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Versions: 00 01 02 draft-ietf-jose-use-cases

JOSE                                                           R. Barnes
Internet-Draft                                          BBN Technologies
Intended status: Informational                         February 25, 2013
Expires: August 29, 2013


Use Cases and Requirements for JSON Object Signing and Encryption (JOSE)
                   draft-barnes-jose-use-cases-02.txt

Abstract

   Many Internet applications have a need for object-based security
   mechanisms in addition to security mechanisms at the network layer or
   transport layer.  In the past, the Cryptographic Message Syntax has
   provided a binary secure object format based on ASN.1.  Over time,
   the use of binary object encodings such as ASN.1 has been overtaken
   by text-based encodings, for example JavaScript Object Notation.
   This document defines a set of use cases and requirements for a
   secure object format encoded using JavaScript Object Notation, drawn
   from a variety of application security mechanisms currently in
   development.

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 August 29, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   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
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Basic Requirements . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Security Tokens and Authorization  . . . . . . . . . . . .  6
     4.2.  XMPP . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  ALTO . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     4.4.  Emergency Alerting . . . . . . . . . . . . . . . . . . . . 11
     4.5.  Web Cryptography . . . . . . . . . . . . . . . . . . . . . 13
   5.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.1.  Functional Requirements  . . . . . . . . . . . . . . . . . 14
     5.2.  Security Requirements  . . . . . . . . . . . . . . . . . . 15
     5.3.  Desiderata . . . . . . . . . . . . . . . . . . . . . . . . 15
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 18
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19






















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1.  Introduction

   Internet applications rest on the layered architecture of the
   Internet, and take advantage of security mechanisms at all layers.
   Many applications rely primarily on channel-based security
   technologies, which create a secure channel at the IP layer or
   transport layer over which application data can flow
   [RFC4301][RFC5246].  These mechanisms, however, cannot provide end-
   to-end security in some cases.  For example, in protocols with
   application-layer intermediaries, channel-based security protocols
   would protect messages from attackers between intermediaries, but not
   from the intermediaries themselves.  These cases require object-based
   security technologies, which embed application data within a secure
   object that can be safely handled by untrusted entities.

   The most well-known example of such a protocol today is the use of
   Secure/Multipurpose Internet Mail Extensions (S/MIME) protections
   within the email system [RFC5751][RFC5322].  An email message
   typically passes through a series of intermediate Mail Transfer
   Agents (MTAs) en route to its destination.  While these MTAs often
   apply channel-based security protections to their interactions (e.g.,
   [RFC3207]), these protections do not prevent the MTAs from
   interfering with the message.  In order to provide end-to-end
   security protections in the presence of untrusted MTAs, mail users
   can use S/MIME to embed message bodies in a secure object format that
   can provide confidentiality, integrity, and data origin
   authentication.

   S/MIME is based on the Cryptographic Message Syntax for secure
   objects (CMS) [RFC5652].  CMS is defined using Abstract Syntax
   Notation 1 (ASN.1) and traditionally encoded using the ASN.1
   Distinguished Encoding Rules (DER), which define a binary encoding of
   the protected message and associated parameters [ITU.X690.1994].  In
   recent years, usage of ASN.1 has decreased (along with other binary
   encodings for general objects), while more applications have come to
   rely on text-based formats such as the Extensible Markup Language
   (XML) or the JavaScript Object Notation (JSON)
   [W3C.REC-xml-1998][RFC4627].

   Many current applications thus have much more robust support for
   processing objects in these text-based formats than ASN.1 objects;
   indeed, many lack the ability to process ASN.1 objects at all.  To
   simplify the addition of object-based security features to these
   applications, the IETF JSON Object Signing and Encryption (JOSE)
   working group has been chartered to develop a secure object format
   based on JSON.  While the basic requirements for this object format
   are straightforward -- namely, confidentiality and integrity
   mechanisms, encoded in JSON -- early discussions in the working group



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   indicated that many applications hoping to use the formats define in
   JOSE have additional requirements.  This document summarizes the use
   cases for JOSE envisioned by those applications and the resulting
   requirements for security mechanisms and object encoding.

