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Versions: 00 01 02 03

Network Working Group                                           A. Biggs
Internet-Draft                                                 S. Cooley
Intended status: Standards Track                           Cisco Systems
Expires: May 21, 2015                                  November 17, 2014


                  Key Management Service Architecture
              draft-abiggs-saag-key-management-service-00

Abstract

   In the interest of addressing pervasive threats to the
   confidentiality and integrity of online communications identified by
   the Internet community [I-D.barnes-pervasive-problem] this
   specification introduces an open architecture for the establishment,
   management, and secure distribution of cryptographic keys for use in
   the end-to-end (E2E) encryption of online communications and shared
   content.  This architecture allows for the independent deployment of
   dedicated key management services in a manner that supports the
   adoption of third-party communications and data sharing services by
   individuals and organizations that require full and exclusive
   discretion over the confidentiality of their data.

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 May 21, 2015.

Copyright Notice

   Copyright (c) 2014 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



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   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 . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Security Terms  . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Notational Conventions  . . . . . . . . . . . . . . . . .   5
   2.  Architectural Overview  . . . . . . . . . . . . . . . . . . .   6
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Securing an HTTP File Sharing Service . . . . . . . . . .   9
     3.2.  Securing an XMPP Multi-User Chat  . . . . . . . . . . . .  10
     3.3.  KMS to KMS Key Federation . . . . . . . . . . . . . . . .  12
   4.  KMS Protocol  . . . . . . . . . . . . . . . . . . . . . . . .  14
     4.1.  Secure Channel  . . . . . . . . . . . . . . . . . . . . .  15
     4.2.  User Identity . . . . . . . . . . . . . . . . . . . . . .  16
     4.3.  KMS Identity  . . . . . . . . . . . . . . . . . . . . . .  16
     4.4.  Object Types  . . . . . . . . . . . . . . . . . . . . . .  17
       4.4.1.  KMS Key Objects . . . . . . . . . . . . . . . . . . .  17
       4.4.2.  KMS Authorization Objects . . . . . . . . . . . . . .  19
       4.4.3.  KMS Resource Objects (KRO)  . . . . . . . . . . . . .  20
     4.5.  Request Types . . . . . . . . . . . . . . . . . . . . . .  21
     4.6.  Message Structure . . . . . . . . . . . . . . . . . . . .  22
       4.6.1.  Basic Request Payload . . . . . . . . . . . . . . . .  22
       4.6.2.  Basic Response Payload  . . . . . . . . . . . . . . .  24
       4.6.3.  Error Response Payload  . . . . . . . . . . . . . . .  25
     4.7.  Requests  . . . . . . . . . . . . . . . . . . . . . . . .  25
       4.7.1.  Create Ephemeral Key  . . . . . . . . . . . . . . . .  25
       4.7.2.  Delete Ephemeral Key  . . . . . . . . . . . . . . . .  28
       4.7.3.  Create Resource . . . . . . . . . . . . . . . . . . .  29
       4.7.4.  Create Unbound Keys . . . . . . . . . . . . . . . . .  32
       4.7.5.  Update Unbound Key (Bind) . . . . . . . . . . . . . .  35
       4.7.6.  Retrieve Keys . . . . . . . . . . . . . . . . . . . .  37
       4.7.7.  Create Authorizations . . . . . . . . . . . . . . . .  41
       4.7.8.  Delete Authorization  . . . . . . . . . . . . . . . .  43
   5.  Mandatory-to-Implement  . . . . . . . . . . . . . . . . . . .  44
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  45
   7.  Appendix A. Acknowledgments . . . . . . . . . . . . . . . . .  45
   8.  Appendix B. Document History  . . . . . . . . . . . . . . . .  45
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  45
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  46
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  47
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  47



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1.  Introduction

   Providers of cloud-based services commonly secure user data at the
   transport level using established protocols such as TLS [RFC5246] or
   IPSec [RFC4301].  These protocols can be effective in protecting
   transmitted user data from third party tampering and eavesdropping;
   however, by themselves these protocols do not secure user data from
   abuses, negligence, or coerced behavior on the part of the cloud
   provider.  This is a concern for individuals and organizations that
   wish to take advantage of cloud-based communications and
   collaboration but cannot accept the risk of trusting cloud providers
   with unfettered access to the contents of their communications.

   E2E encryption describes a category of solutions that can be employed
   to address this problem by establishing secure channels among
   clients.  To the extent that a user can trust their collaboration
   client software, E2E encryption mitigates exposure of user data to
   untrusted parties by ensuring that intermediaries never possess
   unencrypted user data or have access to the keying material necessary
   to decrypt it.

   Existing E2E strategies such as ECS [RFC5652], PGP [RFC4880], and
   Off-the-Record Messaging [OTR] can be effective at securing two-party
   communications.  However, E2E encryption for the growing domain of
   multiparty communications and online content sharing remains a
   generally unsolved problem to which these existing approaches do not
   readily adapt.  In particular, a core challenge exists in providing
   for the secure distribution and rotation of E2E encryption keys among
   an arbitrary and potentially dynamic set of communicating clients.
   In cases where the communications to be secured are persistent or
   archived, the additional challenge exists for providing trusted long-
   term storage and retrieval of these keys.

   Equally problematic is the paucity of E2E encryption options that
   satisfy common organizational obligations such as regulatory
   compliance and legal discovery.  Entities that must operate within
   such frameworks require mechanisms by which they (and they alone) may
   recover the keys used to secure their communications.  Existing E2E
   encryption solutions are not, by themselves, well suited for this
   purpose.

   In the interest of addressing these challenges this document presents
   an architecture for the deployment of E2E encryption key management
   services (KMS).  In this architecture a KMS service provides to its
   users a means by which their communications clients may securely
   create, share, rotate, and store E2E encryption keying material.  It
   does so in a fashion that permits the decoupling of such services
   from the communications media, thereby permitting the former to



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   reside under the direct control of the communicating parties or the
   organizations within which they do business.

1.1.  Terminology

   This document uses the terminology from
   [I-D.ietf-jose-json-web-signature],
   [I-D.ietf-jose-json-web-encryption], [I-D.ietf-jose-json-web-key],
   and [I-D.ietf-jose-json-web-algorithms] when discussing JOSE
   technologies.

   This document makes use of the following terminology, and
   additionally adopts nomenclature defined in
   [I-D.barnes-pervasive-problem] for the purpose of describing aspects
   of pervasive attacks.

   communications resource

      A communications resource is any uniquely identifiable continuous
      data channel or discrete shared content that represents an
      exchange of personal communications between two or more users.

   communications resource client

      A communications resource client consumes communications resources
      on behalf of a user and, when deployed in conformance with the KMS
      architecture, consumes the services of KMS server(s) to facilitate
      the E2E encryption of those communications resources.

   communications resource server

      A communications resource server is a provider of services through
      which communications resources are made available.

   cloud provider

      An individual or organization responsible for, and in control of,
      one or more communications resource servers.

   E2E encryption

      Shorthand for end-to-end encryption, as defined in [RFC4949],
      particularly as it applies to the establishment of confidentiality
      and integrity of communications resources.

   KMS server





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      A key management server (KMS) is responsible for creating,
      storing, and providing access to E2E encryption keying material by
      communications resource clients.

   KMS protocol

      The protocol through which communications resource clients
      interoperate with KMS servers.

   KMS provider

      An individual or organization responsible for, and in control of,
      a KMS server deployment.

   KMS transport

      Any service or protocol that provides the basic transport over
      which KMS protocol messages are exchanged.

   resource client

      See communications resource client.

   resource server

      See communications resource server.

   trusted party

      A trusted party is an individual or organization that is trusted
      by one or more communicating users to maintain the confidentiality
      and integrity of their communications resources.

1.2.  Security Terms

   Most security-related terms in this document are to be understood in
   the sense defined in [RFC4949]; such terms include, but are not
   limited to, "attack", "authentication", "authorization",
   "certification authority", "certification path", "certificate",
   "credential", "identity", "self-signed certificate", "trust", "trust
   anchor", "trust chain", "validate", and "verify".

