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2309 lines
56 KiB
XML
2309 lines
56 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE xep SYSTEM 'xep.dtd' [
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<!ENTITY % ents SYSTEM "xep.ent">
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%ents;
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]>
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
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<xep>
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<header>
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<title>A Framework For Securing Jabber Conversations</title>
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<abstract>
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Although the value and utility of contemporary instant messaging
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systems, like Jabber, are now indisputable, current security
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features to protect message data are generally inadequate for
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many deployments; this is particularly true in security conscious
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environments like large, commercial enterprises and government
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agencies. These current features suffer from issues of
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scalability, usability, and supported features. Furthermore, there is a
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lack of standardization.
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We present a protocol to allow communities of Jabber users to
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apply cryptographic protection to selected conversation data.
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</abstract>
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<number>0031</number>
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<status>Deferred</status>
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<type>Standards Track</type>
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<sig>Standards</sig>
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<author>
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<firstname>
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Paul
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</firstname>
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<surname>
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Lloyd
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</surname>
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<email>
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paul_lloyd@hp.com
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</email>
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<jid>
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paul_lloyd@jabber.hp.com (private)
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</jid>
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</author>
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<revision>
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<version>0.2</version>
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<date>2002-07-09</date>
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<initials>
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PCL
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</initials>
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<remark>
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updated to reflect group consensus to incorporate XML Encryption, as well
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as other group comments from Draft 0.9.
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</remark>
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</revision>
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<revision>
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<version>0.1</version>
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<date>2002-05-07</date>
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<initials>
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PCL
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</initials>
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<remark>
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initial version
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</remark>
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</revision>
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</header>
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<section1 topic="Introduction">
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<p>
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Instant messaging has clearly crossed the chasm from experimental
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to mainstream in a short amount of time. It is particularly
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interesting to note the extent to which the employees and
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affiliates of large enterprises have adopted instant messaging as
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part of their daily professional lives. IM is no longer simply
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used on Friday evening to select which movie to watch; it's now
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used on Monday morning to select which company to acquire.
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</p>
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<p>
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While the benefits of IM are clear and compelling, the risks
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associated with sharing sensitive information in an IM
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environment are often overlooked. We need a mechanism that
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permits communities of users to protect their IM conversations.
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This document presents an extension protocol that can be
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incorporated into the existing Jabber protocol to provide such a
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mechanism. We hope that this protocol spurs both interest
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and further investigation into mechanisms to protect Jabber
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conversations. We also hope that the Jabber community can
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accelerate the adoption of standardized security mechanisms.
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</p>
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<p>
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In addition to its ability to protect traditional messaging data,
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the proposed protocol may also serve as a foundation for securing
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other data transported via other Jabber extensions.
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</p>
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<p>
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We use the following terms throughout this document to describe
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the most relevant aspects of the IM environment that we wish to
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address:
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</p>
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<ul>
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<li>
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<p>
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user. A user is simply any Jabber user. Users are uniquely
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identified by a JID; they connect to Jabber hosts using a
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Jabber node.
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</p>
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<p>
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Users produce and consume information, and we wish to
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provide them with mechanisms that can be used to protect
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this information.
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</p>
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</li>
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<li>
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<p>
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community. A community is a collection of users who wish to
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communicate via Jabber. No restrictions or assumptions are
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made about the size of communities or the geographical,
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organizational, or national attributes of the members.
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Communities are assumed to be dynamic and ad-hoc. Users
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typically join communities by the simple act of invitation.
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All members of a community are assumed to be peers.
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</p>
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<p>
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The members of communities share information among
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themselves, and we wish to provide them with mechanisms
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that can permit information to only be shared by community
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members.
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</p>
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</li>
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<li>
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<p>
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conversation. A conversation is the set of messages
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that flows among the members of a community via some
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network. Conversations consist of both the actual
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conversation data produced and consumed by the various
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users as well as the Jabber protocol elements that
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transport it. Members participate in a conversation when
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they are the source or destination of this traffic.
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</p>
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<p>
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In hostile network environments, like the Internet,
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conversation data is vulnerable to a variety of well-known
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attacks.
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</p>
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</li>
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</ul>
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<p>
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Other Jabber and IM terms are used in a traditional, intuitive
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fashion.
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</p>
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</section1>
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<section1 topic="Requirements And Considerations">
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<p>
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The proposed protocol is designed to address the specific
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requirements and considerations presented in this section.
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</p>
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<section2 topic="Security Requirements">
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<section3 topic="Data Protection Requirements">
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<p>
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A secure IM system must permit conversation participants to
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preserve the following properties of their conversation data:
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</p>
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<ul>
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<li>
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<p>
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confidentiality. Conversation data must only be disclosed
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to authorized recipients
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</p>
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</li>
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<li>
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<p>
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integrity. Conversation data must not be altered
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</p>
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</li>
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<li>
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<p>
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data origin authentication. Recipients must be able to
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determine the identity of the sender and trust that the
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message did, in fact, come from the sender. It is important
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to note that this requirement does not include the
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requirement of a durable digital signature on conversation
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data.
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</p>
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</li>
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<li>
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<p>
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replay protection. Recipients must be able to detect and
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ignore duplicate conversation data.
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</p>
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</li>
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</ul>
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<p>
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These are established, traditional goals of information security
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applied to the conversation data. In the IM environment, these
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goals protect against these attacks:
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</p>
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<ul>
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<li>
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<p>
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eavesdropping, snooping, etc.
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</p>
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</li>
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<li>
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<p>
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masquerading as a conversation participant
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</p>
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</li>
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<li>
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<p>
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forging messages
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</p>
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</li>
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</ul>
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<p>
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Preserving the availability of conversation data is not addressed
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by this protocol.
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</p>
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<p>
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Preserving the anonymity of conversation participants is an
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interesting topic which we defer for future exploration.
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</p>
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<p>
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Finally, note that this protocol does not concern any authentication
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between a Jabber node and a Jabber host.
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</p>
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</section3>
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<section3 topic="Data Classification Requirements">
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<p>
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A secure IM system must support a data classification feature through the use
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of security labeling. Conversation participants must be
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able to associate a security label with each piece of
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conversation data. This label may be used to specify a data
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classification level for the conversation data.
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</p>
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</section3>
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<section3 topic="The End To End Requirement">
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<p>
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It is easy to imagine Jabber systems in which the servers play
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active, fundamental roles in the protection of conversation
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data. Such systems could offer many advantages, like:
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</p>
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<ul>
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<li>
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<p>
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allowing the servers to function as credential issuing
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authorities,
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</p>
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</li>
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<li>
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<p>
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allowing the servers to function as policy enforcement
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points.
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</p>
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</li>
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</ul>
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<p>
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Unfortunately, such systems have significant disadvantages when
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one considers the nature of instant messaging:
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</p>
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<ul>
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<li>
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<p>
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Many servers may be untrusted, public servers.
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</p>
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</li>
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<li>
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<p>
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In many conversation communities, decisions of trust and
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membership can only be adequately defined by the members
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themselves.
