Network Working Group P. Saint-Andre Internet-Draft J. Miller Expires: October 6, 2003 Jabber Software Foundation April 7, 2003 XMPP Core draft-ietf-xmpp-core-08 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 6, 2003. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document describes the core features of the Extensible Messaging and Presence Protocol (XMPP), a protocol for streaming XML elements in order to exchange messages and presence information in close to real time. XMPP is used mainly for the purpose of building instant messaging (IM) and presence applications, such as the servers and clients that comprise the Jabber network. Saint-Andre & Miller Expires October 6, 2003 [Page 1] Internet-Draft XMPP Core April 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 5 1.4 Intellectual Property Notice . . . . . . . . . . . . . . . . 5 2. Generalized Architecture . . . . . . . . . . . . . . . . . . 6 2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 Server . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Client . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.4 Gateway . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.5 Network . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Addressing Scheme . . . . . . . . . . . . . . . . . . . . . 8 3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Domain Identifier . . . . . . . . . . . . . . . . . . . . . 8 3.3 Node Identifier . . . . . . . . . . . . . . . . . . . . . . 8 3.4 Resource Identifier . . . . . . . . . . . . . . . . . . . . 9 4. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2 Stream Attributes . . . . . . . . . . . . . . . . . . . . . 11 4.3 Namespace Declarations . . . . . . . . . . . . . . . . . . . 12 4.4 Stream Features . . . . . . . . . . . . . . . . . . . . . . 13 4.5 Stream Errors . . . . . . . . . . . . . . . . . . . . . . . 13 4.5.1 Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.5.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.5.3 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.5.4 Extensibility . . . . . . . . . . . . . . . . . . . . . . . 16 4.6 Simple Streams Example . . . . . . . . . . . . . . . . . . . 16 5. Stream Encryption . . . . . . . . . . . . . . . . . . . . . 18 5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.2 Narrative . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.3 Client-to-Server Example . . . . . . . . . . . . . . . . . . 20 5.4 Server-to-Server Example . . . . . . . . . . . . . . . . . . 21 6. Stream Authentication . . . . . . . . . . . . . . . . . . . 24 6.1 SASL Authentication . . . . . . . . . . . . . . . . . . . . 24 6.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.1.2 Narrative . . . . . . . . . . . . . . . . . . . . . . . . . 25 6.1.3 SASL Definition . . . . . . . . . . . . . . . . . . . . . . 26 6.1.4 Client-to-Server Example . . . . . . . . . . . . . . . . . . 27 6.1.5 Server-to-Server Example . . . . . . . . . . . . . . . . . . 29 6.2 Dialback Authentication . . . . . . . . . . . . . . . . . . 31 6.2.1 Dialback Protocol . . . . . . . . . . . . . . . . . . . . . 34 7. XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . . 37 7.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 37 7.2 Common Attributes . . . . . . . . . . . . . . . . . . . . . 37 7.2.1 to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 7.2.2 from . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Saint-Andre & Miller Expires October 6, 2003 [Page 2] Internet-Draft XMPP Core April 2003 7.2.3 id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 7.2.4 type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 7.2.5 xml:lang . . . . . . . . . . . . . . . . . . . . . . . . . . 38 7.3 Message Stanzas . . . . . . . . . . . . . . . . . . . . . . 38 7.3.1 Types of Message . . . . . . . . . . . . . . . . . . . . . . 39 7.3.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 39 7.4 Presence Stanzas . . . . . . . . . . . . . . . . . . . . . . 40 7.4.1 Types of Presence . . . . . . . . . . . . . . . . . . . . . 41 7.4.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 41 7.5 IQ Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 42 7.5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 43 7.5.2 Types of IQ . . . . . . . . . . . . . . . . . . . . . . . . 43 7.5.3 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 44 7.6 Extended Namespaces . . . . . . . . . . . . . . . . . . . . 44 7.7 Stanza Errors . . . . . . . . . . . . . . . . . . . . . . . 45 7.7.1 Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 7.7.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 7.7.3 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 46 7.7.4 Extensibility . . . . . . . . . . . . . . . . . . . . . . . 47 8. XML Usage within XMPP . . . . . . . . . . . . . . . . . . . 48 8.1 Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 48 8.2 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . 48 8.3 Validation . . . . . . . . . . . . . . . . . . . . . . . . . 48 8.4 Character Encodings . . . . . . . . . . . . . . . . . . . . 49 8.5 Inclusion of Text Declaration . . . . . . . . . . . . . . . 49 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 50 9.1 XML Namespace Name for Stream Errors . . . . . . . . . . . . 50 9.2 XML Namespace Name for Stanza Errors . . . . . . . . . . . . 50 9.3 Existing Registrations . . . . . . . . . . . . . . . . . . . 50 10. Internationalization Considerations . . . . . . . . . . . . 51 11. Security Considerations . . . . . . . . . . . . . . . . . . 52 11.1 High Security . . . . . . . . . . . . . . . . . . . . . . . 52 11.2 Client-to-Server Communications . . . . . . . . . . . . . . 52 11.3 Server-to-Server Communications . . . . . . . . . . . . . . 52 11.4 Firewalls . . . . . . . . . . . . . . . . . . . . . . . . . 53 11.5 Mandatory to Implement Technologies . . . . . . . . . . . . 53 References . . . . . . . . . . . . . . . . . . . . . . . . . 54 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 56 A. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . 57 A.1 Streams namespace . . . . . . . . . . . . . . . . . . . . . 57 A.2 TLS namespace . . . . . . . . . . . . . . . . . . . . . . . 58 A.3 SASL namespace . . . . . . . . . . . . . . . . . . . . . . . 58 A.4 Dialback namespace . . . . . . . . . . . . . . . . . . . . . 59 A.5 Client namespace . . . . . . . . . . . . . . . . . . . . . . 60 A.6 Server namespace . . . . . . . . . . . . . . . . . . . . . . 63 A.7 Stream error namespace . . . . . . . . . . . . . . . . . . . 66 A.8 Stanza error namespace . . . . . . . . . . . . . . . . . . . 67 B. Revision History . . . . . . . . . . . . . . . . . . . . . . 69 Saint-Andre & Miller Expires October 6, 2003 [Page 3] Internet-Draft XMPP Core April 2003 B.1 Changes from draft-ietf-xmpp-core-07 . . . . . . . . . . . . 69 B.2 Changes from draft-ietf-xmpp-core-06 . . . . . . . . . . . . 69 B.3 Changes from draft-ietf-xmpp-core-05 . . . . . . . . . . . . 69 B.4 Changes from draft-ietf-xmpp-core-04 . . . . . . . . . . . . 69 B.5 Changes from draft-ietf-xmpp-core-03 . . . . . . . . . . . . 70 B.6 Changes from draft-ietf-xmpp-core-02 . . . . . . . . . . . . 70 B.7 Changes from draft-ietf-xmpp-core-01 . . . . . . . . . . . . 70 B.8 Changes from draft-ietf-xmpp-core-00 . . . . . . . . . . . . 70 B.9 Changes from draft-miller-xmpp-core-02 . . . . . . . . . . . 71 Intellectual Property and Copyright Statements . . . . . . . 72 Saint-Andre & Miller Expires October 6, 2003 [Page 4] Internet-Draft XMPP Core April 2003 1. Introduction 1.1 Overview The Extensible Messaging and Presence Protocol (XMPP) is an open XML [1] protocol for near-real-time messaging, presence, and request-response services. The basic syntax and semantics were developed originally within the Jabber open-source community, mainly in 1999. In 2002, the XMPP WG was chartered with developing an adaptation of the Jabber protocol that would be suitable as an IETF instant messaging and presence technology. As a result of work by the XMPP WG, the current document defines the core features of XMPP; XMPP IM [2] defines the extensions required to provide the instant messaging (IM) and presence functionality defined in RFC 2779 [3]. 1.2 Terminology The capitalized 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 RFC 2119 [4]. 1.3 Discussion Venue The authors welcome discussion and comments related to the topics presented in this document. The preferred forum is the mailing list, for which archives and subscription information are available at . 1.4 Intellectual Property Notice This document is in full compliance with all provisions of Section 10 of RFC 2026. Parts of this specification use the term "jabber" for identifying namespaces and other protocol syntax. Jabber[tm] is a registered trademark of Jabber, Inc. Jabber, Inc. grants permission to the IETF for use of the Jabber trademark in association with this specification and its successors, if any. Saint-Andre & Miller Expires October 6, 2003 [Page 5] Internet-Draft XMPP Core April 2003 2. Generalized Architecture 2.1 Overview Although XMPP is not wedded to any specific network architecture, to this point it has usually been implemented via a typical client-server architecture, wherein a client utilizing XMPP accesses a server over a TCP [5] socket. The following diagram provides a high-level overview of this architecture (where "-" represents communications that use XMPP and "=" represents communications that use any other protocol). C1 - S1 - S2 - C3 / \ C2 - G1 = FN1 = FC1 The symbols are as follows: o C1, C2, C3 -- XMPP clients o S1, S2 -- XMPP servers o G1 -- A gateway that translates between XMPP and the protocol(s) used on a foreign (non-XMPP) messaging network o FN1 -- A foreign messaging network o FC1 -- A client on a foreign messaging network 2.2 Server A server acts as an intelligent abstraction layer for XMPP communications. Its primary responsibilities are to manage connections from or sessions for other entities (in the form of XML streams to and from authorized clients, servers, and other entities) and to route appropriately-addressed XML data "stanzas" among such entities over XML streams. Most XMPP-compliant servers also assume responsibility for the storage of data that is used by clients (e.g., contact lists for users of XMPP-based IM applications); in this case, the XML data is processed directly by the server itself on behalf of the client and is not routed to another entity. Compliant server implementations MUST ensure in-order processing of XML stanzas between any two entities. 2.3 Client Saint-Andre & Miller Expires October 6, 2003 [Page 6] Internet-Draft XMPP Core April 2003 Most clients connect directly to a server over a TCP socket and use XMPP to take full advantage of the functionality provided by a server and any associated services, although it must be noted that there is no necessary coupling of an XML stream to a TCP socket (e.g., a client COULD connect via HTTP polling or some other mechanism). Multiple resources (e.g., devices or locations) MAY connect simultaneously to a server on behalf of each authorized client, with each resource connecting over a discrete TCP socket and differentiated by the resource identifier of a JID (Section 3) (e.g., user@domain/home vs. user@domain/work). The port registered with the IANA [6] for connections between a Jabber client and a Jabber server is 5222. For further details about client-to-server communications expressly for the purpose of instant messaging and presence, refer to XMPP IM [2]. 