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Network Working Group                                            B. WeisRequest for Comments: 5374                                 Cisco SystemsCategory: Standards Track                                       G. Gross                                           Secure Multicast Networks LLC                                                             D. Ignjatic                                                                 Polycom                                                           November 2008Multicast Extensions to theSecurity Architecture for the Internet ProtocolStatus 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.Copyright Notice   Copyright (c) 2008 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document.   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.Abstract   The Security Architecture for the Internet Protocol describes   security services for traffic at the IP layer.  That architecture   primarily defines services for Internet Protocol (IP) unicast   packets.  This document describes how the IPsec security services are   applied to IP multicast packets.  These extensions are relevant only   for an IPsec implementation that supports multicast.Weis, et al.                Standards Track                     [Page 1]

RFC 5374            Multicast Extensions toRFC 4301       November 2008Table of Contents1. Introduction ....................................................31.1. Scope ......................................................31.2. Terminology ................................................42. Overview of IP Multicast Operation ..............................63. Security Association Modes ......................................73.1. Tunnel Mode with Address Preservation ......................74. Security Association ............................................84.1. Major IPsec Databases ......................................84.1.1. Group Security Policy Database (GSPD) ...............84.1.2. Security Association Database (SAD) ................124.1.3. Group Peer Authorization Database (GPAD) ...........124.2. Group Security Association (GSA) ..........................14           4.2.1. Concurrent IPsec SA Life Spans and Re-key Rollover .154.3. Data Origin Authentication ................................174.4. Group SA and Key Management ...............................184.4.1. Co-Existence of Multiple Key Management Protocols ..185. IP Traffic Processing ..........................................185.1. Outbound IP Traffic Processing ............................185.2. Inbound IP Traffic Processing .............................196. Security Considerations ........................................226.1. Security Issues Solved by IPsec Multicast Extensions ......226.2. Security Issues Not Solved by IPsec Multicast Extensions ..236.2.1. Outsider Attacks ...................................236.2.2. Insider Attacks ....................................236.3. Implementation or Deployment Issues that Impact Security ..24           6.3.1. Homogeneous Group Cryptographic Algorithm                  Capabilities .......................................24           6.3.2. Groups that Span Two or More Security                  Policy Domains .....................................24           6.3.3. Source-Specific Multicast Group Sender                  Transient Locators .................................257. Acknowledgements ...............................................258. References .....................................................258.1. Normative References ......................................258.2. Informative References ....................................26Appendix A - Multicast Application Service Models .................28A.1 Unidirectional Multicast Applications ......................28A.2 Bi-directional Reliable Multicast Applications .............28A.3 Any-To-Any Multicast Applications ..........................30Appendix B - ASN.1 for a GSPD Entry ...............................30B.1 Fields Specific to a GSPD Entry ............................30B.2 SPDModule ..................................................31Weis, et al.                Standards Track                     [Page 2]

RFC 5374            Multicast Extensions toRFC 4301       November 20081.  Introduction   The Security Architecture for the Internet Protocol [RFC4301]   provides security services for traffic at the IP layer.  It describes   an architecture for IPsec-compliant systems and a set of security   services for the IP layer.  These security services primarily   describe services and semantics for IPsec Security Associations (SAs)   shared between two IPsec devices.  Typically, this includes SAs with   traffic selectors that include a unicast address in the IP   destination field, and results in an IPsec packet with a unicast   address in the IP destination field.  The security services defined   inRFC 4301 can also be used to tunnel IP multicast packets, where   the tunnel is a pairwise association between two IPsec devices.RFC4301 defined manually keyed transport mode IPsec SA support for IP   packets with a multicast address in the IP destination address field.   However,RFC 4301 did not define the interaction of an IPsec   subsystem with a Group Key Management protocol or the semantics of a   tunnel mode IPsec SA with an IP multicast address in the outer IP   header.   This document describes OPTIONAL extensions toRFC 4301 that further   define the IPsec security architecture in order for groups of IPsec   devices to share SAs.  In particular, it supports SAs with traffic   selectors that include a multicast address in the IP destination   field and that result in an IPsec packet with an IP multicast address   in the IP destination field.  It also describes additional semantics   for IPsec Group Key Management (GKM) subsystems.  Note that this   document uses the term "GKM protocol" generically and therefore does   not assume a particular GKM protocol.   An IPsec implementation that does not support multicast is not   required to support these extensions.   Throughout this document,RFC 4301 semantics remain unchanged by the   presence of these multicast extensions unless specifically noted to   the contrary.1.1.  Scope   The IPsec extensions described in this document support IPsec   Security Associations that result in IPsec packets with IPv4 or IPv6   multicast group addresses as the destination address.  Both   Any-Source Multicast (ASM) and Source-Specific Multicast (SSM)   [RFC3569] group addresses are supported.  These extensions are used   when management policy requires that IP multicast packets protected   by IPsec remain IP multicast packets.  When management policyWeis, et al.                Standards Track                     [Page 3]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   requires that the IP multicast packets be encapsulated as IP unicast   packets (e.g., because the network connected to the unprotected   interface does not support IP multicast), the extensions in this   document are not used.   These extensions also support Security Associations with IPv4   Broadcast addresses that result in an IPv4 link-level Broadcast   packet, and IPv6 Anycast addresses [RFC2526] that result in an IPv6   Anycast packet.  These destination address types share many of the   same characteristics of multicast addresses because there may be   multiple candidate receivers of a packet protected by IPsec.   The IPsec architecture does not make requirements upon entities not   participating in IPsec (e.g., network devices between IPsec   endpoints).  As such, these multicast extensions do not require   intermediate systems in a multicast-enabled network to participate in   IPsec.  In particular, no requirements are placed on the use of   multicast routing protocols (e.g., Protocol Independent Multicast -   Sparse Mode (PIM-SM) [RFC4601]) or multicast admission protocols   (e.g., Internet Group Management Protocol (IGMP) [RFC3376]).   All implementation models of IPsec (e.g., "bump-in-the-stack",   "bump-in-the-wire") are supported.   This version of the multicast IPsec extension specification requires   that all IPsec devices participating in a Security Association be   homogeneous.  They MUST share a common set of cryptographic transform   and protocol-handling capabilities.  The semantics of an "IPsec   composite group" [COMPGRP], a heterogeneous IPsec cryptographic group   formed from the union of two or more sub-groups, is an area for   future standardization.1.2.  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 inRFC 2119 [RFC2119].   The following key terms are used throughout this document.   Any-Source Multicast (ASM)      The Internet Protocol (IP) multicast service model as defined inRFC 1112 [RFC1112].  In this model, one or more senders source      packets to a single IP multicast address.  When receivers join the      group, they receive all packets sent to that IP multicast address.      This is known as a (*,G) group.Weis, et al.                Standards Track                     [Page 4]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   Group      A set of devices that work together to protect group      communications.   Group Controller Key Server (GCKS)      A Group Key Management (GKM) protocol server that manages IPsec      state for a group.  A GCKS authenticates and provides the IPsec SA      policy and keying material to GKM Group Members.   Group Key Management (GKM) Protocol      A key management protocol used by a GCKS to distribute IPsec      Security Association policy and keying material.  A GKM protocol      is used when a group of IPsec devices require the same SAs.  For      example, when an IPsec SA describes an IP multicast destination,      the sender and all receivers need to have the group SA.   Group Key Management Subsystem      A subsystem in an IPsec device implementing a Group Key Management      protocol.  The GKM subsystem provides IPsec SAs to the IPsec      subsystem on the IPsec device.  Refer toRFC 3547 [RFC3547] andRFC 4535 [RFC4535] for additional information.   Group Member      An IPsec device that belongs to a group.  A Group Member is      authorized to be a Group Sender and/or a Group Receiver.   Group Owner      An administrative entity that chooses the policy for a group.   Group Security Association (GSA)      A collection of IPsec Security Associations (SAs) and GKM      subsystem SAs necessary for a Group Member to receive key updates.      A GSA describes the working policy for a group.  Refer toRFC 4046      [RFC4046] for additional information.   Group Security Policy Database (GSPD)      The GSPD is a multicast-capable security policy database, as      mentioned inRFC 3740 andSection 4.4.1.1. of RFC 4301.  Its      semantics are a superset of the unicast Security Policy Database      (SPD) defined bySection 4.4.1 of RFC 4301.  Unlike a unicast      SPD-S, in which point-to-point traffic selectors are inherently      bi-directional, multicast security traffic selectors in the GSPD-S      include a "sender only", "receiver only", or "symmetric"      directional attribute.  Refer toSection 4.1.1 for more details.   GSPD-S, GSPD-I, GSPD-O      Group Security Policy Database (secure traffic), (inbound), and      (outbound), respectively.  SeeSection 4.4.1 of RFC 4301.Weis, et al.                Standards Track                     [Page 5]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   Group Receiver      A Group Member that is authorized to receive packets sent to a      group by a Group Sender.   Group Sender      A Group Member that is authorized to send packets to a group.   Source-Specific Multicast (SSM)      The Internet Protocol (IP) multicast service model as defined inRFC 3569 [RFC3569].  In this model, each combination of a sender      and an IP multicast address is considered a group.  This is known      as an (S,G) group.   Tunnel Mode with Address Preservation      A type of IPsec tunnel mode used by security gateway      implementations when encapsulating IP multicast packets such that      they remain IP multicast packets.  This mode is necessary for IP      multicast routing to correctly route IP multicast packets      protected by IPsec.2.  Overview of IP Multicast Operation   IP multicasting is a means of sending a single packet to a "host   group", a set of zero or more hosts identified by a single IP   destination address.  IP multicast packets are delivered to all   members of the group either with "best-efforts" reliability [RFC1112]   or as part of a reliable stream (e.g., NACK-Oriented Reliable   Multicast (NORM) [RFC3940]).   A sender to an IP multicast group sets the destination of the packet   to an IP address that has been allocated for IP multicast.  Allocated   IP multicast addresses are defined in [RFC3171], [RFC3306], and   [RFC3307].  Potential receivers of the packet "join" the IP multicast   group by registering with a network routing device ([RFC3376],   [RFC3810]), signaling its intent to receive packets sent to a   particular IP multicast group.   Network routing devices configured to pass IP multicast packets   participate in multicast routing protocols (e.g., PIM-SM) [RFC4601].   Multicast routing protocols maintain state regarding which devices   have registered to receive packets for a particular IP multicast   group.  When a router receives an IP multicast packet, it forwards a   copy of the packet out of each interface for which there are known   receivers.Weis, et al.                Standards Track                     [Page 6]