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</p>
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</li>
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<li>
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<p>
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In many conversation communities, membership in the
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community changes in real time based upon the dynamics of
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the conversation.
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</p>
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</li>
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<li>
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<p>
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In many conversation communities, the data classifaction of
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the conversation changes in real time based upon the
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dynamics of the conversation.
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</p>
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</li>
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</ul>
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<p>
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Furthermore, the widespread use of gateways to external IM
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systems is a further complication.
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</p>
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<p>
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Based on this analysis, we propose that security be entirely
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controlled in an end to end fashion by the conversation
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participants themselves via their user agent software.
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</p>
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</section3>
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<section3 topic="Trust Issues">
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<p>
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We believe that, ultimately, trust decisions are in the hands of
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the conversation participants. A security protocol and
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appropriate conforming user agents must provide a mechanism for them to make
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informed decisions.
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</p>
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</section3>
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<section3 topic="Cryptosystem Design Considerations">
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<p>
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One of the accepted axioms of security is that people must avoid
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the temptation to start from scratch and produce new, untested
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algorithms and protocols. History has demonstrated that such
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approaches are likely to contain flaws and that considerable time
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and effort are required to identify and address all of these
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flaws. Any new security protocol should be based on existing,
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established algorithms and protocols.
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</p>
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</section3>
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</section2>
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<section2 topic="Environmental Considerations">
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<p>
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Any new IM security protocol must integrate smoothly into the
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existing IM environment, and it must also recognize the nature of
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the transactions performed by conversation participants. These
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considerations are especially important:
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</p>
|
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<ul>
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<li>
|
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<p>
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dynamic communities. The members of a community are defined
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in near real time by the existing members.
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</p>
|
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</li>
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<li>
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<p>
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dynamic conversations. Conversations may involve any
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possible subset of the entire set of community members.
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</p>
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</li>
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</ul>
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|
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<p>
|
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Addressing these considerations becomes especially crucial when
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selecting a conference keying mechanism.
|
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</p>
|
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|
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</section2>
|
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|
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<section2 topic="Usability Requirements">
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|
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<p>
|
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Given the requirement to place the responsibility for the
|
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protection of conversation data in the hands of the participants,
|
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it is imperative to address some fundamental usability issues:
|
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</p>
|
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<ul>
|
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<li>
|
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<p>
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First, overall ease of use is a requirement. For protocol
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purposes, one implication is that some form of
|
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authentication via passphrases is necessary. While we
|
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recognize that this can have appalling consequences,
|
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especially when we realize that a passphrase may be shared
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by all of the community members, we also recognize the
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utility.
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</p>
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</li>
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<li>
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<p>
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PKIs are well established in many large organizations, and
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some communities will prefer to rely on credentials issued
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from these authorities. To ensure ease of use, we must
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strive to allow the use of existing PKI credentials and
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trust models rather than impose closed, Jabber-specific
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credentials.
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</p>
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</li>
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<li>
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<p>
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Finally, performance must not be negatively impacted; this
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is particularly true if we accept that most communities are
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composed of human users conversing in real time. For
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protocol purposes, one obvious implication is the desire to
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minimize computationally expensive public key operations.
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</p>
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</li>
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</ul>
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<p>
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We note that, in practice, the design and construction of user
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agents will also have a major impact on ease of use.
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</p>
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</section2>
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<section2 topic="Development And Deployment Requirements">
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|
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<p>
|
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To successfully integrate into the existing Jabber environment,
|
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an extension protocol for security must satisfy the following:
|
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</p>
|
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<ul>
|
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<li>
|
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<p>
|
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It must be an optional extension of the existing Jabber protocol.
|
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</p>
|
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</li>
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<li>
|
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<p>
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It must be transparent to existing Jabber servers.
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</p>
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</li>
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<li>
|
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<p>
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It must function gracefully in cases where some community
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members are not running a user agent that supports the
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protocol.
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</p>
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</li>
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<li>
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<p>
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It must make good use of XML.
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</p>
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</li>
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<li>
|
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<p>
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It must avoid encumbered algorithms.
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</p>
|
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</li>
|
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<li>
|
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<p>
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It must be straightforward to implement using widely
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available cryptographic toolkits.
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</p>
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</li>
|
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<li>
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<p>
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It must not require a PKI.
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</p>
|
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</li>
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</ul>
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<p>
|
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Failure to accommodate these will impede or prohibit adoption of
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any security protocol.
|
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</p>
|
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|
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</section2>
|
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|
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</section1>
|
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|
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<section1 topic="Protocol Specification">
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|
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<section2 topic="Protocol Overview">
|
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<p>
|
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Ultimately, conversation data is protected by the application of
|
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keyed cryptographic operations. One operation is used to provide
|
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confidentiality, and a separate operation is used to provide
|
|
integrity and data origin authentication. The keys used to
|
|
parameterize these operations are called conversation keys. Each
|
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conversation should have its own unique set of conversation keys
|
|
shared among the conversation participants.
|
|
</p>
|
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|
|
<p>
|
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Conversation keys are transported among the conversation
|
|
participants within a negotiated security session. A security session allows
|
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pairs of conversation participants to securely share conversation keys
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throught all participants in the conversation as required.
|
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</p>
|
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|
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</section2>
|
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|
|
<section2 topic="Definitions And Notation">
|
|
|
|
<p>
|
|
The following terms are used throughout this specification:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
initiator. The initiator is the user who requested a security session
|
|
negotiation. Initiator's are identified by their JID.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
responder. The responder is the user who responded to a security session
|
|
negotiation request. Responder's are identified by their JID.
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|
</p>
|
|
</li>
|
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<li>
|
|
<p>
|
|
hmac. This indicates the HMAC algorithm. The notation hmac (key, value)
|
|
indicates the HMAC computation of value using key.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
concatentation operator. The '|' character is used in character or octet
|
|
string expressions to indicate concatenation.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
security session ID. A character string that uniquely identifies a
|
|
security session between two users. Security session IDs MUST only
|
|
consist of Letters, Digits, and these characters: '.', '+', '-',
|
|
'_', '@'. Security session IDs are case sensitive.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
SS. This term indicates the security session secret that is agreed to
|
|
during a security session negotiation.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
SKc. This term indicates the keying material used within a security session
|
|
to protect confidentiality. The SKc is derived from the security session secret, SS.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
SKi. This term indicates the keying material used within a security session
|
|
to protect integrity and to provide authnetication. The SKi is derived from the
|
|
security session secret, SS.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
conversation key ID. A character string that uniquely identifies a
|
|
conversation key shared by a community of users. Conversation key IDs MUST only
|
|
consist of Letters, Digits, and these characters: '.', '+', '-',
|
|
'_', '@'. Conversation key IDs are case sensitive. Conversation key IDs SHOULD
|
|
be generated from at least 128 random bits.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
passphrase ID. A character string that uniquely identifies a
|
|
passphrase shared by a community of users. Passphrase IDs MUST only
|
|
consist of Letters, Digits, and these characters: '.', '+', '-',
|
|
'_', '@'. Passphrase IDs are case sensitive.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="XML Processing">
|
|
|
|
<p>
|
|
Since cryptographic operations are applied to data that is
|
|
transported within an XML stream, the protocol defines a set of
|
|
rules to ensure a consistent interpretation by all conversation
|
|
participants.