2.4 Gateway A gateway is a special-purpose server-side service whose primary function is to translate XMPP into the protocol(s) of another messaging system, as well as to translate the return data back into XMPP. Examples are gateways to SIMPLE, Internet Relay Chat (IRC), Short Message Service (SMS), SMTP, and foreign instant messaging networks such as Yahoo!, MSN, ICQ, and AIM. Communications between gateways and servers, and between gateways and the foreign messaging system, are not defined in this document. 2.5 Network Because each server is identified by a network address (typically a DNS hostname) and because server-to-server communications are a straightforward extension of the client-to-server protocol, in practice the system consists of a network of servers that inter-communicate. Thus user-a@domain1 is able to exchange messages, presence, and other information with user-b@domain2. This pattern is familiar from messaging protocols (such as SMTP) that make use of network addressing standards. Upon opening a TCP socket on the IANA-registered port 5269, there are two methods for negotiating a connection between any two servers: server dialback (Section 6.2) and SASL authentication (Section 6.1). Saint-Andre & Miller Expires October 6, 2003 [Page 7] Internet-Draft XMPP Core April 2003 3. Addressing Scheme 3.1 Overview An entity is anything that can be considered a network endpoint (i.e., an ID on the network) and that can communicate using XMPP. All such entities are uniquely addressable in a form that is consistent with RFC 2396 [7]. In particular, a valid Jabber Identifier (JID) contains a set of ordered elements formed of a domain identifier, node identifier, and resource identifier in the following format: [node@]domain[/resource]. All JIDs are based on the foregoing structure. The most common use of this structure is to identify an IM user, the server to which the user connects, and the user's active session or connection (e.g., a specific client) in the form of user@domain/resource. However, node types other than clients are possible; for example, a specific chat room offered by a multi-user chat service could be addressed as (where "room" is the name of the chat room and "service" is the hostname of the multi-user chat service) and a specific occupant of such a room could be addressed as (where "nick" is the occupant's room nickname). Many other JID types are possible (e.g., could be a server-side script or service). 3.2 Domain Identifier The domain identifier is the primary identifier and is the only REQUIRED element of a JID (a mere domain identifier is a valid JID). It usually represents the network gateway or "primary" server to which other entities connect for XML routing and data management capabilities. However, the entity referenced by a domain identifier is not always a server, and may be a service that is addressed as a subdomain of a server and that provides functionality above and beyond the capabilities of a server (a multi-user chat service, a user directory, a gateway to a foreign messaging system, etc.). The domain identifier for every server or service that will communicate over a network SHOULD resolve to a Fully Qualified Domain Name. A domain identifier MUST conform to RFC 952 [8] and RFC 1123 [9]. A domain identifier MUST be no more than 1023 bytes in length and MUST conform to the nameprep [10] profile of stringprep [11]. 3.3 Node Identifier The node identifier is an optional secondary identifier. It usually represents the entity requesting and using network access provided by the server or gateway (i.e., a client), although it can also Saint-Andre & Miller Expires October 6, 2003 [Page 8] Internet-Draft XMPP Core April 2003 represent other kinds of entities (e.g., a multi-user chat room associated with a multi-user chat service). The entity represented by a node identifier is addressed within the context of a specific domain; within IM applications of XMPP this address is called a "bare JID" and is of the form . A node identifier MUST be no more than 1023 bytes in length and MUST conform to the nodeprep [12] profile of stringprep [11]. 3.4 Resource Identifier The resource identifer is an optional tertiary identifier. It usually represents a specific session, connection (e.g., a device or location), or object (e.g., a participant in a multi-user chat room) belonging to the entity associated with a node identifier. An entity may maintain multiple resources simultaneously. A resource identifier MUST be no more than 1023 bytes in length and MUST conform to the resourceprep [13] profile of stringprep [11]. Saint-Andre & Miller Expires October 6, 2003 [Page 9] Internet-Draft XMPP Core April 2003 4. XML Streams 4.1 Overview Two fundamental concepts make possible the rapid, asynchronous exchange of relatively small payloads of structured information between presence-aware entities, XML streams and XML stanzas: Definition of XML stream: An XML stream is a container for the exchange of XML elements between any two entities over a network. An XML stream is negotiated from an initiating entity (usually a client or server) to a receiving entity (usually a server), normally over a TCP socket. An XML stream corresponds to the initiating entity's "session" with the receiving entity. The start of the XML stream is denoted unambiguously by an opening XML tag with appropriate attributes and namespace declarations, and the end of the XML stream is denoted unambiguously be a closing XML tag. An XML stream is unidirectional; in order to enable bidirectional information exchange, one stream must be negotiated from initiating entity to receiving entity and another stream must be negotiated from receiving entity to initiating entity. Definition of XML stanza: An XML stanza is a discrete semantic unit of structured information that is sent from one entity to another over an XML stream. An XML stanza exists at the direct child level of the root element and is said to be well-balanced if it matches production [43] content of the XML specification [1]). The start of any XML stanza is denoted unambiguously by the element start tag at depth=1 (e.g., ), and the end of any XML stanza is denoted unambiguously by the corresponding close tag at depth=1 (e.g., ). An XML stanza MAY contain child elements (with accompanying attributes, elements, and CDATA) as necessary in order to convey the desired information. Consider the example of a client's session with a server. In order to connect to a server, a client must initiate an XML stream by sending an opening tag to the server, optionally preceded by a text declaration specifying the XML version supported and the character encoding. The server SHOULD then reply with a second XML stream back to the client, again optionally preceded by a text declaration. Once the client has authenticated with the server (see Section 6), the client MAY send an unlimited number of XML stanzas over the stream to any recipient on the network. When the client desired to close the stream, it simply sends a closing tag to the server (alternatively, the session may be closed by the server). Thus a client's session with a server can be seen as two open-ended Saint-Andre & Miller Expires October 6, 2003 [Page 10] Internet-Draft XMPP Core April 2003 XML documents that are built up through the accumulation of the XML stanzas sent over the two XML streams (i.e., one from the client to the server and one from the server to the client), and the root element can be considered the document entity for each document. In essence, then, an XML stream acts as an envelope for all the XML stanzas sent during a session. We can represent this graphically as follows: |-------------------| | | |-------------------| | | | | | | |-------------------| | | | | | | |-------------------| | | | | | | |-------------------| | ... | |-------------------| | | |-------------------| 4.2 Stream Attributes The attributes of the stream element are as follows: o to -- The 'to' attribute SHOULD be used only in the XML stream from the initiating entity to the receiving entity, and MUST be set to the XMPP address of the receiving entity. There SHOULD be no 'to' attribute set in the XML stream by which the receiving entity replies to the initiating entity; however, if a 'to' attribute is included, it SHOULD be ignored by the initiating entity. o from -- The 'from' attribute SHOULD be used only in the XML stream from the receiving entity to the initiating entity, and MUST be set to the XMPP address of the receiving entity granting access to the initiating entity. There SHOULD be no 'from' attribute on the XML stream sent from the initiating entity to the receiving entity; however, if a 'from' attribute is included, it SHOULD be ignored by the receiving entity. Saint-Andre & Miller Expires October 6, 2003 [Page 11] Internet-Draft XMPP Core April 2003 o id -- The 'id' attribute SHOULD be used only in the XML stream from the receiving entity to the initiating entity. This attribute is a unique identifier created by the receiving entity to function as a session key for the initiating entity's session with the receiving entity. There SHOULD be no 'id' attribute on the XML stream sent from the initiating entity to the receiving entity; however, if an 'id' attribute is included, it SHOULD be ignored by the receiving entity. o version -- The 'version' attribute MAY be used in the XML stream from the initiating entity to the receiving entity in order signal compliance with the protocol defined herein; this is done by setting the value of the attribute to "1.0". If the initiating entity includes the version attribute and the receiving entity supports XMPP 1.0, the receiving entity MUST reciprocate by including the attribute in its response. We can summarize these values as follows: | initiating to receiving | receiving to initiating ------------------------------------------------------------ to | JID of receiver | ignored from | ignored | JID of receiver id | ignored | session key version | signals XMPP 1.0 support | signals XMPP 1.0 support 4.3 Namespace Declarations The stream element MAY contain namespace declarations as defined in the XML namespaces specification [14]. A default namespace declaration ('xmlns') is REQUIRED and is used in both XML streams in order to scope the allowable first-level children of the root stream element for both streams. This namespace declaration MUST be the same for the initiating stream and the responding stream so that both streams are scoped consistently. The default namespace declaration applies to the stream and all stanzas sent within a stream. A stream namespace declaration (e.g., 'xmlns:stream') is REQUIRED in both XML streams. A compliant entity SHOULD accept any namespace prefix on the element; however, for historical reasons some entities MAY accept only a 'stream' prefix, resulting in the use of a element as the stream root. The name of the stream namespace MUST be "http://etherx.jabber.org/streams". Since XML streams function as containers for any XML stanzas sent Saint-Andre & Miller Expires October 6, 2003 [Page 12] Internet-Draft XMPP Core April 2003 asynchronously between network endpoints, it should be possible to scope an XML stream with any default namespace declaration (i.e., it should be possible to send any properly-namespaced XML stanza over an XML stream). At a minimum, a compliant implementation MUST support the following two namespaces (for historical reasons, existing implementations MAY support only these two default namespaces): o jabber:client -- this default namespace is declared when the stream is used for communications between a client and a server o jabber:server -- this default namespace is declared when the stream is used for communications between two servers The jabber:client and jabber:server namespaces are nearly identical but are used in different contexts (client-to-server communications for jabber:client and server-to-server communications for jabber:server). The only difference between the two is that the 'to' and 'from' attributes are OPTIONAL on stanzas sent within jabber:client, whereas they are REQUIRED on stanzas sent within jabber:server. If a compliant implementation accepts a stream that is scoped by the 'jabber:client' or 'jabber:server' namespace, it MUST support all three core stanza types (message, presence, and IQ) as described herein and defined in the schema. 