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Versions: (draft-sheffer-acme-star-lurk) 00 01 02 draft-ietf-acme-star

ACME Working Group                                            Y. Sheffer
Internet-Draft                                                    Intuit
Intended status: Standards Track                                D. Lopez
Expires: October 21, 2017                            O. Gonzalez de Dios
                                                          Telefonica I+D
                                                              T. Fossati
                                                                   Nokia
                                                          April 19, 2017


Use of Short-Term, Automatically-Renewed (STAR) Certificates to Delegate
                        Authority over Web Sites
                       draft-sheffer-acme-star-00

Abstract

   This memo proposes two mechanisms that work in concert to allow a
   third party (e.g., a content delivery network) to terminate TLS
   sessions on behalf of a domain name owner (e.g., a content provider).

   The proposed mechanisms are:

   1.  An extension to the ACME protocol to enable the issuance of
       short-term and automatically renewed certificates, and
   2.  A protocol that allows a domain name owner to delegate to a third
       party control over a certificate that bears its own name.

   It should be noted that these are in fact independent building blocks
   that could be used separately to solve completely different problems.

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 October 21, 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
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   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.  A Solution for the HTTPS CDN Use Case . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Preconditions . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Bootstrap . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Refresh . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  Termination . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Protocol Details  . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  STAR API  . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.1.1.  Creating a Registration . . . . . . . . . . . . . . .   8
       4.1.2.  Polling the Registration  . . . . . . . . . . . . . .   9
     4.2.  Transport Security for the STAR Protocol Leg  . . . . . .  10
     4.3.  ACME Extensions between Proxy and Server  . . . . . . . .  10
       4.3.1.  Extending the Order Resource  . . . . . . . . . . . .  10
       4.3.2.  Canceling a Recurrent Order . . . . . . . . . . . . .  11
       4.3.3.  Indicating Support of Recurrent Orders  . . . . . . .  11
     4.4.  Fetching the Certificates . . . . . . . . . . . . . . . .  11
   5.  CDNI Use Cases  . . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Multiple Parallel Delegates . . . . . . . . . . . . . . .  12
     5.2.  Chained Delegation  . . . . . . . . . . . . . . . . . . .  12
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
     6.1.  Restricting CDNs to the Delegation Mechanism  . . . . . .  12
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  15
     A.1.  draft-sheffer-acme-star-00  . . . . . . . . . . . . . . .  15
     A.2.  draft-sheffer-acme-star-lurk-00 . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15




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1.  A Solution for the HTTPS CDN Use Case

   A content provider that we refer to as a Domain Name Owner (DNO), has
   agreements in place with one or more Content Delivery Networks (CDN)
   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, CDN providers
   would rather not have to handle other parties' long-term secrets.
   This problem has been discussed at the IETF under the LURK (limited
   use of remote keys) title.

   This document proposes a solution to the above problem that involves
   the use of short-term certificates with a DNO's name on them, and a
   scheme for handling the naming delegation from the DNO to the CDN.
   The generated short-term credentials are automatically renewed by an
   ACME Certification Authority (CA) [I-D.ietf-acme-acme] and routinely
   rotated by the CDN on its edge cache servers.  The DNO can end the
   delegation at any time by simply instructing the CA to stop the
   automatic renewal and let the certificate expire shortly after.

   Using short-term certificates makes revocation cheap and effective
   [Topalovic] [I-D.iab-web-pki-problems] in case of key compromise or
   of termination of the delegation; seamless certificate issuance and
   renewal enable the level of workflow automation that is expected in
   today's cloud environments.  Also, compared to other keyless-TLS
   solutions [I-D.cairns-tls-session-key-interface]
   [I-D.erb-lurk-rsalg], the proposed approach doesn't suffer from
   scalability issues or increase in connection setup latency, while
   requiring virtually no changes to existing COTS caching software used
   by the CDN.

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].

   TODO: glossary.

3.  Protocol Flow

   The protocol flow can be split into two: a STAR interface, used by
   CDN and DNO to agree on the name delegation, and the extended ACME
   interface, used by DNO to obtain the short-term and automatically



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   renewed certificate from the CA, which is eventually consumed by the
   CDN.  The latter is also used to terminate the delegation, if so
   needed.

   The following subsections describe the preconditions (Section 3.1),
   and the three main phases of the protocol:

   o  Bootstrap: the CDN requests from the DNO the delegation of a
      specific name and in turn DNO asks an ACME CA to create the
      corresponding short-term and auto-renewed (STAR) certificate
      (Section 3.2);
   o  Auto-renewal: the ACME CA periodically re-issues the short-term
      certificate and posts it to a public URL (Section 3.3);
   o  Termination: the DNO (indirectly) stops name delegation by
      explicitly requesting the ACME CA to discontinue the automatic
      renewal of the certificate (Section 3.4).