   Some systems that use XML have specified the use of XML-based
   security mechanisms for object security, namely XML Digital
   Signatures and XML Encryption
   [W3C.CR-xmldsig-core2-20120124][W3C.CR-xmlenc-core1-20120313].  These
   mechanisms are defined for use with several security token systems
   (e.g., SAML, WS-Federation, and OpenID connect
   [OASIS.saml-core-2.0-os][WS-Federation][OpenID.Messages]) and the CAP
   emergency alerting format [CAP].  In practice, however, XML-based
   secure object formats introduce similar levels of complexity to
   ASN.1, so developers that lack the tools or motivation to handle
   ASN.1 aren't able to use XML security either.  This situation
   motivates the creation of a JSON-based secure object format that is
   simple enough to implement and deploy that it can be easily adopted
   by developers with minimal effort and tools.


2.  Definitions

   This document makes extensive use of standard security terminology
   [RFC4949].  In addition, because the use cases for JOSE and CMS are
   similar, we will sometimes make analogies to some CMS concepts
   [RFC5652].

   The JOSE working group charter calls for the group to define three
   basic JSON object formats:

   1.  Confidentiality-protected object format

   2.  Integrity-protected object format

   3.  A format for expressing public keys

   In the below, we will refer to these as the "encrypted object
   format", the "signed object format", and the "key format",
   respectively.  In general, where there is no need to distinguish
   between asymmetric and symmetric operations, we will use the terms
   "signing", "signature", etc. to denote both true digital signatures
   involving asymmtric cryptography as well as message authentication
   codes using symmetric keys(MACs).

   In the lifespan of a secure object, there are two basic roles, an
   entity that creates the object (e.g., encrypting or signing a
   payload), and an entity that uses the object (decrypting, verifying).



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   We will refer to these roles as "sender" and "recipient",
   respectively.  Note that while some requirements and use cases may
   refer to these as single entities, each object may have multiple
   entities in each role.  For example, a message may be signed by
   multiple senders, or decrypted by multiple recipients.


3.  Basic Requirements

   Obviously, for the encrypted and signed object formats, the necessary
   protections will be created using appropriate cryptographic
   mechanisms: symmetric or asymmetric encryption for confidentiality
   and MACs or digital signatures for integrity protection.  In both
   cases, it is necessary for the JOSE format to support both symmetric
   and asymmetric operations.

   o  The JOSE encrypted object format must support object encryption in
      the case where the sender and receiver share a symmetric key.

   o  The JOSE encrypted object format must support object encryption in
      the case where the sender has only a public key for the receiver.

   o  The JOSE signed object format must integrity protection using
      Message Authentication Codes (MACs), for the case where the sender
      and receiver share only a symmetric key.

   o  The JOSE signed object format must integrity protection using
      digital signatures, for the case where the receiver has only a
      public key for the sender.

   In cases where two entities are going to be exchanging several JOSE
   objects, it might be helpful to pre-negotiate some parameters so that
   they do not have to be signaled in every JOSE object.  However, in
   order to not interfere with endpoints that do not support pre-
   negotiation, it is necessary to signal when pre-negotiated parameters
   are in use.

   o  The JOSE signed and encrypted object formats must include a field
      that indicates that pre-negotiated parameters are to be used to
      process the object.  This field may also provide an indication of
      which parameters are to be used.

   The purpose of the key format is to provide the recipient with
   sufficient information to use the encoded key to process
   cryptographic messages.  Thus it is necessary to include additional
   parameters along with the bare key.





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   o  The JOSE key format must include all algorithm parameters
      necesssary to use the encoded key, including an identifier for the
      algorithm with which the key is used as well as any additional
      parameters required by the algorithm (e.g., elliptic curve
      parameters).


4.  Use Cases

   Based on early discussions of JOSE, several working groups developing
   application-layer protocols have expressed a desire to use JOSE in
   their designs for end-to-end security features.  In this section, we
   summarize the use cases proposed by these groups and discuss the
   requirements that they imply for the JOSE object formats.