4.4 Stream Features The root stream element MAY contain a features child element (e.g., if the stream namespace prefix is 'stream'). This is used to communicate generic stream-level capabilities including stream-level features that can be negotiated as the streams are set up. If the initiating entity sends a "version='1.0'" flag in its initiating stream element, the receiving entity MUST send a features child element to the initiating entity if there are any capabilities that need to be advertised or features that can be negotiated for the stream. Currently this is used for SASL and TLS negotiation only, but it could be used for other negotiable features in the future (usage is defined under Stream Encryption (Section 5) and Stream Authentication (Section 6) below). If an entity does not understand or support some features, it SHOULD ignore them. 4.5 Stream Errors The root stream element MAY contain an error child element (e.g., if the stream namespace prefix is 'stream'). The error child MUST be sent by a Jabber entity (usually a server rather than a client) if it perceives that a stream-level error has occurred. Saint-Andre & Miller Expires October 6, 2003 [Page 13] Internet-Draft XMPP Core April 2003 4.5.1 Rules The following rules apply to stream-level errors: o It is assumed that all stream-level errors are unrecoverable; therefore, if an error occurs at the level of the stream, the entity that detects the error MUST send a stream error to the other entity and then send a closing tag. o If the error occurs while the stream is being set up, the receiving entity MUST still send the opening and closing stream tags and include the error element as a child of the stream element. In this case, if the initiating entity provides an unknown host in the 'to' attribute (or provides no 'to' attribute at all), the server SHOULD provide the server's authoritative hostname in the 'from' attribute of the stream header. 4.5.2 Syntax The syntax for stream errors is as follows: The value of the 'class' attribute must be one of the following: o address -- the condition relates to the JID or domain to which the stream was addressed o format -- the condition relates to XML format or structure o redirect -- the condition relates to a host redirection o server -- the condition relates to the internal state of the server The element MUST contain a child element that specifies a particular stream-level error condition, as defined in the next section. (Note: the XML namespace name 'urn:ietf:params:xml:ns:xmpp-streams' that scopes the element adheres to the format defined in The IETF XML Registry [15].) Saint-Andre & Miller Expires October 6, 2003 [Page 14] Internet-Draft XMPP Core April 2003 4.5.3 Conditions The following stream-level error conditions are defined: o -- the value of the 'to' attribute provided by the initiating entity in the stream header corresponds to a hostname that is no longer hosted by the server; the associated class is "address". o -- the value of the 'to' attribute provided by the initiating entity in the stream header does not correspond to a hostname that is hosted by the server; the associated class is "address". o -- the server has experienced a misconfiguration or an otherwise-undefined internal server error that prevents it from servicing the stream; the associated class is "server". o -- the stream namespace name is something other than "http://etherx.jabber.org/streams"; the associated class is "format". o -- the server is resource-contrained and is unable to service the stream; the associated class is "server". o -- the server will not provide service to the initiating entity but is redirecting traffic to another host; this element SHOULD contain CDATA specifying the alternate hostname or IP address to which the initiating entity MAY attempt to connect; the associated class is "redirect". o -- the server is being shut down and all active streams are being closed; the associated class is "server". o -- the initiating entity has sent a first-level child of the stream that is not supported by the server; the associated class is "format". o -- the value of the 'version' attribute provided by the initiating entity in the stream header specifies a version of XMPP that is not supported by the server; this element MAY contain CDATA specifying the XMPP version(s) supported by the server; the associated class is "format". o -- the initiating entity has sent XML that is not well-formed as defined by the XML specification [1]; the associated class is "format". Saint-Andre & Miller Expires October 6, 2003 [Page 15] Internet-Draft XMPP Core April 2003 4.5.4 Extensibility If desired, an XMPP application MAY provide custom error information; this MUST be contained in a properly-namespaced child of the element (i.e., the namespace name MUST NOT be one of the namespace names defined herein). 4.6 Simple Streams Example The following is a stream-based session of a client on a server (where the "C" lines are sent from the client to the server, and the "S" lines are sent from the server to the client): A basic session: C: S: ... authentication ... C: C: Watson come here, I want you! C: S: S: I'm on my way! S: C: S: These are in actuality a sending stream and a receiving stream, which can be viewed a-chronologically as two XML documents: Saint-Andre & Miller Expires October 6, 2003 [Page 16] Internet-Draft XMPP Core April 2003 C: C: C: Watson come here, I want you! C: C: S: S: S: I'm on my way! S: S: A session gone bad: C: S: C: Bad XML, no closing body tag! S: S: Saint-Andre & Miller Expires October 6, 2003 [Page 17] Internet-Draft XMPP Core April 2003 5. Stream Encryption 5.1 Overview XMPP includes a method for securing the stream from tampering and eavesdropping. This channel encryption method makes use of the Transport Layer Security (TLS) [16] protocol, along with a "STARTTLS" extension that is modelled on similar extensions for the IMAP [17], POP3 [18], and ACAP [19] protocols as described in RFC 2595 [20]. The namespace identifier for the STARTTLS extension is 'http:// www.ietf.org/rfc/rfc2595.txt'. TLS SHOULD be used between any initiating entity and any receiving entity (e.g., a stream from a client to a server or from one server to another). The following rules MUST be observed: 1. If the initiating entity is capable of using the STARTTLS extension, it MUST include the "version='1.0'" flag in the initiating stream header. 2. If the receiving entity is capable of using the STARTTLS extension, it MUST send the element in the defined namespace along with the list of features that it sends in response to the opening stream tag received from the initiating entity. 3. If the initiating entity chooses to use TLS for stream encryption, TLS negotiation MUST be completed before proceeding to authenticate the stream using SASL. 4. The initiating entity MUST validate the certificate presented by the receiving entity: 1. If the initiating entity has been configured with a set of trusted roots, either a well-known public set or a manually configured Certificate Authority (e.g., an organization's own Certificate Authority), normal certificate validation processing is appropriate. 2. If the initiating entity has been configured with the receiving entity's public key or certificate, a simple comparison is appropriate. If the above methods fail, the certificate MAY be presented to a user for approval; the user SHOULD be given the option to store the certificate and not ask again for at least some reasonable period of time. Saint-Andre & Miller Expires October 6, 2003 [Page 18] Internet-Draft XMPP Core April 2003 5. If the TLS negotiation is successful, the receiving entity MUST discard any knowledge obtained from the initiating entity before TLS takes effect. 6. If the TLS negotiation is successful, the initiating entity MUST discard any knowledge obtained from the receiving entity before TLS takes effect. 7. If the TLS negotiation is successful, the receiving entity MUST NOT offer the STARTTLS extension to the initiating entity along with the other stream features that are offered when the stream is restarted. 8. Whether the TLS negotiation results in success or failure, the initiating entity SHOULD continue with SASL negotiation. 5.2 Narrative When an initiating entity secures a stream with a receiving entity, the steps involved are as follows: 1. Then initiating entity opens a TCP connection and initiates the stream by sending the opening XML stream header to the receiving entity, including the "version='1.0'" flag. 2. The receiving entity responds by opening a TCP connection and sending an XML stream header to the initiating entity. 3. The receiving entity offers the STARTTLS extension to the initiating entity by sending it along with the list of supported stream features. 4. Then initiating entity issues the STARTTLS command to instruct the receiving entity that it wishes to begin a TLS negotiation to secure the stream. 5. The receiving entity MUST reply with either an empty element or an empty element, but keep the underlying TCP connection open. 6. Then initiating entity begins a TLS negotiation in accordance with RFC 2246 [16]. Upon completion of the negotiation, the initiating entity initiates a new stream by sending a new opening XML stream header to the receiving entity. 7. The receiving entity responds by sending an XML stream header to the initiating entity along with the remaining available features Saint-Andre & Miller Expires October 6, 2003 [Page 19] Internet-Draft XMPP Core April 2003 (but NOT including the STARTTLS element). 