1.3.  Notational Conventions

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119].



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2.  Architectural Overview

   The architectural reference model for this specification is
   illustrated in Figure 1.  Central to this model is the
   _communications resource server_ which is presumed to be operated by
   a _cloud provider_ for the purpose of offering some form of
   communications service.  The nature of this service is not prescribed
   by this specification and may take the form of any of a variety of
   communications or collaboration services including file sharing,
   messaging, and VoIP.  Consuming the services of the communications
   resource server are _communications resource clients_ which may be
   supplied by the cloud provider or developed by third parties.

                            +-----------------+
                            | Communications  |
        +-------------------| Resource Server |-------------------+
        |                   | (Cloud Provider)|                   |
        |                   +-----------------+                   |
        |                                                         |
        |                                                         |
        |                   +-----------------+                   |
        |       +-----------|  KMS Transport  |-----------+       |
        |       |           +-----------------+           |       |
        |       |                    |                    |       |
        |       |   Untrusted        |                    |       |
   - - -|- - - -|- - - - - - - - - - | - - - - - - - - - -|- - - -|- - -
        |       |   Trusted          |                    |       |
        |       |                    |                    |       |
   +-----------------+      +-----------------+      +-----------------+
   | Communications  |      |    KMS Server   |      | Communications  |
   | Resource Client |      |  (KMS Provider) |      | Resource Client |
   +-----------------+      +-----------------+      +-----------------+
            |                                                 |
   +-----------------+                               +-----------------+
   |      Alice      |                               |       Bob       |
   +-----------------+                               +-----------------+

                Figure 1: KMS Architecture Reference Model

   In addition to the familiar elements described above, this model also
   includes a key management server, or _KMS_, operated by a _KMS
   provider_. The KMS server exposes an API through which clients may
   securely establish and share cryptographic keying material used for
   the E2E encryption of content that is transited through the cloud
   provider's services.  This API is secured in such a way as to ensure
   these keys are visible to none but the KMS server itself and the
   clients authorized to consume the content they protect.  This
   highlights an important distinction between the KMS provider and the



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   cloud provider: while the KMS provider is necessarily a _trusted
   party_, the cloud provider need not be.

   It is an explicit objective of this specification to promote an
   ecosystem of providers of KMS implementations and KMS services that
   are distinct and independent of the cloud providers over whose
   services users communicate.  To that end, this specification seeks to
   standardize a KMS service protocol though which clients and KMS
   servers interoperate.  This protocol provides for the establishment
   of a confidential and authenticated channel between each client and
   KMS server, and defines an API of request and response messages to be
   exchanged over this secure channel for the purpose of creating,
   retrieving, and exchanging keys.

   While the KMS service protocol constitutes a central focus of this
   specification, the means by which this protocol is transported is
   expressly out of scope.  This role may be readily addressed through
   either standards-based or proprietary protocols, and so we refer to
   this simply as the _KMS transport_ for the remainder of this
   document.  Over this transport, the communication paths between
   clients and KMS server are encrypted using keys established through
   an authenticated ephemeral key agreement.  As such, the KMS transport
   provider need not be regarded as a trusted party, and in fact may be
   the cloud provider itself.

   An important non-goal of this specification is the standardization of
   any aspect of the cloud provider's services or the means by which
   clients utilize shared keys for the E2E encryption of data transiting
   those services.  By avoiding the application of constraints on the
   communications services and protocols we enable the use of this
   specification in the context of existing service deployments, both
   standards-based and proprietary.  It is similarly a non-goal of this
   specification to enable federation of secure communications between
   vendors of different cloud services, as that is the realm of
   standardized application protocols.  The scope of this specification
   is intended to be narrowly focused on the task of separating E2E
   encryption key management from the communications services they
   secure, thereby facilitating the broadest possible adoption of secure
   communications though existing services.

3.  Use Cases

   The use cases described in this section are non-normative examples
   meant to illustrate how the KMS architecture may be deployed to
   provide E2E encryption of different types of communications
   resources.  These use cases differ in detail, but generally follow a
   common logical sequence as given below.




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   Note that all requests to the KMS server are via the KMS transport
   which, for clarity, has been omitted from the sequence diagrams
   included in this section.

     Resource          Resource          Resource            KMS
     Client B          Client A           Server            Server
        |                 |                 |                 |
        |                 |                 |       (1)       |
        |                 |-----------------|---------------->|
        |                 |       (2)       |                 |
        |                 |---------------->|                 |
        |                 |                 |       (3)       |
        |                 |-----------------|---------------->|
        |                 |       (4)       |                 |
        |-----------------|---------------->|                 |
        |                 |                 |                 |
    (5) |                 |                 |                 |
        |                 |                 |       (6)       |
        |-----------------|-----------------|---------------->|
        |                 |                 |                 |
    (7) |                 |                 |                 |
        |                 |                 |                 |


                        Figure 2: Nominal Use Case

   1.  Client A requests the generation of a new unbound key from the
       KMS.

   2.  Client A encrypts a communications resource using the unbound KMS
       key and shares it via a resource server.

   3.  Client A requests the creation of a new KMS resource object (KRO)
       to represent the communications resource.  Client A also
       instructs the KMS to bind the KMS key used in step (2) to the new
       KRO and to authorize user B to retrieve keys bound to the KRO.

   4.  Client B accesses the communications resource shared by client A
       and receives the encrypted data.

   5.  Client B obtains, through some means not defined by this
       specification, the URL of the KMS key used to encrypt the
       communications resource.

   6.  Client B requests the KMS key from the KMS server.  The KMS
       server, recognizing user B as authorized on the KRO to which the
       key is bound, returns the KMS key.




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   7.  Client B decrypts the communications resource using the KMS key.

3.1.  Securing an HTTP File Sharing Service

   Let A be a user that wishes to share a file with users B and C
   through some HTTP based file sharing service.  In the context of the
   KMS architecture we may regard the file sharing provider's HTTP API
   as the resource server and the users' HTTP clients as the resource
   clients.

   For this scenario we also assume that the file sharing service is
   trusted by user A with the role of providing a file sharing service
   but is not necessarily trusted to adequately protect the
   confidentiality of the file contents.  User A's concerns may then be
   addressed through the introduction of an HTTP based KMS transport
   (not shown) and KMS server deployed by an entity that A regards as a
   trusted party.

        HTTP           HTTP           HTTP       HTTP File         KMS
      Client C       Client B       Client A    Share Server      Server
         |              |              |              |             |
         |              |              |              |     (1)     |
         |              |              |--------------|------------>|
         |              |              |      (2)     |             |
         |              |              |------------->|             |
         |      (3)     |      (3)     |              |             |
         |<-------------|<-------------|--------------|             |
         |              |              |              |     (4)     |
         |              |              |--------------|------------>|
         |              |              |      (5)     |             |
         |              |--------------|------------->|             |
         |              |              |              |     (6)     |
         |              |--------------|--------------|------------>|
         |              |              |              |             |
         |          (7) |              |              |             |
         |              |              |              |             |
     (8) |              |              |              |             |
         |              |              |              |             |

                      Figure 3: File Sharing Use Case

   This sequence begins with the assumption that each client has, at
   some point, already established a secure channel to the KMS via
   authenticated key agreement.

   1.  Client A requests from the KMS some number of unbound KMS keys.





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   2.  Client A selects an unbound key from the set of keys obtained
       step (1), encrypts the file to be shared, and posts the encrypted
       content to the file sharing service.  The file sharing service
       responds with a URL that uniquely identifies the shared file.

   3.  Clients B and C learn of the newly shared file from the file
       sharing service (the mechanism by which this occurs is out of
       scope for this specification).

   4.  Client A requests the creation of a KMS resource object (KRO) on
       the KMS to represent the shared file.  In this message the client
       also requests that the key from step (2) be bound to the newly
       created KRO and that the users of clients B and C be authorized
       to retrieve keys bound to the KRO.

