[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-sheffer-acme-star) 00

ACME Working Group                                            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


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

Abstract

   This memo proposes an ACME extension to enable the issuance of short-
   term and automatically renewed certificates.  This allows a domain
   name owner to delegate the use of certificates to another party,
   while retaining the capability to cancel this delegation at any time
   with no need to rely on certificate revocation mechanisms.

   [RFC Editor: please remove before publication]

   While the draft is being developed, the editor's version can be found
   at https://github.com/yaronf/I-D/tree/master/STAR.

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.







Sheffer, et al.         Expires December 18, 2017               [Page 1]


Internet-Draft                  ACME STAR                      June 2017


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: A Solution for the HTTPS CDN Use Case . . . . .   3
     1.1.  Cloud Use Case  . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Conventions used in this document . . . . . . . . . . . .   4
   2.  Protocol Flow . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Bootstrap . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Refresh . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Termination . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Protocol Details  . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  ACME Extensions between Proxy and Server  . . . . . . . .   7
       3.1.1.  Extending the Order Resource  . . . . . . . . . . . .   7
       3.1.2.  Canceling a Recurrent Order . . . . . . . . . . . . .   8
     3.2.  Indicating Support of Recurrent Orders  . . . . . . . . .   8
     3.3.  ACME Authorization  . . . . . . . . . . . . . . . . . . .   8
     3.4.  Fetching the Certificates . . . . . . . . . . . . . . . .   9
   4.  Operational Considerations  . . . . . . . . . . . . . . . . .   9
     4.1.  Certificate Transparency (CT) Logs  . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     5.1.  Restricting CDNs to the Delegation Mechanism  . . . . . .   9
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  12
     A.1.  draft-ietf-acme-star-00 . . . . . . . . . . . . . . . . .  12
     A.2.  draft-sheffer-acme-star-02  . . . . . . . . . . . . . . .  12
     A.3.  draft-sheffer-acme-star-01  . . . . . . . . . . . . . . .  12
     A.4.  draft-sheffer-acme-star-00  . . . . . . . . . . . . . . .  12
     A.5.  draft-sheffer-acme-star-lurk-00 . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12




Sheffer, et al.         Expires December 18, 2017               [Page 2]


Internet-Draft                  ACME STAR                      June 2017


1.  Introduction: A Solution for the HTTPS CDN Use Case

   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,
   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 thereafter.

   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.

   This document describes the ACME extension.  A companion document [I-
   D.sheffer-acme-star-request] describes how the CDN can request the
   DNO to initiate the protocol with the ACME server.

1.1.  Cloud Use Case

   A similar use case is that of cloud infrastructure components, such
   as load balancers and Web Application Firewalls (WAF).  These
   components are typically provisioned with the DNO's certificate, and
   similarly to the CDN use case, many organizations would prefer to
   manage the private key only on their own cloud-based or on-premise
   hosts, often on Hardware Security Modules (HSMs).





Sheffer, et al.         Expires December 18, 2017               [Page 3]


Internet-Draft                  ACME STAR                      June 2017


   Here again, the STAR solution allows the DNO to delegate authority
   over the domain to the cloud provider, with the ability to revoke
   this authority at any time.

1.2.  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.

1.3.  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

   For clarity, we describe how the proposed ACME extension can be used
   in a system that consists of an NDC, an ACME Client (the DNO) and an
   ACME Server.  Only the latter part (ACME Client to ACME Server) is in
   scope of this document.

   The protocol flow can be split into two: a STAR interface, used by
   NDC and DNO to agree on the name delegation, and the extended ACME
   interface, used by DNO to obtain the short-term and automatically
   renewed certificate from the CA, which is eventually consumed by the
   NDC.  The latter is also used to terminate the delegation, if so
   needed.

   Communication between the NDC and the DNO (the STAR interface) is out
   of scope of this document.  It may take the form described in [I-
   D.sheffer-acme-star-request], some other online protocol, or may even
   be through manual generation of the CSR.

   The following subsections describe the three main phases of the
   protocol:




Sheffer, et al.         Expires December 18, 2017               [Page 4]


Internet-Draft                  ACME STAR                      June 2017


   o  Bootstrap: the DNO asks an ACME CA to create a corresponding
      short-term and auto-renewed (STAR) certificate, possibly on a
      request from an NDC which is out of scope for this document;
   o  Auto-renewal: the ACME CA periodically re-issues the short-term
      certificate and posts it to a public URL (Section 2.2);
   o  Termination: the DNO (indirectly) stops name delegation by
      explicitly requesting the ACME CA to discontinue the automatic
      renewal of the certificate (Section 2.3).