RFC 5374            Multicast Extensions toRFC 4301       November 20083.  Security Association Modes   IPsec supports two modes of use: transport mode and tunnel mode.  In   transport mode, IP Authentication Header (AH) [RFC4302] and IP   Encapsulating Security Payload (ESP) [RFC4303] provide protection   primarily for next layer protocols; in tunnel mode, AH and ESP are   applied to tunneled IP packets.   A host implementation of IPsec using the multicast extensions MAY use   either transport mode or tunnel mode to encapsulate an IP multicast   packet.  These processing rules are identical to the rules described   inSection 4.1 of [RFC4301].  However, the destination address for   the IPsec packet is an IP multicast address, rather than a unicast   host address.   A security gateway implementation of IPsec MUST use a tunnel mode SA,   for the reasons described inSection 4.1 of [RFC4301].  In   particular, the security gateway needs to use tunnel mode to   encapsulate incoming fragments, since IPsec cannot directly operate   on fragments.3.1.  Tunnel Mode with Address Preservation   New (tunnel) header construction semantics are required when tunnel   mode is used to encapsulate IP multicast packets that are to remain   IP multicast packets.  These semantics are due to the following   unique requirements of IP multicast routing protocols (e.g., PIM-SM   [RFC4601]).  This document describes these new header construction   semantics as "tunnel mode with address preservation", which is   described as follows.   - When an IP multicast packet is received by a host or router, the     destination address of the packet is compared to the local IP     multicast state.  If the (outer) destination IP address of an IP     multicast packet is set to another IP address, the host or router     receiving the IP multicast packet will not process it properly.     Therefore, an IPsec security gateway needs to populate the     multicast IP destination address in the outer header using the     destination address from the inner header after IPsec tunnel     encapsulation.   - IP multicast routing protocols typically create multicast     distribution trees based on the source address as well as the group     address.  If an IPsec security gateway populates the (outer) source     address of an IP multicast packet (with its own IP address, as     called for inRFC 4301), the resulting IPsec-protected packet may     fail Reverse Path Forwarding (RPF) checks performed by other     routers.  A failed RPF check may result in the packet beingWeis, et al.                Standards Track                     [Page 7]