5.3 Client-to-Server Example The following example shows the data flow for a client securing a stream using STARTTLS. Step 1: Client initiates stream to server: Step 2: Server responds by sending a stream tag to the client: Step 3: Server sends the STARTTLS extension to the client along with authentication mechanisms and any other stream features: DIGEST-MD5 PLAIN Step 4: Client sends the STARTTLS command to the server: Step 5: Server informs client to proceed: Step 5 (alt): Server informs client that TLS negotiation has failed (client SHOULD continue with stream authentication (Section 6)): Saint-Andre & Miller Expires October 6, 2003 [Page 20] Internet-Draft XMPP Core April 2003 Step 6: Client and server complete TLS negotiation via TCP. Step 7: Client initiates a new stream to the server: Step 8: Server responds by sending a stream header to the client along with any remaining negotiatiable stream features: DIGEST-MD5 PLAIN EXTERNAL Step 9: Client SHOULD continue with stream authentication (Section 6). 5.4 Server-to-Server Example By bilateral agreement, server administrators SHOULD choose to use TLS between two domains for the purpose of securing server-to-server communications. The following example shows the data flow for two servers securing a stream using STARTTLS. Step 1: Server1 initiates stream to Server2: Saint-Andre & Miller Expires October 6, 2003 [Page 21] Internet-Draft XMPP Core April 2003 Step 2: Server2 responds by sending a stream tag to Server1: Step 3: Server2 sends the STARTTLS extension to Server1 along with authentication mechanisms and any other stream features: DIGEST-MD5 KERBEROS_V4 Step 4: Server1 sends the STARTTLS command to Server2: Step 5: Server2 informs Server1 to proceed: Step 5 (alt): Server2 informs Server1 that TLS negotiation has failed (Server1 SHOULD continue with stream authentication (Section 6)): Step 6: Server1 and Server2 complete TLS negotiation via TCP. Step 7: Server1 initiates a new stream to Server2: Saint-Andre & Miller Expires October 6, 2003 [Page 22] Internet-Draft XMPP Core April 2003 Step 8: Server2 responds by sending a stream header to Server1 along with any remaining negotiatiable stream features: DIGEST-MD5 KERBEROS_V4 EXTERNAL Step 9: Server1 SHOULD continue with stream authentication (Section 6). Saint-Andre & Miller Expires October 6, 2003 [Page 23] Internet-Draft XMPP Core April 2003 6. Stream Authentication XMPP includes two methods for enforcing authentication at the level of XML streams. When one entity is already known to another (i.e., there is an existing trust relationship between the entities such as that established when a user registers with a server or an administrator configures a server to trust another server), the preferred method for authenticating streams between the two entities uses an XMPP adaptation of the Simple Authentication and Security Layer (SASL) [21]. When there is no existing trust relationship between two servers, some level of trust MAY be established based on existing trust in DNS; the authentication method used in this case is the server dialback protocol that is native to XMPP (no such ad-hoc method is defined between a client and a server). If SASL is used for server-to-server authentication, the servers MUST NOT use dialback. Both SASL authentication and dialback are described in this section. Stream authentication is REQUIRED for all direct communications between two entities; if an entity sends a stanza to an unauthenticated stream, the receiving entity SHOULD silently drop the stanza and MUST NOT process it. 6.1 SASL Authentication 6.1.1 Overview The Simple Authentication and Security Layer (SASL) provides a generalized method for adding authentication support to connection-based protocols. XMPP uses a generic XML namespace profile for SASL that conforms to section 4 ("Profiling Requirements") of RFC 2222 [21] (the namespace identifier for this protocol is 'http:// www.iana.org/assignments/sasl-mechanisms'). The following rules MUST be observed: 1. If TLS is used for stream encryption, SASL MUST NOT be used for anything but stream authentication (i.e., a security layer MUST NOT be negotiated using SASL). Conversely, if a security layer is to be negotiated via SASL, TLS MUST NOT be used. 2. If the initiating entity is capable of authenticating via SASL, it it MUST include the "version='1.0'" flag in the initiating stream header. 3. If the receiving entity is capable of accepting authentications via SASL, it MUST send one or more authentication mechanisms within a element in response to the opening stream tag received from the initiating entity. Saint-Andre & Miller Expires October 6, 2003 [Page 24] Internet-Draft XMPP Core April 2003 4. If the SASL negotiation involves negotiation of a security layer, the receiving entity MUST discard any knowledge obtained from the initiating entity which was not obtained from the SASL negotiation itself. 5. If the SASL negotiation involves negotiation of a security layer, the initiating entity MUST discard any knowledge obtained from the receiving entity which was not obtained from the SASL negotiation itself. 6.1.2 Narrative When an initiating entity authenticates with a receiving entity, the steps involved are as follows: 1. The initiating entity requests SASL authentication by including a 'version' attribute in the opening XML stream header sent to the receiving entity, with the value set to "1.0". 2. After sending an XML stream header in response, the receiving entity sends a list of available SASL authentication mechanisms, each of which is a element included as a child within a container element that is sent as a child of the first-level element. If channel encryption must be established before a particular authentication mechanism may be used, the receiving entity MUST NOT provide that mechanism in the list of available SASL authentication methods. If the initiating entity presents a valid initiating entity certificate during TLS negotiation, the receiving entity MAY offer the SASL EXTERNAL mechanism to the initiating entity during stream authentication (see RFC 2222 [21]). 3. The initiating entity selects a mechanism by sending an element to the receiving entity; this element MAY optionally contain character data (in SASL terminology the "initial response") if the mechanism supports or requires it. If the initiating entity selects the EXTERNAL mechanism for authentication, the authentication credentials shall be taken from the certificate presented during TLS negotiation. 4. If necessary, the receiving entity challenges the initiating entity by sending a element to the initiating entity; this element MAY optionally contain character data. 5. The initiating entity responds to the challenge by sending a element to the receiving entity; this element MAY optionally contain character data. Saint-Andre & Miller Expires October 6, 2003 [Page 25] Internet-Draft XMPP Core April 2003 6. If necessary, the receiving entity sends more challenges and the initiating entity sends more responses. This series of challenge/response pairs continues until one of three things happens: 1. The initiating entity aborts the handshake by sending an element to the receiving entity. 2. The receiving entity reports failure of the handshake by sending a element to the initiating entity. The particular cause of failure optionally may be communicated in the 'code' attribute of the element, and may be 432 (password transition is needed), 534 (authentication mechanism is too weak), or 454 (temporary authentication failure). 3. The receiving entity reports success of the handshake by sending a element to the initiating entity; this element MAY optionally contain character data (in SASL terminology "additional data with success"). Any character data contained within these elements MUST be encoded using base64. 6.1.3 SASL Definition Section 4 of the SASL specification [21] requires that the following information be supplied by a protocol definition: service name: "xmpp" initiation sequence: After the initiating entity provides an opening XML stream header and the receiving entity replies in kind, the receiving entity provides a list of acceptable authentication methods. The initiating entity chooses one method from the list and sends it to the receiving entity as the value of the 'mechanism' attribute possesed by an element, optionally including an initial response to avoid a round trip. exchange sequence: Challenges and responses are carried through the exchange of elements from receiving entity to initiating entity and elements from initiating entity to receiving entity. The receiving entity reports failure by sending a element and success by sending a element; the initiating entity aborts the exchange by sending an element. Saint-Andre & Miller Expires October 6, 2003 [Page 26] Internet-Draft XMPP Core April 2003 security layer negotiation: If a security layer is negotiated, both sides consider the original stream closed and new headers are sent by both entities. The security layer takes effect immediately following the ">" character of the empty element for the client and immediately following the closing ">" character of the element for the server. use of the authorization identity: The authorization identity, if present, is unused by xmpp. 6.1.4 Client-to-Server Example The following example shows the data flow for a client authenticating with a server using SASL. Step 1: Client initiates stream to server: Step 2: Server responds with a stream tag sent to the client: Step 3: Server informs client of available authentication mechanisms: DIGEST-MD5 PLAIN Saint-Andre & Miller Expires October 6, 2003 [Page 27] Internet-Draft XMPP Core April 2003 Step 4: Client selects an authentication mechanism ("initial response"): Step 5: Server sends a base64-encoded challenge to the client: cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIi xxb3A9ImF1dGgiLGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNz The decoded challenge is: realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",\ qop="auth",charset=utf-8,algorithm=md5-sess Step 6: Client responds to the challenge: dXNlcm5hbWU9InJvYiIscmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik 9BNk1HOXRFUUdtMmhoIixcIGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLG5j PTAwMDAwMDAxLHFvcD1hdXRoLFwgZGlnZXN0LXVyaT0ieG1wcC9jYXRhY2 x5c20uY3giLFwgcmVzcG9uc2U9ZDM4OGRhZDkwZDRiYmQ3NjBhMTUyMzIxZ jIxNDNhZjcsY2hhcnNldD11dGYtOA== The decoded response is: username="rob",realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",\ cnonce="OA6MHXh6VqTrRk",nc=00000001,qop=auth,\ digest-uri="xmpp/ cataclysm.cx",\ response=d388dad90d4bbd760a152321f2143af7,charset=utf-8 Step 7: Server sends another challenge to the client: cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA== The decoded challenge is: rspauth=ea40f60335c427b5527b84dbabcdfffd Saint-Andre & Miller Expires October 6, 2003 [Page 28] Internet-Draft XMPP Core April 2003 Step 8: Client responds to the challenge: Step 9: Server informs client of successful authentication: Step 9 (alt): Server informs client of failed authentication: Step 10: Client initiates a new stream to the server: Step 11: Server responds by sending a stream header to the client, with the stream already authenticated (not followed