|
|
</p>
|
|
|
|
<section3 topic="Transporting Binary Content">
|
|
|
|
<p>
|
|
Binary data, such as the result of an HMAC, is always transported
|
|
in an encoded form; the two supported encoding schemes are base64
|
|
and hex.
|
|
</p>
|
|
|
|
<p>
|
|
Senders MAY include arbitrary white space within the character
|
|
stream. Senders SHOULD NOT include any other characters outside
|
|
of the encoding set.
|
|
</p>
|
|
|
|
<p>
|
|
Receivers MUST ignore all characters not in the encoding set.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Transporting Encrypted Content">
|
|
|
|
<p>
|
|
Encrypted data, including wrapped cryptographic keys, are always
|
|
wrapped per XML Encryption.
|
|
</p>
|
|
|
|
|
|
</section3>
|
|
|
|
<section3 topic="HMAC Computation">
|
|
|
|
<p>
|
|
HMACs are computed over a specific collection of attribute values
|
|
and character data; when computing an HMAC the following rules
|
|
apply:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
All characters MUST be encoded in UTF-8.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The octets in each character MUST be processed in network
|
|
byte order.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
For a given element, the attribute values that are HMACed
|
|
MUST be processed in the specified order regardless of the
|
|
order in which they appear in the element tag.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
For each attribute value, the computation MUST only include
|
|
characters from the anticipated set defined in this
|
|
specification; in particular, white space MUST always be
|
|
ignored.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
For character data that is represented in an encoded form,
|
|
such as base64 or hex, the computation MUST only include
|
|
valid characters from the encoding set.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Performing Cryptographic Operations">
|
|
|
|
<p>
|
|
The following algorithm is used to encrypt a character string, such as
|
|
an XML element:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The character string MUST be encoded in UTF-8.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The octets in each character MUST be processed in network byte order.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Appropriate cryptographic algorithm parameters, such as an
|
|
IV for a block cipher, are generated.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
</section3>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="XML Namespaces">
|
|
|
|
<p>
|
|
In order to integrate smoothly with the existing Jabber protocol,
|
|
this protocol utilizes a new XML namespace, jabber:security.
|
|
</p>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="Security Sessions">
|
|
|
|
<section3 topic="Overview">
|
|
|
|
<p>
|
|
A security session is a pair-wise relationship between two users
|
|
in which the users have achieved the following:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
They have mutually authenticated each other using credentials acceptable to both.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
They have agreed on a set of key material known only to both.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
Security sessions are identified by a 3-tuple consisting of the following items:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
initiator. This is the JID of the user who initiated the session.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
responder. This is the JID of the user who responded to the initiator's request.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
sessionId. A label generated by the initiator.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
Security sessions are used to transport conversation keys between the conversation participants.
|
|
</p>
|
|
|
|
<p>
|
|
Scalabilty is an immediate, obvious concern with such an approach. We expect this
|
|
approach to be viable in practice because:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The number of participants in typical, interactive conversations is generally on the order of 10^1.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
New participants are usually invited to dynamically join a
|
|
conversation by being invited by an existing participant;
|
|
this existing participant is the only one who needs to
|
|
establish a security session with the new participant,
|
|
because this single security session can be used to
|
|
transport all of the required conversation keys.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
User agents can permit the lifetime of security sessions to
|
|
last long enough to allow transport of conversation keys
|
|
for a variety of converstions.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Conversation keys can be established with a suitable lifetime.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
Other approaches, including the incorporation of more
|
|
sophisticated conference keying algorithms, are a topic for
|
|
future exploration.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Security Session Negotiation">
|
|
|
|
<p>
|
|
Security sessions are negotiated using an authenticated Diffie-Hellman key agreement
|
|
exchange. The two goals of the exchange are to perform the mutual authentication
|
|
and to agree to a secret that is know only to each.
|
|
</p>
|
|
|
|
<p>
|
|
The exchange also allows the parties to negotiate the various algorithms
|
|
and authentication mechanisms that will be used.
|
|
</p>
|
|
|
|
<p>
|
|
Once the pair agree on a shared secret, they each derive key material from the
|
|
secret; this key material is used to securely transport the conversation keys,
|
|
which are used to actually protect conversation data.
|
|
</p>
|
|
|
|
<p>
|
|
The protocol data units (PDUs) that comprise the exchange are transported
|
|
within existing Jabber protocol elements.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="DTDs">
|
|
|
|
<example>
|
|
|
|
<!ELEMENT session1
|
|
(nonce, keyAgreement, algorithms, authnMethods) >
|
|
<!ATTLIST session1
|
|
version CDATA #REQUIRED
|
|
initiator CDATA #REQUIRED
|
|
responder CDATA #REQUIRED
|
|
sessionId CDATA #REQUIRED
|
|
hmac (hmac-sha1) #REQUIRED >
|
|
|
|
<!ELEMENT nonce
|
|
(#PCDATA)* >
|
|
<!ATTLIST nonce
|
|
encoding (base64 | hex) #REQUIRED >
|
|
|
|
<!ELEMENT keyAgreement
|
|
(dh) >
|
|
|
|
<!ELEMENT dh
|
|
(publicKey) >
|
|
<!ATTLIST dh
|
|
group (modp1024 | modp2048 | modp4096 | modp8192) #REQUIRED >
|
|
|
|
<!ELEMENT publicKey
|
|
(#PCDATA)* >
|
|
<!ATTLIST publicKey
|
|
encoding (base64 | hex) #REQUIRED >
|
|
|
|
<!ELEMENT algorithms
|
|
(algorithm)+ >
|
|
|
|
<!ELEMENT algorithm
|
|
(confAlg, hmacAlg) >
|
|
|
|
<!ELEMENT confAlg EMPTY >
|
|
<!ATTLIST confAlg
|
|
cipher (3des-cbc | aes-128-cbc | aes-256-cbc) #REQUIRED >
|
|
|
|
<!ELEMENT hmacAlg EMPTY >
|
|
<!ATTLIST hmacAlg
|
|
alg (hmac-sha1 | hmac-md5) #REQUIRED>
|
|
|
|
<!ELEMENT authnMethods
|
|
(authnMethod)+ >
|
|
|
|
<!ELEMENT authnMethod
|
|
(digSig | passphrase) >
|
|
|
|
<!ELEMENT digSig
|
|
(certificate+, caCertificate*) >
|
|
<!ATTLIST digSig
|
|
alg (rsa) #REQUIRED>
|
|
|
|
<!ELEMENT certificate
|
|
(#PCDATA)* >
|
|
<!ATTLIST certificate
|
|
type (x509 | pkcs7) #REQUIRED
|
|
encoding (base64 | hex) #REQUIRED >
|
|
|
|
<!ELEMENT caCertificate
|
|
(#PCDATA)* >
|
|
<!ATTLIST caCertificate
|
|
type (x509 | pkcs7) #REQUIRED
|
|
encoding (base64 | hex) #REQUIRED >
|
|
|
|
<!ELEMENT passphrase EMPTY >
|
|
<!ATTLIST passphrase
|
|
passphraseId CDATA #REQUIRED >
|
|
|
|
|
|
<!ELEMENT session2
|
|
(nonce, keyAgreement, algorithm, authnMethod, authenticator) >
|
|
<!ATTLIST session2
|
|
version CDATA #REQUIRED
|
|
initiator CDATA #REQUIRED
|
|
responder CDATA #REQUIRED
|
|
sessionId CDATA #REQUIRED
|
|
hmac (hmac-sha1) #REQUIRED >
|
|
|
|
<!ELEMENT authenticator
|
|