   5.  Client B retrieves the shared file from the file sharing service.

   6.  Client B requests from the KMS all keys bound to the KRO
       associated with the shared file's URL.  Recognizing client B as
       authorized on the KRO, the KMS returns the key bound to the KRO
       by client A in step (4).

   7.  Client B decrypts the shared file using the key obtained in step
       (6).

   8.  Client C performs steps (5) through (7) in the same fashion as
       client B.

   It is worth noting that a race condition does exist where step (6)
   could occur before step (4) completes.  This will result in a client
   being temporarily denied access to the key used to encrypt the shared
   file.

3.2.  Securing an XMPP Multi-User Chat

   Let A, B and C be users that wish to engage in secure chat through an
   existing XMPP multi-user chat room.  In the context of the KMS
   architecture we may regard the XMPP MUC service as the resource
   server, the users' XMPP clients as the resource clients, and the XMPP
   service itself (not shown) as the KMS transport.











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        XMPP           XMPP           XMPP         XMPP MUC        KMS
      Client C       Client B       Client A        Server        Server
         |              |              |              |             |
         |              |              |              |     (1)     |
         |              |              |--------------|------------>|
         |              |              |              |     (2)     |
         |              |              |--------------|------------>|
         |              |              |      (3)     |             |
         |              |              |------------->|             |
         |      (4)     |      (4)     |              |             |
         |<-------------|<-------------|--------------|             |
         |              |              |              |     (5)     |
         |              |--------------|--------------|------------>|
         |              |              |              |             |
         |          (6) |              |              |             |
         |              |              |              |             |
     (7) |              |              |              |             |

                    Figure 4: Multi-User Chat Use Case

   This sequence begins with the assumption that a MUC room already
   exists on the MUC server and that each client has already established
   a secure channel to the KMS via authenticated key agreement.  All
   messages are transmitted over XMPP.

   1.  Client A requests from the KMS some number of unbound KMS keys.
       Client A selects one of these keys for encrypting MUC room
       messages.

   2.  Client A requests the creation of a KMS resource object (KRO) on
       the KMS to represent the MUC room.  In this message the client
       also requests that the key selected in step (1) be bound to the
       newly created KRO and that the users of clients B and C be
       authorized to retrieve keys bound to the KRO.

   3.  Client A encrypts a message with the key selected in step (1) and
       sends it to the MUC room.

   4.  The MUC service delivers client A's encrypted message to clients
       B and C.

   5.  Client B requests from the KMS all keys bound to the KRO
       associated with the MUC room's URI.  Recognizing client B as
       authorized on the KRO, the KMS returns the key bound to the KRO
       by client A in step (2).

   6.  Client B decrypts the shared file using the key selected in step
       (1).



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   7.  Client C performs steps (5) and (6) in the same fashion as client
       B.

3.3.  KMS to KMS Key Federation

   This use case illustrates two KMS instances federating keys
   associated with a resource.  As KMS servers are deployed to serve
   groups of users it is inevitable that users will want to share
   resources across groups or organizations.  This cross-organization
   sharing of keys leads to several problems.  First, each user is only
   known to and only knows of one logical KMS.  Second, each
   organization might have very different archiving requirements due to
   differing legal compliance regulations due to jurisdiction or
   industry differences.  Lastly, one or both of the users might be
   employees of enterprises that need to be able to respond to legal
   discovery requests.  To address these issues, KMS servers may
   federate in such a way as to allow for limited copying of keys from
   one KMS to another.  This permits each KMS' owning organization the
   ability to control the ongoing policy regarding access to keys for
   which their respective users are authorized.

   Let Alice@DomainA and Bob@DomainB be users of a common file sharing
   service and who happen to use different KMS servers to secure their
   communications.  Assume then that Alice wishes to share a file with
   Bob and therefore relies on KMS server federation to facilitate the
   key exchange.

























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   HTTP Client    HTTP Client     HTTP File      KMS Server   KMS Server
   Bob@DomainB   Alice@DomainA   Share Server     DomainA       DomainB
        |              |              |      (1)     |             |
        |              |--------------|------------->|             |
        |              |      (2)     |              |             |
        |              |------------->|              |             |
        |      (3)     |              |              |             |
        |<-------------|--------------|              |             |
        |              |              |      (4)     |             |
        |              |--------------|------------->|             |
        |              |      (5)     |              |             |
        |--------------|------------->|              |             |
        |              |              |              |     (6)     |
        |--------------|--------------|--------------|------------>|
        |              |              |              |     (7)     |
        |              |              |              |<------------|
        |              |              |              |     (8)     |
        |              |              |              |<------------|
        |              |              |              |             |
        |              |              |              |             | (9)
        |              |              |              |             |
   (10) |              |              |              |             |
        |              |              |              |             |

            Figure 5: File Sharing with KMS Federation Use Case

   This sequence begins with the assumption that each client has, at
   some point, already established a secure channel to their respective
   KMS via authenticated key agreement.

   1.   Alice@DomainA requests from the DomainA KMS some number of
        unbound KMS keys.  Each KMS key is uniquely identified by a URL.

   2.   Alice@DomainA selects a key from the set of KMS keys obtained in
        step (1), uses that key to encrypt the file to be shared, and
        posts the encrypted content to the file sharing service.  The
        file sharing service responds with a URL that uniquely
        identifies the shared file.

   3.   Bob@DomainB is notified of the newly shared file URL and
        corresponding KMS key URL through a notification from the file
        sharing service (or potentially some other means, such an an
        email from Alice).

   4.   Alice@DomainA requests the creation of a KMS resource object
        (KRO) on the DomainA KMS to represent the shared file.  In this
        message Alice also requests that the KMS key from step (2) be




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        bound to the newly created KRO and that the user Bob@DomainB be
        authorized to retrieve KMS keys bound to the KRO.

   5.   Bob@DomainB retrieves the shared file from the file sharing
        service.

   6.   Using the KMS key URL obtained in step (3), Bob@DomainB requests
        the KMS key from the DomainB KMS.

   7.   The DomainB KMS recognizes the KMS key URL as actually hosted by
        the DomainA KMS.  The DomainB KMS establishes a secure and
        mutually authenticated channel with the DomainA KMS via the KMS
        transport.

   8.   The DomainB KMS requests from the DomainA KMS the KRO object to
        which the KMS key is bound, along with all DomainB user
        authorizations and other KMS keys that have been bound to that
        KRO.  The DomainA KMS recognizes that the DomainB KMS is
        authorized to retrieve all KMS keys for which users in the
        DomainB domain have been authorized.  It then recognizes that at
        least one DomainB user (Bob) has been authorized on the KRO
        created in step (4).  The DomainA KMS therefore decides the
        DomainB KMS is authorized to make this request and returns the
        requested information.

   9.   Using the information received from the DomainA KMS, the DomainB
        KMS verifies that Bob@DomainB is authorized on the KRO, and
        satisfies the request from step (6) by returning the KMS key to
        Bob@DomainB.

   10.  Client Bob@DomainB decrypts the shared file using the key
        obtained in step (9).

   Note that in step (9) the DomainB KMS is enforcing authorization
   policy for the KRO hosted on the DomainA KMS as it pertains to
   DomainB users.  This is a necessary consequence of KMS federation,
   where the act of authorizing access to a KRO by a user residing in a
   federated domain engenders an implicit trust of the KMS server that
   controls the federated domain.  For that reason, a KMS provider
   should restrict federation of its KMS servers to domains that the KMS
   provider regards as trusted.

4.  KMS Protocol

   The KMS protocol is composed of a message oriented request and
   response API and a secure channel over which those messages are
   exchanged.  The API provides clients with the ability to generate E2E
   encryption keys, associate those keys with communications resources,



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   and explicitly manage access authorizations on those keys.  The
   secure channel provides a mutually authenticated and E2E encrypted
   channel over which the clients and KMS server may exchange API
   messages securely.  The API and secure channel are described in
   detail through the remainder of this section.

4.1.  Secure Channel

   The secure channel is an encrypted and mutually authenticated
   communication path between each client and the KMS server.  It
   transits the KMS transport which, in the context of this document,
   represents any service or protocol that may be utilized for the
   relaying of KMS API request and response messages.  This
   specification presumes the KMS transport to be untrusted.