by further stream features): 6.1.5 Server-to-Server Example By bilateral agreement, server administrators MAY choose to use SASL between two domains for the purpose of securing server-to-server communications. The following example shows the data flow for a server authenticating with another server using SASL. Step 1: Server1 initiates stream to Server2: Saint-Andre & Miller Expires October 6, 2003 [Page 29] Internet-Draft XMPP Core April 2003 Step 2: Server2 responds with a stream tag sent to Server1: Step 3: Server2 informs Server1 of available authentication mechanisms: DIGEST-MD5 KERBEROS_V4 Step 4: Server1 selects an authentication mechanism ("initial response"): Step 5: Server2 sends a base64-encoded challenge to Server1: cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIi xxb3A9ImF1dGgiLGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNz The decoded challenge is: realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",\ qop="auth",charset=utf-8,algorithm=md5-sess Step 6: Server1 responds to the challenge: cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIixjbm9uY2U9Ik9B Nk1IWGg2VnFUclJrIixuYz0wMDAwMDAwMSxxb3A9YXV0aCxkaWdlc3QtdXJpPSJ4bXBwL2Nh dGFjbHlzbS5jeCIscmVzcG9uc2U9ZDM4OGRhZDkwZDRiYmQ3NjBhMTUyMzIxZjIxNDNhZjcs Y2hhcnNldD11dGYtOAo= The decoded response is: Saint-Andre & Miller Expires October 6, 2003 [Page 30] Internet-Draft XMPP Core April 2003 realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",\ cnonce="OA6MHXh6VqTrRk",nc=00000001,qop=auth,\ digest-uri="xmpp/ cataclysm.cx",\ response=d388dad90d4bbd760a152321f2143af7,charset=utf-8 Step 7: Server2 sends another challenge to Server1: cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA== The decoded challenge is: rspauth=ea40f60335c427b5527b84dbabcdfffd Step 8: Server1 responds to the challenge: Step 9: Server2 informs Server1 of successful authentication: Step 9 (alt): Server2 informs Server1 of failed authentication: Step 10: Server1 initiates a new stream to Server2: Step 11: Server2 responds by sending a stream header to Server1, with the stream already authenticated (not followed by further stream features): 6.2 Dialback Authentication XMPP includes a protocol-level method for verifying that a connection Saint-Andre & Miller Expires October 6, 2003 [Page 31] Internet-Draft XMPP Core April 2003 between two servers can be trusted (at least as much as the DNS can be trusted). The method is called dialback and is used only within XML streams that are declared under the "jabber:server" namespace. The purpose of the dialback protocol is to make server spoofing more difficult, and thus to make it more difficult to forge XML stanzas. Dialback is not intended as a mechanism for securing or encrypting the streams between servers as is done via SASL and TLS, only for helping to prevent the spoofing of a server and the sending of false data from it. Domains requiring more robust security SHOULD use TLS or SASL as defined above. Server dialback is made possible by the existence of DNS, since one server can verify that another server which is connecting to it is authorized to represent a given server on the Jabber network. All DNS hostname resolutions MUST first resolve the hostname using an SRV [23] record of _jabber._tcp.server. If the SRV lookup fails, the fallback is a normal A lookup to determine the IP address, using the jabber-server port of 5269 assigned by the Internet Assigned Numbers Authority [6]. Note: the method for generating and verifying the keys used in the dialback protocol MUST take into account the hostnames being used, along with a secret known only by the receiving server and the random ID generated for the stream. Generating unique but verifiable keys is important to prevent common man-in-the-middle attacks and server spoofing. In the description that follows we use the following terminology: o Originating Server -- the server that is attempting to establish a connection between the two servers o Receiving Server -- the server that is trying to authenticate that Originating Server represents the Jabber server which it claims to be o Authoritative Server -- the server that is given when a DNS lookup is performed on the name that Originating Server initially gave; for basic environments this will be Originating Server, but it could be a separate machine in Originating Server's network The following is a brief summary of the order of events in dialback: 1. Originating Server establishes a connection to Receiving Server. 2. Originating Server sends a 'key' value over the connection to Receiving Server. Saint-Andre & Miller Expires October 6, 2003 [Page 32] Internet-Draft XMPP Core April 2003 3. Receiving Server establishes a connection to Authoritative Server. 4. Receiving Server sends the same 'key' value to Authoritative Server. 5. Authoritative Server replies that key is valid or invalid. 6. Receiving Server tells Originating Server whether it is authenticated or not. We can represent this flow of events graphically as follows: Originating Receiving Server Server ----------- --------- | | | establish connection | | ----------------------> | | | | send stream header | | ----------------------> | | | | establish connection | | <---------------------- | | | | send stream header | | <---------------------- | | | Authoritative | send dialback key | Server | ----------------------> | ------------- | | | | establish connection | | ----------------------> | | | | send stream header | | ----------------------> | | | | establish connection | | <---------------------- | | | | send stream header | | <---------------------- | | | | send dialback key | | ----------------------> | | | | validate dialback key | Saint-Andre & Miller Expires October 6, 2003 [Page 33] Internet-Draft XMPP Core April 2003 | <---------------------- | | | report dialback result | | <---------------------- | | | 6.2.1 Dialback Protocol The traffic sent between the servers is as follows: 1. Originating Server establishes TCP connection to Receiving Server 2. Originating Server sends a stream header to Receiving Server (the 'to' and 'from' attributes are NOT REQUIRED on the root stream element): Note: the value of the xmlns:db namespace declaration indicates to Receiving Server that Originating Server supports dialback. 3. Receiving Server sends a stream header back to Originating Server (the 'to' and 'from' attributes are NOT REQUIRED on the root stream element): 4. Originating Server sends a dialback key to Receiving Server: 98AF014EDC0... Note: this key is not examined by Receiving Server, since Receiving Server does not keep information about Originating Server between sessions. Saint-Andre & Miller Expires October 6, 2003 [Page 34] Internet-Draft XMPP Core April 2003 5. Receiving Server now establishes a connection back to Originating Server, getting Authoritative Server. 6. Receiving Server sends Authoritative Server a stream header (the 'to' and 'from' attributes are NOT REQUIRED on the root stream element): 7. Authoritative Server sends Receiving Server a stream header: 8. Receiving Server sends Authoritative Server a stanza indicating it wants Authoritative Server to verify a key: 98AF014EDC0... Note: passed here are the hostnames, the original identifier from Receiving Server's stream header to Originating Server in step 2, and the key Originating Server gave Receiving Server in step 3. Based on this information and shared secret information within the 'Originating Server' network, the key is verified. Any verifiable method can be used to generate the key. 9. Authoritative Server sends a stanza back to Receiving Server verifying whether the key was valid or invalid: or Saint-Andre & Miller Expires October 6, 2003 [Page 35] Internet-Draft XMPP Core April 2003 10. Receiving Server informs Originating Server of the result: Note: At this point the connection has either been validated via a type='valid', or reported as invalid. Once the connection is validated, data can be sent by Originating Server and read by Receiving Server; before that, all data stanzas sent to Receiving Server SHOULD be dropped. As a final guard against domain spoofing, Receiving Server MUST verify that all XML stanzas received from Originating Server include a 'from' attribute and that the value of that attribute includes the validated domain. In addition, all XML stanzas MUST include a 'to' attribute. Saint-Andre & Miller Expires October 6, 2003 [Page 36] Internet-Draft XMPP Core April 2003 7. XML Stanzas 7.1 Overview Once the XML streams in each direction have been authenticated and (if desired) encrypted, XML stanzas can be sent over the streams. Three XML stanza types are defined for the 'jabber:client' and 'jabber:server' namespaces: , , and . In essence, the stanza type can be seen as a "push" mechanism whereby one entity pushes information to another entity, similar to the communications that occur in a system such as email. The element can be seen as a basic broadcast or "publish-subscribe" mechanism, whereby multiple entities receive information (in this case, presence information) about an entity to which they have subscribed. The element can be seen as a "request-response" mechanism similar to HTTP, whereby two entities can engage in a structured conversation using 'get' or 'set' requests and 'result' or 'error' responses. The syntax for these stanza types is defined below. 7.2 Common Attributes Five attributes are common to message, presence, and IQ stanzas. These are defined below. 7.2.1 to The 'to' attribute specifies the JID of the intended recipient for the stanza. In the 'jabber:client' namespace, a stanza SHOULD possess a 'to' attribute, although a stanza sent from a client to a server for handling by that server (e.g., presence sent to the server for broadcasting to other entities) MAY legitimately lack a 'to' attribute. In the 'jabber:server' namespace, a stanza MUST possess a 'to' attribute. 7.2.2 from The 'from' attribute specifies the JID of the sender. In the 'jabber:client' namespace, a client MUST NOT include a 'from' attribute on the stanzas it sends to a server; if a server receives a stanza from a client and the stanza possesses a 'from' attribute, it MUST ignore the value of the 'from' attribute and MAY return an error to the sender. In addition, a server MUST stamp stanzas received from a client with the user@domain/resource (full JID) of the connected resource that generated the stanza. Saint-Andre & Miller Expires October 6, 2003 [Page 37] Internet-Draft XMPP Core April 2003 In the 'jabber:server' namespace, a stanza MUST possess a 'from' attribute. In particular, a server MUST include a 'from' attribute on stanzas it routes to other servers. The domain identifier of the JID contained in the 'from' attribute MUST match the hostname of the server (or a subdomain thereof) as communicated in the SASL negotiation or dialback negotiation. 7.2.3 id The optional 'id' attribute MAY be used to track stanzas sent and received. The 'id' attribute is generated by the sender. An 'id' attribute included in an IQ request of type "get" or "set" SHOULD be returned to the sender in any IQ response of type "result" or "error" generated by the recipient of the request. A recipient of a message or presence stanza MAY return that 'id' in any replies, but is NOT REQUIRED to do so. The value of the 'id' attribute is not intended to be unique -- globally, within a domain, or within a stream. It is generated by a sender only for internal tracking of information within the sending application. 