(#PCDATA)* >
|
|
<!ATTLIST authenticator
|
|
encoding (base64 | hex) #REQUIRED>
|
|
|
|
|
|
<!ELEMENT session3
|
|
(authenticator, keyTransport*) >
|
|
<!ATTLIST session3
|
|
version CDATA #REQUIRED
|
|
initiator CDATA #REQUIRED
|
|
responder CDATA #REQUIRED
|
|
sessionId CDATA #REQUIRED
|
|
hmac (hmac-sha1) #REQUIRED >
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Generating And Sending the session1 PDU">
|
|
|
|
<p>
|
|
The initiator's user agent employs the following algorithm to generate the session1 PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
Appropriate values for the version, initiator, responder,
|
|
sessionId, and hmac attributes are assembled. The version of
|
|
this specification is '1.0'. The values of initiator and
|
|
responder MUST be the JIDs of the two participants,
|
|
respectively.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The nonce is prepared by first generating a string of 20
|
|
random octets (160 random bits). The octets are then
|
|
encoded into a string of 40 hex characters representing the
|
|
random string.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
A Diffie-Hellman group is selected. The appropriate values
|
|
for g and p will be used to generate the initiator's public
|
|
key.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
An ephemeral private key, x, is generated using g and p
|
|
for the selected group. This key MUST be generated using an
|
|
appropriate random number source. The corresponding public
|
|
key, g^x, is generated and encoded.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The desired set of confidentiality and HMAC cryptographic
|
|
algorithms is selected. The manner in which these
|
|
algorithms are selected and all related policy issues are
|
|
outside the scope of this specification.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The desired set of authentication algorithms is selected.
|
|
The manner in which these algorithms are selected and all
|
|
related policy issues are outside the scope of this
|
|
specification. When the digital signature form of
|
|
authentication is selected, the relevant end-entity
|
|
certificate and, optionally, a chain of CA certificates
|
|
representing a validation path, is assembled and encoded. A
|
|
set of trusted CA certificates MAY optionally be included
|
|
via caCertificate elements; if so, the set MUST include the
|
|
issuer of the initiator's end-entity certificate.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
These values are then used to prepare the XML session1 element;
|
|
this element is transmitted via the existing Jabber iq mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="initiator's JID" to="responder's JID" type="get" id="whatever">
|
|
<query xmlns="jabber:security:session">
|
|
<session1>...</session1>
|
|
</query>
|
|
</iq>
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Receiving And Processing the session1 PDU">
|
|
|
|
<p>
|
|
The responder's user agent employs the following algorithm to process each session1 PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The version and hmac attributes are checked against the
|
|
values supported by the user agent. An unsupported version
|
|
results in an error code of 10000, and an unsupported hmac
|
|
results in an error code of 10001. The responder attribute MUST
|
|
match the JID of the receiver; a mismatch results in an error code of 10009
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The nonce is decoded, and its length is checked. The nonce
|
|
may also be checked to detect replays. An invalid nonce
|
|
results in an error code of 10002.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The Diffie-Hellman group is checked against the values
|
|
supported by the user agent. An unsupported group results
|
|
in an error code of 10003
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The desired confidentiality and HMAC cryptographic
|
|
algorithms are selected from the proposed set. The manner
|
|
in which these algorithms are selected and all related
|
|
policy issues are outside the scope of this specification.
|
|
If none of the proposed algorithms are supported, an error
|
|
code of 10004 occurs.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The desired authentication algorithm is selected from the
|
|
proposed set. The manner in which this algorithm is
|
|
selected and all related policy issues are outside the
|
|
scope of this specification. In the digital signature case,
|
|
the responder's end-entity
|
|
certificate MUST be issued by one of the trusted CAs listed
|
|
in the session1 PDU or by the same issuer as the
|
|
initiator's end-entity certificate. If none of the proposed
|
|
algorithms are supported, an error code of 10005 results.
|
|
If the responder does not have acceptable credentials, an
|
|
error code of 10006 occurs.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
If any errors occur during processing, the session negotiation
|
|
fails, and the error is communicated via the existing Jabber iq
|
|
mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="responder's JID" to="initiator's JID" type="error" id="whatever">
|
|
<error code="???">...</error>
|
|
</iq>
|
|
</example>
|
|
|
|
<p>
|
|
If no errors occur, then the responder's user agent proceeds with
|
|
the session2 PDU.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Generating And Sending the session2 PDU">
|
|
|
|
<p>
|
|
The responder's user agent employs the following algorithm to generate the session2 PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
Appropriate values for the version, initiator, responder,
|
|
sessionId, and hmac attributes are assembled. The version of
|
|
this specification is '1.0'. The values of initiator and
|
|
responder MUST be the JIDs of the two participants,
|
|
respectively. The sessionId and hmac values MUST match the
|
|
sessionId and hmac values contained in the session1 PDU.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The nonce is prepared by first generating a string of 20
|
|
random octets (160 random bits). The octets are then
|
|
encoded into a string of 40 hex characters representing the
|
|
random string.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
An ephemeral private key, y, is generated using g and p
|
|
for the group indicated by the session1 PDU. This key MUST
|
|
be generated using an appropriate random number source. The
|
|
corresponding public key, g^y, is generated and encoded.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The desired pair of confidentiality and HMAC cryptographic
|
|
algorithms is selected. The manner in which this pair is
|
|
selected and all related policy issues are outside the
|
|
scope of this specification.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The desired authentication algorithm is selected. The
|
|
manner in which this algorithm is selected and all related
|
|
policy issues are outside the scope of this specification.
|
|
When the digital signature form of authentication is
|
|
selected, the relevant end-entity certificate and,
|
|
optionally, a chain of CA certificates representing a
|
|
validation path, is assembled and encoded.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Based on the selected authentication algorithm, the
|
|
responder's authenticator is constructed. A digital signature algorithm
|
|
requires calculating:
|
|
</p>
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
HK = hmac (initiator's nonce | responder's nonce, g^xy)
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
HASH_R = hmac (HK, version | sessionId | g^y | g^x | responder's JID)
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
<p>
|
|
HASH_R is signed using the responder's private key and encoded in PKCS#1 format.
|
|
The PKCS#1 octets are then further encoded in base64 or hex.