                             (3) Secure Channel
           +===================================================+
           V                                                   V
   +-----------------+  (2)   +---------------+   (1)  +---------------+
   | Resource Client |<------>| KMS Transport |<------>|   KMS Server  |
   +-----------------+        +---------------+        +---------------+
                         |                         |
        Trusted          |        Untrusted        |        Trusted

                Figure 6: Establishment of a Secure Channel

   At a high level, the communication path between a resource client and
   KMS is established as follows.

   1.  The KMS actively connects to the KMS transport.  The protocol
       used for this connection is out of scope for this document,
       however it MUST support the asynchronous flow of encrypted KMS
       request and response messages between the KMS and KMS transport.

   2.  A resource client connects to the KMS transport.  The protocol
       used for this connection is out of scope for this document,
       however it MUST support the flow of encrypted KMS request and
       response messages between the resource client and the KMS
       transport.

   3.  Through an elliptic curve Diffie-Helman key exchange, augmented
       by server and client authentication, the resource client and KMS
       establish a shared secret and derived ephemeral key.  This is
       discussed in greater detail in Section 4.7.1.

   On successful mutual authentication and ephemeral key agreement, the
   resource client and KMS communicate through the exchange of sequenced
   request and response messages encrypted using the ephemeral key.



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4.2.  User Identity

   Central to the KMS server's role as a key store is its ability to
   restrict access to stored keying material to only authorized users.
   This requires robust user authentication and a means for the
   unambiguous and unique identification of each user.

   Conforming KMS architecture deployments MUST rely on an identity
   provider that supports the generation of OAuth 2.0 [RFC6749] access
   tokens.  The KMS server MUST rely on same identity provider for the
   purpose of validating access tokens received from the client.  Access
   tokens used by clients to demonstrate identity and authorization for
   access to KMS resources MUST NOT be used for any other service.  Any
   exposure of a KMS recognized access token to third parties (such as
   providers of other services) jeopardizes the security of all KMS keys
   for which the user whose identity is represented by the token is
   authorized.

   The identity provider on which the KMS server relies MAY be the same
   identity provider as relied upon by the resource server(s) whose
   communications resources are encrypted with keys managed by the KMS
   server.  Note, however, the reliable authentication and authorization
   of clients to the KMS server is critical to the security of the KMS
   keys it holds.  The identity provider on which the KMS relies must
   therefore necessarily be regarded as a trusted party within the
   context of the KMS architecture.

   Access tokens MUST be conveyed to the KMS server as part of the
   payload of encrypted KMS API requests as described in Section 4.6.1
   and MUST NOT be conveyed in any other manner.

4.3.  KMS Identity

   Given the untrusted nature of the KMS transport by both the KMS and
   clients, it is critical for clients to be able to verify the identity
   of their KMS and ensure that no MITM attacks are carried out on
   client to KMS or KMS to client communications.  Therefore, the KMS
   MUST make use of at least one PKIX certificate [RFC5280] and clients
   MUST validate the PKIX certificate presented by the KMS through the
   comparison of the certificate's common name (CN) or subject
   alternative name (SAN) [RFC6125] fields to the Internet domain
   portion of the user's Addr-spec [RFC2822] formatted unique identifier
   using the procedures defined in section 6 of [RFC6125].  An
   acceptable alternative to direct CN or SAN validation is defined in
   [I-D.ietf-xmpp-posh].

   PKIX certificates presented by the KMS can be issued by either a
   public or private certification authority with the stipulation that



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   clients MUST be able to validate the KMS's entire certificate path
   through the pre-established trust of the root certificate used to
   anchor the certificate path.  The mechanism for establishing trust of
   the root certificate is out of scope for this specification, but it
   is usually carried out through pre-installed trusted root
   certificates on various operating systems for public certification
   authorities or through enterprise endpoint management solutions or
   manual installation tasks for private certification authorities.

4.4.  Object Types

   The KMS protocol defines three object types: resources, keys, and
   authorizations.  It is through the creation and manipulation of
   instances of these object types that clients interact with the KMS.

   Resource

      A resource is an object that represents, within the KMS object
      model, a communications resource as defined in Section 1.1.  Keys
      and user authorizations are associated (bound) to the resource
      object as a means of representing their logical association with
      that communications resource.

   Key

      A key is an object representing symmetric keying material
      generated and made available to authorized clients by the KMS.  A
      key may exist in one of two states: "bound", and "unbound".  An
      unbound key is not associated with any resource, whereas a bound
      key is associated with exactly one resource.

   Authorization

      An authorization is the association of a user with a particular
      resource.  When such an association exists between a user and a
      resource this implies that the user is entitled to retrieve any
      key that is bound to that resource, and to add or remove
      authorizations for other users on the same resource.

   The KMS protocol is composed from representations of these
   fundamental object types.  These representations are defined in the
   following sections.

4.4.1.  KMS Key Objects

   The JSON representations for KMS key objects is defined as follows
   using JSON content rules [I-D.newton-json-content-rules].




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   jwk : ; see [JWK]

   kmsUri (
     "uri" : uri relative
   )

   keyRep {
     kmsUri,
     "jwk" : jwk,
     "userId" : string,
     "clientId" : string,
     "createDate" : date-time,
     "expirationDate" : date-time,
     ?"resourceUri" : kmsUri,
     ?"bindDate" : date-time
   }

   key (
     "key" : keyRep
   )

   keys (
     "keys" : [ *keyRep ]
   )

   keyUris (
     "keyUris" : [ *kmsUri ]
   )

   The attributes of a KMS key object are defined as follows.

   uri

      A standard definition for KMS object identifiers.

   jwk

      Symmetric keying material represented as a JWK object (see
      [I-D.ietf-jose-json-web-key]).

   userId

      The authenticated unique identifier of the user that created the
      key.

   clientId





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      An opaque unique identifier provided by the client that created
      the key.

   createDate

      The point in time when the key was created, in RFC-3339 date-time
      format.

   expirationDate

      The point in time after which the key may no longer be bound (if
      unbound) or may no longer be used for encrypting data (if bound or
      an ephemeral key).

   resourceUri

      The uri of the KMS resource object to which the key is bound.

   bindDate

      The point in time when the key was bound, in RFC-3339 date-time
      format.

4.4.2.  KMS Authorization Objects

   The JSON representations for KMS authorization objects is defined as
   follows using JSON content rules with references to rules defined in
   previous sections.

   authorizationRep {
     kmsUri,
     "userId" : string,
     "resourceUri" : kmsUri,
   }

   authorization (
     "authorization" : authorizationRep
   )

   authorizations (
     "authorizations" : [ *authorizationRep ]
   )

   authorizationUris (
     "authorizationUris" : [ *kmsUri ]
   )

   The attributes of a KMS authorization object are defined as follows.



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   uri

      A standard definition for KMS object identifiers.

   userId

      The unique identifier of the user that is authorized.

   resourceUri

      The object identifier of the resource to which the authorization
      applies.

   Note, with respect to this specification user identifiers are opaque,
   however they MUST map to unique identifiers provided as part of user
   authentication.

4.4.3.  KMS Resource Objects (KRO)

   The JSON representation for KMS resource objects is defined as
   follows using JSON content rules with references to rules defined in
   previous sections.

   resourceRep {
     kmsUri,
     keys / keyUris,
     authorizations / authorizationUris
   }

   resource (
     "resource" : resourceRep
   )

   resources (
     "resources" : [ *resourceRep ]
   )

   resourceUris (
     "resourceUris" : [ *kmsUri ]
   )

   The attributes of a KMS resource object are defined as follows.

   uri

      A standard definition for KMS object identifiers.

   keys



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      An array of key object representations, one for each key bound to
      the resource.

   keyUris

      An array of key object identifiers, one for each key bound to the
      resource.  Only one of either keys or keyUris may be present in a
      resource object representation.

   authorizations

      An array of authorization object representations, one for each
      authorization on the resource.

   authorizationUris

      An array of authorization object identifiers, one for each
      authorization on the resource.  Only one of either authorizations
      or authorizationUris may be present in a resource object
      representation.

