One document matched: draft-barnes-jose-use-cases-00.xml
<?xml version="1.0" encoding="US-ASCII"?>
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<rfc category="info" docName="draft-barnes-jose-use-cases-00.txt"
ipr="trust200902">
<!-- category values: std, bcp, info, exp, and historic
ipr values: full3667, noModification3667, noDerivatives3667
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<!-- ***** FRONT MATTER ***** -->
<front>
<!-- The abbreviated title is used in the page header - it is only necessary if the
full title is longer than 39 characters -->
<title abbrev="JOSE Use Cases">Use Cases and Requirements for JSON Object
Signing and Encryption (JOSE)</title>
<!-- add 'role="editor"' below for the editors if appropriate -->
<author fullname="Richard Barnes" initials="R.L." surname="Barnes">
<organization>BBN Technologies</organization>
<address>
<postal>
<street>9861 Broken Land Parkway</street>
<city>Columbia</city>
<region>MD</region>
<code>21046</code>
<country>US</country>
</postal>
<phone>+1 410 290 6169</phone>
<email>rbarnes@bbn.com</email>
</address>
</author>
<date day="6" month="April" year="2012" />
<!-- If the month and year are both specified and are the current ones, xml2rfc will fill
in the current day for you. If only the current year is specified, xml2rfc will fill
in the current day and month for you. If the year is not the current one, it is
necessary to specify at least a month (xml2rfc assumes day="1" if not specified for the
purpose of calculating the expiry date). With drafts it is normally sufficient to
specify just the year. -->
<area>SEC</area>
<workgroup>JOSE</workgroup>
<!-- WG name at the upperleft corner of the doc,
IETF is fine for individual submissions.
If this element is not present, the default is "Network Working Group",
which is used by the RFC Editor as a nod to the history of the IETF. -->
<keyword>cms, s/mime, jose, xmpp, alto, oauth</keyword>
<!-- Keywords will be incorporated into HTML output
files in a meta tag but they have no effect on text or nroff
output. If you submit your draft to the RFC Editor, the
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<abstract>
<t>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.</t>
</abstract>
</front>
<middle>
<section anchor="intro-sec" title="Introduction">
<t>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 <xref target="RFC4301"></xref><xref target="RFC5246"></xref>. 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.</t>
<t>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 <xref target="RFC5751"></xref><xref target="RFC5322"></xref>. 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., <xref target="RFC3207"></xref>), 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.</t>
<t>S/MIME is based on the Cryptographic Message Syntax for secure
objects (CMS) <xref target="RFC5652"></xref>. 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 <xref target="X.680"></xref><xref target="X.690"></xref>.
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) <xref target="XML"></xref><xref target="RFC4627"></xref>.</t>
<t>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 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.</t>
</section>
<section anchor="def-sec" title="Definitions">
<!--
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref
target="RFC2119">RFC 2119</xref>.</t>
-->
<t>This document makes extensive use of standard security terminology
<xref target="RFC4949"></xref>. In addition, because the use cases for JOSE and CMS are
similar, we will sometimes make analogies to some CMS concepts
<xref target="RFC5652"></xref>.</t>
<t>The JOSE working group charter calls for the group to define three
basic JSON object formats:<list style="numbers">
<t>Confidentiality-protected object format</t>
<t>Integrity-protected object format</t>
<t>A format for expressing public keys</t>
</list>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).</t>
<t>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). 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.</t>
</section>
<section title="Basic Requirements">
<t>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.<list style="symbols">
<t>The JOSE encrypted object format MUST support object encryption
in the case where the sender and receiver share a symmetric key.</t>
<t>The JOSE encrypted object format MUST support object encryption
in the case where the sender has only a public key for the
receiver.</t>
<t>The JOSE signed object format MUST integrity protection using
Message Authentication Codes (MACs), for the case where the sender
and receiver share a symmetric key.</t>
<t>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.</t>
</list></t>
<t>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.</t>
<t><list style="symbols">
<t>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).</t>
</list></t>
</section>
<section anchor="lock-sec" title="Use Cases">
<t>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.</t>
<section title="OAuth">
<t>The OAuth protocol defines a mechanism for distributing and using
authorization tokens using HTTP <xref target="I-D.ietf-oauth-v2"></xref>. 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.</t>
<figure anchor="figOAuth" title="The OAuth process">
<artwork><![CDATA[ +---------------+ +---------------+
| | | |
| Resource |<........>| Authorization |
| Server | | Server |
| | | |
+---------------+ +---------------+
^ |
| |
| |
| |
| |
+------------|--+ +--|------------+
| +----------------+ |
| | | Resource |
| Client | | Owner |
| | | |
+---------------+ +---------------+]]></artwork>
<postamble></postamble>