|
|
</p>
|
|
<p>
|
|
The passphrase algorithm requires calculating:
|
|
</p>
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
HK = hmac (hash (passphrase), initiator's nonce | responder's nonce)
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
HASH_R = hmac (HK, version | sessionId | g^y | g^x | responder's JID)
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
<p>
|
|
The octets of HASH_R are simply encoded in base64 or hex.
|
|
</p>
|
|
<p>
|
|
The manner in which the responder's user agent gains access
|
|
to the responder's credentials is outside the scope of this
|
|
specification.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
These values are then used to prepare the XML session2 element;
|
|
this element is transmitted via the existing Jabber iq mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="responder's JID" to="initiator's JID" type="result" id="whatever">
|
|
<query xmlns="jabber:security:session">
|
|
<session2>...</session2>
|
|
</query>
|
|
</iq>
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Receiving And Processing the session2 PDU">
|
|
|
|
<p>
|
|
The initiator's user agent employs the following algorithm to process each session2 PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The attribute values are checked against the values sent in
|
|
the session1 PDU. A mismatch results in an error code of
|
|
10008.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The nonce is decoded, and its length is checked. The nonce
|
|
may also be checked to detect replays. An invalid nonce
|
|
results in an error code of 10002.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The Diffie-Hellman group is checked against the value sent
|
|
in the session1 PDU. A mismatch results in an error code of 10003
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The confidentiality and HMAC cryptographic algorithms are
|
|
validated against the set proposed in the session1 PDU. A
|
|
mismatch results in an error code of 10004.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The authentication algorithm is validated against the set
|
|
proposed in the session1 PDU. A mismatch results in an
|
|
error code of 10005.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The authenticator is verified. A failure results in an error code of 10007.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
If any errors occur during processing, the session negotiation
|
|
fails, and the error is communicated via the existing Jabber iq
|
|
mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="initiator's JID" to="responder's JID" type="error" id="whatever">
|
|
<error code="???">...</error>
|
|
</iq>
|
|
</example>
|
|
|
|
<p>
|
|
If no errors occur, then the initiator's user agent proceeds with the session3 PDU.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Generating And Sending the session3 PDU">
|
|
|
|
<p>
|
|
The initiator's user agent employs the following algorithm to generate the session3 PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
Appropriate values for the version, initiator, responder,
|
|
sessionId, and hmac attributes are assembled. The version of
|
|
this specification is '1.0'. The values of initiator and
|
|
responder MUST be the JIDs of the two participants,
|
|
respectively. The sessionId and hmac values MUST match the
|
|
sessionId and hmac values contained in both the session1 and
|
|
session2 PDUs.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Based on the selected authentication algorithm, the
|
|
initiator's authenticator is constructed. A digital signature algorithm
|
|
requires calculating:
|
|
</p>
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
HK = hmac (initiator's nonce | responder's nonce, g^xy)
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
HASH_I = hmac (HK, version | sessionId | g^x | g^y | initiator's JID)
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
<p>
|
|
HASH_I is signed using the responder's private key and encoded in PKCS#1 format.
|
|
The PKCS#1 octets are then further encoded in base64 or hex.
|
|
</p>
|
|
<p>
|
|
The passphrase algorithm requires calculating:
|
|
</p>
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
HK = hmac (hash (passphrase), initiator's nonce | responder's nonce)
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
HASH_I = hmac (HK, version | sessionId | g^x | g^y | initiator's JID)
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
<p>
|
|
The octets of HASH_I are simply encoded in base64 or hex.
|
|
</p>
|
|
<p>
|
|
The manner in which the initiator's user agent gains access
|
|
to the initiator's credentials is outside the scope of this
|
|
specification.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
A set of conversation keys may optionally be included in
|
|
the response. This should typically be the case since
|
|
security sessions are negotiated for the sole purpose of
|
|
key transport.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
These values are then used to prepare the XML session3 element;
|
|
this element is transmitted via the existing Jabber iq mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="initiator's JID" to="responder's JID" type="result" id="whatever">
|
|
<query xmlns="jabber:security:session">
|
|
<session3>...</session3>
|
|
</query>
|
|
</iq>
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Receiving And Processing the session3 PDU">
|
|
|
|
<p>
|
|
The responder's user agent employs the following algorithm to process each session3 PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The attribute values are checked against the values sent in
|
|
the session2 PDU. A mismatch results in an error code of
|
|
10008.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The authenticator is verified. A failure results in an error code of 10007.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Any keys included in the PDU are processed and added to the user agent's key store.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
If any errors occur during processing, the session negotiation
|
|
fails, and the error is communicated via the existing Jabber iq
|
|
mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="responder's JID" to="initiator's JID" type="error" id="whatever">
|
|
<error code="???">...</error>
|
|
</iq>
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Session Key Material Derivation">
|
|
|
|
<p>
|
|
TBA
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="Key Transport">
|
|
|
|
<section3 topic="Overview">
|
|
|
|
<p>
|
|
Conversation keys are used to protect conversation data.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="The Key Transport Mechanism">
|
|
|
|
<p>
|
|
Conversation keys are transported using the symmetric key wrap feature of
|
|
XML Encryption embedded in the keyTransport PDU.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="DTDs">
|
|
|
|
<example>
|
|
<!ELEMENT keyTransport
|
|
(convId, payload, hmac) >
|
|
<!ATTLIST keyTransport
|
|
version CDATA #REQUIRED
|
|
initiator CDATA #REQUIRED
|
|
responder CDATA #REQUIRED
|
|
sessionId CDATA #REQUIRED >
|
|
|
|
<!ELEMENT convId
|
|
(#PCDATA)* >
|
|
|
|
<!-- These are actually instances of xenc:EncryptedKey -->
|
|
<!ELEMENT payload
|
|
(confKey, hmacKey) >
|
|
|
|
<!ELEMENT hmac
|
|
(#PCDATA)* >
|
|
<!ATTLIST hmac
|
|
encoding (base64 | hex) #REQUIRED >
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Generating And Sending the keyTransport PDU">
|
|
|
|
<p>
|
|
The sender's user agent employs the following algorithm to generate the keyTransport PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
Appropriate values for the version, initiator, responder, and
|
|
sessionId attributes are assembled. The version of
|
|
this specification is '1.0'. The values of initiator and
|
|
responder MUST be the JIDs of the two participants who negotiated the
|
|
security session, respectively, and they
|
|
MUST correspond to an existing security session.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The key's identifier, convId, is assembled.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The payload, which consists of the confidentiality key and the integrity key, is wrapped
|
|
in instances of xenc:EncryptedKey as follows:
|
|
</p>
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The Type attribute of the xenc:EncryptedKey element MUST indicate 'content'.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The Id, MimeType and Encoding attributes of the xenc:EncryptedKey element MUST NOT
|
|
be present.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The xenc:EncryptionMethod element MUST be present, and the Algorithm attribute
|
|
MUST indicate a valid symmetric key wrap algorithm. Furthermore, the
|
|
algorithm MUST be the same as was negotiated for the security session.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The ds:KeyInfo element MUST NOT be present. The key to use is SKc of the
|
|
security session.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The xenc:CipherData element MUST be present, and it MUST use the CipherValue choice.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The HMAC is computed using SKi of the security session over the following values:
|
|
</p>
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
the version attribute of the keyTransport element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the initiator attribute of the keyTransport element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the responder attribute of the keyTransport element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the sessionId attribute of the keyTransport element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the character string used to construct the body of the convId element
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
These values are then used to prepare the XML keyTransport element;
|
|
this element is transmitted via the existing Jabber iq mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="sender's JID" to="receiver's JID" type="set" id="whatever">
|
|
<query xmlns="jabber:security:keyTransport">
|
|
<keyTransport>...</keyTransport>
|
|
</query>
|
|
</iq>
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Receiving and Processing the keyTransport PDU">
|
|
|
|
<p>
|
|
The receiver's user agent employs the following algorithm to process each keyTransport PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The values of the version, initiator, responder, and sessionId are validated; initiator,
|
|
responder, and sessionId MUST indicate an existing security session.