4.5.  Request Types

   The KMS protocol defines four types of requests: create, retrieve,
   update, delete, each of which may be applied to one of the three KMS
   object types.  Note that not all object types support all requests
   types.  A KMS need only support those combinations of request type
   and object type explicitly defined in this document.

   Create

      A create operation acts upon an object type, creating one or more
      new instances of that object type.

   Retrieve

      A retrieve operation acts upon an object or object type, returning
      in the response a representation of one or more object instances.

   Update

      An update operation acts upon an object, altering mutable
      properties of that object.

   Delete

      A delete operation acts upon an object, removing that object from
      the KMS.



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4.6.  Message Structure

   Every KMS request and response message is composed of a JSON
   [RFC7159] formatted payload encapsulated within either a JWE
   [I-D.ietf-jose-json-web-encryption] or JWS
   [I-D.ietf-jose-json-web-signature] object.  These messages may be
   divided into three types.

   Common Messages

      Common messages include all those which do not meet the definition
      of either key agreement message or error message.  Common messages
      are encrypted as JWE objects using the shared ephemeral key
      established during initial key agreement between the client and
      KMS (see Section 4.7.1).  The value of the JWE header "kid"
      attribute of a common message MUST match that of the KMS ephemeral
      key object URI attribute established during initial key agreement.

   Ephemeral Key Agreement Messages

      Ephemeral key agreement messages are those exchanged between the
      client and KMS for the purpose of establishing a new shared
      ephemeral key (see Section 4.7.1).  Key agreement request payloads
      are encrypted as JWE objects using the authenticated and validated
      static public key of the KMS.  Key agreement response payloads are
      signed as JWS objects using the static private key of the KMS.

   Error Messages

      Error messages are those originated by the KMS to indicate a
      failed request.  Error messages are composed in the same fashion
      as common messages; however, in the event that the KMS does not
      recognize the ephemeral key used in the request, or that key is
      determined to have expired, the KMS MUST respond with an
      unencrypted message composed as a JWS, with a payload as described
      in Section 4.6.3, and signed using the KMS server's static public
      key.

   The basic JSON representations for the request and response payloads
   are defined in the following sections.

4.6.1.  Basic Request Payload

   The basic JSON representation for KMS request message payloads is
   defined as follows using JSON content rules with references to rules
   defined in previous sections.





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   sequence (
     "sequence" : integer
   )

   credential {
     "userId": string
     "bearer": string / "jwk": jwk
   }

   client {
     "clientId": string,
     "credential": credential
   )

   method: string /create|retrieve|update|delete/

   request (
     "client" : client,
     "method" : method,
     kmsUri,
     sequence
   )

   The attributes of a KMS request message payload are defined as
   follows.

   sequence

      An integer selected by the client and provided in a monotonically
      increasing order with each request, beginning with the initial
      create ephemeral key request.

   userId

      The unique identifier of the user making the request.

   bearer

      An [RFC6749] access token issued by the client's identity provider
      and validated by the KMS in cooperation with the identity
      provider.  See Section 4.2.

   jwk

      A JWK object, in JSON format as defined in
      [I-D.ietf-jose-json-web-key], containing the public key of the
      client (presumably a server).  This JWK MUST contain an x5c header




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      with a certificate chain that may be used to positively validate
      the public key.

   clientId

      An opaque unique identifier provided by the client (not used for
      authentication, only to assist multiple clients of a single user
      in differentiating between their respective unbound keys).

   method

      Indicates the request type: create, retrieve, update, or delete.

   uri

      The KMS object or object type to which the request applies.

   The JSON content rules above are used in conjunction with additional
   request type specific rules, defined later in this document, to
   produce the full request payload definition for each KMS operation.

4.6.2.  Basic Response Payload

   The basic JSON representation for KMS request message payloads is
   defined as follows using JSON content rules with references to rules
   defined in previous sections.

   response (
     "status" : integer,
     ?"reason" : string
     sequence
   )

   The attributes of a KMS request message payload are defined as
   follows.

   status

      Indicates the success or failure of the request.  The value
      returned in a response status attribute SHOULD be that of an
      [RFC7231] defined status code with semantics that correspond to
      the success or failure condition of the KMS request.

   reason

      An optional natural language string to describe the response
      status in terms that are useful for tracing and troubleshooting
      the API.



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   sequence

      An echo of the sequence number provided in the request.

   The JSON content rules above are used in conjunction with additional
   response type specific rules, defined later in this document, to
   produce the full response payload definition for each KMS operation.

4.6.3.  Error Response Payload

   The JSON representation for KMS error response message payloads is
   defined as follows using JSON content rules with references to rules
   defined in previous sections.

   Error response payload definition:

   root {
     response
   }

   Error response message example:

   JWS(K_kms_priv, {
     "status": 403,
     "reason": "The ephemeral key used in the request has expired.",
     "sequence": 7
   })

4.7.  Requests

   The following sections provide detailed descriptions for each of the
   request and response operations that may occur between a resource
   client and the KMS.

4.7.1.  Create Ephemeral Key

   The first operation between a client and KMS MUST be the
   establishment of a shared secret and derived ephemeral key.  This is
   necessary as all other requests and responses are encrypted with the
   ephemeral key.

   The client request for creating an ephemeral key conforms to the
   basic request message payload, where the method is "create" and the
   uri is "/ecdhe".  In addition to the basic payload, the client
   provides a jwk attribute for which the value is a JWK object
   [I-D.ietf-jose-json-web-key] containing the public part of an EC key
   pair generated by the client.  Unlike a basic request message,
   however, the request payload is encrypted as the content of a JWE



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   [I-D.ietf-jose-json-web-key] secured with the static public key of
   the KMS server (K_kms_pub) as obtained from the server's validated
   PKIX certificate [RFC5280].

   Note, the client MUST generate a new EC key pair for every create
   ephemeral key request sent to the KMS server.

   Request payload definition:

   root {
     request,
     jwk
   }

   Request message example:

   JWE(K_kms_pub, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     },
     "method": "create",
     "uri": "/ecdhe",
     "sequence": 0,
     "jwk" : {
       "kty": "EC",
       "crv": "P-256",
       "x": "VoFkf6Wk5kDQ1ob6csBmiMPHU8jALwdtaap35Fsj20M",
       "y": "XymwN6u2PmsKbIPy5iij6qZ-mIyej5dvZWB_75lnRgQ"
     }
   })

   On receiving the ephemeral key creation request, the KMS server MUST
   verify the credential provided in the request.  If a bearer token is
   provided, the KMS MUST validate the token in cooperation with the
   identity provider.  If a jwk is provided, the KMS MUST validate the
   included PKIX certificate chain against the KMS server's trust root.
   In either case, the identity of the requesting client MUST be
   authenticated and verified to correspond to either an authorized user
   of the KMS or an authorized trusted service.  If verification fails,
   the KMS MUST NOT use the server response to continue with key
   agreement.

   Upon successful authentication and authorization of the request, the
   KMS responds by generating its own EC key pair using the same curve



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   as indicated in the "crv" attribute of the request message JWK.  The
   KMS server returns the public part of this key pair to the resource
   client in the form of a KMS key object within the response payload.
   The KMS also generates and includes within the response payload a
   universally unique identifier to be regarded by both client and KMS
   as the key identifier of the agreed upon ephemeral key.  The response
   payload is returned to the resource client as the content of a JWS
   [I-D.ietf-jose-json-web-signature] signed using the static private
   key of the KMS server (K_kms_priv).