RFC 5374            Multicast Extensions toRFC 4301       November 2008     dropped.  To accommodate routing protocol RPF checks, the security     gateway implementing the IPsec multicast extensions SHOULD populate     the outer IP address from the original packet IP source address.     However, it should be noted that a security gateway performing     source address preservation will not receive ICMP Path MTU (PMTU)     or other messages intended for the security gateway (triggered by     packets that have had the outer IP source address set to that of     the inner header).  Security gateway applications not requiring     source address preservation will be able to receive ICMP PMTU     messages and process them as described inSection 6.1 of RFC 4301.   Because some applications of address preservation may require that   only the destination address be preserved, specification of   destination address preservation and source address preservation are   separated in the above description.  Destination address preservation   and source address preservation attributes are described in the Group   Security Policy Database (GSPD) (defined later in this document), and   are copied into corresponding Security Association Database (SAD)   entries.   Address preservation is applicable only for tunnel mode IPsec SAs   that specify the IP version of the encapsulating header to be the   same version as that of the inner header.  When the IP versions are   different, IP multicast packets can be encapsulated using a tunnel   interface, for example as described in [RFC4891], where the tunnel is   also treated as an interface by IP multicast routing protocols.   In summary, propagating both the IP source and destination addresses   of the inner IP header into the outer (tunnel) header allows IP   multicast routing protocols to route a packet properly when the   packet is protected by IPsec.  This result is necessary in order for   the multicast extensions to allow a host or security gateway to   provide IPsec services for IP multicast packets.  This method ofRFC4301 tunnel mode is known as "tunnel mode with address preservation".4.  Security Association4.1.  Major IPsec Databases   The following sections describe the GKM subsystem and IPsec extension   interactions with the IPsec databases.  The major IPsec databases   need expanded semantics to fully support multicast.4.1.1.  Group Security Policy Database (GSPD)   The Group Security Policy Database is a security policy database   capable of supporting both unicast Security Associations as defined   byRFC 4301 and the multicast extensions defined by thisWeis, et al.                Standards Track                     [Page 8]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   specification.  The GSPD is considered to be the SPD, with the   addition of the semantics relating to the multicast extensions   described in this section.Appendix B provides an example of an   ASN.1 definition of a GSPD entry.   This document describes a new "address preservation" (AP) flag   indicating that tunnel mode with address preservation is to be   applied to a GSPD entry.  The AP flag has two attributes: AP-L, used   in the processing of the local tunnel address, and AP-R, used in the   processing of the remote tunnel process.  This flag is added to the   GSPD "Processing info" field of the GSPD.  The following text   reproduced fromSection 4.4.1.2 of RFC 4301 is amended to include   this additional processing.  (Note: for brevity, only the "Processing   info" text related to tunnel processing has been reproduced.)         o Processing info -- which action is required -- PROTECT,           BYPASS, or DISCARD.  There is just one action that goes with           all the selector sets, not a separate action for each set.           If the required processing is PROTECT, the entry contains the           following information.           - IPsec mode -- tunnel or transport           - (if tunnel mode) local tunnel address -- For a non-mobile             host, if there is just one interface, this is             straightforward; if there are multiple interfaces, this             must be statically configured.  For a mobile host, the             specification of the local address is handled externally to             IPsec.  If tunnel mode with address preservation is             specified for the local tunnel address, the AP-L attribute             is set to TRUE for the local tunnel address and the local             tunnel address is unspecified.  The presence of the AP-L             attribute indicates that the inner IP header source address             will be copied to the outer IP header source address during             IP header construction for tunnel mode.           - (if tunnel mode) remote tunnel address -- There is no             standard way to determine this.  See Section 4.5.3 ofRFC4301, "Locating a Security Gateway".  If tunnel mode with             address preservation is specified for the remote tunnel             address, the AP-R attribute is set to TRUE for the remote             tunnel address and the remote tunnel address is             unspecified.  The presence of the AP-R attribute indicates             that the inner IP header destination address will be copied             to the outer IP header destination address during IP header             construction for tunnel mode.   This document describes unique directionality processing for GSPD   entries with a remote IP multicast address.  Since an IP multicast   address must not be sent as the source address of an IP packetWeis, et al.                Standards Track                     [Page 9]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   [RFC1112], directionality of Local and Remote addresses and ports is   maintained during incoming SPD-S and SPD-I checks rather than being   swapped.Section 4.4.1 of RFC 4301 is amended as follows:         Representing Directionality in an SPD Entry           For traffic protected by IPsec, the Local and Remote address           and ports in an SPD entry are swapped to represent           directionality, consistent with IKE conventions.  In general,           the protocols that IPsec deals with have the property of           requiring symmetric SAs with flipped Local/Remote IP           addresses.  However, SPD entries with a remote IP multicast           address do not have their Local and Remote addresses and           ports in an SPD entry swapped during incoming SPD-S and SPD-I           checks.   A new Group Security Policy Database (GSPD) attribute is introduced:   GSPD entry directionality.  The following text is added to the bullet   list of SPD fields described inSection 4.4.1.2 of RFC 4301.         o Directionality -- can be one of three types: "symmetric",           "sender only", or "receiver only".  "Symmetric" indicates           that a pair of SAs are to be created (one in each direction,           as specified byRFC 4301).  GSPD entries marked as "sender           only" indicate that one SA is to be created in the outbound           direction.  GSPD entries marked as "receiver only" indicate           that one SA is to be created in the inbound direction.  GSPD           entries marked as "sender only" or "receiver only" SHOULD           support multicast IP addresses in their destination address           selectors.  If the processing requested is BYPASS or DISCARD           and a "sender only" type is configured, the entry MUST be put           in GSPD-O only.  Reciprocally, if the type is "receiver           only", the entry MUST go to GSPD-I only.   GSPD entries created by a GCKS may be assigned identical Security   Parameter Indexes (SPIs) to SAD entries created by IKEv2 [RFC4306].   This is not a problem for the inbound traffic as the appropriate SAs   can be matched using the algorithm described in Section 4.1 ofRFC4301.  However, the outbound traffic needs to be matched against the   GSPD selectors so that the appropriate SA can be created.   To facilitate dynamic group keying, the outbound GSPD MUST implement   a policy action capability that triggers a GKM protocol registration   exchange (as perSection 5.1 of [RFC4301]).  For example, the Group   Sender GSPD policy might trigger on a match with a specified   multicast application packet that is entering the implementation via   the protected interface or that is emitted by the implementation on   the protected side of the boundary and directed toward theWeis, et al.                Standards Track                    [Page 10]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   unprotected interface.  The ensuing Group Sender registration   exchange would set up the Group Sender's outbound SAD entry that   encrypts the multicast application's data stream.  In the inverse   direction, group policy may also set up an inbound IPsec SA.   At the Group Receiver endpoint(s), the IPsec subsystem MAY use GSPD   policy mechanisms that initiate a GKM protocol registration exchange.   One such policy mechanism might be on the detection of a device in   the protected network joining a multicast group matching GSPD policy   (e.g., by receiving a IGMP/MLD (Multicast Listener Discovery) join   group message on a protected interface).  The ensuing Group Receiver   registration exchange would set up the Group Receiver's inbound SAD   entry that decrypts the multicast application's data stream.  In the   inverse direction, the group policy may also set up an outbound IPsec   SA (e.g., when supporting an ASM service model).   Note: A security gateway triggering on the receipt of unauthenticated   messages arriving on a protected interface may result in early Group   Receiver registration if the message is not the result of a device on   the protected network actually wishing to join a multicast group.   The unauthenticated messages will only cause the Group Receiver to   register once; subsequent messages will have no effect on the Group   Receiver.   The IPsec subsystem MAY provide GSPD policy mechanisms that   automatically initiate a GKM protocol de-registration exchange.   De-registration allows a GCKS to minimize exposure of the group's   secret key by re-keying a group on a group membership change event.   It also minimizes cost on a GCKS for those groups that maintain   member state.  One such policy mechanism could be the detection of   IGMP/MLD leave group exchange.  However, a security gateway Group   Member would not initiate a GKM protocol de-registration exchange   until it detects that there are no more receivers behind a protected   interface.   Additionally, the GKM subsystem MAY set up the GSPD/SAD state   information independent of the multicast application's state.  In   this scenario, the Group Owner issues management directives that tell   the GKM subsystem when it should start GKM registration and   de-registration protocol exchanges.  Typically, the registration   policy strives to make sure that the group's IPsec subsystem state is   "always ready" in anticipation of the multicast application starting   its execution.Weis, et al.                Standards Track                    [Page 11]