|
|
A version mismatch results in an error code of 10000; an invalid security session
|
|
results in an error of 10010.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The payload, which consists of the confidentiality key and the intergrity key, is unwrapped.
|
|
Any failures result in an error code of 10012.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The body of the HMAC element is decoded into the actual HMAC octet string.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The HMAC is validated. An invalid HMAC results in an error code of 10011.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The keys are added to the user agent's key store.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
If any errors occur during processing, the error is communicated via the existing Jabber iq
|
|
mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="receiver's JID" to="sender's JID" type="error" id="whatever">
|
|
<error code="???">...</error>
|
|
</iq>
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="Message Protection">
|
|
|
|
<section3 topic="Overview">
|
|
|
|
<p>
|
|
The ultimate goal is, of course, the protection of conversation data. The protocol exchanges
|
|
described above allow the conversation participants to cryptographically protect their conversation data using the conversation keys that they share.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="The Message Protection Mechanism">
|
|
|
|
<p>
|
|
A protected message is defined as a traditional Jabber message whose body content
|
|
is extended to include the transport of a cryptographically protected message body.
|
|
The two key features are
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
First, the usual body element contains some arbitrary text. Those familiar with the
|
|
evolution of email protocols will recognize this trick as the same one used
|
|
when MIME was introduced.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Second, the message contains a Jabber x element defining the Jabber:security:message
|
|
namespace; this element transports the protected message.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
This mechanism has the advantages of allowing transparent integration with existing
|
|
Jabber servers and existing Jabber clients.
|
|
</p>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="DTD">
|
|
|
|
<example>
|
|
<!ELEMENT protectedMessage
|
|
(securityLabel?, payload, hmac) >
|
|
<!ATTLIST protectedMessage
|
|
version CDATA #REQUIRED
|
|
from CDATA #REQUIRED
|
|
to CDATA #REQUIRED
|
|
convId #REQUIRED
|
|
seqNum #REQUIRED >
|
|
|
|
<!ELEMENT securityLabel
|
|
(#PCDATA)* >
|
|
|
|
<!-- this is actually an instance of xenc:EncryptedData -->
|
|
<!ELEMENT payload
|
|
(#PCDATA)* >
|
|
|
|
<!ELEMENT hmac
|
|
(#PCDATA)* >
|
|
<!ATTLIST hmac
|
|
encoding (base64 | hex) #REQUIRED >
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Generating And Sending the protectedMessage PDU">
|
|
|
|
<p>
|
|
The sender's user agent employs the following algorithm to generate the protectedMessage PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
Appropriate values for the version, from, to, convId, and
|
|
seqNum attributes are assembled. The version of
|
|
this specification is '1.0'. The value of convId MUST correspond to an existing, valid key.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The actual message body is encoded into a character string corresponding to a Jabber message body element. This character string is then wrapped in an instance of xenc:EncryptedData as follows:
|
|
</p>
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The Type attribute of the xenc:EncryptedData element MUST indicate 'element'.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The Id, MimeType and Encoding attributes of the xenc:EncryptedData element MUST NOT
|
|
be present.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The xenc:EncryptionMethod element MUST be present, and the Algorithm attribute
|
|
MUST indicate a valid block encryption algorithm.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The ds:KeyInfo element MUST NOT be present. The key to be used is the confidentiality
|
|
key indicated by the convId attribute.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The xenc:CipherData element MUST be present, and it MUST use the CipherValue choice.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Using the HMAC key indicated by the convId attribute, the HMAC is computed
|
|
over the following values:
|
|
</p>
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
the version attribute of the protectedMessage element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the from attribute of the protectedMessage element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the to attribute of the protectedMessage element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the convId attribute of the protectedMessage element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the seqNum attribute of the protectedMessage element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
any securityLabel element
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
the character string used to construct the body of the payload element
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
These values are then used to prepare the XML protectedMessage element;
|
|
this element is transmitted via the existing Jabber message mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<message from="sender's JID" to="reveiver's JID" id="whatever">
|
|
<body>The real body is protected.</body>
|
|
<x xmlns="jabber:security:message">
|
|
<protectedMessage>...</protectedMessage>
|
|
</x>
|
|
</iq>
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
<section3 topic="Receiving and Processing the protectedMessage PDU">
|
|
|
|
<p>
|
|
The receiver's user agent employs the following algorithm to process each protectedMessage PDU:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
The values of the version, from, to, convId, and seqNum are validated.
|
|
A version mismatch results in an error code of 10000. An unknown convId
|
|
results in an error code of 10015. If replay protection is utilized, a
|
|
duplicate seqNum results in an error code of 10016.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The body of the HMAC element is decoded into the actual HMAC octet string.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The payload, which consists of the actual message body, is unwrapped.
|
|
Any failures result in an error code of 10012.
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
The HMAC is validated. An invalid HMAC results in an error code of 10011.
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
If any errors occur during processing, the error is communicated via the existing Jabber iq
|
|
mechanism:
|
|
</p>
|
|
|
|
<example>
|
|
<iq from="receiver's JID" to="sender's JID" type="error" id="whatever">
|
|
<error code="???">...</error>
|
|
</iq>
|
|
</example>
|
|
|
|
</section3>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="Requesting Keys">
|
|
|
|
TBA
|
|
|
|
</section2>
|
|
|
|
<section2 topic="Conformance Profile">
|
|
|
|
<p>
|
|
The following block encryption algorithms are required, as
|
|
specified by XML Encryption:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
http://www.w3.org/2001/04/xmlenc#tripledes-cbc
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
http://www.w3.org/2001/04/xmlenc#aes128-cbc
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
http://www.w3.org/2001/04/xmlenc#aes256-cbc
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
The following symmetric key wrap algorithms are required, as
|
|
specified by XML Encryption:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
http://www.w3.org/2001/04/xmlenc#kw-tripledes
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
http://www.w3.org/2001/04/xmlenc#kw-aes128
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
http://www.w3.org/2001/04/xmlenc#kw-aes256
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
</section2>
|
|
|
|
</section1>
|
|
|
|
<section1 topic="Diffie-Hellman Groups">
|
|
|
|
<p>
|
|
This protocol makes use of the following Diffie-Hellman groups adopted from IKE.