4.1.  Security Tokens and Authorization

   Security tokens are a common use case for object-based security, for
   example, SAML assertions [OASIS.saml-core-2.0-os].  Security tokens
   are used to convey information about a subject entity ("claims" or
   "assertions") from an issuer to a recipient.  The security features
   of a token format enable the recipient to verify that the claims came
   from the issuer and, if the object is confidentiality-protected, that
   they were not visible to other parties.

   Security tokens are used in federation protocols such as SAML 2.0,
   WS-Federation, and OpenID Connect
   [OASIS.saml-core-2.0-os][WS-Federation][OpenID.Messages], as well as
   in resource authorization protocols such as OAuth 2.0 [RFC6749].  In
   some cases, security tokens are used for client authentication and
   for access control
   [I-D.ietf-oauth-jwt-bearer][I-D.ietf-oauth-saml2-bearer].

   The OAuth protocol defines a mechanism for distributing and using
   authorization tokens using HTTP [RFC6749].  A Client that wishes to
   access a protected resource requests authorization from the Resource
   Owner.  If the Resource Owner allows this access, he directs an
   Authorization Server to issue an access token to the Client.  When
   the Client wishes to access the protected resource, he presents the
   token to the relevant Resource Server, which verifies the validity of
   the token before providing access to the protected resource.










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                 +---------------+          +---------------+
                 |               |          |               |
                 |   Resource    |<........>| Authorization |
                 |    Server     |          |     Server    |
                 |               |          |               |
                 +---------------+          +---------------+
                              ^                |
                              |                |
                              |                |
                              |                |
                              |                |
                 +------------|--+          +--|------------+
                 |            +----------------+            |
                 |               |          |   Resource    |
                 |     Client    |          |     Owner     |
                 |               |          |               |
                 +---------------+          +---------------+

                        Figure 1: The OAuth process

   In effect, this process moves the token from the Authorization Server
   (as a sender of the object) to the Resource Server (recipient), via
   the Client as well as the Resource Owner (the latter because of the
   HTTP mechanics underlying the protocol).  So again we have a case
   where an application object is transported via untrusted
   intermediaries.

   This application has two essential security requirements: Integrity
   and data origin authentication.  Integrity protection is required so
   that the Resource Owner and the Client cannot modify the permission
   encoded in the token.  Data origin authentication is required so that
   the Resource Server can verify that the token was issued by a trusted
   Authorization Server.  Confidentiality protection may also be needed,
   if the Authorization Server is concerned about the visibility of
   permissions information to the Resource Owner or Client.  For
   example, permissions related to social networking might be considered
   private information.  Note, however, that OAuth already requires that
   the underlying HTTP transactions be protected by TLS, so
   confidentiality protection is not strictly necessary for this use
   case.

   The confidentiality and integrity needs are met by the basic
   requirements for signed and encrypted object formats, whether the
   signing and encryption are provided using asymmetric or symmetric
   cryptography.  The choice of which mechanism is applied will depend
   on the relationship between the two servers, namely whether they
   share a symmetric key or only public keys.




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   Authentication requirements will also depend on deployment
   characteristics.  Where there is a relatively strong binding between
   the resource server and the authorization server, it may suffice for
   the Authorization Server issuing a token to be identified by the key
   used to sign the token.  This requires that the token carry either
   the public key of the Authorization Server or an identifier for the
   public or symmetric key.

   There may also be more advanced cases, where the Authorization
   Server's key is not known in advance to the Resource Server.  This
   may happen, for instance, if an entity instantiated a collection of
   Authorization Servers (say for load balancing), each of which has an
   independent key pair.  In these cases, it may be necessary to also
   include a certificate or certificate chain for the Authorization
   Server, so that the Resource Server can verify that the Authorization
   Server is an entity that it trusts.

   The HTTP transport for OAuth imposes a particular constraint on the
   encoding.  In the OAuth protocol, tokens frequently need to be passed
   as query parameters in HTTP URIs [RFC2616], after having been
   base64url encoded [RFC4648].  While there is no specified limit on
   the length of URIs (and thus of query parameters), in practice URIs
   of more than around 2,000 characters are rejected by some user
   agents.  So this use case requires that a JOSE object have
   sufficiently small size even after signing, possibly encrypting,
   while still being simple to include in an HTTP URI query parameter.