</figure>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
<t>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 <xref target="RFC2616"></xref>, after having been
base64url encoded <xref target="RFC4648"></xref>. While there is no prescribed 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, and base64url encoding.</t>
</section>
<section title="XMPP">
<t>The Extensible Messaging and Presence Protocol (XMPP) routes
messages from one end client to another by way of XMPP servers
<xref target="RFC6120"></xref>. There are typically two servers involved in delivering
any given message: The first client (Alice) sends a message for
another client (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.</t>
<figure anchor="fig-xmpp" title="Delivering an XMPP message">
<artwork><![CDATA[
+-------+ +----------+ +----------+ +-----+
| Alice |-->| Server A |-->| Server B |-->| Bob |
+-------+ +----------+ +----------+ +-----+]]></artwork>
</figure>
<t>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 <xref target="RFC3923"></xref>, in part
because of key management challenges and because of the difficulty of
processing S/MIME objects.</t>
<t>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 <xref target="I-D.miller-xmpp-e2e"></xref>. 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.</t>
<figure anchor="fig-xmpp-sec" title="Delivering a secure XMPP message">
<artwork><![CDATA[
+-------+ +----------+ +----------+ +-----+
| Alice |<->| Server A |<->| Server B |<->| Bob |
+-------+ +----------+ +----------+ +-----+
| | | |
|------------Encrypted--message--------->|
| | | |
|<---------------Public-key--------------|
| | | |
|---------------Wrapped CEK------------->|
| | | |]]></artwork>
</figure>
<t>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
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.</t>
<t>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). </t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
<section title="ALTO">
<t>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 <xref target="I-D.ietf-alto-reqs"></xref>. The ALTO protocol distributes
topology information in the form of JSON objects carried in HTTP
<xref target="RFC2616"></xref><xref target="I-D.ietf-alto-protocol"></xref>. The basic version of ALTO
is simply a client-server protocol, so simple use of HTTPS suffices
for this case <xref target="RFC2818"></xref>. 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."</t>
<t>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.</t>
<t>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.</t>
<t>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.</t>
</section>
</section>
<section title="Other Requirements">
<t>[[ For the initial version of this document, this section is a
placeholder, to incorporate any further requirements not directly
derived from the above use cases. ]]</t>
</section>
<section anchor="ack-sec" title="Acknowledgements">
<t>Thanks to Matt Miller for discussions related to XMPP end-to-end
security model.</t>
</section>
<section anchor="iana-sec" title="IANA Considerations">
<t>This document makes no request of IANA.</t>
</section>
<section anchor="sec-cons-sec" title="Security Considerations">
<t>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 <xref target="RFC5652"></xref>.
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.</t>
</section>
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<references title="Normative References">
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4627.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4648.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4949.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.6120.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-alto-protocol.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-alto-reqs.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-oauth-v2.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml3/reference.I-D.miller-xmpp-e2e.xml"?>
</references>
<references title="Informative References">
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5246.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5322.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5652.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.5751.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2818.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.3207.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.3923.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.4301.xml"?>
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2616.xml"?>
<reference anchor="X.680">
<front>
<title>Recommendation X.680, "Information Technology -- Abstract
Syntax Notation One (ASN.1) -- Specification of Basic
Notation</title>
<author fullname="---"></author>
<date month="November" year="1994" />
</front>
</reference>
<reference anchor="X.690">
<front>
<title>Recommendation X.690, "Information Technology -- ASN.1
Encoding Rules -- Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished Encoding Rules
(DER)</title>
<author fullname="---"></author>
<date month="November" year="1994" />
</front>
</reference>
<reference anchor="XML">
<front>
<title>Extensible Markup Language (XML) 1.0 (Second Edition)</title>
<author initials="T." surname="Bray"></author>
<author initials="J." surname="Paoli"></author>
<author initials="C.M." surname="Sperberg-McQueen"></author>
<author initials="E." surname="Maler"></author>
<date month="October" year="2000" />
</front>
<seriesInfo name="World Wide Web Consortium Recommendation"
value="REC-xml" />
</reference>
</references>
</back>
</rfc>
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