3.1.  Preconditions

   The protocol assumes the following preconditions are met:

   o  A mutually authenticated channel between CDN and DNO pre-exists.
      This is called "STAR channel" and all STAR protocol exchanges
      between CDN and DNO are run over it.  It provides the guarantee
      that requests and responses are authentic [[_1: Note that, under
      this assumption, the key used to authenticate the CDN to the DNO
      becomes a critical asset for the security of the proposed
      protocol, and that certain interactions (e.g., CSR submission)
      might require a stronger authentication mechanism.  For example,
      stacking a further authentication factor on top of CDN's STAR key
      would allow to distinguish an attacker that has only managed to
      successfully attack the CDN's STAR key from the legitimate CDN.
      --tf]].
   o  CDN and DNO have agreed on a "CSR template" to use, including at a
      minimum:

      -  Subject name (e.g., "somesite.DNO.com"),
      -  Validity (e.g., 24 to 72 hours),
      -  Requested algorithms,
      -  Key length,
      -  Key usage.

      The CDN 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.  The DNO shall, at the registration stage, query the
      ACME server for the supported STAR capabilities - for example: the



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      minimum validity period of the issued certificate, the maximum
      duration of the automatic renewal process (either as a maximum
      number of renewal events, or as its maximum absolute life-span).

3.2.  Bootstrap

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

   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.  The DNO is given back a unique identifier 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 202 response has been sent back to the CDN 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 CDN can retrieve it.  The information that is passed on to the
   CDN at this stage also includes details about how much time before
   the certificate expires can the CDN expect the replacement to be
   ready.










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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       |
   |<--------------------->|               |<--------------------->|
   |   202, in progress    |               |    :  Response        |
   |                  :    |               |    :                  |
   |                  :    |               |  Finalize/Certificate |
   |                  :    |               |<----------------------+
   |  GET "completion URL" |< - - - - - - -|    : + STAR Id        |
   +---------------------->|               |    :                  |
   |                  :    |               |    :                  |
   |  200, certificate URL |               |    :                  |
   |<----------------------+               |    :                  |
   |   and other metadata  |               |    :                  |
   |                  :    |               |    :                  |
                      `.........................'

                            Figure 1: Bootstrap

3.3.  Refresh

   The CA automatically re-issues the certificate (using the same CSR)
   before it expires and publishes it to the URL that the CDN has come
   to know at the end of the bootstrap phase.  The CDN 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

3.4.  Termination

   DNO requests termination of the STAR certificate by including the
   previously obtained identifier in a STAR certificate termination
   request to the ACME interface.  After 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 CDN;

   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 STAR Id    |
     |                       +---------------------->|
     |                       |                       +-------.
     |                       |                       |       |
     |                       |                       |  End auto renewal
     |                       |                       |  Remove cert link
     |                       |                       |  etc.
     |                       |                       |       |
     |                       |         Done          |<------'
     |                       |<----------------------+
     |                       |                       |
     |                                               |
     |                 Retrieve cert                 |
     +---------------------------------------------->|
     |                 Error: terminated             |
     |<----------------------------------------------+
     |                                               |

                           Figure 3: Termination

4.  Protocol Details

   This section describes the protocol's details.  We start with the
   STAR API between the STAR Client and the STAR Proxy.  Then we
   describe a few extensions to the ACME protocol running between the
   STAR Proxy and the ACME Server.

4.1.  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 and then the Registration
   instance is polled to obtain its details.

4.1.1.  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
   }

   Upon success, the call returns the new Registration resource.

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

4.1.2.  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, see
   Section 4.4.

   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.

4.2.  Transport Security for the STAR Protocol Leg

   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.

4.3.  ACME Extensions between Proxy and Server

   We propose to extend the ACME protocol slightly, by allowing
   recurrent orders.

4.3.1.  Extending the Order Resource

   The Order resource is extended with the following attributes:

 {
     "recurrent": true,
     "recurrent-total-lifetime": 365, // requested lifetime of the
                                      // recurrent registration, in days
     "recurrent-certificate-validity": 7
        // requested validity of each certificate, in days
 }

   These attributes are included in a POST message when creating the
   order, as part of the "payload" encoded object.  They are returned
   when the order has been created, possibly with adjusted values.




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4.3.2.  Canceling a Recurrent Order

   An important property of the recurrent order is that it can be
   cancelled by the domain name owner, with no need for certificate
   revocation.  We use the DELETE message for that:

   DELETE /acme/order/1 HTTP/1.1
   Host: acme-server.example.org

   Which returns:

   HTTP/1.1 202 Deleted

   The server MUST NOT issue any additional certificates for this Order,
   beyond the certificate that is available for collection at the time
   of deletion.