RFC 5374            Multicast Extensions toRFC 4301       November 20084.1.2.  Security Association Database (SAD)   The SAD contains an item describing whether tunnel or transport mode   is applied to traffic on this SA.  The text inRFC 4301 Section 4.4.2.1 is amended to describe address preservation.         o IPsec protocol mode: tunnel or transport.  Indicates which           mode of AH or ESP is applied to traffic on this SA.  When           tunnel mode is specified, the data item also indicates           whether or not address preservation is applied to the outer           IP header.  Address preservation MUST NOT be specified when           the IP version of the encapsulating header and IP version of           the inner header do not match.  The local address, remote           address, or both addresses MAY be marked as being preserved           during tunnel encapsulation.4.1.3.  Group Peer Authorization Database (GPAD)   The multicast IPsec extensions introduce a new data structure called   the Group Peer Authorization Database (GPAD).  The GPAD is analogous   to the PAD defined inRFC 4301.  It provides a link between the GSPD   and a Group Key Management (GKM) Subsystem.  The GPAD embodies the   following critical functions:         o identifies a GCKS (or group of GCKS devices) that is           authorized to communicate with this IPsec entity         o specifies the protocol and method used to authenticate each           GCKS         o provides the authentication data for each GKCS         o constrains the traffic selectors that can be asserted by a           GCKS with regard to SA creation         o constrains the types and values of Group Identifiers for           which a GCKS is authorized to provide group policy   The GPAD provides these functions for a Group Key Management   subsystem.  The GPAD is not consulted by IKE or other authentication   protocols that do not act as GKM protocols.   To provide these functions, the GPAD contains an entry for each GCKS   that the IPsec entity is configured to contact.  An entry contains   one or more GCKS Identifiers, the authentication protocol (e.g.,   Group Domain of Interpretation (GDOI) or Group Secure Association Key   Management Protocol (GSAKMP)), the authentication method used (e.g.,   certificates or pre-shared secrets), and the authentication dataWeis, et al.                Standards Track                    [Page 12]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   (e.g., the pre-shared secret or trust anchor relative to which the   peer's certificate will be validated).  For certificate-based   authentication, the entry also may provide information to assist in   verifying the revocation status of the peer, e.g., a pointer to a   Certificate Revocation List (CRL) repository or the name of an Online   Certificate Status Protocol (OCSP) server associated with either the   peer or the trust anchor associated with the peer.  The entry also   contains constraints a Group Member applies to the policy received   from the GKCS.4.1.3.1.  GCKS Identifiers   GCKS Identifiers are used to identify one or more devices that are   authorized to act as a GCKS for this group.  GCKS Identifiers are   specified as PAD entry IDs inSection 4.4.3.1 of RFC 4301 and follow   the matching rules described therein.4.1.3.2.  GCKS Peer Authentication Data   Once a GPAD entry is located, it is necessary to verify the asserted   identity, i.e., to authenticate the asserted GCKS Identifier.  PAD   authentication data types and semantics specified inSection 4.4.3.2   of RFC 4301 are used to authenticate a GCKS.   See GDOI [RFC3547] and GSAKMP [RFC4535] for details of how a GKM   protocol performs peer authentication using certificates and   pre-shared secrets.4.1.3.3.  Group Identifier Authorization Data   A Group Identifier is used by a GKM protocol to identify a particular   group to a GCKS.  A GPAD entry includes a Group Identifier to   indicate that the GKCS Identifiers in the GPAD entry are authorized   to act as a GCKS for the group.   The Group Identifier is an opaque byte string of IKE ID type Key ID   that identifies a secure multicast group.  The Group Identifier byte   string MUST be at least four bytes long and less than 256 bytes long.   IKE ID types other than Key ID MAY be supported.4.1.3.4.  IPsec SA Traffic Selector Authorization Data   Once a GCKS is authenticated, the GCKS delivers IPsec SA policy to   the Group Member.  Before the Group Member accepts the IPsec SA   Policy, the source and destination traffic selectors of the SA are   compared to a set of authorized data flows.  Each data flow includes   a set of authorized source traffic selectors and a set of authorizedWeis, et al.                Standards Track                    [Page 13]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   destination traffic selectors.  Traffic selectors are represented as   a set of IPv4 and/or IPv6 address ranges.  (A peer may be authorized   for both address types, so there MUST be provision for both v4 and v6   address ranges.)4.1.3.5.  How the GPAD Is Used   When a GKM protocol registration exchange is triggered, the Group   Member and GCKS each assert their identity as a part of the exchange.   Each GKM protocol registration exchange MUST use the asserted ID to   locate an identity in the GPAD.  The GPAD entry specifies the   authentication method to be employed for the identified GCKS.  The   entry also specifies the authentication data that will be used to   verify the asserted identity.  This data is employed in conjunction   with the specified method to authenticate the GCKS before accepting   any group policy from the GCKS.   During the GKM protocol registration, a Group Member includes a Group   Identifier.  Before presenting that Group Identifier to the GCKS, a   Group Member verifies that the GPAD entry for authenticated GCKS GPAD   entry includes the Group Identifier.  This ensures that the GCKS is   authorized to provide policy for the Group.   When IPsec SA policy is received, each data flow is compared to the   data flows in the GPAD entry.  The Group Member accepts policy   matching a data flow.  Policy not matching a data flow is discarded,   and the reason SHOULD be recorded in the audit log.   A GKM protocol may distribute IPsec SA policy to IPsec devices that   have previously registered with it.  The method of distribution is   part of the GKM protocol and is outside the scope of this memo.  When   the IPsec device receives this new policy, it compares the policy to   the data flows in the GPAD entry as described above.4.2.  Group Security Association (GSA)   An IPsec implementation supporting these extensions will support a   number of Security Associations: one or more IPsec SAs plus one or   more GKM SAs used to download the parameters that are used to create   IPsec SAs.  These SAs are collectively referred to as a Group   Security Association (GSA)  [RFC3740].4.2.1.  Concurrent IPsec SA Life Spans and Re-key Rollover   During a secure multicast group's lifetime, multiple IPsec Group   Security Associations can exist concurrently.  This occurs   principally due to two reasons:Weis, et al.                Standards Track                    [Page 14]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   - There are multiple Group Senders authorized in the group, each with     its own IPsec SA, which maintains anti-replay state.  A group that     does not rely on IP security anti-replay services can share one     IPsec SA for all of its Group Senders.   - The life spans of a Group Sender's two (or more) IPsec SAs are     allowed to overlap in time so that there is continuity in the     multicast data stream across group re-key events.  This capability     is referred to as "re-key rollover continuity".   The re-key continuity rollover algorithm depends on an IPsec SA   management interface between the GKM subsystem and the IPsec   subsystem.  The IPsec subsystem MUST provide management interface   mechanisms for the GKM subsystem to add IPsec SAs and to delete IPsec   SAs.  For illustrative purposes, this text defines the re-key   rollover continuity algorithm in terms of two timer parameters that   govern IPsec SA life spans relative to the start of a group re-key   event.  However, it should be emphasized that the GKM subsystem   interprets the group's security policy to direct the correct timing   of IPsec SA activation and deactivation.  A given group policy may   choose timer values that differ from those recommended by this text.   The two re-key rollover continuity timer parameters are:   1. Activation Time Delay (ATD) - The ATD defines how long after the      start of a re-key event to activate new IPsec SAs.  The ATD      parameter is expressed in units of seconds.  Typically, the ATD      parameter is set to the maximum time it takes to deliver a      multicast message from the GCKS to all of the group's members.      For a GCKS that relies on a Reliable Multicast Transport Protocol      (RMTP), the ATD parameter could be set equal to the RTMP's maximum      error recovery time.  When an RMTP is not present, the ATD      parameter might be set equal to the network's maximum multicast      message delivery latency across all of the group's endpoints.  The      ATD is a GKM group policy parameter.  This value SHOULD be      configurable at the Group Owner management interface on a per      group basis.   2. Deactivation Time Delay (DTD) - The DTD defines how long after the      start of a re-key event to deactivate those IPsec SAs that are      destroyed by the re-key event.  The purpose of the DTD parameter      is to minimize the residual exposure of a group's keying material      after a re-key event has retired that keying material.  The DTD is      independent of, and should not to be confused with, the IPsec SA      soft lifetime attribute.  The DTD parameter is expressed in units      of seconds.  Typically, the DTD parameter would be set to the ADT      plus the maximum time it takes to deliver a multicast message from      the Group Sender to all of the group's members.  For a Group      Sender that relies on an RMTP, the DTD parameter could be setWeis, et al.                Standards Track                    [Page 15]

