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PROPOSED STANDARD
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Network Working Group                                   M. Garcia-MartinRequest for Comments: 5364                                  G. CamarilloCategory: Standards Track                                       Ericsson                                                            October 2008Extensible Markup Language (XML) Format Extension for RepresentingCopy Control Attributes in Resource ListsStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Abstract   In certain types of multimedia communications, a Session Initiation   Protocol (SIP) request is distributed to a group of SIP User Agents   (UAs).  The sender sends a single SIP request to a server which   further distributes the request to the group.  This SIP request   contains a list of Uniform Resource Identifiers (URIs), which   identify the recipients of the SIP request.  This URI list is   expressed as a resource list XML document.  This specification   defines an XML extension to the XML resource list format that allows   the sender of the request to qualify a recipient with a copy control   level similar to the copy control level of existing email systems.Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .33.  Overview of Operation  . . . . . . . . . . . . . . . . . . . .34.  Extension to the Resource List Data Format . . . . . . . . . .65.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . .86.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .97.  Carrying URI Lists in SIP  . . . . . . . . . . . . . . . . . .108.  Security Considerations  . . . . . . . . . . . . . . . . . . .119.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .139.1.  Disposition Type Registration  . . . . . . . . . . . . . .139.2.  XML Namespace Registration . . . . . . . . . . . . . . . .139.3.  XML Schema Registration  . . . . . . . . . . . . . . . . .1410. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .1411. References . . . . . . . . . . . . . . . . . . . . . . . . . .1411.1. Normative References . . . . . . . . . . . . . . . . . . .1411.2. Informative References . . . . . . . . . . . . . . . . . .15Garcia-Martin & Camarillo   Standards Track                     [Page 1]

RFC 5364        Copy Control Attribute in Resource Lists    October 20081.  IntroductionRFC 5363 [RFC5363] describes a generic framework for carrying Uniform   Resource Identifier (URI) lists in SIP [RFC3261] messages.   Specifically, the document provides a common framework for specific   implementations of URI-list services, such as conferences initiated   with INVITE requests [RFC5366] or Multiple-recipient MESSAGE requests   [RFC5365].   Common to all URI-list services is the presence of a SIP request that   contains a collection of resources, typically expressed as an XML   resource list [RFC4826].  SIP requests carrying resource lists can   appear either in requests received by the URI-list server, indicating   the list of intended recipients, or in each of the requests that the   URI-list server sends to recipients, indicating the list of   recipients of the same SIP request.   Although the XML resource list [RFC4826] provides a powerful   mechanism for describing a list of resources, there is a need for a   copy control attribute to determine whether a resource is receiving a   SIP request as a primary recipient, a carbon copy, or a blind carbon   copy.  This is similar to common email systems, where the sender can   categorize each recipient as a "to", "cc", or "bcc" recipient.   This document addresses this problem by providing an extension to the   XML resource list [RFC4826] that enables the sender to supply a copy   control attribute that labels each recipient as a "to", "cc", or   "bcc" recipient.  This attribute indicates whether the recipient is   receiving a primary copy of the SIP request, a carbon copy, or a   blind carbon copy.  Additionally, we provide the sender with the   capability of indicating in the URI list that one or more resources   should be anonymized, so that some recipients' URIs are not disclosed   to the other recipients.  Instead, these URIs are replaced with   anonymous URIs.   The remainder of this document is organized as follows:Section 2   introduces the terminology used throughout this specification.Section 3 gives an overview of operation.Section 4 formally defines   an extension to URI lists.  The XML schema definition is provided inSection 5.Section 6 shows examples of the URI lists with the   extensions defined in this document.Section 7 discusses the   implications of carrying URI lists in SIP messages.Garcia-Martin & Camarillo   Standards Track                     [Page 2]