7.2.4 type The 'type' attribute specifies detailed information about the purpose or context of the message, presence, or IQ stanza. The particular allowable values for the 'type' attribute vary depending on whether the stanza is a message, presence, or IQ, and thus are specified in the following sections. 7.2.5 xml:lang Any message or presence stanza MAY possess an 'xml:lang' attribute specifying the default language of any CDATA sections of the stanza or its child elements. An IQ stanza SHOULD NOT possess an 'xml:lang' attribute, since it is merely a vessel for data in other namespaces and does not itself contain children that have CDATA. The value of the 'xml:lang' attribute MUST be an NMTOKEN and MUST conform to the format defined in RFC 3066 [22]. 7.3 Message Stanzas Message stanzas in the 'jabber:client' or 'jabber:server' namespace are used to "push" information to another entity. Common uses in the context of instant messaging include single messages, messages sent in the context of a chat conversation, messages sent in the context of a multi-user chat room, headlines, and errors. These messages types are identified more fully below. Saint-Andre & Miller Expires October 6, 2003 [Page 38] Internet-Draft XMPP Core April 2003 7.3.1 Types of Message The 'type' attribute of a message stanza is OPTIONAL; if included, it specifies the conversational context of the message. The sending of a message stanza without a 'type' attribute signals that the message stanza is a single message. However, the 'type' attribute MAY also have one of the following values: o chat o error o groupchat o headline For information about the meaning of these message types, refer to XMPP IM [2]. 7.3.2 Children As described under extended namespaces (Section 7.6), a message stanza MAY contain any properly-namespaced child element as long as the namespace name is not "jabber:client", "jabber:server", or "http://etherx.jabber.org/streams", and as long as the element name does not match that of one of the core data elements, stream elements, or defined children thereof. In accordance with the default namespace declaration, by default a message stanza is in the 'jabber:client' or 'jabber:server' namespace, which defines certain allowable children of message stanzas. If the message stanza is of type "error", it MUST include an child; for details, see Section 7.7. If the message stanza has no 'type' attribute or has a 'type' attribute with a value of "chat", "groupchat", or "headline", it MAY contain any of the following child elements without an explicit namespace declaration: 7.3.2.1 Body The element contains the textual contents of the message; normally included but NOT REQUIRED. The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the element MAY be included but only if each instance possesses an 'xml:lang' attribute with a distinct language value. The element MUST NOT contain mixed content. Saint-Andre & Miller Expires October 6, 2003 [Page 39] Internet-Draft XMPP Core April 2003 7.3.2.2 Subject The element specifies the topic of the message. The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the element MAY be included for the purpose of providing alternate versions of the same subject, but only if each instance possesses an 'xml:lang' attribute with a distinct language value. The element MUST NOT contain mixed content. 7.3.2.3 Thread The element contains a random string that is generated by the sender and that SHOULD be copied back in replies; it is used for tracking a conversation thread (sometimes referred to as an "IM session") between two entities. If used, it MUST be unique to that conversation thread within the stream and MUST be consistent throughout that conversation. The use of the element is optional and is not used to identify individual messages, only conversations. Only one element MAY be included in a message stanza, and it MUST NOT possess any attributes. The element MUST be treated as an opaque string by entities; no semantic meaning may be derived from it, and only exact, case-insensitve comparisons be made against it. The element MUST NOT contain mixed content. The method for generating thread IDs SHOULD be as follows: 1. concatenate the sender's full JID (user@host/resource) with the recipient's full JID 2. concatenate these JID strings with a full ISO-8601 timestamp including year, month, day, hours, minutes, seconds, and UTC offset in the following format: yyyy-mm-dd-Thh:mm:ss-hh:mm 3. hash the resulting string according to the SHA1 algorithm 4. convert the hexidecimal SHA1 output to all lowercase 7.4 Presence Stanzas Presence stanzas are used in the 'jabber:client' or 'jabber:server' namespace to express an entity's current availability status (offline or online, along with various sub-states of the latter and optional user-defined descriptive text) and to communicate that status to other entities. Presence stanzas are also used to negotiate and manage subscriptions to the presence of other entities. Saint-Andre & Miller Expires October 6, 2003 [Page 40] Internet-Draft XMPP Core April 2003 7.4.1 Types of Presence The 'type' attribute of a presence stanza is optional. A presence stanza that does not possess a 'type' attribute is used to signal to the server that the sender is online and available for communication. If included, the 'type' attribute specifies a lack of availability, a request to manage a subscription to another entity's presence, a request for another entity's current presence, or an error related to a previously-sent presence stanza. The 'type' attribute MAY have one of the following values: o unavailable -- Signals that the entity is no longer available for communication. o subscribe -- The sender wishes to subscribe to the recipient's presence. o subscribed -- The sender has allowed the recipient to receive their presence. o unsubscribe -- A notification that an entity is unsubscribing from another entity's presence. o unsubscribed -- The subscription request has been denied or a previously-granted subscription has been cancelled. o probe -- A request for an entity's current presence. In general SHOULD NOT be sent by a client. o error -- An error has occurred regarding processing or delivery of a previously-sent presence stanza. Information about the subscription model used within XMPP can be found in XMPP IM [2]. 7.4.2 Children As described under extended namespaces (Section 7.6), a presence stanza MAY contain any properly-namespaced child element as long as the namespace name is not "jabber:client", "jabber:server", or "http://etherx.jabber.org/streams", and as long as the element name does not match that of one of the core data elements, stream elements, or defined children thereof. In accordance with the default namespace declaration, by default a presence stanza is in the 'jabber:client' or 'jabber:server' namespace, which defines certain allowable children of presence stanzas. If the presence stanza is of type "error", it MUST include Saint-Andre & Miller Expires October 6, 2003 [Page 41] Internet-Draft XMPP Core April 2003 an child; for details, see Section 7.7. If the presence stanza possesses no 'type' attribute, it MAY contain any of the following child elements (note that the child MAY be sent in a presence stanza of type "unavailable" or, for historical reasons, "subscribe"): 7.4.2.1 Show The element specifies describes the availability status of an entity or specific resource. Only one element MAY be included in a presence stanza, and it MUST NOT possess any attributes. The value SHOULD be one of the following (values other than these four MAY be ignored; additional availability types could be defined through a properly-namespaced child element of the presence stanza): o away o chat o xa o dnd For information about the meaning of these values, refer to XMPP IM [2]. 7.4.2.2 Status The optional element specifies a natural-language description of availability status. It is normally used in conjunction with the show element to provide a detailed description of an availability state (e.g., "In a meeting"). The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the element MAY be included but only if each instance possesses an 'xml:lang' attribute with a distinct language value. 7.4.2.3 Priority The optional element specifies the priority level of the connected resource. The value may be any integer between -128 to 127. Only one element MAY be included in a presence stanza, and it MUST NOT possess any attributes. For information regarding the use of priority values in stanza routing within IM applications, see XMPP IM [2]. 7.5 IQ Stanzas Saint-Andre & Miller Expires October 6, 2003 [Page 42] Internet-Draft XMPP Core April 2003 7.5.1 Overview Info/Query, or IQ, is a request-response mechanism, similar in some ways to HTTP [24]. IQ stanzas in the 'jabber:client' or 'jabber:server' namespace enable an entity to make a request of, and receive a response from, another entity. The data content of the request and response is defined by the namespace declaration of a direct child element of the IQ element, and the interaction is tracked by the requesting entity through use of the 'id' attribute, which responding entities SHOULD return in any response. Most IQ interactions follow a common pattern of structured data exchange such as get/result or set/result (although an error may be returned in response to a request if appropriate): Requesting Responding Entity Entity ---------- ---------- | | | | | ------------------------> | | | | | | <------------------------ | | | | | | ------------------------> | | | | | | <------------------------ | | | An entity that receives an IQ request of type 'get' or 'set' MUST reply with an IQ response of type 'result' or 'error' (which response MUST preserve the 'id' attribute of the request). An entity that receives a stanza of type 'result' or 'error' MUST NOT respond to the stanza by sending a further IQ response of type 'result' or 'error'; however, as shown above, the requesting entity MAY send another request (e.g., an IQ of type 'set' in order to provide required information discovered through a get/result pair). 7.5.2 Types of IQ The 'type' attribute of an IQ stanza is REQUIRED. The 'type' attribute specifies a distinct step within a request-response interaction. The value SHOULD be one of the following (all other values MAY be ignored): Saint-Andre & Miller Expires October 6, 2003 [Page 43] Internet-Draft XMPP Core April 2003 o get -- The stanza is a request for information. o set -- The stanza provides required data, sets new values, or replaces existing values. o result -- The stanza is a response to a successful get or set request. o error -- An error has occurred regarding processing or delivery of a previously-sent get or set. 7.5.3 Children As described under extended namespaces (Section 7.6), an IQ stanza MAY contain any properly-namespaced child element as long as the namespace name is not "jabber:client", "jabber"server", or "http:// etherx.jabber.org/streams", and as long as the element name does not match that of one of the core data elements, stream elements, or defined children thereof. However, an IQ stanza contains no children in the 'jabber:client' or 'jabber:server' namespace since it is a vessel for XML in another namespace. If the IQ stanza is of type "error", it MUST include an child; for details, see Section 7.7. 