|
|
</p>
|
|
|
|
<section2 topic="1024 bit Group, modp1024">
|
|
|
|
<p>
|
|
The hexidecimal value of the prime, p, is
|
|
</p>
|
|
|
|
<example>
|
|
FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
|
|
29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
|
|
EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
|
|
E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
|
|
EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE65381
|
|
FFFFFFFF FFFFFFFF
|
|
</example>
|
|
|
|
<p>
|
|
The decimal value of the generator, g, is 2.
|
|
</p>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="2048 bit Group, modp2048">
|
|
|
|
<p>
|
|
The hexidecimal value of the prime, p, is
|
|
</p>
|
|
|
|
<example>
|
|
FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
|
|
29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
|
|
EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
|
|
E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
|
|
EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
|
|
C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
|
|
83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
|
|
670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B
|
|
E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9
|
|
DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510
|
|
15728E5A 8AACAA68 FFFFFFFF FFFFFFFF
|
|
</example>
|
|
|
|
<p>
|
|
The decimal value of the generator, g, is 2.
|
|
</p>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="4096 bit Group, modp4096">
|
|
|
|
<p>
|
|
The hexidecimal value of the prime, p, is
|
|
</p>
|
|
|
|
<example>
|
|
FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
|
|
29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
|
|
EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
|
|
E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
|
|
EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
|
|
C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
|
|
83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
|
|
670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B
|
|
E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9
|
|
DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510
|
|
15728E5A 8AAAC42D AD33170D 04507A33 A85521AB DF1CBA64
|
|
ECFB8504 58DBEF0A 8AEA7157 5D060C7D B3970F85 A6E1E4C7
|
|
ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226 1AD2EE6B
|
|
F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C
|
|
BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31
|
|
43DB5BFC E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7
|
|
88719A10 BDBA5B26 99C32718 6AF4E23C 1A946834 B6150BDA
|
|
2583E9CA 2AD44CE8 DBBBC2DB 04DE8EF9 2E8EFC14 1FBECAA6
|
|
287C5947 4E6BC05D 99B2964F A090C3A2 233BA186 515BE7ED
|
|
1F612970 CEE2D7AF B81BDD76 2170481C D0069127 D5B05AA9
|
|
93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34063199
|
|
FFFFFFFF FFFFFFFF
|
|
</example>
|
|
|
|
<p>
|
|
The decimal value of the generator, g, is 2.
|
|
</p>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="8192 bit Group, modp8192">
|
|
|
|
<p>
|
|
The hexidecimal value of the prime, p, is
|
|
</p>
|
|
|
|
<example>
|
|
FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
|
|
29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
|
|
EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
|
|
E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
|
|
EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
|
|
C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
|
|
83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
|
|
670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B
|
|
E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9
|
|
DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510
|
|
15728E5A 8AAAC42D AD33170D 04507A33 A85521AB DF1CBA64
|
|
ECFB8504 58DBEF0A 8AEA7157 5D060C7D B3970F85 A6E1E4C7
|
|
ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226 1AD2EE6B
|
|
F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C
|
|
BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31
|
|
43DB5BFC E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7
|
|
88719A10 BDBA5B26 99C32718 6AF4E23C 1A946834 B6150BDA
|
|
2583E9CA 2AD44CE8 DBBBC2DB 04DE8EF9 2E8EFC14 1FBECAA6
|
|
287C5947 4E6BC05D 99B2964F A090C3A2 233BA186 515BE7ED
|
|
1F612970 CEE2D7AF B81BDD76 2170481C D0069127 D5B05AA9
|
|
93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34028492
|
|
36C3FAB4 D27C7026 C1D4DCB2 602646DE C9751E76 3DBA37BD
|
|
F8FF9406 AD9E530E E5DB382F 413001AE B06A53ED 9027D831
|
|
179727B0 865A8918 DA3EDBEB CF9B14ED 44CE6CBA CED4BB1B
|
|
DB7F1447 E6CC254B 33205151 2BD7AF42 6FB8F401 378CD2BF
|
|
5983CA01 C64B92EC F032EA15 D1721D03 F482D7CE 6E74FEF6
|
|
D55E702F 46980C82 B5A84031 900B1C9E 59E7C97F BEC7E8F3
|
|
23A97A7E 36CC88BE 0F1D45B7 FF585AC5 4BD407B2 2B4154AA
|
|
CC8F6D7E BF48E1D8 14CC5ED2 0F8037E0 A79715EE F29BE328
|
|
06A1D58B B7C5DA76 F550AA3D 8A1FBFF0 EB19CCB1 A313D55C
|
|
DA56C9EC 2EF29632 387FE8D7 6E3C0468 043E8F66 3F4860EE
|
|
12BF2D5B 0B7474D6 E694F91E 6DBE1159 74A3926F 12FEE5E4
|
|
38777CB6 A932DF8C D8BEC4D0 73B931BA 3BC832B6 8D9DD300
|
|
741FA7BF 8AFC47ED 2576F693 6BA42466 3AAB639C 5AE4F568
|
|
3423B474 2BF1C978 238F16CB E39D652D E3FDB8BE FC848AD9
|
|
22222E04 A4037C07 13EB57A8 1A23F0C7 3473FC64 6CEA306B
|
|
4BCBC886 2F8385DD FA9D4B7F A2C087E8 79683303 ED5BDD3A
|
|
062B3CF5 B3A278A6 6D2A13F8 3F44F82D DF310EE0 74AB6A36
|
|
4597E899 A0255DC1 64F31CC5 0846851D F9AB4819 5DED7EA1
|
|
B1D510BD 7EE74D73 FAF36BC3 1ECFA268 359046F4 EB879F92
|
|
4009438B 481C6CD7 889A002E D5EE382B C9190DA6 FC026E47
|
|
9558E447 5677E9AA 9E3050E2 765694DF C81F56E8 80B96E71
|
|
60C980DD 98EDD3DF FFFFFFFF FFFFFFFF
|
|
</example>
|
|
|
|
<p>
|
|
The decimal value of the generator, g, is 2.
|
|
</p>
|
|
|
|
</section2>
|
|
|
|
</section1>
|
|
|
|
<section1 topic="Security Considerations">
|
|
|
|
<p>
|
|
This entire document is about security.
|
|
</p>
|
|
|
|
<p>
|
|
This version of the protocol deliberately incorporates only a minimal amount
|
|
of cryptographic choice. Examples of possible choices that can readily
|
|
added in future drafts include:
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>
|
|
Support for the Digital Signature Standard
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Support for Elliptic Curve Cryptography
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Additional symmetric algorithms
|
|
</p>
|
|
</li>
|
|
<li>
|
|
<p>
|
|
Additional hash algorithms
|
|
</p>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>
|
|
Furthermore, additional credential formats, such as OpenPGP, may be addressed
|
|
in future drafts.
|
|
</p>
|
|
|
|
<p>
|
|
This version of the protocol includes a mechanism that derives a cryptographic key from a
|
|
passphrase shared by a community of users. It is impossible to overstate the security
|
|
issues that such a mechanism raises.