RFC 5374            Multicast Extensions toRFC 4301       November 2008      equal to ADT plus the RMTP's maximum error recovery time.  When an      RMTP is not present, the DTD parameter might be set equal to ADT      plus the network's maximum multicast message delivery latency      across all of the group's endpoints.  A GKM subsystem MAY      implement the DTD as a group security policy parameter.  If a GKM      subsystem does not implement the DTD parameter, then other group      security policy mechanisms MUST determine when to deactivate an      IPsec SA.   Each group re-key multicast message sent by a GCKS signals the start   of a new Group Sender IPsec SA time epoch, with each such epoch   having an associated set of two IPsec SAs.  Note that this document   refers to re-key mechanisms as being multicast because of the   inherent scalability of IP multicast distribution.  However, there is   no particular reason that re-keying mechanisms must be multicast.   For example, [ZLLY03] describes a method of re-key employing both   unicast and multicast messages.   The group membership interacts with these IPsec SAs as follows:   - As a precursor to the Group Sender beginning its re-key rollover     continuity processing, the GCKS periodically multicasts a Re-Key     Event (RKE) message to the group.  The RKE multicast MAY contain     group policy directives, new IPsec SA policy, and group keying     material.  In the absence of an RMTP, the GCKS may re-transmit the     RKE a policy-defined number of times to improve the availability of     re-key information.  The GKM subsystem starts the ATD and DTD     timers after it receives the last RKE re-transmission.   - The GKM subsystem interprets the RKE multicast to configure the     group's GSPD/SAD with the new IPsec SAs.  Each IPsec SA that     replaces an existing SA is called a "leading edge" IPsec SA.  The     leading edge IPsec SA has a new Security Parameter Index (SPI) and     its associated keying material, which keys it.  For a time period     of ATD seconds after the GCKS multicasts the RKE, a Group Sender     does not yet transmit data using the leading edge IPsec SA.     Meanwhile, other Group Members prepare to use this IPsec SA by     installing the leading edge IPsec SAs to their respective GSPD/SAD.   - After waiting for the ATD period, such that all of the Group     Members have received and processed the RKE message, the GKM     subsystem directs the Group Sender to begin to transmit using the     leading edge IPsec SA with its data encrypted by the new keying     material.  Only authorized Group Members can decrypt these IPsec SA     multicast transmissions.Weis, et al.                Standards Track                    [Page 16]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   - The Group Sender's "trailing edge" SA is the oldest Security     Association in use by the group for that sender.  All authorized     Group Members can receive and decrypt data for this SA, but the     Group Sender does not transmit new data using the trailing edge     IPsec SA after it has transitioned to the leading edge IPsec SA.     The trailing edge IPsec SA is deleted by the group's GKM subsystems     after the DTD time period has elapsed since the RKE transmission.   This re-key rollover strategy allows the group to drain its   in-transit datagrams from the network while transitioning to the   leading edge IPsec SA.  Staggering the roles of each respective IPsec   SA as described above improves the group's synchronization even when   there are high network propagation delays.  Note that due to group   membership joins and leaves, each Group Sender IPsec SA time epoch   may have a different group membership set.   It is a group policy decision whether the re-key event transition   between epochs provides forward and backward secrecy.  The group's   re-key protocol keying material and algorithm (e.g., Logical Key   Hierarchy; refer to [RFC2627] andAppendix A of [RFC4535]) enforces   this policy.  Implementations MAY offer a Group Owner management   interface option to enable/disable re-key rollover continuity for a   particular group.  This specification requires that a GKM/IPsec   implementation MUST support at least two concurrent IPsec SAs per   Group Sender as well as this re-key rollover continuity algorithm.4.3.  Data Origin Authentication   As defined in [RFC4301], data origin authentication is a security   service that verifies the identity of the claimed source of data.  A   Message Authentication Code (MAC) is often used to achieve data   origin authentication for connections shared between two parties.   However, typical MAC authentication methods using a single shared   secret are not sufficient to provide data origin authentication for   groups with more than two parties.  With a MAC algorithm, every Group   Member can use the MAC key to create a valid MAC tag, whether or not   they are the authentic originator of the group application's data.   When the property of data origin authentication is required for an   IPsec SA shared by more than two parties, an authentication transform   where the receiver is assured that the sender generated that message   should be used.  Two possible algorithms are Timed Efficient Stream   Loss-Tolerant Authentication (TESLA) [RFC4082] or RSA digital   signature [RFC4359].   In some cases (e.g., digital signature authentication transforms),   the processing cost of the algorithm is significantly greater than a   Hashed Message Authentication Code (HMAC) authentication method.  ToWeis, et al.                Standards Track                    [Page 17]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   protect against denial-of-service attacks from a device that is not   authorized to join the group, the IPsec SA using this algorithm may   be encapsulated with an IPsec SA using a MAC authentication   algorithm.  However, doing so requires the packet to be sent across   the IPsec boundary a second time for additional outbound processing   on the Group Sender (seeSection 5.1 of [RFC4301]) and a second time   for inbound processing on Group Receivers (seeSection 5.2 of   [RFC4301]).  This use of AH or ESP encapsulated within AH or ESP   accommodates the constraint that AH and ESP define an Integrity Check   Value (ICV) for only a single authenticator transform.4.4.  Group SA and Key Management4.4.1.  Co-Existence of Multiple Key Management Protocols   Often, the GKM subsystem will be introduced to an existent IPsec   subsystem as a companion key management protocol to IKEv2 [RFC4306].   A fundamental GKM protocol IP security subsystem requirement is that   both the GKM protocol and IKEv2 can simultaneously share access to a   common Group Security Policy Database and Security Association   Database.  The mechanisms that provide mutually exclusive access to   the common GSPD/SAD data structures are a local matter.  This   includes the GSPD-O cache and the GSPD-I cache.  However,   implementers should note that IKEv2 SPI allocation is entirely   independent from GKM SPI allocation because Group Security   Associations are qualified by a destination multicast IP address and   may optionally have a source IP address qualifier.  SeeSection 2.1   of [RFC4303] for further explanation.   The Peer Authorization Database does require explicit coordination   between the GKM protocol and IKEv2.Section 4.1.3 describes these   interactions.5.  IP Traffic Processing   Processing of traffic followsSection 5 of [RFC4301], with the   additions described below when these IP multicast extensions are   supported.5.1.  Outbound IP Traffic Processing   If an IPsec SA is marked as supporting tunnel mode with address   preservation (as described inSection 3.1), either or both of the   outer header source or destination addresses are marked as being   preserved.   Header construction for tunnel mode is described inSection 5.1.2 of   RFC 4301.  The first bullet of that section is amended as follows:Weis, et al.                Standards Track                    [Page 18]