7.6 Extended Namespaces While the core data elements in the "jabber:client" or "jabber:server" namespace (along with their attributes and child elements) provide a basic level of functionality for messaging and presence, XMPP uses XML namespaces to extend the core data elements for the purpose of providing additional functionality. Thus a message, presence, or IQ stanza MAY house one or more optional child elements containing content that extends the meaning of the message (e.g., an encrypted form of the message body). This child element MAY be any element (other than the core data elements, stream elements, or defined children thereof). The child element MUST possess an 'xmlns' namespace declaration (other than the stream namespace and the default namespace) that defines all data contained within the child element. Support for any given extended namespace is OPTIONAL on the part of any implementation. If an entity does not understand such a namespace, it MUST ignore the associated XML data (if the stanza is being routed on to another entity, ignore means "pass it on untouched"). If an entity receives a message or presence stanza that contains XML data in an extended namespace it does not understand, Saint-Andre & Miller Expires October 6, 2003 [Page 44] Internet-Draft XMPP Core April 2003 the portion of the stanza that is in the unknown namespace SHOULD be ignored. If an entity receives a message stanza without a element but containing only a child element bound by a namespace it does not understand, it MUST ignore the entire stanza. If an entity receives an IQ stanza in a namespace it does not understand, the entity SHOULD return an IQ stanza of type "error" with an error condition of . 7.7 Stanza Errors As defined below, stanza-related errors are handled in a manner similar to stream errors (Section 4.5). 7.7.1 Rules The following rules apply to stanza-related errors: o A stanza of type "error" MUST contain an child element. o The receiving or processing entity that returns an error to the sending entity SHOULD include the original XML sent along with the element and its children so that the sender can inspect and if necessary correct the XML before re-sending. o An entity that receives a message stanza of type 'error' MUST NOT respond to the stanza by sending a further message stanza of type 'error'; this helps to prevent looping. o An child MUST NOT be included if the stanza type is something other than "error". 7.7.2 Syntax The syntax for stanza-related errors is as follows: [include sender XML here] The stanza name is one of message, presence, or iq. The value of the 'class' attribute must be one of the following: Saint-Andre & Miller Expires October 6, 2003 [Page 45] Internet-Draft XMPP Core April 2003 o access -- the condition relates to access rights, permissions, or authorization o address -- the condition relates to the JID or domain to which the stanza was addressed o app -- the condition is particular to an application and is specified in a namespace other than 'urn:ietf:params:xml:ns:xmpp-stanzas' o format -- the condition relates to XML format or structure o recipient -- the condition relates to the state or capabilities of the recipient (which may be the server) o server -- the condition relates to the internal state of the server The element MUST contain a child element that specifies a particular stanza-related error condition, as defined in the next section. (Note: the XML namespace name 'urn:ietf:params:xml:ns:xmpp-stanzas' that scopes the element adheres to the format defined in The IETF XML Registry [15].) 7.7.3 Conditions The following stanza-related error conditions are defined: o -- the sender has sent XML that is malformed or cannot be processed (e.g., a client-generated stanza includes a 'from' address, or an IQ stanza includes an unrecognized value of the 'type' attribute); the associated class is "format". o -- the feature requested is not implemented by the recipient or server and therefore cannot be processed; the associated class is "recipient". o -- the stanza is understood but the action is forbidden; the associated class is "access". o -- the server could not process the stanza because of a misconfiguration or an otherwise-undefined internal server error; the associated class is "server". o -- the value of the 'to' attribute in the sender's stanza does not adhere to the syntax defined in Addressing (Section 3); the associated class is "address". Saint-Andre & Miller Expires October 6, 2003 [Page 46] Internet-Draft XMPP Core April 2003 o -- the value of the 'to' attribute in the sender's stanza does not correspond to a Jabber ID on the user's server or a remote server; the associated class is "address". o -- the action is not permitted when attempted by the sender; the associated class is "access". o -- the specific recipient requested is currently unavailable; the associated class is "recipient". o -- the user is not authorized to access the requested service because registration is required; the associated class is "access". o -- a remote server or service specified as part or all of the JID of the intended recipient does not exist; the associated class is "address". o -- a remote server or service specified as part or all of the JID of the intended recipient could not be contacted within a reasonable amount of time; the associated class is "server". o -- the service requested is currently unavailable on the server; the associated class is "server". 7.7.4 Extensibility If desired, an XMPP application MAY provide custom error information; this MUST be contained in a properly-namespaced child of the element (i.e., the namespace name MUST NOT be one of namespace names defined herein). Saint-Andre & Miller Expires October 6, 2003 [Page 47] Internet-Draft XMPP Core April 2003 8. XML Usage within XMPP 8.1 Restrictions XMPP is a simplified and specialized protocol for streaming XML elements in order to exchange messages and presence information in close to real time. Because XMPP does not require the parsing of arbitrary and complete XML documents, there is no requirement that XMPP must support the full XML specification [1]. In particular, the following restrictions apply: With regard to XML generation, an XMPP implementation MUST NOT inject into an XML stream any of the following: o comments (as defined in Section 2.5 of the XML specification [1]) o processing instructions (Section 2.6) o internal or external DTD subsets (Section 2.8) o internal or external entity references (Section 4.2) with the exception of predefined entities (Section 4.6) With regard to XML processing, if an XMPP implementation receives such restricted XML data, it MUST ignore the data. 8.2 Namespaces XML Namespaces [14] are used within all XMPP-compliant XML to create strict boundaries of data ownership. The basic function of namespaces is to separate different vocabularies of XML elements that are structurally mixed together. Ensuring that XMPP-compliant XML is namespace-aware enables any XML to be structurally mixed with any data element within XMPP. Additionally, XMPP is more strict about namespace prefixes than the XML namespace specification requires. 8.3 Validation A server is not responsible for validating the XML elements forwarded to a client or another server; an implementation MAY choose to provide only validated data elements but is NOT REQUIRED to do so. Clients SHOULD NOT rely on the ability to send data which does not conform to the schemas, and SHOULD ignore any non-conformant elements or attributes on the incoming XML stream. Validation of XML streams and stanzas is NOT REQUIRED or recommended, and schemas are included herein for descriptive purposes only. Saint-Andre & Miller Expires October 6, 2003 [Page 48] Internet-Draft XMPP Core April 2003 8.4 Character Encodings Software implementing XML streams MUST support the UTF-8 (RFC 2279 [25]) and UTF-16 (RFC 2781 [26]) transformations of Universal Character Set (ISO/IEC 10646-1 [27]) characters. Software MUST NOT attempt to use any other encoding for transmitted data. The encodings of the transmitted and received streams are independent. Software MAY select either UTF-8 or UTF-16 for the transmitted stream, and SHOULD deduce the encoding of the received stream as described in the XML specification [1]. For historical reasons, existing implementations MAY support UTF-8 only. 8.5 Inclusion of Text Declaration An application MAY send a text declaration. Applications MUST follow the rules in the XML specification [1] regarding the circumstances under which a text declaration is included. Saint-Andre & Miller Expires October 6, 2003 [Page 49] Internet-Draft XMPP Core April 2003 9. IANA Considerations 9.1 XML Namespace Name for Stream Errors A URN sub-namespace for XMPP stream error tags is defined as follows. URI: urn:ietf:params:xml:ns:xmpp-streams Specification: [RFCXXXX] Description: This is the XML namespace name for XMPP stream errors as defined by [RFCXXXX]. Registrant Contact: IETF, XMPP Working Group, 9.2 XML Namespace Name for Stanza Errors A URN sub-namespace for XMPP stanza error tags is defined as follows. URI: urn:ietf:params:xml:ns:xmpp-stanzas Specification: [RFCXXXX] Description: This is the XML namespace name for XMPP stanza errors as defined by [RFCXXXX]. Registrant Contact: IETF, XMPP Working Group, 9.3 Existing Registrations The IANA registers "xmpp" as a GSSAPI [29] service name, as specified in Section 6.1.3. Additionally, the IANA registers "jabber-client" and "jabber-server" as keywords for TCP ports 5222 and 5269 respectively. Saint-Andre & Miller Expires October 6, 2003 [Page 50] Internet-Draft XMPP Core April 2003 10. Internationalization Considerations Usage of the 'xml:lang' attribute is described above. If a client includes an 'xml:lang' attribute in a stanza, a server MUST NOT modify or delete it. Saint-Andre & Miller Expires October 6, 2003 [Page 51] Internet-Draft XMPP Core April 2003 11. Security Considerations 11.1 High Security For the purposes of XMPP communications (client-to-server and server-to-server), the term "high security" refers to the use of security technologies that provide both mutual authentication and integrity-checking; in particular, when using certificate-based authentication to provide high security, a chain-of-trust must be established out-of-band (i.e., self-signed certificates are not sufficient). Implementations MUST support high security. Service provisioning SHOULD use high security, subject to local security policies. 