   Two related security token systems have similar requirements:

   o  The JSON Web Token format (JWT) is a security token format based
      on JSON and JOSE [I-D.ietf-oauth-json-web-token].  It is used with
      both OpenID Connect and OAuth.  Because JWTs are often used in
      contexts with limited space (e.g., HTTP query parameters), it is a
      core requirement for JWTs, and thus JOSE, to have a compact
      representation.

   o  The OpenID Connect protocol is a simple, REST/JSON-based identity
      federation protocol layered on OAuth 2.0 [OpenID.Messages].  It
      uses the JWT and JOSE formats both to represent security tokens
      and to provide security for other protocol messages (signing and
      optionally encryption).

4.2.  XMPP

   The Extensible Messaging and Presence Protocol (XMPP) routes messages
   from one end client to another by way of XMPP servers [RFC6120].
   There are typically two servers involved in delivering any given
   message: The first client (Alice) sends a message for another client



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   (B) to her server (A).  Server A uses Bob's identity and the DNS to
   locate the server for Bob's domain (B), then delivers the message to
   that server.  Server B then routes the message to Bob.

            +-------+   +----------+   +----------+   +-----+
            | Alice |-->| Server A |-->| Server B |-->| Bob |
            +-------+   +----------+   +----------+   +-----+

                   Figure 2: Delivering an XMPP message

   The untrusted-intermediary problems are especially acute for XMPP
   because in many current deployments, the holder of an XMPP domain
   outsources the operation of the domain's servers to a different
   entity.  In this environment, there is a clear risk of exposing the
   domain holder's private information to the domain operator.  XMPP
   already has a defined mechanism for end-to-end security using S/MIME,
   but it has failed to gain widespread deployment [RFC3923], in part
   because of key management challenges and because of the difficulty of
   processing S/MIME objects.

   The XMPP working group is in the process of developing a new end-to-
   end encryption system with an encoding based on JOSE and a clearer
   key management system [I-D.miller-xmpp-e2e].  The process of sending
   an encrypted message in this system involves two steps: First, the
   sender generates a symmetric Content Encryption Key (CEK), encrypts
   the message content, and sends the encrypted message to the desired
   set of recipients.  Second, each recipient "dials back" to the
   sender, providing his public key; the sender then responds with the
   relevent CEK, wrapped with the recipient's public key.

            +-------+   +----------+   +----------+   +-----+
            | Alice |<->| Server A |<->| Server B |<->| Bob |
            +-------+   +----------+   +----------+   +-----+
                |             |              |           |
                |------------Encrypted--message--------->|
                |             |              |           |
                |<---------------Public-key--------------|
                |             |              |           |
                |---------------Wrapped CEK------------->|
                |             |              |           |

                Figure 3: Delivering a secure XMPP message

   The main thing that this system requires from the JOSE formats is
   confidentiality protection via content encryption, plus an integrity
   check via a MAC derived from the same symmetric key.  The separation
   of the key exchange from the transmission of the encrypted content,
   however, requires that the JOSE encrypted object format allow wrapped



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   symmetric keys to be carried separately from the encrypted payload.
   In addition, the encrypted object will need to have a tag for the key
   that was used to encrypt the content, so that the recipient (Bob) can
   present the tag to the sender (Alice) when requesting the wrapped
   key.

   Another important feature of XMPP is that it allows for the
   simultaneous delivery of a message to multiple recipients.  In the
   diagrams above, Server A could deliver the message not only to Server
   B (for Bob) but also to Servers C, D, E, etc. for other users.  In
   such cases, to avoid the multiple "dial back" transactions implied by
   the above mechanism, XMPP systems will likely cache public keys for
   end recipients, so that wrapped keys can be sent along with content
   on future messages.  This implies that the JOSE encrypted object
   format must support the provision of multiple versions of the same
   wrapped CEK (much as a CMS EnvelopedData structure can include
   multiple RecipientInfo structures).