RFC 5364        Copy Control Attribute in Resource Lists    October 20082.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inBCP 14,RFC 2119   [RFC2119] and indicate requirement levels for compliant   implementations.   URI-list service:  SIP application service that receives a SIP      request containing a URI list and sends a similar SIP request to      each URI in the list.   Intended recipient:  The intended final recipient of the request to      be generated by URI-list service.   Copy control:   An attribute assigned by the sender to a URI in an      XML resource list.  Its purpose is to indicate to the recipient      whether he is getting a primary, carbon, or blind carbon copy of      the SIP request.   Recipient list or recipient XML resource list:   An XML resource list      containing the list of intended recipients.  The sender sets this      list in the SIP request he sends to the URI-list server.   Recipient-history list or recipient-history XML resource list:   An      XML resource list containing the visible list of recipients (i.e.,      those non-anonymous non-bcc).  The URI-list server creates this      list, based on the recipient list, and includes it in each of the      SIP requests it sends to each recipient.3.  Overview of Operation   Figure 1 depicts a general overview of the operation of a URI-list   server.  A SIP User Agent Client (UAC) issuer sends a SIP request   (F1) to a URI-list server containing a recipient list.  The URI-list   server generates a SIP request to each recipient, according to the   specific SIP method.  Each of these SIP requests contains a   recipient-history list that indicates the visible list of recipients   of the SIP request.Garcia-Martin & Camarillo   Standards Track                     [Page 3]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008   +--------+        +---------+        +--------+ +--------+ +--------+   |SIP UAC |        | URI-list|        |intended| |intended| |intended|   | issuer |        |  server |        | recip. | | recip. | | recip. |   |        |        |         |        |   1    | |   2    | |   3    |   +--------+        +---------+        +--------+ +--------+ +--------+       |                  |                 |          |          |       | F1 SIP request   |                 |          |          |       |  (recipt. list)  |                 |          |          |       | ---------------->|                 |          |          |       | F2 2xx response  |                 |          |          |       |<---------------- | F3 SIP request  |          |          |       |                  | (recp-hist.list)|          |          |       |                  | --------------->|          |          |       |                  | F4 SIP request  |          |          |       |                  | (recp-hist.list)|          |          |       |                  | -------------------------->|          |       |                  | F5 SIP request  |          |          |       |                  | (recp-hist.list)|          |          |       |                  | ------------------------------------->|       |                  |  F6 200 OK      |          |          |       |                  |<--------------- |          |          |       |                  |  F7 200 OK      |          |          |       |                  |<-------------------------- |          |       |                  |  F8 200 OK      |          |          |       |                  |<------------------------------------- |       |                  |                 |          |          |       |                  |                 |          |          |       |                  |                 |          |          |                      Figure 1: Example of operation   The URI-list mechanism allows a sender to specify multiple targets   for a SIP request by including a recipient XML resource list   [RFC4826] in the body of the SIP request.  This recipient list   includes the target URIs of the SIP request (the actual procedures   are method specific and outside the scope of this document).  Each   target URI may also be marked with a copy control attribute to   indicate the copy level in which the recipient is receiving the SIP   request.  This is achieved by the sender qualifying each URI in the   URI list with a 'copyControl' attribute.  The available values of the   'copyControl' attribute include "to", "cc", and "bcc" (analogous to   email).  This is discussed in greater detail inSection 4.  When the   URI-list server expands the request to each recipient, the URI-list   server includes a recipient-history XML resource list built upon the   recipient list received from the sender.  The recipient-history XML   resource list replaces the recipient list in the SIP requests   generated by the URI-list server towards each recipient.  The URI-   list server copies from the recipient list those targets that areGarcia-Martin & Camarillo   Standards Track                     [Page 4]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008   marked with the "to" and "cc" copy control level, and pastes them in   the recipient-history list.  The URI-list server explicitly excludes   from the recipient-history list those URIs marked with a "bcc" copy   control, although it is able to preserve the address of a "bcc"   tagged URI when it matches the URI of the recipient of the SIP   request (this is described later inSection 4).  When a recipient   receives the SIP request containing the recipient-history XML   resource list, he is able to determine which other visible recipients   are getting a copy of the SIP request, and whether they are marked   with the "to" or "cc" copy control level.  