11.2 Client-to-Server Communications The TLS protocol for encrypting XML streams (defined under Section 5) provides a reliable mechanism for helping to ensure the confidentiality and data integrity of data exchanged between two entities. The SASL protocol for authenticating XML streams (defined under Section 6.1) provides a reliable mechanism for validating that a client connecting to a server is who it claims to be. The IP address and method of access of clients MUST NOT be made available by a server, nor are any connections other than the original server connection required. This helps protect the client's server from direct attack or identification by third parties. End-to-end encryption of message bodies and presence status information MAY be effected through use of the methods defined in End-to-End Object Encryption in XMPP [28]. 11.3 Server-to-Server Communications A compliant implementation MUST support both TLS and SASL for inter-domain communications. For historical reasons, a compliant implementation SHOULD also support the lower-security Dialback Protocol (Section 6.2), which provides a mechanism for helping to prevent the spoofing of domains. Because service provisioning is a matter of policy, it is OPTIONAL for any given domain to communicate with other domains, and server-to-server communications MAY be disabled by the administrator of any given deployment. If a particular domain enables inter-domain communications, it SHOULD enable high security. In the absence of Saint-Andre & Miller Expires October 6, 2003 [Page 52] Internet-Draft XMPP Core April 2003 high security, a domain MAY use server dialback for inter-domain communications. 11.4 Firewalls Communications using XMPP normally occur over TCP sockets on port 5222 (client-to-server) or port 5269 (server-to-server), as registered with the IANA [6]. Use of these well-known ports allows administrators to easily enable or disable XMPP activity through existing and commonly-deployed firewalls. 11.5 Mandatory to Implement Technologies At a minimum, all implementations MUST support the following mechanisms: for authentication: the SASL DIGEST-MD5 mechanism for confidentiality: TLS (using the TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher) for both: TLS (using the TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher supporting client-side certificates) Saint-Andre & Miller Expires October 6, 2003 [Page 53] Internet-Draft XMPP Core April 2003 References [1] World Wide Web Consortium, "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C xml, October 2000, . [2] Saint-Andre, P. and J. Miller, "XMPP Instant Messaging (draft-ietf-xmpp-im-08, work in progress)", April 2003. [3] Day, M., Aggarwal, S., Mohr, G. and J. Vincent, "A Model for Presence and Instant Messaging", RFC 2779, February 2000, . [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [5] University of Southern California, "Transmission Control Protocol", RFC 793, September 1981, . [6] Internet Assigned Numbers Authority, "Internet Assigned Numbers Authority", January 1998, . [7] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998, . [8] Harrenstien, K., Stahl, M. and E. Feinler, "DoD Internet host table specification", RFC 952, October 1985. [9] Braden, R., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, October 1989. [10] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile for Internationalized Domain Names (draft-ietf-idn-nameprep-11, work in progress)", June 2002. [11] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ("stringprep")", RFC 3454, December 2002. [12] Saint-Andre, P. and J. Hildebrand, "Nodeprep: A Stringprep Profile for Node Identifiers in XMPP (draft-ietf-xmpp-nodeprep-01, work in progress)", February 2003. [13] Saint-Andre, P. and J. Hildebrand, "Resourceprep: A Stringprep Profile for Resource Identifiers in XMPP (draft-ietf-xmpp-resourceprep-01, work in progress)", February Saint-Andre & Miller Expires October 6, 2003 [Page 54] Internet-Draft XMPP Core April 2003 2003. [14] World Wide Web Consortium, "Namespaces in XML", W3C xml-names, January 1999, . [15] Mealling, M., "The IANA XML Registry", draft-mealling-iana-xmlns-registry-04 (work in progress), June 2002. [16] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [17] Crispin, M., "Internet Message Access Protocol - Version 4rev1", RFC 2060, December 1996. [18] Myers, J. and M. Rose, "Post Office Protocol - Version 3", STD 53, RFC 1939, May 1996. [19] Newman, C. and J. Myers, "ACAP -- Application Configuration Access Protocol", RFC 2244, November 1997. [20] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595, June 1999. [21] Myers, J., "Simple Authentication and Security Layer (SASL)", RFC 2222, October 1997. [22] Alvestrand, H., "Tags for the Identification of Languages", BCP 47, RFC 3066, January 2001. [23] Gulbrandsen, A. and P. Vixie, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2052, October 1996. [24] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [25] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [26] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 10646", RFC 2781, February 2000. [27] International Organization for Standardization, "Information Technology - Universal Multiple-octet coded Character Set (UCS) - Amendment 2: UCS Transformation Format 8 (UTF-8)", ISO Saint-Andre & Miller Expires October 6, 2003 [Page 55] Internet-Draft XMPP Core April 2003 Standard 10646-1 Addendum 2, October 1996. [28] Saint-Andre, P. and J. Hildebrand, "End-to-End Object Encryption in XMPP (draft-ietf-xmpp-e2e-00, work in progress)", February 2003. [29] Linn, J., "Generic Security Service Application Program Interface, Version 2", RFC 2078, January 1997. Authors' Addresses Peter Saint-Andre Jabber Software Foundation EMail: stpeter@jabber.org URI: http://www.jabber.org/people/stpeter.php Jeremie Miller Jabber Software Foundation EMail: jeremie@jabber.org URI: http://www.jabber.org/people/jer.php Saint-Andre & Miller Expires October 6, 2003 [Page 56] Internet-Draft XMPP Core April 2003 Appendix A. XML Schemas The following XML schemas are descriptive, not normative. A.1 Streams namespace Saint-Andre & Miller Expires October 6, 2003 [Page 57] Internet-Draft XMPP Core April 2003 A.2 TLS namespace A.3 SASL namespace Saint-Andre & Miller Expires October 6, 2003 [Page 58] Internet-Draft XMPP Core April 2003 A.4 Dialback namespace Saint-Andre & Miller Expires October 6, 2003 [Page 59] Internet-Draft XMPP Core April 2003 A.5 Client namespace Saint-Andre & Miller Expires October 6, 2003 [Page 60] Internet-Draft XMPP Core April 2003 Saint-Andre & Miller Expires October 6, 2003 [Page 61] Internet-Draft XMPP Core April 2003 Saint-Andre & Miller Expires October 6, 2003 [Page 62] Internet-Draft XMPP Core April 2003 A.6 Server namespace Saint-Andre & Miller Expires October 6, 2003 [Page 64] Internet-Draft XMPP Core April 2003 Saint-Andre & Miller Expires October 6, 2003 [Page 65] Internet-Draft XMPP Core April 2003 A.7 Stream error namespace Saint-Andre & Miller Expires October 6, 2003 [Page 66] Internet-Draft XMPP Core April 2003 A.8 Stanza error namespace Saint-Andre & Miller Expires October 6, 2003 [Page 68] Internet-Draft XMPP Core April 2003 Appendix B. Revision History Note to RFC editor: please remove this entire appendix, and the corresponding entries in the table of contents, prior to publication. B.1 Changes from draft-ietf-xmpp-core-07 o Made several small editorial changes. B.2 Changes from draft-ietf-xmpp-core-06 o Added text regarding certificate validation in TLS negotiation per list discussion. o Clarified nature of XML restrictions per discussion with W3C, and moved XML Restrictions subsection under "XML Usage within XMPP". o Further clarified that XML streams are unidirectional. o Changed stream error and stanza error namespace names to conform to the format defined in The IETF XML Registry [15]. o Removed note to RFC editor regarding provisional namespace names. B.3 Changes from draft-ietf-xmpp-core-05 o Added as a stream error condition. o Adjusted security considerations per discussion at IETF 56 and on list. B.4 Changes from draft-ietf-xmpp-core-04 o Added server-to-server examples for TLS and SASL. o Changed error syntax, rules, and examples based on list discussion. o Added schemas for the TLS, stream error, and stanza error namespaces. o Added note to RFC editor regarding provisional namespace names. o Made numerous small editorial changes and clarified text throughout. Saint-Andre & Miller Expires October 6, 2003 [Page 69] Internet-Draft XMPP Core April 2003 B.5 Changes from draft-ietf-xmpp-core-03 o Clarified rules and procedures for TLS and SASL. o Amplified stream error code syntax per list discussion. o Made numerous small editorial changes. B.6 Changes from draft-ietf-xmpp-core-02 o Added dialback schema. o Removed all DTDs since schemas provide more complete definitions. o Added stream error codes. o Clarified error code "philosophy". B.7 Changes from draft-ietf-xmpp-core-01 o Updated the addressing restrictions per list discussion and added references to the new nodeprep and resourceprep profiles. o Corrected error in Stream Authentication regarding "version='1.0'" flag. o Made numerous small editorial changes. B.8 Changes from draft-ietf-xmpp-core-00 o Added information about TLS from list discussion. o Clarified meaning of "ignore" based on list discussion. o Clarified information about Universal Character Set data and character encodings. o Provided base64-decoded information for examples. o Fixed several errors in the schemas. o Made numerous small editorial fixes. Saint-Andre & Miller Expires October 6, 2003 [Page 70] Internet-Draft XMPP Core April 2003 B.9 Changes from draft-miller-xmpp-core-02 o Brought Streams Authentication section into line with discussion on list and at IETF 55 meeting. o Added information about the optional 'xml:lang' attribute per discussion on list and at IETF 55 meeting. o Specified that validation is neither required nor recommended, and that the formal definitions (DTDs and schemas) are included for descriptive purposes only. o Specified that the response to an IQ stanza of type 'get' or 'set' must be an IQ stanza of type 'result' or 'error'. o Specified that compliant server implementations must process stanzas in order. o Specified that for historical reasons some server implementations may accept 'stream:' as the only valid namespace prefix on the root stream element. o Clarified the difference between 'jabber:client' and 'jabber:server' namespaces, namely, that 'to' and 'from' attributes are required on all stanzas in the latter but not the former. o Fixed typo in Step 9 of the dialback protocol (changed db:result to db:verify). o Removed references to TLS pending list discussion. o Removed the non-normative appendix on OpenPGP usage pending its inclusion in a separate I-D. o Simplified the architecture diagram, removed most references to services, and removed references to the 'jabber:component:*' namespaces. o Noted that XMPP activity respects firewall administration policies. o Further specified the scope and uniqueness of the 'id' attribute in all stanza types and the element in message stanzas. o Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from "host" to "server" and from "node" to "client" (except with regard to definition of the addressing scheme). 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