|
|
</p>
|
|
|
|
<p>
|
|
This version of the protocol does not include a specific rekeying capability. Data volumes
|
|
in IM environments are expected to be small, and the protocol prefers to simply instantiate
|
|
new conversation keys. It is straightforward to extend the security session protocol to
|
|
enable negotiation of a new key.
|
|
</p>
|
|
|
|
</section1>
|
|
|
|
<section1 topic="Examples">
|
|
|
|
<section2 topic="Security Session">
|
|
|
|
<example>
|
|
<iq from='initiator@some.tld'
|
|
to='responder@other.tld'
|
|
type='get'
|
|
id='whatever' >
|
|
<x xmlns='jabber:security:session>
|
|
<session1 version='1.0'
|
|
initiator='initiator@some.tld'
|
|
responder='responder@other.tld'
|
|
sessionId='session11223344556677@some.tld'
|
|
hmac='hmac-sha1'>
|
|
<nonce encoding='hex'>
|
|
...
|
|
</nonce>
|
|
<keyAgreement>
|
|
<dh group='modp4096'>
|
|
<publicKey encoding='base64'>
|
|
...
|
|
</publicKey>
|
|
</dh>
|
|
</keyAgreement>
|
|
<algorithms>
|
|
<algorithm>
|
|
<confAlg cipher='3des-cbc'/>
|
|
<hmacAlg alg='hmac-sha1'/>
|
|
</algorithm>
|
|
</algorithms>
|
|
<authnMethods>
|
|
<authnMethod>
|
|
<digSig alg='rsa'>
|
|
<certificate type='x509' encoding='base64'>
|
|
...
|
|
</certificate>
|
|
</digSig>
|
|
</authnMethod>
|
|
</authnMethods>
|
|
</session1>
|
|
</x>
|
|
</iq>
|
|
|
|
<iq from='responder@other.tld'
|
|
to='initiator@some.tld'
|
|
type='result'
|
|
id='whatever' >
|
|
<x xmlns='jabber:security:session>
|
|
<session2 version='1.0'
|
|
initiator='initiator@some.tld'
|
|
responder='responder@other.tld'
|
|
sessionId='session11223344556677@some.tld'
|
|
hmac='hmac-sha1'>
|
|
<nonce encoding='hex'>
|
|
...
|
|
</nonce>
|
|
<keyAgreement>
|
|
<dh group='modp4096'>
|
|
<publicKey encoding='base64'>
|
|
...
|
|
</publicKey>
|
|
</dh>
|
|
</keyAgreement>
|
|
<algorithm>
|
|
<confAlg cipher='3des-cbc'/>
|
|
<hmacAlg alg='hmac-sha1'/>
|
|
</algorithm>
|
|
<authnMethod>
|
|
<digSig alg='rsa'>
|
|
<certificate type='x509' encoding='base64'>
|
|
...
|
|
</certificate>
|
|
</digSig>
|
|
</authnMethod>
|
|
<authenticator encoding='base64'>
|
|
...
|
|
</authenticator>
|
|
</session2>
|
|
</x>
|
|
</iq>
|
|
|
|
<iq from='initiator@some.tld'
|
|
to='responder@other.tld'
|
|
type='result'
|
|
id='whatever' >
|
|
<x xmlns='jabber:security:session>
|
|
<session3 version='1.0'
|
|
initiator='initiator@some.tld'
|
|
responder='responder@other.tld'
|
|
sessionId='session11223344556677@some.tld'
|
|
hmac='hmac-sha1'>
|
|
<authenticator encoding='base64'>
|
|
...
|
|
</authenticator>
|
|
</session3>
|
|
</x>
|
|
</iq>
|
|
</example>
|
|
|
|
|
|
</section2>
|
|
|
|
<section2 topic="Key Transport">
|
|
|
|
<example>
|
|
<iq type='set' >
|
|
<x xmlns='jabber:security:key>
|
|
<keyTransport version='1.0'
|
|
initiator='initiator@some.tld'
|
|
responder='responder@other.tld'
|
|
sessionId='session11223344556677@some.tld'>
|
|
<convId>
|
|
44d2d2d2d2@some.tld
|
|
</convId>
|
|
<EncryptedKey xmlns='http://www.w3.org/2001/04/xmlenc#'
|
|
Type='http://www.w3.org/2001/04/xmlenc#Content'>
|
|
<EncryptionMethod Algorithm='http://www.w3.org/2001/04/xmlenc#kw-tripledes>
|
|
</EncryptionMethod>
|
|
<CipherData>
|
|
<CipherValue>
|
|
...
|
|
</CipherValue>
|
|
</CipherData>
|
|
</EncryptedKey>
|
|
<EncryptedKey xmlns='http://www.w3.org/2001/04/xmlenc#'
|
|
Type='http://www.w3.org/2001/04/xmlenc#Content'>
|
|
<EncryptionMethod Algorithm='http://www.w3.org/2001/04/xmlenc#kw-tripledes>
|
|
</EncryptionMethod>
|
|
<CipherData>
|
|
<CipherValue>
|
|
...
|
|
</CipherValue>
|
|
</CipherData>
|
|
</EncryptedKey>
|
|
<hmac encoding='hex'>
|
|
...
|
|
</hmac>
|
|
</keyTransport>
|
|
</x>
|
|
</iq>
|
|
</example>
|
|
|
|
</section2>
|
|
|
|
<section2 topic="Message Protection">
|
|
|
|
<example>
|
|
<message from='initiator@some.tld'
|
|
to='responder@other.tld'>
|
|
<body>
|
|
The real body is protected.
|
|
</body>
|
|
<x xmlns='jabber:security:message'>
|
|
<protectedMessage version='1.0'
|
|
from='initiator@some.tld'
|
|
to='responder@other.tld'
|
|
convId='44d2d2d2d2@some.tld'
|
|
seqNum='1'>
|
|
<securityLabel>
|
|
Confidential
|
|
</securityLabel>
|
|
<EncryptedData xmlns='http://www.w3.org/2001/04/xmlenc#'
|
|
Type='http://www.w3.org/2001/04/xmlenc#Element'>
|
|
<EncryptionMethod Algorithm='http://www.w3.org/2001/04/xmlenc#tripledes-cbc>
|
|
</EncryptionMethod>
|
|
<CipherData>
|
|
<CipherValue>
|
|
...
|
|
</CipherValue>
|
|
</CipherData>
|
|
</EncryptedData>
|
|
<hmac encoding='hex'>
|
|
...
|
|
</hmac>
|
|
</protectedMessage>
|
|
</x>
|
|
</message>
|
|
</example>
|
|
|
|
</section2>
|
|
|
|
</section1>
|
|
|
|
<section1 topic="References">
|
|
|
|
<p>
|
|
"XML Encryption Syntax and Processing"; http://www.w3.org/TR/xmlenc-core
|
|
</p>
|
|
|
|
<p>
|
|
more to be added
|
|
</p>
|
|
|
|
</section1>
|
|
|
|
</xep>
|