Later, if needed, the   recipient can generate a reply to those visible recipients.   In addition to the 'copyControl' attribute for a URI in an XML   resource list, we define a second boolean attribute called   'anonymize'.  The sender of a SIP request can mark a URI in a   recipient XML resource list with the 'anonymize' attribute to   indicate the URI-list server that the URI marked with that attribute   is to be replaced with an anonymous URI in the recipient-history XML   resource list.  This provides knowledge to the recipients of a SIP   request of the number of additional visible recipients whose URIs   have not been disclosed.   There are cases when the sender marks several URIs with the   'anonymize' attribute.  The URI-list server can group the anonymized   URIs in a single anonymized URI within its copy control level, and   provide a count of the number of anonymized URIs.  To support this   scenario, we define a new 'count' attribute to a URI in the   recipient-history XML resource list.  It is expected that the 'count'   attribute is only used with anonymous URIs, although syntactically it   is possible to add a 'count' attribute to any URI in any XML resource   list.   Initially, it may be thought that the 'anonymize' attribute overlaps   with the "bcc" value of the 'copyControl' attribute.  However, there   are differences between them.  If the sender qualifies a URI with a   'copyControl' attribute of "bcc" in the recipient XML resource list,   the URI-list server will typically remove that URI from the   recipient-history XML resource list (unless the URI-list server   decides to preserve a "bcc" marked URI when that URI is itself the   recipient of the SIP request).  Recipients of the SIP request will   not notice that one or more extra "bcc" URIs also received the   request.  However, if the sender qualifies a URI with the 'anonymize'   attribute in the recipient XML resource list, the URI-list server   will replace the URI with an anonymous one in the recipient-history   list.  Recipients of the SIP request will notice that there have been   one or more additional recipients of the same request, but their URIs   are not disclosed.Garcia-Martin & Camarillo   Standards Track                     [Page 5]

RFC 5364        Copy Control Attribute in Resource Lists    October 20084.  Extension to the Resource List Data Format   This document defines an extension to the XML resource list data   format [RFC4826] that allows the sender to indicate a copy control   attribute that qualifies a recipient with a copy control level.  We   define a new 'copyControl' attribute to the <entry> element of the   resource list document format [RFC4826].  The 'copyControl' attribute   has similar semantics to the type of destination address in email   systems.  It can take the values "to", "cc", and "bcc".  A "to" value   of the 'copyControl' attribute indicates that the resource is   considered a primary recipient of the SIP request.  A "cc" value   indicates that the resource receives a carbon copy of the SIP   request.  A "bcc" value indicates that the resource receives a blind   carbon copy of the SIP request (i.e., this URI is not disclosed to   other recipients of the SIP request).  The default 'copyControl'   value is "bcc".  That is, the absence of a 'copyControl' attribute   MUST be treated as if the 'copyControl' was set to "bcc".   When creating a recipient-history list, URI-list servers use "bcc"   'copyControl' attributes to route SIP requests.  In addition, URI-   list servers behave similarly to email systems [RFC2822] with respect   to the treatment of these URIs marked with a "bcc" copy control,   because they have two ways of treating "bcc" marked URIs.  URI-list   servers MUST treat these "bcc" marked URIs in either of the following   two ways:   o  URI-list servers MUST remove all URIs marked with a "bcc" copy      control in recipient-history lists.  This mechanism allows URI-      list servers to send the same recipient-history list to each      recipient of the SIP request.  However, recipients who are tagged      with "bcc" values are not explicitly informed about it.   o  URI-list servers MUST preserve with a "bcc" copy control in the      recipient-history list the URI that identifies the recipient (if      any) and MUST remove the remaining URIs marked with a "bcc" copy      control.  Consequently, each recipient receives a different      recipient-history list.  However, recipients who have been marked      with a "bcc" copy control are explicitly informed about it.   Implementations that are able to receive recipient-history lists must   pay attention to the contents of the list.  If the recipient's URI is   not included in the recipient-history list or if it is included but   tagged with a "bcc" copy control, then implementations SHOULD prevent   the user from replying to all the recipients of the SIP request.   This would allow the non-blind recipients to notice the existence of   blind recipients of the SIP request.Garcia-Martin & Camarillo   Standards Track                     [Page 6]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008   A new 'anonymize' attribute can be included in a <entry> element of   the resource list document format [RFC4826].  