   Response payload definition:

   root {
     response,
     key
   }

   Response message example:

   JWS(K_kms_priv, {
     "status": 201,
     "sequence": 0,
     "key": {
       "uri": "/ecdhe/ea9f3858-1240-4328-ae22-a15f6072306f",
       "jwk" : {
         "kty": "EC",
         "crv": "P-256",
         "x": "8mdasnEZac2LWxMwKExikKU5LLacLQlcOt7A6n1ZGUC",
         "y": "lxs7ln5LtZUE_GE7yzc6BZOwBxtOftdsr8HVh-14ksS"
       },
       "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "createDate": "2014-10-09T15:54:48Z",
       "expirationDate": "2014-10-09T16:54:48Z"
     }
   })

   If successful, the KMS response to a create ephemeral key request
   MUST have a status of 201.  In the case of a request failure, the KMS
   response status SHOULD be that of an [RFC7231] defined status code
   with semantics that correspond to the failure condition.  In
   addition, the ephemeral key SHOULD have the createDate assigned as
   the current time and an expirationDate assigned as the latest point
   in time before which the key may be used for encrypting messages
   (both in [RFC3339] date-time format).

   On receiving the ephemeral key creation response, the resource client
   MUST verify the received JWS against the KMS server's validated



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   static public key.  If verification fails, the client MUST NOT use
   the server response to continue with key agreement.

   To generate the shared secret, both resource client and KMS server
   use ECDH shared secret derivation with the private part of the local
   EC key pair and the public part of the remote EC key pair.  The
   shared secret is then provided as input to HKDF (with both extract
   and expand, and empty salt) [RFC5869] to generate the ephemeral key
   (K_ephemeral).

   The ephemeral key generated by this operation is used to encrypt all
   subsequent KMS requests submitted by the requesting resource client.
   The encryption of subsequent requests takes the form of a JWE object
   for which the kid attribute value MUST be the key object URI provided
   by the KMS in the response message described above.

   The KMS SHOULD accept messages encrypted with the ephemeral key up to
   and until the key expiration date as provided in the response message
   described above.  On expiration of the ephemeral key, the KMS MUST
   reject all further requests submitted using this key, and a client
   wishing to submit further requests to the KMS MUST re-establish the
   secure channel by requesting the creation of a new ephemeral key.

4.7.2.  Delete Ephemeral Key

   In the event that a resource client's ephemeral key has become
   compromised, a client SHOULD submit a request to the KMS to delete
   the ephemeral key.

   The request message conforms to the basic request message structure,
   where the method is "delete", and the uri is that of the ephemeral
   key to be deleted.

   Request payload definition:

   root {
     request
   }

   Request message example:











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   JWE(K_ephemeral, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "delete",
     "uri": "/ecdhe/ea9f3858-1240-4328-ae22-a15f6072306f",
     "sequence": 7
   })

   The response message conforms to the basic response message
   structure, and MUST NOT include a representation of the deleted
   ephemeral key.

   Response payload definition:

   root {
     response
   }

   Response message example:

   JWE(K_ephemeral, {
     "status": 204,
     "sequence": 7
   })

   If successful, the KMS response to a delete ephemeral key request
   MUST have a status of 204.  In the case of a request failure, the KMS
   response status SHOULD be that of an [RFC7231] defined status code
   with semantics that correspond to the failure condition.

   On successful deletion of an ephemeral key, the KMS MUST NOT, from
   that time forward, accept any requests encrypted with that ephemeral
   key.

4.7.3.  Create Resource

   When a client intends to initiate E2E encryption of a communications
   resource, it begins by requesting the creation of a KMS resource
   object.  This resource object logically represents the communications
   resource within the KMS data model.

   As part of a create resource request, a KMS server MUST create at
   least one authorization object on the newly created resource object



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   to explicitly authorize the user making the request.  A client MAY
   request the immediate creation of one or more additional
   authorizations such that corresponding users may be immediately
   authorized to access and operate on the new resource object.  If for
   any reason one or more requested authorizations cannot be applied to
   the new resource object, the entire create resource request MUST be
   failed by the KMS.

   As part of a create resource request, a client MAY request the
   immediate binding of one or more unbound KMS keys to the new resource
   object.  If any key indicated in the request is already bound, or is
   otherwise invalid (e.g. expired), the entire create resource request
   MUST be failed by the KMS.

   The request message conforms to the basic request message structure,
   where the method is "create", the uri is "/resources", and additional
   user identifiers and/or key URIs are provided in a manner consistent
   with the following.

   Request payload definition:

   userIds (
     "userIds" : [ *string ]
   )

   root {
     request,
     ?userIds,
     ?keyUris
   }

   Request message example:



















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   JWE(K_ephemeral, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "create",
     "uri": "/resources",
     "sequence": 7,
     "userIds": [
       "b46e8124-b6e8-47e0-af0d-e7f1a2072dac",
       "39d56a84-c6f9-459e-9fd1-40ab4ad3e89a"
     ],
     "keyUris": [
       "/keys/b4cba4da-a984-4af2-b54f-3ca04acfe461",
       "/keys/2671413c-ab80-4f19-a0a4-ae07e1a94e90"
     ]
   })

   The response message conforms to the basic response message
   structure, and includes a representation of the created KMS resource
   object.

   Response payload definition:

   root {
     response,
     resource
   }

   Response message example:


















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   JWE(K_ephemeral, {
     "status": 201,
     "sequence": 7,
     "resource": {
         "uri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094",
         "authorizationUris": [
           "/authorizations/50e9056d-0700-4919-b55f-84cd78a2a65e",
           "/authorizations/db4c95ab-3fbf-42a8-989f-f53c1f13cc9a"
         ],
         "keyUris": [
           "/keys/b4cba4da-a984-4af2-b54f-3ca04acfe461",
           "/keys/2671413c-ab80-4f19-a0a4-ae07e1a94e90"
         ]
     }
   })

   If successful, the KMS response to a create resource request MUST
   have a status of 201.  In the case of a request failure, the KMS
   response status SHOULD be that of an [RFC7231] defined status code
   with semantics that correspond to the failure condition.

4.7.4.  Create Unbound Keys

   When a client requires a symmetric key for use in the E2E encryption
   of a communications resource, it begins by requesting the creation of
   one or more unbound keys from the KMS.  A client may submit this
   request at any time, even before the communications resource exists.
   The keys returned by this request are unbound, which is to say not
   yet associated with any KMS resource object.

   The request message conforms to the basic request message structure,
   where the method is "create", the uri is "/keys", and an additional
   count attribute is introduced to indicate the number of keys to be
   created.

   Request payload definition:

   root {
     request,
     "count": integer
   }

   Request message example:








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   JWE(K_ephemeral, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "create",
     "uri": "/keys",
     "sequence": 7,
     "count": 2
   })

   The response message conforms to the basic response message structure
   with the addition of an array of key object representations, one for
   each unbound key created.

   Response payload definition:

   root {
     response,
     keys / keyUris
   }

   Response message example:

























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   JWE(K_ephemeral, {
     "status": 201,
     "sequence": 7,
     "keys": [
       {
         "uri": "/keys/52100fa4-c222-46d0-994d-1ca885e4a3a2",
         "jwk": {
           "kid": "52100fa4-c222-46d0-994d-1ca885e4a3a2",
           "kty": "oct",
           "k": "ZMpktzGq1g6_r4fKVdnx9OaYr4HjxPjIs7l7SwAsgsg"
         }
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
         "createDate": "2014-10-09T15:54:48Z",
         "expirationDate": "2014-10-09T16:04:48Z"
       },
       {
         "uri": "/keys/fed33890-f9fa-43ad-a9f8-ab55a983a543",
         "jwk": {
           "kid": "fed33890-f9fa-43ad-a9f8-ab55a983a543",
           "kty": "oct",
           "k": "q2znCXQpbBPSZBUddZvchRSH5pSSKPEHlgb3CSGIdpL"
         }
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
         "createDate": "2014-10-09T15:54:48Z",
         "expirationDate": "2014-10-09T16:04:48Z"
       }
     ]
   })

   Each key object in the response to a create unbound keys request
   includes a single JWK [I-D.ietf-jose-json-web-key] representing a new
   symmetric key of 256 bits generated by a cryptographically secure
   PRNG.  Note that, as unbound keys, the resourceUri attribute of each
   key is either undefined or null.  All keys SHOULD have the createDate
   assigned as the current time and an expirationDate assigned as the
   latest point in time before which the key may be bound to a resource
   (both in [RFC3339] date-time format).