   In the current draft of the XMPP end-to-end security system, each
   party is authenticated by virtue of the other party's trust in the
   XMPP message routing system.  The sender is authenticated to the
   receiver because he can receive messages for the identifier "Alice"
   (in particular, the request for wrapped keys), and can originate
   messages for that identifier (the wrapped key).  Likewise, the
   receiver is authenticated to the sender because he received the
   original encrypted message and originated the request for wrapped
   key.  So the authentication here requires not only that XMPP routing
   be done properly, but also that TLS be used on every hop.  Moreover,
   it requires that the TLS channels have strong authentication, since a
   man in the middle on any of the three hops can masquerade as Bob and
   obtain the key material for an encrypted message.

   Because this authentication is quite weak (depending on the use of
   transport-layer security on three hops) and unverifiable by the
   endpoints, it is possible that the XMPP working group will integrate
   some sort of credentials for end recipients, in which case there
   would need to be a way to associate these credentials with JOSE
   objects.

   Finally, it's worth noting that XMPP is based on XML, not JSON.  So
   by using JOSE, XMPP will be carrying JSON objects within XML.  It is
   thus a desirable property for JOSE objects to be encoded in such a
   way as to be safe for inclusion in XML.  Otherwise, an explicit CDATA
   indication must be given to the parser to indicate that it is not to
   be parsed as XML.  One way to meet this requirement would be to apply
   base64url encoding, but for XMPP messages of medium-to-large size,
   this could impose a fair degree of overhead.




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4.3.  ALTO

   Application-Layer Traffic Optimization (ALTO) is a system for
   distributing network topology information to end devices, so that
   those devices can modify their behavior to have a lower impact on the
   network [I-D.ietf-alto-reqs].  The ALTO protocol distributes topology
   information in the form of JSON objects carried in HTTP
   [RFC2616][I-D.ietf-alto-protocol].  The basic version of ALTO is
   simply a client-server protocol, so simple use of HTTPS suffices for
   this case [RFC2818].  However, there is beginning to be some
   discussion of use cases for ALTO in which these JSON objects will be
   distributed through a collection of intermediate servers before
   reaching the client, while still preserving the ability of the client
   to authenticate the original source of the object.  Even the base
   ALTO protocol notes that "ALTO clients obtaining ALTO information
   must be able to validate the received ALTO information to ensure that
   it was generated by an appropriate ALTO server."

   In this case, the security requirements are straightforward.  JOSE
   objects carrying ALTO payloads will need to bear digital signatures
   from the originating servers, which will be bound to certificates
   attesting to the identities of the servers.  There is no requirement
   for confidentiality in this case, since ALTO information is generally
   public.

   The more interesting questions are encoding questions.  ALTO objects
   are likely to be much larger than payloads in the two cases above,
   with sizes of up to several megabytes.  Processing of such large
   objects can be done more quickly if it can be done in a single pass,
   which may be possible if JOSE objects require specific orderings of
   fields within the JSON structure.

   In addition, because ALTO objects are also encoded as JSON, they are
   already safe for inclusion in a JOSE object.  Signed JOSE objects
   will likely carry the signed data in a string alongside the
   signature.  JSON objects have the property that they can be safely
   encoded in JSON strings.  All they require is that unnecessary white
   space be removed, a much simpler transformation than, say base64url
   encoding.  This raises the question of whether it might be possible
   to optimize the JOSE encoding for certain "JSON-safe" cases.

4.4.  Emergency Alerting

   Emergency alerting is an emerging use case for IP networks
   [I-D.ietf-atoca-requirements].  Alerting systems allow authorities to
   warn users of impending danger by sending alert messages to connected
   devices.  For example, in the event of hurricane or tornado, alerts
   might be sent to all devices in the path of the storm.



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   The most critical security requirement for alerting systems is that
   it must not be possible for an attacker to send false alerts to
   devices.  Such a capability would potentially allow an attacker to
   create wide-spread panic.  In practice, alert systems prevent these
   attacks both by controls on sending messages at points where alerts
   are originated, as well as by having recipients of alerts verify that
   the alert was sent by an authorized source.  The former type of
   control implemented with local security on hosts from which alerts
   can be originated.  The latter type implemented by digital signatures
   on alert messages (using channel-based or object-based mechanisms).