If set to a "true"   value, it provides an indication to the URI-list server for not   disclosing the URI itself in a URI list sent to the recipient, but   instead to anonymize the URI (i.e., making it bogus in the recipient-   history XML resource list).  URI-list servers can use URIs tagged   with the 'anonymize' attribute for routing SIP requests, but MUST   convert them to the SIP URI "sip:anonymous@anonymous.invalid" in   recipient-history lists.  The default value of the 'anonymize'   attribute is "false".   There are occasions where the URI-list server encounters the same URI   entry duplicated in a resource list, where duplicated URI entries are   tagged with the same or different values of the 'copyControl'   attribute.  There are no reasonable usages that justify duplicated   URIs in resource lists; thus, this is considered an error.  URI-list   servers should not send duplicated copies of the same SIP request to   the same intended recipient.  In case the URI-list server encounters   the same URI entry duplicated in a resource list, it should send at   most a single copy of the request to that intended recipient.  For   each set of duplicated URI entries, the URI-list server MUST select   the highest precedence value of the 'copyControl' attribute for the   same intended recipient.  The order of precedence of the values of   the 'copyControl' attribute is: "to", "cc", and "bcc".  Once the URI-   list server has selected a value for the 'copyControl' attribute of   an intended recipient, the URI-list server can continue processing   the request.   Processing of URIs tagged with a 'copyControl' attribute set to a   "bcc" value has higher precedence over the 'anonymize' attribute.   Thus, if the 'copyControl' of a URI is set to "bcc", the URI-list   server MUST remove that URI from the recipient-history list, and the   'anonymize' attribute will be ignored.  Therefore, the 'anonymize'   attribute is only useful for those URIs tagged with a 'copyControl'   of "to" or "cc".   A new 'count' attribute can be also included in an <entry> element of   the resource list document format [RFC4826].  It provides the number   of equal URIs.  Typically, recipient lists created by UACs will not   have equal (or duplicate) URI entries; thus, it is not expected to   contain URIs tagged with 'count' attributes.  However, recipient-   history lists can contain duplicated anonymized URIs; therefore, it   is expected that recipient-history lists will contain 'count'   attributes.  The default value of the 'count' attribute is "1".Garcia-Martin & Camarillo   Standards Track                     [Page 7]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008   The 'copyControl', 'anonymize', and 'count' attributes SHOULD be   included as modifiers of any of the child elements included in the   <list> element of a resource list (e.g., attribute of the <entry> or   <external> elements).Section 5 describes the format of the 'copyControl', 'anonymize', and   'count' attributes.  Implementations according to this specification   MUST support this XML schema.   Implementations that receive recipient-history lists must pay   attention to the contents of the list.  If the recipient's URI is not   included in recipient-history list or if it is included but tagged   with a "bcc" copy control, then they SHOULD prevent the user from   replying to all the recipients of the SIP request.  This would allow   the non-blind recipients to notice the existence of blind recipients   in the original SIP request.5.  XML Schema   <?xml version="1.0" encoding="UTF-8"?>   <xs:schema targetNamespace="urn:ietf:params:xml:ns:copycontrol"       xmlns="urn:ietf:params:xml:ns:copycontrol"       xmlns:rls="urn:ietf:params:xml:ns:resource-lists"       xmlns:xs="http://www.w3.org/2001/XMLSchema"       elementFormDefault="qualified"       attributeFormDefault="unqualified">       <xs:annotation>         <xs:documentation xml:lang="en">            Adds the copyControl, anonymize, and count attributes            to URIs included in a resource list.         </xs:documentation>       </xs:annotation>      <xs:import namespace="urn:ietf:params:xml:ns:resource-lists"            schemaLocation="urn:ietf:params:xml:schema:resource-lists"/>       <xs:attribute name="copyControl">          <xs:simpleType>             <xs:restriction base="xs:string">                <xs:enumeration value="to"/>                <xs:enumeration value="cc"/>                <xs:enumeration value="bcc"/>             </xs:restriction>          </xs:simpleType>       </xs:attribute>Garcia-Martin & Camarillo   Standards Track                     [Page 8]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008      <xs:attribute name="anonymize" type="xs:boolean" default="false"/>      <xs:attribute name="count" type="xs:nonNegativeInteger"                                 default="1"/>   </xs:schema>     Figure 2: XML schema of the extension to the resource list format6.  Examples   This section shows two examples of URI lists that can be included in   SIP requests.  The first example in Figure 3 shows a recipient list   that the UAC sends to the URI-list server.  This corresponds to a   list that will be included in the flow F2 in Figure 1.  