RFC 5374            Multicast Extensions toRFC 4301       November 2008         o If address preservation is not marked in the SAD entry for           either the outer IP header Source Address or Destination           Address, the outer IP header Source Address and Destination           Address identify the "endpoints" of the tunnel (the           encapsulator and decapsulator).  If address preservation is           marked for the IP header Source Address, it is copied from           the inner IP header Source Address.  If address preservation           is marked for the IP header Destination Address, it is copied           from the inner IP header Destination Address.  The inner IP           header Source Address and Destination Addresses identify the           original sender and recipient of the datagram (from the           perspective of this tunnel), respectively.  Address           preservation MUST NOT be marked when the IP version of the           encapsulating header and IP version of the inner header do           not match.   Note (3), regarding construction of tunnel addresses inSection5.1.2.1 of RFC 4301, is amended as follows. (Note: for brevity, Note   (3) ofRFC 4301 is not reproduced in its entirety.)         (3) Unless marked for address preservation, Local and Remote             addresses depend on the SA, which is used to determine the             Remote address, which in turn determines which Local             address (net interface) is used to forward the packet.  If             address preservation is marked for the Local address, it is             copied from the inner IP header.  If address preservation             is marked for the Remote address, that address is copied             from the inner IP header.5.2.  Inbound IP Traffic Processing   IPsec-protected packets generated by an IPsec device supporting these   multicast extensions may (depending on its GSPD policy) populate an   outer tunnel header with a destination address such that it is not   addressed to an IPsec device.  This requires an IPsec device   supporting these multicast extensions to accept and process IP   traffic that is not addressed to the IPsec device itself.  The   following additions to IPsec inbound IP traffic processing are   necessary.   For compatibility withRFC 4301, the phrase "addressed to this   device" is taken to mean packets with a unicast destination address   belonging to the system itself, and also multicast packets that are   received by the system itself.  However, multicast packets not   received by the IPsec device are not considered addressed to this   device.Weis, et al.                Standards Track                    [Page 19]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   The discussion of processing inbound IP Traffic described inSection5.2 of RFC 4301 is amended as follows.   The first dash in item 2 is amended as follows:         - If the packet appears to be IPsec protected and it is           addressed to this device, or appears to be IPsec protected           and is addressed to a multicast group, an attempt is made to           map it to an active SA via the SAD.  Note that the device may           have multiple IP addresses that may be used in the SAD           lookup, e.g., in the case of protocols such as SCTP.   A new item is added to the list between items 3a and 3b to describe   processing of IPsec packets with destination address preservation   applied:         3aa. If the packet is addressed to a multicast group and AH or              ESP is specified as the protocol, the packet is looked up              in the SAD.  Use the SPI plus the destination or SPI plus              destination and source addresses, as specified inSection4.1.  If there is no match, the packet is directed to              SPD-I lookup.  Note that if the IPsec device is a security              gateway, and the SPD-I policy is to BYPASS the packet, a              subsequent security gateway along the routed path of the              multicast packet may decrypt the packet.   Figure 3 inRFC 4301 is updated to show the new processing path   defined in item 3aa.Weis, et al.                Standards Track                    [Page 20]

RFC 5374            Multicast Extensions toRFC 4301       November 2008                        Unprotected Interface                                 |                                 V                              +-----+   IPsec protected          ------------------->|Demux|--------------------+          |                   +-----+                    |          |                      |                       |          |            Not IPsec |                       |          |                      |  IPsec protected, not |          |                      V  addressed to device, |          |     +-------+    +---------+ and not in SAD  |          |     |DISCARD|<---|SPD-I (*)|<------------+   |          |     +-------+    +---------+             |   |          |                   |                      |   |          |                   |-----+                |   |          |                   |     |                |   |          |                   |     V                |   |          |                   |  +------+            |   |          |                   |  | ICMP |            |   |          |                   |  +------+            |   |          |                   |                      |   V       +---------+            |                   +-----------+   ....|SPD-O (*)|............|...................|PROCESS(**)|...IPsec       +---------+            |                   | (AH/ESP)  | Boundary          ^                   |                   +-----------+          |                   |       +---+              |          |            BYPASS |   +-->|IKE|              |          |                   |   |   +---+              |          |                   V   |                      V          |               +----------+          +---------+   +----+          |--------<------|Forwarding|<---------|SAD Check|-->|ICMP|            nested SAs    +----------+          | (***)   |   +----+                                |               +---------+                                V                        Protected Interface             Figure 1.  Processing Model for Inbound Traffic                         (amending Figure 3 ofRFC 4301)Weis, et al.                Standards Track                    [Page 21]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   The discussion of processing inbound IP traffic in Section 5.2 ofRFC4301 is amended to insert a new item 6 as follows.         6. If an IPsec SA is marked as supporting tunnel mode with            address preservation (as described inSection 3.1), the            marked address(es) (i.e., source and/or destination            address(es)) in the outer IP header MUST be verified to be            the same value(s) as in the inner IP header.  If the            addresses are not consistent, the IPsec system MUST discard            the packet and treat the inconsistency as an auditable            event.6.  Security Considerations   The IP security multicast extensions defined by this specification   build on the unicast-oriented IP security architecture [RFC4301].   Consequently, this specification inherits many ofRFC 4301's security   considerations, and the reader is advised to review it as companion   guidance.6.1.  Security Issues Solved by IPsec Multicast Extensions   The IP security multicast extension service provides the following   network layer mechanisms for secure group communications:   - Confidentiality using a group shared encryption key.   - Group source authentication and integrity protection using a group     shared authentication key.   - Group Sender data origin authentication using a digital signature,     TESLA, or other mechanism.   - Anti-replay protection for a limited number of Group Senders using     the ESP (or AH) sequence number facility.   - Filtering of multicast transmissions identified with a source     address of systems that are not authorized by group policy to be     Group Senders.  This feature leverages the IPsec stateless firewall     service (i.e., SPD-I and/or SDP-O entries with a packet disposition     specified as DISCARD).   In support of the above services, this specification enhances the   definition of the SPD, PAD, and SAD databases to facilitate the   automated group key management of large-scale cryptographic groups.Weis, et al.                Standards Track                    [Page 22]