   Alerts typically reach end recipients via a series of intermediaries.
   For example, while a national weather service might originate a
   hurricane alert, it might first be delivered to a national gateway,
   and then to network operators, who broadcast it to end subscribers.

           +------------+    +------------+    +------------+
           | Originator |    | Originator |    | Originator |
           +------------+    +------------+    +------------+
                 |                 .                 .
                 +-----------------+..................
                                   |
                                   V
                              +---------+
                              | Gateway |
                              +---------+
                                   |
                      +------------+------------+
                      |                         |
                      V                         V
                 +---------+               +---------+
                 | Network |               | Network |
                 +---------+               +---------+
                      |                         |
               +------+-----+            +------+-----+
               |            |            |            |
               V            V            V            V
           +--------+   +--------+   +--------+   +--------+
           | Device |   | Device |   | Device |   | Device |
           +--------+   +--------+   +--------+   +--------+


                  Figure 4: Delivering an emergency alert

   In order to verify alert signatures, recipients must be provisioned
   with the proper public keys for trusted alert authorities.  This
   trust may be "piece-wise" along the path the alert takes.  For
   example, the alert relays operated by networks might have a full set



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   of ceritificates for all alert originators, while end devices may
   only trust their local alert relay.  Or devices might require that a
   device be signed by an authorized originator and by its local
   network's relay.

   This scenario creates a need for multiple signatures on alert
   documents, so that an alert can bear signatures from any or all of
   the entities that processed it along the path.  In order to minimize
   complexity, these signatures should be "modular", in the sense that a
   new signature can be added without a need to alter or recompute
   previous signatures.

4.5.  Web Cryptography

   The W3C Web Cryptography API defines a standard cryptographic API for
   the web [WebCrypto].  If a browser exposes this API, then JavaScript
   provided as part of a web page can ask the browser to perform
   cryptographic operations, such as digest, MAC, encryption, or digital
   signing.

   One of the key reasons to have the browser perform cryptographic
   operations to avoid allowing JavaScript code to access the keying
   material used for these operations.  For example, this separation
   would prevent code injected through a cross-site scripting (XSS)
   attack from reading and exfiltrating keys stored within a browser.
   While the malicious code could still use the key while running in the
   browser, this vulnerability can only be exercised while the
   vulnerable page is active in a user's browser.

   However, the WebCryptography API also provides a key export
   functionality, which can allow JavaScript to extract a key from the
   API in wrapped form.  For example, the JavaScript might provide a
   public key for which the corresponding private key is held by another
   device.  The wrapped key provided by the API could then be used to
   safely transport the key to the new device.  While this could
   potentially allow malicious code to export a key, the need for an
   explicit export operation provides a control point, allowing for user
   notification or consent verification.

   The Web Cryptography API also allows browsers to impose limitations
   on the usage of the keys it handles.  For example, a symmetric key
   might be marked as usable only for encryption, and not for MAC.  When
   a key is exported in wrapped form, these attributes should be carried
   along with it.

   The Web Cryptography API thus requires formats to express several
   forms of keys.  Obviously, the public key from an asymmetric key pair
   can be freely imported to and exported from the browser, so there



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   needs to be a format for public keys.  There is also a need for a
   format to express private keys and symmetric keys.  For non-public
   keys, the primary need is for a wrapped form, where the
   confidentiality and integrity of the key is assured
   cryptographically; these protections should also apply to any
   attributes of the key.  It may also be useful to define a direct,
   unwrapped format, for use within a security boundary.


5.  Requirements

   This section summarizes the requirements from the above uses cases,
   and lists further requirements not directly derived from the above
   use cases.  There are also some constraints that are not hard
   requrirements, but which are still desireable properties for the JOSE
   system to have.