4.3.3.  Indicating Support of Recurrent Orders

   ACME supports sending arbitrary extensions when creating an Order,
   and as a result, there is no need to explicitly indicate support of
   this extension.  The Proxy MUST verify that the "recurrent" attribute
   was understood, as indicated by the "recurrent" attribute included in
   the created Order.  Since the standard ACME protocol does not allow
   to explicitly cancel a pending Order (the DELETE operation above is
   an extension), an unhappy Proxy will probably let the Order expire
   instead of following through with the authorization process.

4.4.  Fetching the Certificates

   The certificate is fetched from the certificate endpoint, as per
   [I-D.ietf-acme-acme], Sec. 7.4.2 "Downloading the Certificate".  The
   server MUST include an Expires header that indicates expiry of the
   specific certificate.  When the certificate expires, the client MAY
   assume that a newer certificate is already in place.

   A certificate MUST be replaced by its successor at the latest 24
   hours before its "Not After" time.

5.  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.




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5.1.  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.

5.2.  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.

6.  Security Considerations

   o  CDN's client certificate key is first order security asset and
      MUST be protected.  Absent 2FA/MFA, an attacker that can
      compromise the key might be able to obtain certificates bearing
      DNO's identity.
   o  Consider collusion of two or more CDNs with contracts with the
      same DNO (?)

6.1.  Restricting CDNs to the Delegation Mechanism

   Currently there are no standard methods for the DNO to ensure that
   the CDN cannot issue a certificate through mechanisms other than the
   one described here, for the URLs under the CDN's control.  For
   example, regardless of the STAR solution, a rogue CDN employee can
   use the ACME protocol (or proprietary mechanisms used by various CAs)
   to create a fake certificate for the DNO's content.

   The best solution currently being worked on would consist of several
   related configuration steps:

   o  Make sure that the CDN cannot modify the DNS records for the
      domain.  Typically this would mean that the content owner
      establishes a CNAME resource record from a subdomain into a CDN-
      managed domain.



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   o  Restrict certificate issuance for the domain to specific CAs that
      comply with ACME.  This assumes universal deployment of CAA
      [RFC6844] by CAs, which is not the case yet.
   o  Deploy ACME-specific methods to restrict issuance to a specific
      authorization key which is controlled by the content owner
      [I-D.landau-acme-caa], and/or to specific ACME authorization
      methods.

   This solution is recommended in general, even if an alternative to
   the mechanism described here is used.

7.  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.

8.  References

8.1.  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.

   [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>.

8.2.  Informative References

   [I-D.cairns-tls-session-key-interface]
              Cairns, K., Mattsson, J., Skog, R., and D. Migault,
              "Session Key Interface (SKI) for TLS and DTLS", draft-
              cairns-tls-session-key-interface-01 (work in progress),
              October 2015.

   [I-D.erb-lurk-rsalg]
              Erb, S. and R. Salz, "A PFS-preserving protocol for LURK",
              draft-erb-lurk-rsalg-01 (work in progress), May 2016.




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   [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.

   [I-D.iab-web-pki-problems]
              Housley, R. and K. O'Donoghue, "Improving the Public Key
              Infrastructure (PKI) for the World Wide Web", draft-iab-
              web-pki-problems-05 (work in progress), October 2016.

   [I-D.landau-acme-caa]
              Landau, H., "CA Account URI Binding for CAA Records",
              draft-landau-acme-caa-01 (work in progress), October 2016.

   [RFC6844]  Hallam-Baker, P. and R. Stradling, "DNS Certification
              Authority Authorization (CAA) Resource Record", RFC 6844,
              DOI 10.17487/RFC6844, January 2013,
              <http://www.rfc-editor.org/info/rfc6844>.

   [Topalovic]
              Topalovic, E., Saeta, B., Huang, L., Jackson, C., and D.
              Boneh, "Towards Short-Lived Certificates", 2012,
              <http://www.w2spconf.com/2012/papers/w2sp12-final9.pdf>.




























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Internet-Draft                  ACME STAR                     April 2017


Appendix A.  Document History

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

A.1.  draft-sheffer-acme-star-00

   o  Renamed draft to prevent confusion with other work in this space.
   o  Added an initial STAR protocol: a REST API.
   o  Discussion of CDNI use cases.

A.2.  draft-sheffer-acme-star-lurk-00

   o  Initial version.

Authors' Addresses

   Yaron Sheffer
   Intuit

   EMail: yaronf.ietf@gmail.com


   Diego Lopez
   Telefonica I+D

   EMail: diego@telefonica.es


   Oscar Gonzalez de Dios
   Telefonica I+D

   EMail: oscar.gonzalezdedios@telefonica.com


   Thomas Fossati
   Nokia

   EMail: thomas.fossati@nokia.com













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