   The clientId attribute of each created key MUST be the clientId
   provided by the client in the client.clientId attribute of the
   request.

   As shown in the response payload definition, the KMS MUST return
   either an array of key object representations or an array of key
   object uris.  It is at the KMS server's discretion which of these is
   returned.



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   If successful, the KMS response to a create unbound keys request MUST
   have a status of 201.  In the case of a request failure, the KMS
   response status SHOULD be that of an [RFC7231] defined status code
   with semantics that correspond to the failure condition.

4.7.5.  Update Unbound Key (Bind)

   To initiate the use of an unbound KMS key in securing a
   communications resource, a client will create a corresponding KMS
   resource object and subsequently bind the unbound key to that
   resource.  A client MAY begin using an unbound KMS key to encrypt a
   communications resource prior to the binding of that key.

   The request message conforms to the basic request message structure,
   where the method is "update", the uri is that of the key to be bound,
   and an additional resourceUri attribute is introduced to indicate the
   KMS resource object to which the key is to be bound.  If the user
   making a bind unbound key request does not have an authorization on
   the resource indicated by the resourceUri, or is not the user for
   whom the unbound key was originally created, the KMS MUST fail the
   request.  The KMS SHOULD fail the request if the clientId of the
   request does not match that of the unbound key.

   Request payload definition:

   root {
     request,
     "resourceUri" : kmsUri
   }

   Request message example:

   JWE(K_ephemeral, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "update",
     "uri": "/keys/52100fa4-c222-46d0-994d-1ca885e4a3a2",
     "sequence": 7,
     "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094"
   })






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   The response message conforms to the basic response message
   structure, and includes a representation of the full state of the
   newly bound key.

   Response payload definition:

   root {
     response,
     key
   }

   Response message example:

   JWE(K_ephemeral, {
   {
     "status": 200,
     "sequence": 7,
     "key": {
       "uri": "/keys/52100fa4-c222-46d0-994d-1ca885e4a3a2",
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "jwk": {
         "kid": "52100fa4-c222-46d0-994d-1ca885e4a3a2",
         "kty": "oct",
         "k": "ZMpktzGq1g6_r4fKVdnx9OaYr4HjxPjIs7l7SwAsgsg"
       }
       "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "createDate": "2014-10-09T15:54:48Z",
       "bindDate": "2014-10-09T15:55:34Z",
       "expirationDate": "2014-10-10T15:55:34Z",
       "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094"
     }
   })

   On successfully binding a formerly unbound KMS key to a resource
   object, the state of the KMS key object MUST reflect the updated
   resourceUri attribute, MUST reflect a bindDate as the current time,
   and MUST reflect an expirationDate as the time after which clients
   MUST NOT use this key for encryption as provided by KMS policy.
   Subsequently, the KMS MUST regard the key as bound to the KMS
   resource object identified by the resourceUri and MUST reject
   subsequent requests to bind the same key to any other resource
   object.

   If successful, the KMS response to a bind unbound key request MUST
   have a status of 200.  In the case of a request failure, the KMS
   response status SHOULD be that of an [RFC7231] defined status code
   with semantics that correspond to the failure condition.



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4.7.6.  Retrieve Keys

   Clients engaging in E2E encryption require a means for retrieving
   keys from the KMS.  A key request may take one of three forms, it may
   be

   o  a request for a specific key,

   o  a request all keys bound to a particular resource, or

   o  a request for a subset of keys bound to a particular resource.

   In all cases, the request message conforms to the basic request
   message structure with "retrieve" as the value for the method
   attribute.

   To retrieve an individual key, the uri of the request is that of the
   key object to be retrieved.  If the key is unbound, the KMS MUST
   reject the request unless it originates from the user that requested
   the key's creation, and SHOULD reject the request unless it
   originates from the same clientId that requested the key's creation.
   If the key is bound, the KMS MUST reject the request unless the
   request originates from a user for which there exists a corresponding
   authorization on the resource to which the requested key is bound.

   To retrieve all keys bound to a particular resource, the uri of the
   request is that of the resource concatenated with "/keys".  To
   retrieve a select subset of keys bound to a particular resource, the
   client constructs a request for all keys and augments this with the
   additional attributes "count" and "prefer".  The count attribute
   specifies the maximum number of keys that the KMS may return in the
   response message, and the prefer attribute is a token indicating a
   preference criterion.  Defined preference criteria are:

   o  recently-bound

   o  recently-requested

   The recently-bound criterion prefers keys that have been most
   recently bound to the resource.  The recently-requested criterion
   prefers keys that have been most recently requested by their specific
   uri (including requests made by other clients).  The KMS MUST reject
   the request unless the request originates from a user for which there
   exists a corresponding authorization on the resource from which bound
   keys are being requested.

   Request payload definition:




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   root {
     request,
     ?(
        "prefer": string /recently-bound|recently-requested/,
        "count": integer
     )
   }

   Request message example (individual key):

   JWE(K_ephemeral, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "retrieve",
     "uri": "/keys/52100fa4-c222-46d0-994d-1ca885e4a3a2",
     "sequence": 7
   })

   Request message example (all keys bound to a resource):

   JWE(K_ephemeral, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "retrieve",
     "uri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094/keys",
     "sequence": 7
   })

   Request message example (10 keys most recently bound to a resource):












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   JWE(K_ephemeral, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "retrieve",
     "uri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094/keys",
     "sequence": 7,
     "prefer": "recently-bound",
     "count": 10
   })

   The response message conforms to the basic response message structure
   and includes a representation of the key or keys selected by the
   request.  In the case of a request for a specific individual key, the
   response will contain a representation of a single key.  In the case
   of a request for all keys bound to a resource, the response will
   contain an array representing all KMS keys currently bound to the
   resource.

   In the case of a request for a select subset of keys bound to a
   resource, the response will contain an array representing the set of
   KMS keys currently bound to the resource and which most closely
   satisfy the preference criterion indicated in the request.  In this
   case, the size of the keys array in the response MUST NOT exceed the
   count as given in the request.

   Response payload definition:

   root {
     response,
     key / keys
   }

   Response message example (for specific key):













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   JWE(K_ephemeral, {
   {
     "status": 200,
     "sequence": 7,
     "key": {
       "uri": "/keys/52100fa4-c222-46d0-994d-1ca885e4a3a2",
       "jwk": {
         "kid": "52100fa4-c222-46d0-994d-1ca885e4a3a2",
         "kty": "oct",
         "k": "ZMpktzGq1g6_r4fKVdnx9OaYr4HjxPjIs7l7SwAsgsg"
       }
       "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "createDate": "2014-10-09T15:54:48Z",
       "bindDate": "2014-10-09T15:55:34Z",
       "expirationDate": "2014-10-10T15:55:34Z",
       "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094"
     }
   })

   Response message example (all keys bound to a resource):






























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   JWE(K_ephemeral, {
   {
     "status": 200,
     "sequence": 7,
     "keys": [
     {
       "uri": "/keys/52100fa4-c222-46d0-994d-1ca885e4a3a2",
       "jwk": {
         "kid": "52100fa4-c222-46d0-994d-1ca885e4a3a2",
         "kty": "oct",
         "k": "ZMpktzGq1g6_r4fKVdnx9OaYr4HjxPjIs7l7SwAsgsg"
       }
       "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "createDate": "2014-10-09T15:54:48Z",
       "bindDate": "2014-10-09T15:55:34Z",
       "expirationDate": "2014-10-10T15:55:34Z",
       "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094"
     },
     {
       "uri": "/keys/fed33890-f9fa-43ad-a9f8-ab55a983a543",
       "jwk": {
         "kid": "fed33890-f9fa-43ad-a9f8-ab55a983a543",
         "kty": "oct",
         "k": "q2znCXQpbBPSZBUddZvchRSH5pSSKPEHlgb3CSGIdpL"
       }
       "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "createDate": "2014-10-09T15:54:48Z",
       "bindDate": "2014-10-09T15:56:43Z",
       "expirationDate": "2014-10-10T15:56:43Z",
       "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094"
     }]
   })

   If successful, the KMS response to a retrieve bound keys request MUST
   have a status of 200.  In the case of a request failure, the KMS
   response status SHOULD be that of an [RFC7231] defined status code
   with semantics that correspond to the failure condition.