5.1.  Functional Requirements

   F1 Define formats for secure objects that provide the following
      security properties:

      *  Digital signature (integrity/authentication under an asymmetric
         key pair)

      *  Message authentication (integrity/authentication under a
         symmetric key)

      *  Encryption

      *  Authenticated encryption

      That is, the secure objects defined by this working group should
      provide equivalent security properties to the CMS SignedData,
      AuthenticatedData, EnvelopedData, and AuthEnveloped data objects
      [RFC5652] [RFC5083].

   F2 Define a format for public keys and private keys for asymmetric
      cryptographic algorithms, with associated attributes, including a
      wrapped form for private keys.

   F3 Define a format for symmetric keys with associated attributes,
      allowing for both wrapped and unwrapped keys.

   F4 Define a JSON serialization for the above objects.  An object in
      this encoding must be valid according to the JSON ABNF syntax
      [RFC4627]




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   F5 Define a compact, URL-safe text serialization for the above
      objects.

   F6 Allow for attributes associated to wrapped keys to be bound to
      them cryptographically

   F7 Allow for wrapped keys to be separated from a secure object that
      uses a symmetric key.  In such cases, cryptographic components of
      the secure object other than the wrapped key (e.g., ciphertext,
      MAC values) must be independent of the wrapped form of the key.
      For example, if an encrypted object is prepared for multiple
      recipients, then only the wrapped key may vary, not the
      ciphertext.

5.2.  Security Requirements

   S1 Provide key management functions for all symmetric keys, including
      encryption keys and MAC keys.  It should be possible to use any of
      the key management techniques provided in CMS [RFC5652]:

      *  Key transport (wrapping for a public key)

      *  Key encipherment (wrapping for a symmetric key)

      *  Key agreement (wrapping for a DH public key)

      *  Password-based encryption (wrapping under a derived key)

   S2 Use cryptographic algorithms in a manner compatible with major
      validation processes.  For example, if a FIPS standard allows
      algorithm A to be used for purpose X but not purpose Y, then JOSE
      should not recommend using algorithm A for purpose Y.

   S3 Support operation with or without pre-negotiation.  It must be
      possible to create or process a secure object without any
      configuration beyond key provisioning.  If it is possible to
      negotiate parameters out of band, then the object must signal that
      pre-negotiated parameters are to be used.

5.3.  Desiderata

   D1 Maximize compatibility with the W3C WebCrypto specification, e.g.,
      by using the same identifiers for algorithms.

   D2 Avoid JSON canonicalization to the extent possible possible.  That
      is, all other things being equal, techniques that rely on fixing a
      serialization of an object (e.g., by base64url encoding it) are
      preferred over those that require converting an object to a



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      canonical form.


6.  Acknowledgements

   Thanks to Matt Miller for discussions related to XMPP end-to-end
   security model, and to Mike Jones for considerations related to
   security tokens and XML security.  Thanks to Mark Watson for raising
   the need for representing symmetric keys and binding attributes to
   them.


7.  IANA Considerations

   This document makes no request of IANA.


8.  Security Considerations

   The primary focus of this document is the requirements for a JSON-
   based secure object format.  At the level of general security
   considerations for object-based security technologies, the security
   considerations for this format are the same as for CMS [RFC5652].
   The primary difference between the JOSE format and CMS is that JOSE
   is based on JSON, which does not have a canonical representation.
   The lack of a canonical form means that it is difficult to determine
   whether two JSON objects represent the same information, which could
   lead to vulnerabilities in some usages of JOSE.


9.  References

9.1.  Normative References

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-13 (work in progress),
              September 2012.

   [I-D.ietf-alto-reqs]
              Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and
              Y. Yang, "Application-Layer Traffic Optimization (ALTO)
              Requirements", draft-ietf-alto-reqs-16 (work in progress),
              June 2012.

   [I-D.ietf-atoca-requirements]
              Schulzrinne, H., Norreys, S., Rosen, B., and H.
              Tschofenig, "Requirements, Terminology and Framework for



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              Exigent Communications", draft-ietf-atoca-requirements-03
              (work in progress), March 2012.

   [I-D.ietf-oauth-json-web-token]
              Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", draft-ietf-oauth-json-web-token-06 (work in
              progress), December 2012.