The recipient   list contains a flat list according to the resource list data format   specified inRFC 4826 [RFC4826].  Each resource indicates the copy   control of a resource with a 'copyControl' attribute.  Some of the   resources are also marked with the 'anonymize' attribute.  This   provides an indication to the URI-list service for not disclosing   their URIs in a recipient-history list.  The last two <entry>   elements are marked with a 'copyControl' attribute of "bcc".  This   provides an indication to the URI-list server for removing these URIs   in the recipient-history list.   <?xml version="1.0" encoding="UTF-8"?>   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"             xmlns:cp="urn:ietf:params:xml:ns:copycontrol">     <list>       <entry uri="sip:bill@example.com" cp:copyControl="to" />       <entry uri="sip:randy@example.net" cp:copyControl="to"                                          cp:anonymize="true"/>       <entry uri="sip:eddy@example.com" cp:copyControl="to"                                         cp:anonymize="true"/>       <entry uri="sip:joe@example.org" cp:copyControl="cc" />       <entry uri="sip:carol@example.net" cp:copyControl="cc"                                          cp:anonymize="true"/>       <entry uri="sip:ted@example.net" cp:copyControl="bcc" />       <entry uri="sip:andy@example.com" cp:copyControl="bcc" />     </list>   </resource-lists>     Figure 3: Recipient list sent from the UAC to the URI-list server   Upon receipt of the SIP request containing the recipient list of   Figure 3, the URI-list server creates a SIP request to each of the   URIs listed in the recipient list (so, in our example, it creates 7   SIP requests).  The URI-list server processes the recipient list and   creates a recipient-history list that is included in each of theGarcia-Martin & Camarillo   Standards Track                     [Page 9]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008   outgoing SIP requests.  The process is as follows: the URI-list   server creates a new recipient-history list, based on the recipient   list, but with changes.  First, it copies all the URIs (<entry>   elements) marked with the "to" or "cc" 'copyControl' attributes,   which do not contain an 'anonymize' attribute (or when the   'anonymize' attribute is set to "false").  Then all the URIs marked   with a 'copyControl' attribute set to "to" and 'anonymize' attribute   set to "true" are replaced with the SIP anonymous URI   "sip:anonymous@anonymous.invalid".  In this entry, the URI-list   server also adds the original value of the 'copyControl' attribute   ("to" in our example), and it adds a 'count' attribute containing the   number of anonymous entries in this group ("2" in our example).  Then   the URI-list server does the same operation to the URIs tagged with   the 'copyControl' attribute set to "cc" and 'anonymize' attribute set   to "true", adding also the 'count' attribute containing the number of   anonymous attributes in this group ("1" in the example).  Last, the   URI-list server removes all URIs marked with the "bcc" 'copyControl'   attribute.  The resulting recipient-history list is shown in   Figure 4.   <?xml version="1.0" encoding="UTF-8"?>   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"             xmlns:cp="urn:ietf:params:xml:ns:copycontrol">     <list>       <entry uri="sip:bill@example.com" cp:copyControl="to" />       <entry uri="sip:anonymous@anonymous.invalid" cp:copyControl="to"                                                    cp:count="2"/>       <entry uri="sip:joe@example.org" cp:copyControl="cc" />       <entry uri="sip:anonymous@anonymous.invalid" cp:copyControl="cc"                                                    cp:count="1"/>     </list>   </resource-lists>     Figure 4: Recipient-history list sent from the URI-list server to                              each recipient7.  Carrying URI Lists in SIP   A SIP UAC (User Agent Client) that composes a SIP request can include   a URI list with the extensions specified in this document to indicate   the list of intended recipients.  On doing so, as specified inRFC5363 [RFC5363], the UAC adds a Content-Disposition [RFC2183] header   field set to the value 'recipient-list'.  Typically UACs send these   'recipient-list' bodies to URI-list services (this corresponds to   flow F1 in Figure 1).  A body whose Content-Disposition type is   'recipient-list' contains a URI list that includes the intended   recipients of the SIP request, something known throughout thisGarcia-Martin & Camarillo   Standards Track                    [Page 10]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008   document as a recipient list.  The <entry> element in the URI list   MAY also include a 'copyControl' and 'anonymize' attributes, as   specified inSection 4.   To be able to inform intended recipients of who else is receiving a   copy of the SIP request, we define a new mail disposition type to be   included in a Content-Disposition [RFC2183] header field of a SIP   request.  The value of this new disposition type is 'recipient-list-   history' and its purpose is to indicate a list of recipients that a   SIP request was sent to, something known throughout this document as   a recipient-history list.  