4.7.7.  Create Authorizations

   An authorization establishes a relationship between a resource and a
   user that entitles the user to retrieve bound keys from, and bind new
   keys to, that resource.  The KMS resource authorization model is
   viral in the sense that, once a user has been authorized on a
   resource, that user is also entitled to authorize other users on that




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   resource.  These authorizations are created through create
   authorization requests.

   The request message conforms to the basic request message structure,
   where the method is "create", and the uri is "/authorizations".
   Additional attributes are required to indicate the resource on which
   authorizations are to be added, as well as the set of users for whom
   these new authorizations are to be created.

   root {
     request,
     "resourceUri" : kmsUri,
     "userIds" : [ *string ]
   }

   Request message example:

   JWE(K_ephemeral, {
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "create",
     "uri": "/authorizations",
     "sequence": 7,
     "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094",
     "userIds": [
       "119a0582-2e2b-4c0c-ba6a-753d05171803",
       "557ac05d-5751-43b4-a04b-e7eb1499ee0a"
     ]
   })

   The response message conforms to the basic response message
   structure, and includes a representation of the set of KMS
   authorization objects created by the request.

   Response payload definition:

   root {
     response,
     authorizations
   }

   Response message example:




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   JWE(K_ephemeral, {
   {
     "status": 201,
     "sequence": 7,
     "collection": [
     {
       "uri": "/authorizations/79a39ed9-a8e5-4d1f-9ae2-e27857fc5901",
       "userId": "119a0582-2e2b-4c0c-ba6a-753d05171803",
       "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094"
     },
     {
       "uri": "/authorizations/5aaca3eb-ca4c-47c9-b8e2-b20f47568b7b",
       "userId": "557ac05d-5751-43b4-a04b-e7eb1499ee0a",
       "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094"
     }]
   })

   If successful, the KMS response to a create authorizations request
   MUST have a status of 201.  In the case of a request failure, the KMS
   response status SHOULD be that of an [RFC7231] defined status code
   with semantics that correspond to the failure condition.  If for any
   reason one or more requested authorizations cannot be created or
   applied to the resource object, the entire create authorizations
   request MUST be failed by the KMS.

4.7.8.  Delete Authorization

   To remove an authorization from a KMS resource object, any user
   currently authorized on the same resource object may issue a delete
   authorization request.  The request message conforms to the basic
   request message structure, where the method is "delete", and the uri
   is that of the authorization object to be deleted.

   Request payload definition:

   root {
     request
   }

   Request message example:











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   JWE(K_ephemeral, {
     "requestId": "1234",
     "client": {
       "clientId": "android_a6aa012a-0795-4fb4-bddb-f04abda9e34f",
       "credential": {
         "userId": "842e2d82-7e71-4040-8eb9-d977fe888807",
         "bearer": "ZWU5NGE2YWYtMGE2NC0..."
       }
     }
     "method": "delete",
     "uri": "/authorizations/5aaca3eb-ca4c-47c9-b8e2-b20f47568b7b"
   })

   The response message conforms to the basic response message
   structure, and includes a representation of the authorization object
   that was deleted.

   Response payload definition:

   root {
     response,
     authorization
   }

   Response message example:

   JWE(K_ephemeral, {
   {
     "status": 200,
     "sequence": 7,
     "object": {
       "uri": "/authorizations/5aaca3eb-ca4c-47c9-b8e2-b20f47568b7b",
       "userId": "557ac05d-5751-43b4-a04b-e7eb1499ee0a",
       "resourceUri": "/resources/7f35c3eb-95d6-4558-a7fc-1942e5f03094"
     }
   })

   If successful, the KMS response to a delete authorization request
   MUST have a status of 200.  In the case of a request failure, the KMS
   response status SHOULD be that of an [RFC7231] defined status code
   with semantics that correspond to the failure condition.

5.  Mandatory-to-Implement

   Implementations MUST support the following JWK key types from
   [I-D.ietf-jose-json-web-algorithms]:

   o  "RSA" for the KMS static public/private key



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   o  "EC" for the Ephemeral Diffie Hellman exchange

   o  "oct" for all symmetric keys

   Implementations MUST support "PS256" (RSASSA-PSS using SHA-256 and
   MGF1 with SHA-256) from [I-D.ietf-jose-json-web-algorithms] for
   signatures using the KMS static public/private key for Section 4.7.1.

   Implementations MUST support JWK Elliptic Curve type "P-256" (NIST
   P-256 curve) from [I-D.ietf-jose-json-web-algorithms] for
   Section 4.7.1.

   Implementations MUST support "RSA-OAEP" (RSAES OAEP using default
   parameters) from [I-D.ietf-jose-json-web-algorithms] for key
   encryption using the KMS static public/private key for Section 4.7.1.

   Implementations MUST support "dir" (Direct Key Agreement Key
   Management Mode) from [I-D.ietf-jose-json-web-algorithms] for all
   operations other than Section 4.7.1.

   Implementations MUST support "A256GCM" (AES GCM using 256 bit key)
   from [I-D.ietf-jose-json-web-algorithms] for content encryption for
   all operations other than Section 4.7.1.

6.  Security Considerations

   Security considerations are discussed throughout this document.
   Additional considerations may be added here as needed.

7.  Appendix A.  Acknowledgments

   This specification is the work of several contributors.  In
   particular, the following individuals contributed ideas, feedback,
   and wording that influenced this specification:

   Cullen Jennings, Matt Miller, Suhas Nandakumar, Jonathan Rosenberg

8.  Appendix B.  Document History

   -00

   o  Initial draft.

9.  References







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9.1.  Normative References

   [I-D.ietf-jose-json-web-algorithms]
              Jones, M., "JSON Web Algorithms (JWA)", draft-ietf-jose-
              json-web-algorithms-33 (work in progress), September 2014.

   [I-D.ietf-jose-json-web-encryption]
              Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              draft-ietf-jose-json-web-encryption-33 (work in progress),
              September 2014.

   [I-D.ietf-jose-json-web-key]
              Jones, M., "JSON Web Key (JWK)", draft-ietf-jose-json-web-
              key-33 (work in progress), September 2014.

   [I-D.ietf-jose-json-web-signature]
              Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", draft-ietf-jose-json-web-signature-33
              (work in progress), September 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822, April
              2001.

   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2", RFC
              4949, August 2007.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869, May 2010.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, March 2011.

   [RFC6749]  Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
              6749, October 2012.



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   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014.

   [RFC7231]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Semantics and Content", RFC 7231, June 2014.

9.2.  Informative References

   [I-D.barnes-pervasive-problem]
              Barnes, R., Schneier, B., Jennings, C., and T. Hardie,
              "Pervasive Attack: A Threat Model and Problem Statement",
              draft-barnes-pervasive-problem-01 (work in progress), July
              2014.

   [I-D.ietf-xmpp-posh]
              Miller, M. and P. Saint-Andre, "PKIX over Secure HTTP
              (POSH)", draft-ietf-xmpp-posh-02 (work in progress),
              October 2014.

   [I-D.newton-json-content-rules]
              Newton, A., "A Language for Rules Describing JSON
              Content", draft-newton-json-content-rules-02 (work in
              progress), August 2014.

   [OTR]      Borisov, N., Goldberg, I., and E. Brewer, "Off-the-Record
              Communication, or, Why Not To Use PGP", 2012,
              <https://otr.cypherpunks.ca/otr-wpes.pdf>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4880]  Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
              Thayer, "OpenPGP Message Format", RFC 4880, November 2007.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, September 2009.

Authors' Addresses

   Andrew Biggs
   Cisco Systems

   Email: adb@cisco.com





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   Shaun Cooley
   Cisco Systems

   Email: shcooley@cisco.com















































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