   [I-D.miller-xmpp-e2e]
              Miller, M., "End-to-End Object Encryption for the
              Extensible Messaging and Presence Protocol (XMPP)",
              draft-miller-xmpp-e2e-04 (work in progress),
              February 2013.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

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

   [RFC5083]  Housley, R., "Cryptographic Message Syntax (CMS)
              Authenticated-Enveloped-Data Content Type", RFC 5083,
              November 2007.

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

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, March 2011.

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

   [W3C.CR-xmldsig-core2-20120124]
              Datta, P., Hirsch, F., Eastlake, D., Cantor, S., Roessler,
              T., Reagle, J., Yiu, K., and D. Solo, "XML Signature
              Syntax and Processing Version 2.0", World Wide Web
              Consortium CR CR-xmldsig-core2-20120124, January 2012,
              <http://www.w3.org/TR/2012/CR-xmldsig-core2-20120124>.

   [W3C.CR-xmlenc-core1-20120313]
              Eastlake, D., Reagle, J., Roessler, T., and F. Hirsch,
              "XML Encryption Syntax and Processing Version 1.1", World
              Wide Web Consortium CR CR-xmlenc-core1-20120313,
              March 2012,



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              <http://www.w3.org/TR/2012/CR-xmlenc-core1-20120313>.

   [W3C.REC-xml-1998]
              Bray, T., Paoli, J., and C. Sperberg-McQueen, "Extensible
              Markup Language (XML) 1.0", W3C REC-xml-1998,
              February 1998,
              <http://www.w3.org/TR/1998/REC-xml-19980210/>.

   [WebCrypto]
              Sleevi, R. and D. Dahl, "Web Cryptography API",
              January 2013.

9.2.  Informative References

   [CAP]      Botterell, A. and E. Jones, "Common Alerting Protocol
              v1.1", October 2005.

   [I-D.ietf-oauth-jwt-bearer]
              Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
              (JWT) Bearer Token Profiles for OAuth 2.0",
              draft-ietf-oauth-jwt-bearer-04 (work in progress),
              December 2012.

   [I-D.ietf-oauth-saml2-bearer]
              Campbell, B. and C. Mortimore, "SAML 2.0 Bearer Assertion
              Profiles for OAuth 2.0", draft-ietf-oauth-saml2-bearer-15
              (work in progress), November 2012.

   [ITU.X690.1994]
              International Telecommunications Union, "Information
              Technology - ASN.1 encoding rules: Specification of Basic
              Encoding Rules (BER), Canonical Encoding Rules (CER) and
              Distinguished Encoding Rules (DER)", ITU-T Recommendation
              X.690, 1994.

   [OASIS.saml-core-2.0-os]
              Cantor, S., Kemp, J., Philpott, R., and E. Maler,
              "Assertions and Protocol for the OASIS Security Assertion
              Markup Language (SAML) V2.0", OASIS Standard saml-core-
              2.0-os, March 2005.

   [OpenID.Messages]
              Sakimura, N., Bradley, J., Jones, M., de Medeiros, B.,
              Mortimore, C., and E. Jay, "OpenID Connect Messages 1.0",
              June 2012,
              <http://openid.net/specs/
              openid-connect-messages-1_0.html>.




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   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3207]  Hoffman, P., "SMTP Service Extension for Secure SMTP over
              Transport Layer Security", RFC 3207, February 2002.

   [RFC3923]  Saint-Andre, P., "End-to-End Signing and Object Encryption
              for the Extensible Messaging and Presence Protocol
              (XMPP)", RFC 3923, October 2004.

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

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

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.

   [WS-Federation]
              Kaler, C., McIntosh, M., Goodner, M., and A. Nadalin,
              "OpenID Connect Messages 1.0", May 2009, <http://
              docs.oasis-open.org/wsfed/federation/v1.2/os/
              ws-federation-1.2-spec-os.html>.


Author's Address

   Richard Barnes
   BBN Technologies
   1300 N 17th St
   Arlington, VA  22209
   US

   Email: rlb@ipv.sx









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