-01  . . . . . . . . . . .  13
     A.2.  draft-sheffer-acme-star-request-00  . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13








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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 barebones 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) 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 DNO and the NDC agree on
   a CSR template and the NDC generates a CSR for a private key that it
   holds.  The DNO 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 routinely
   fetched into the NDC and used for HTTPS connections.  The DNO 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

   DNO  Domain Name Owner, the owner of a domain that needs to be
      delegated.
   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 DNO pre-exists.
      This is called "STAR channel" and all STAR protocol exchanges
      between NDC and DNO are run over it.  It provides the guarantee
      that requests and responses are authentic.
   o  NDC and DNO 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  DNO has registered through the ACME interface exposed by the
      Certificate Authority (CA) using the usual ACME registration
      procedure.  In ACME terms, the DNO 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 DNO (STAR Proxy) over the pre-
   established STAR channel.  The DNO 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 DNO, 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 DNO and
   CA, in particular DNO is responsible for satisfying the requested
   ACME challenges until the CA is willing to issue the requested
   certificate.  Per normal ACME processing, the DNO 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 DNO 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  DNO 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 DNO 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

3.  Protocol Details

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

3.1.  STAR API

   This API allows the STAR Client to request a STAR certificate via the
   STAR Proxy, using a previously agreed-upon CSR template.

   The API consists of a single resource, "registration".  A new
   Registration is created with a POST request, and the Registration
   instance is polled to obtain its details.

3.1.1.  Creating a Registration

   To create a registration, use:











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

   {
       "csr": "...",    // CSR in PEM format
       "lifetime": 365, // requested registration lifetime in days,
                        // between 1 and 1095
       "validity": 7    // requested certificate validity in days
   }

   The STAR Proxy MAY treat both "lifetime" and "validity" periods as
   hints.  Upon success, the call returns the new Registration resource.

   HTTP/1.1 201 Created
   Location: https://star-proxy.example.net/star/registration/567

3.1.2.  Polling the Registration

   The returned Registration can be polled until the information is
   available from the ACME server.

   GET /star/registration/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
   Retry-After: 10
   Cache-Control: max-age=9

   {
       "status": "pending"
   }

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








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HTTP/1.1 200 OK
Expires: Sun, 09 Sep 2018 14:09:00 GMT

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

   The Expires header applies to the Registration resource itself, and
   may be as small as a few minutes.  It is unrelated to the Order's
   lifetime which is measured in days or longer.  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.






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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
   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 DNO's identity.  Therefore strong client authentication is
   mandatory.

   When multiple NDCs may connect to the same DNO, the STAR protocol's
   authentication MUST allow the DNO to distinguish between different
   NDCs, and the DNO MUST associate different Registration objects to
   different clients.  Among other benefits, this allows the DNO 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., and J. Kasten, "Automatic
              Certificate Management Environment (ACME)", draft-ietf-
              acme-acme-06 (work in progress), March 2017.








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   [I-D.ietf-acme-star]
              Sheffer, Y., Lopez, D., Dios, O., Pastor, A., and T.
              Fossati, "Use of Short-Term, Automatically-Renewed (STAR)
              Certificates to Delegate Authority over Web Sites", draft-
              ietf-acme-star-00 (work in progress), June 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

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

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-01 (work in
              progress), March 2017.






























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Appendix A.  Document History

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

A.1.  draft-sheffer-acme-star-request-01

   o  Correct reference to WG draft.

A.2.  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


   Thomas Fossati
   Nokia

   EMail: thomas.fossati@nokia.com








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