RFC 5374            Multicast Extensions toRFC 4301       November 20086.2.  Security Issues Not Solved by IPsec Multicast Extensions   As noted inSection 2.2. of RFC 4301, it is out of the scope of this   architecture to defend the group's keys or its application data   against attacks targeting vulnerabilities of the operating   environment in which the IPsec implementation executes.  However, it   should be noted that the risk of attacks originating by an adversary   in the network is magnified to the extent that the group keys are   shared across a large number of systems.   The security issues that are left unsolved by the IPsec multicast   extension service divide into two broad categories: outsider attacks   and insider attacks.6.2.1.  Outsider Attacks   The IPsec multicast extension service does not defend against an   adversary outside of the group who has:   - the capability to launch a multicast, flooding denial-of-service     attack against the group, originating from a system whose IPsec     subsystem does not filter the unauthorized multicast transmissions.   - compromised a multicast router, allowing the adversary to corrupt     or delete all multicast packets destined for the group endpoints     downstream from that router.   - captured a copy of an earlier multicast packet transmission and     then replayed it to a group that does not have the anti-replay     service enabled.  Note that for a large-scale, any-source multicast     group, it is impractical for the Group Receivers to maintain an     anti-replay state for every potential Group Sender.  Group policies     that require anti-replay protection for a large-scale, any-source     multicast group should consider an application layer multicast     protocol that can detect and reject replays.6.2.2.  Insider Attacks   For large-scale groups, the IP security multicast extensions are   dependent on an automated Group Key Management protocol to correctly   authenticate and authorize trustworthy members in compliance to the   group's policies.  Inherent in the concept of a cryptographic group   is a set of one or more shared secrets entrusted to all of the Group   Members.  Consequently, the service's security guarantees are no   stronger than the weakest member admitted to the group by the GKM   system.  The GKM system is responsible for responding to compromised   Group Member detection by executing a re-key procedure.  The GKM   re-keying protocol will expel the compromised Group Members andWeis, et al.                Standards Track                    [Page 23]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   distribute new group keying material to the trusted members.   Alternatively, the group policy may require the GKM system to   terminate the group.   In the event that an adversary has been admitted into the group by   the GKM system, the following attacks are possible and can not be   solved by the IPsec multicast extension service:   - The adversary can disclose the secret group key or group data to an     unauthorized party outside of the group.  After a group key or data     compromise, cryptographic methods such as traitor tracing or     watermarking can assist in the forensics process.  However, these     methods are outside the scope of this specification.   - The insider adversary can forge packet transmissions that appear to     be from a peer Group Member.  To defend against this attack, for     those Group Sender transmissions that merit the overhead, the group     policy can require the Group Sender to multicast packets using the     data origin authentication service.   - If the group's data origin authentication service uses digital     signatures, then the insider adversary can launch a computational     resource denial-of-service attack by multicasting bogus signed     packets.6.3.  Implementation or Deployment Issues that Impact Security6.3.1.  Homogeneous Group Cryptographic Algorithm Capabilities   The IP security multicast extensions service can not defend against a   poorly considered group security policy that allows a weaker   cryptographic algorithm simply because all of the group's endpoints   are known to support it.  Unfortunately, large-scale groups can be   difficult to upgrade to the current best-in-class cryptographic   algorithms.  One possible approach to solving many of these problems   is the deployment of composite groups that can straddle heterogeneous   groups [COMPGRP].  A standard solution for heterogeneous groups is an   activity for future standardization.  In the interim, synchronization   of a group's cryptographic capabilities could be achieved using a   secure and scalable software distribution management tool.6.3.2.  Groups that Span Two or More Security Policy Domains   Large-scale groups may span multiple legal jurisdictions (e.g.,   countries) that enforce limits on cryptographic algorithms or key   strengths.  As currently defined, the IPsec multicast extension   service requires a single group policy per group.  As noted above,   this problem remains an area for future standardization.Weis, et al.                Standards Track                    [Page 24]

RFC 5374            Multicast Extensions toRFC 4301       November 20086.3.3.  Source-Specific Multicast Group Sender Transient Locators   A Source Specific Multicast (SSM) Group Sender's source IP address   can dynamically change during a secure multicast group's lifetime.   Examples of the events that can cause the Group Sender's source   address to change include but are not limited to NAT, a mobility-   induced change in the care-of-address, and a multi-homed host using a   new IP interface.  The change in the Group Sender's source IP address   will cause GSPD entries related to that multicast group to become out   of date with respect to the group's multicast routing state.  In the   worst case, there is a risk that the Group Sender's data originating   from a new source address will be BYPASS processed by a security   gateway.  If this scenario was not anticipated, then it could leak   the group's data.  Consequently, it is recommended that SSM secure   multicast groups have a default DISCARD policy for all unauthorized   Group Sender source IP addresses for the SSM group's destination IP   address.7.  Acknowledgements   The authors wish to thank Steven Kent, Russ Housley, Pasi Eronen, and   Tero Kivinen for their helpful comments.   The "Guidelines for Writing RFC Text on Security Considerations"   [RFC3552] was consulted to develop the Security Considerations   section of this memo.8.  References8.1.  Normative References   [RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,RFC 1112, August 1989.   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate             Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC4301] Kent, S. and K. Seo, "Security Architecture for the             Internet Protocol",RFC 4301, December 2005.   [RFC4302] Kent, S., "IP Authentication Header",RFC 4302, December             2005.   [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",RFC4303, December 2005.Weis, et al.                Standards Track                    [Page 25]

RFC 5374            Multicast Extensions toRFC 4301       November 20088.2.  Informative References   [COMPGRP] Gross G. and H. Cruickshank, "Multicast IP Security             Composite Cryptographic Groups", Work in Progress, February             2007.   [RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast             Addresses",RFC 2526, March 1999.   [RFC2627] Wallner, D., Harder, E., and R. Agee, "Key Management for             Multicast: Issues and Architectures",RFC 2627, June 1999.   [RFC2914] Floyd, S., "Congestion Control Principles",BCP 41,RFC2914, September 2000.   [RFC3171] Albanna, Z., Almeroth, K., Meyer, D., and M. Schipper,             "IANA Guidelines for IPv4 Multicast Address Assignments",BCP 51,RFC 3171, August 2001.   [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6             Multicast Addresses",RFC 3306, August 2002.   [RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast             Addresses",RFC 3307, August 2002.   [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.             Thyagarajan, "Internet Group Management Protocol, Version             3",RFC 3376, October 2002.   [RFC3547] Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The             Group Domain of Interpretation",RFC 3547, July 2003.   [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC             Text on Security Considerations",BCP 72,RFC 3552, July             2003.   [RFC3569] Bhattacharyya, S., Ed., "An Overview of Source-Specific             Multicast (SSM)",RFC 3569, July 2003.   [RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security             Architecture",RFC 3740, March 2004.   [RFC3810] Vida, R., Ed., and L. Costa, Ed., "Multicast Listener             Discovery Version 2 (MLDv2) for IPv6",RFC 3810, June 2004.   [RFC3940] Adamson, B., Bormann, C., Handley, M., and J. Macker,             "Negative-acknowledgment (NACK)-Oriented Reliable Multicast             (NORM) Protocol",RFC 3940, November 2004.Weis, et al.                Standards Track                    [Page 26]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   [RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,             "Multicast Security (MSEC) Group Key Management             Architecture",RFC 4046, April 2005.   [RFC4082] Perrig, A., Song, D., Canetti, R., Tygar, J., and B.             Briscoe, "Timed Efficient Stream Loss-Tolerant             Authentication (TESLA): Multicast Source Authentication             Transform Introduction",RFC 4082, June 2005.   [RFC4306] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) Protocol",RFC 4306, December 2005.   [RFC4359] Weis, B., "The Use of RSA/SHA-1 Signatures within             Encapsulating Security Payload (ESP) and Authentication             Header (AH)",RFC 4359, January 2006.   [RFC4535] Harney, H., Meth, U., Colegrove, A., and G. Gross, "GSAKMP:             Group Secure Association Key Management Protocol",RFC4535, June 2006.   [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,             "Protocol Independent Multicast - Sparse Mode (PIM-SM):             Protocol Specification (Revised)",RFC 4601, August 2006.   [RFC4891] Graveman, R., Parthasarathy, M., Savola, P., and H.             Tschofenig, "Using IPsec to Secure IPv6-in-IPv4 Tunnels",RFC 4891, May 2007.   [ZLLY03]  Zhang, X., et al., "Protocol Design for Scalable and             Reliable Group Rekeying", IEEE/ACM Transactions on             Networking (TON), Volume 11, Issue 6, December 2003.Weis, et al.                Standards Track                    [Page 27]