A body whose Content-Disposition type is   'recipient-list-history' contains a URI list with the visible   (including anonymized) recipients of the SIP request.  The <entry>   element in the URI list MAY also include a 'copyControl' and 'count'   attributes, as specified inSection 4.   On sending a SIP request that contains a recipient-history list, if   the intended recipient does not support this specification, the SIP   request should not fail.  In order to ensure successful receipt of   the SIP requests that include 'recipient-list-history' bodies, User   Agents (such as URI-list servers) that build SIP requests with the   Content-Disposition header field set to 'recipient-list-history'   SHOULD add a "handling" parameter [RFC3204] set to "optional".   Otherwise, the SIP request could fail and never be received by the   intended recipient.   Even though "Message Body Handling in SIP" [SIP_BODY] mandates   support for multipart bodies, legacy recipients may not support them.   In such a case, if the request sent by the relay to the recipient   needs to contain another body (e.g., a MESSAGE request carrying a   message in its body), the relay will not be able to use this   extension because the recipient would not be able to process a   multipart body with the original body plus the 'recipient-list-   history' body.8.  Security ConsiderationsRFC 5363 [RFC5363] discusses issues related to SIP URI-list services.   Implementations of this specification MUST follow the security-   related rules inRFC 5363 [RFC5363].  These rules include opt-in   lists and mandatory authentication and authorization of clients.   User Agent Clients SHOULD NOT hand SIP requests containing URI-list   services to unauthenticated and untrusted parties.  This is to avoid   man-in-the-middle attacks or acquiring URI lists for performing spam   attacks.Garcia-Martin & Camarillo   Standards Track                    [Page 11]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008   URI lists may contain private information, such as SIP URIs.  It is   therefore not desirable that these URI lists are known by third   parties.  Eavesdroppers are able to watch URI lists contained in SIP   requests unless the SIP message is sent over a secured channel, by   using any of the available SIP mechanisms, such as Transport Layer   Security (TLS) [RFC4346], or unless the URI-list body itself is   encrypted with, e.g., S/MIME [RFC3851].  Therefore, it is RECOMMENDED   that URI-list bodies are encrypted with S/MIME [RFC3851] or that the   SIP request is encrypted with TLS [RFC4346] or any other suitable   encryption mechanism.   Note that this URI list does not indicate the actual participants in   the session.  It indicates only the URIs invited and that might   accept the request.  It does not assert that these parties actually   exist, that they are reachable at the given URI, or that they have   accepted the invitation.  No inferences about billing should be made   from this information.  It is subject to spoofing by loading the list   with falsified content.   Issuers of SIP request use the "bcc" copy control attribute described   inSection 4 to facilitate sending SIP requests to recipients without   revealing the URIs of one or more of the other recipients.   Mishandling this use of "bcc" copy control has implications for   confidential information that might be revealed, which could   eventually lead to security problems through knowledge of even the   existence of a particular URI.  For example, if using the first   method described inSection 4, where the "bcc" tagged URIs are   removed from the recipient-history list, blind recipients have no   explicit indication that they have been sent a blind copy of the SIP   request, except insofar as their URI does not appear in the   recipient-history list.  Because of this, one of the blind URIs could   potentially send a reply to all of the shown recipients and   accidentally reveal that the message went to the blind recipient.   When the second method fromSection 4 is used, the blind recipient's   address appears in the recipient-history list of a separate copy of   the list.  If the "bcc" tagged URI sent contains all of the "bcc"   tagged URIs, all of the "bcc" recipients will be seen by each "bcc"   recipient.  Even if a separate message is sent to each "bcc"   recipient with only the individual's URI, implementations still need   to be careful to process replies to the message as perSection 4 so   as not to accidentally reveal the blind recipient to other   recipients.Garcia-Martin & Camarillo   Standards Track                    [Page 12]