   This diagram presents the entities involved in the protocol and their
   interactions during the different phases.

                                    +-----------------+
                                    |    STAR Proxy   |
                                    |      (DNO)      |
                          Bootstrap +-----------------+ Bootstrap
                        +---------->+  STAR  |  ACME  +-----------+
                        |           | Server | Client | Terminate |
                        |           +--------+--------+           |
                        |                                         v
                    +--------+                                +--------+
                    |  STAR  |            Refresh             |  ACME  |
                    | Client +------------------------------->| Server |
                    | (NDC)  |                                |  (CA)  |
                    +--------+                                +--------+

2.1.  Bootstrap

   The DNO, in its role as an ACME client, requests the CA to issue 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.  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.)

   The bootstrap phase ends when the DNO obtains the OK from the ACME
   CA.





Sheffer, et al.         Expires December 18, 2017               [Page 5]


Internet-Draft                  ACME STAR                      June 2017


2.2.  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:

   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 1: Auto renewal

2.3.  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;



Sheffer, et al.         Expires December 18, 2017               [Page 6]


Internet-Draft                  ACME STAR                      June 2017


   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.

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

                           Figure 2: Termination

3.  Protocol Details

   This section describes the protocol's details, namely the extensions
   to the ACME protocol required to issue STAR certificates.

3.1.  ACME Extensions between Proxy and Server

   This protocol extends the ACME protocol, to allow for recurrent
   orders.

3.1.1.  Extending the Order Resource

   The Order resource is extended with the following attributes:








Sheffer, et al.         Expires December 18, 2017               [Page 7]


Internet-Draft                  ACME STAR                      June 2017


 {
     "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, and the ACME server MAY adjust them
   at will, according to its local policy.

3.1.2.  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 to cancel the Order:

   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.

3.2.  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), a Proxy that encounters an non-supporting server will
   probably let the Order expire instead of following through with the
   authorization process.

3.3.  ACME Authorization

   The DNO MUST restrict the authorizations it requests from the ACME
   server to only those that cannot be spoofed by a malicious NDC.  In
   most cases the NDC will have strong control of HTTP content under the




Sheffer, et al.         Expires December 18, 2017               [Page 8]


Internet-Draft                  ACME STAR                      June 2017


   delegated domain, and therefore HTTPS-based authorization MUST NOT be
   used.  See also Section 5.1.

3.4.  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 halfway
   through its lifetime (the period between its notBefore and notAfter
   times).

4.  Operational Considerations

4.1.  Certificate Transparency (CT) Logs

   TBD: larger logs and how to deal with them.

5.  Security Considerations

5.1.  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 because ACME
   authorizes its requests using information that may be under the
   adversary's control.

   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.
   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.  We note that the CA/
      Browser Forum has recently decided to require CAA checking
      [CAB-CAA].
   o  Deploy ACME-specific methods to restrict issuance to a specific
      authorization key which is controlled by the content owner



Sheffer, et al.         Expires December 18, 2017               [Page 9]


Internet-Draft                  ACME STAR                      June 2017


      [I-D.ietf-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.

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.

   [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>.

7.2.  Informative References

   [CAB-CAA]  CA/Browser Forum, "Ballot 187 - Make CAA Checking
              Mandatory", March 2017, <https://cabforum.org/2017/03/08/
              ballot-187-make-caa-checking-mandatory/>.

   [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.

   [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.




Sheffer, et al.         Expires December 18, 2017              [Page 10]


Internet-Draft                  ACME STAR                      June 2017


   [I-D.ietf-acme-caa]
              Landau, H., "CAA Record Extensions for Account URI and
              ACME Method Binding", draft-ietf-acme-caa-01 (work in
              progress), February 2017.

   [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>.





































Sheffer, et al.         Expires December 18, 2017              [Page 11]


Internet-Draft                  ACME STAR                      June 2017


Appendix A.  Document History

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

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

   o  Initial working group version.
   o  Removed the STAR interface, the protocol between NDC and DNO.
      What remains is only the extended ACME protocol.

A.2.  draft-sheffer-acme-star-02

   o  Using a more generic term for the delegation client, NDC.
   o  Added an additional use case: public cloud services.
   o  More detail on ACME authorization.

A.3.  draft-sheffer-acme-star-01

   o  A terminology section.
   o  Some cleanup.

A.4.  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.5.  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.r.lopez@telefonica.com








Sheffer, et al.         Expires December 18, 2017              [Page 12]


Internet-Draft                  ACME STAR                      June 2017


   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



































Sheffer, et al.         Expires December 18, 2017              [Page 13]


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/