RFC 5364        Copy Control Attribute in Resource Lists    October 20089.  IANA Considerations   IANA has made registrations according to the following subsections: a   new disposition type, a new XML namespace, and a new XML schema.9.1.  Disposition Type RegistrationSection 7 defines a new 'recipient-list-history' value of the Mail   Content Disposition Values registry.  This value has been registered   in the IANA registry of Mail Content Disposition Values with the   following registration data:   +------------------------+------------------------------+-----------+   | Name                   | Description                  | Reference |   +------------------------+------------------------------+-----------+   | recipient-list-history | the body contains a list of  | [RFC5364] |   |                        | URIs that indicates the      |           |   |                        | recipients of the request    |           |   +------------------------+------------------------------+-----------+    Table 1: Registration of the 'recipient-list-history' Mail Content                             Disposition Value9.2.  XML Namespace Registration   This section registers a new XML namespace in the IANA XML registry,   as per the guidelines inRFC 3688 [RFC3688].   URI: The URI for this namespace is urn:ietf:params:xml:ns:copycontrol   Registrant Contact: IETF SIPPING working group (sipping@ietf.org),   Miguel Garcia-Martin (miguel.a.garcia@ericsson.com).   XML:         BEGIN         <?xml version="1.0"?>         <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"           "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">         <html xmlns="http://www.w3.org/1999/xhtml">         <head>           <meta http-equiv="content-type"              content="text/html;charset=iso-8859-1"/>           <title>Copy Control Namespace</title>         </head>         <body>           <h1>Namespace for the Copy Control Attribute Extension           in Resource Lists</h1>Garcia-Martin & Camarillo   Standards Track                    [Page 13]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008           <h2>urn:ietf:params:xml:ns:copycontrol</h2>           <p>See <a href="http://www.rfc-editor.org/rfc/rfc5364.txt">RFC5364</a>.</p>         </body>         </html>         END9.3.  XML Schema Registration   This section registers a new XML schema in the IANA XML registry per   the procedures inRFC 3688 [RFC3688].   URI: urn:ietf:params:xml:schema:copycontrol   Registrant Contact: IETF SIPPING working group (sipping@ietf.org),   Miguel Garcia-Martin (miguel.a.garcia@ericsson.com).   The XML for this schema can be found as the sole content ofSection 5.10.  Acknowledgments   Thanks to Dean Willis, Jari Urpalainen, Pekka Kuure, Atsushi Sato,   Brian Rosen, Mary Barnes, James Polk, Brian E. Carpenter, and Chris   Newman for reviewing this document and providing helpful comments.11.  References11.1.  Normative References   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2183]   Troost, R., Dorner, S., and K. Moore, "Communicating               Presentation Information in Internet Messages: The               Content-Disposition Header Field",RFC 2183, August 1997.   [RFC3204]   Zimmerer, E., Peterson, J., Vemuri, A., Ong, L., Audet,               F., Watson, M., and M. Zonoun, "MIME media types for ISUP               and QSIG Objects",RFC 3204, December 2001.   [RFC3261]   Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,               A., Peterson, J., Sparks, R., Handley, M., and E.               Schooler, "SIP: Session Initiation Protocol",RFC 3261,               June 2002.   [RFC3688]   Mealling, M., "The IETF XML Registry",BCP 81,RFC 3688,               January 2004.Garcia-Martin & Camarillo   Standards Track                    [Page 14]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008   [RFC3851]   Ramsdell, B., "Secure/Multipurpose Internet Mail               Extensions (S/MIME) Version 3.1 Message Specification",RFC 3851, July 2004.   [RFC4346]   Dierks, T. and E. Rescorla, "The Transport Layer Security               (TLS) Protocol Version 1.1",RFC 4346, April 2006.   [RFC4826]   Rosenberg, J., "Extensible Markup Language (XML) Formats               for Representing Resource Lists",RFC 4826, May 2007.   [RFC5363]   Camarillo, G. and A.B. Roach, "Framework and Security               Considerations for Session Initiation Protocol (SIP) URI-               List Services",RFC 5363, October 2008.11.2.  Informative References   [RFC2822]   Resnick, P., "Internet Message Format",RFC 2822,               April 2001.   [RFC5366]   Camarillo, G. and A. Johnston, "Conference Establishment               Using Request-Contained Lists in the Session Initiation               Protocol (SIP)",RFC 5366, October 2008.   [RFC5365]   Garcia-Martin, M. and G. Camarillo, "Multiple-Recipient               MESSAGE Requests in the Session Initiation Protocol               (SIP)",RFC 5365, October 2008.   [SIP_BODY]  Camarillo, G., "Message Body Handling in the Session               Initiation Protocol (SIP)", Work in Progress,               August 2008.Garcia-Martin & Camarillo   Standards Track                    [Page 15]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008Authors' Addresses   Miguel A. Garcia-Martin   Ericsson   Via de los Poblados 13   Madrid  28033   Spain   EMail: miguel.a.garcia@ericsson.com   Gonzalo Camarillo   Ericsson   Hirsalantie 11   Jorvas  02420   Finland   EMail: Gonzalo.Camarillo@ericsson.comGarcia-Martin & Camarillo   Standards Track                    [Page 16]

RFC 5364        Copy Control Attribute in Resource Lists    October 2008Full Copyright Statement   Copyright (C) The IETF Trust (2008).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Garcia-Martin & Camarillo   Standards Track                    [Page 17]

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