RFC 5374            Multicast Extensions toRFC 4301       November 2008Appendix A.  Multicast Application Service Models   The vast majority of secure multicast applications can be catalogued   by their service model and accompanying intra-group communication   patterns.  Both the Group Key Management (GKM) subsystem and the   IPsec subsystem MUST be able to configure the GSPD/SAD security   policies to match these dominant usage scenarios. The GSPD/SAD   policies MUST include the ability to configure both Any-Source   Multicast groups and Source-Specific Multicast groups for each of   these service models.  The GKM subsystem management interface MAY   include mechanisms to configure the security policies for service   models not identified by this standard.A.1.  Unidirectional Multicast Applications   Multimedia content-delivery multicast applications that do not have   congestion notification or re-transmission error-recovery mechanisms   are inherently unidirectional.RFC 4301 only defines bi-directional   unicast traffic selectors (as perRFC 4301, Sections4.4.1 and5.1   with respect to traffic selector directionality).  The GKM subsystem   requires that the IPsec subsystem MUST support unidirectional SPD   entries, which cause a Group Security Association (GSA) to be   installed in only one direction.  Multicast applications that have   only one Group Member authorized to transmit can use this type of   Group Security Association to enforce that group policy.  In the   inverse direction, the GSA does not have an SAD entry, and the GSPD   configuration is optionally set up to discard unauthorized attempts   to transmit unicast or multicast packets to the group.   The GKM subsystem's management interface MUST have the ability to set   up a GKM subsystem group having a unidirectional GSA security policy.A.2.  Bi-Directional Reliable Multicast Applications   Some secure multicast applications are characterized as one Group   Sender to many receivers but have inverse data flows required by a   reliable multicast transport protocol (e.g., NORM).  In such   applications, the data flow from the sender is multicast and the   inverse flow from the Group's Receivers is unicast to the sender.   Typically, the inverse data flows carry error repair requests and   congestion control status.   For such applications, it is advantageous to use the same IPsec SA   for protection of both unicast and multicast data flows.  This does   introduce one risk: the IKEv2 application may choose the same SPI for   receiving unicast traffic as the GCKS chooses for a group IPsec SA   covering unicast traffic.  If both SAs are installed in the SAD, the   SA lookup may return the wrong SPI as the result of an SA lookup.  ToWeis, et al.                Standards Track                    [Page 28]

RFC 5374            Multicast Extensions toRFC 4301       November 2008   avoid this problem, IPsec SAs installed by the GKM SHOULD use the 2-   tuple {destination IP address, SPI} to identify each IPsec SA.  In   addition, the GKM SHOULD use a unicast destination IP address that   does not match any destination IP address in use by an IKEv2 unicast   IPsec SA.  For example, suppose a Group Member is using both IKEv2   and a GKM protocol, and the group security policy requires protecting   the NORM inverse data flows as described above.  In this case, group   policy SHOULD allocate and use a unique unicast destination IP   address representing the NORM Group Sender.  This address would be   configured in parallel to the Group Sender's existing IP addresses.   The GKM subsystems at both the NORM Group Sender and Group Receiver   endpoints would install the IPsec SA, protecting the NORM unicast   messages such that the SA lookup uses the unicast destination address   as well as the SPI.   The GSA SHOULD use IPsec anti-replay protection service for the   sender's multicast data flow to the group's Receivers.  Because of   the scalability problem described in the next section, it is not   practical to use the IPsec anti-replay service for the unicast   inverse flows.  Consequently, in the inverse direction, the IPsec   anti-replay protection MUST be disabled.  However, the unicast   inverse flows can use the group's IPsec group authentication   mechanism.  The Group Receiver's GSPD entry for this GSA SHOULD be   configured to only allow a unicast transmission to the sender node   rather than a multicast transmission to the whole group.   If an ESP digital signature authentication is available (e.g.,RFC4359), source authentication MAY be used to authenticate a receiver   node's transmission to the sender.  The GKM protocol MUST define a   key management mechanism for the Group Sender to validate the   asserted signature public key of any receiver node without requiring   that the sender maintain state about every Group Receiver.   This multicast application service model is RECOMMENDED because it   includes congestion control feedback capabilities.  Refer to   [RFC2914] for additional background information.   The GKM subsystem's Group Owner management interface MUST have the   ability to set up a symmetric GSPD entry and one Group Sender.  The   management interface SHOULD be able to configure a group to have at   least 16 concurrent authorized senders, each with their own GSA   anti-replay state.Weis, et al.                Standards Track                    [Page 29]

RFC 5374            Multicast Extensions toRFC 4301       November 2008A.3.  Any-To-Many Multicast Applications   Another family of secure multicast applications exhibits an "any-to-   many" communications pattern.  A representative example of such an   application is a videoconference combined with an electronic   whiteboard.   For such applications, all (or a large subset) of the Group Members   are authorized multicast senders.  In such service models, creating a   distinct IPsec SA with anti-replay state for every potential sender   does not scale to large groups.  The group SHOULD share one IPsec SA   for all of its senders.  The IPsec SA SHOULD NOT use the IPsec anti-   replay protection service for the sender's multicast data flow to the   Group Receivers.   The GKM subsystem's management interface MUST have the ability to set   up a group having an Any-To-Many Multicast GSA security policy.Appendix B.  ASN.1 for a GSPD Entry   This appendix describes an additional way to describe GSPD entries,   as defined inSection 4.1.1.  It uses ASN.1 syntax that has been   successfully compiled.  This syntax is merely illustrative and need   not be employed in an implementation to achieve compliance.  The GSPD   description inSection 4.1.1 is normative.  As shown inSection4.1.1, the GSPD updates the SPD and thus this appendix updates the   SPD object identifier.B.1.  Fields Specific to a GSPD Entry   The following fields summarize the fields of the GSPD that are not   present in the SPD.   - direction (in IPsecEntry)   - DirectionFlags   - noswap (in SelectorList)   - ap-l, ap-r (in TunnelOptions)Weis, et al.                Standards Track                    [Page 30]

RFC 5374            Multicast Extensions toRFC 4301       November 2008B.2.  SPDModule  SPDModule  {iso(1) org (3) dod (6) internet (1) security (5) mechanisms (5)   ipsec (8) asn1-modules (3) spd-module (1) }     DEFINITIONS IMPLICIT TAGS ::=     BEGIN     IMPORTS         RDNSequence FROM PKIX1Explicit88           { iso(1) identified-organization(3)             dod(6) internet(1) security(5) mechanisms(5) pkix(7)             id-mod(0) id-pkix1-explicit(18) } ;     -- An SPD is a list of policies in decreasing order of preference     SPD ::= SEQUENCE OF SPDEntry     SPDEntry ::= CHOICE {         iPsecEntry       IPsecEntry,               -- PROTECT traffic         bypassOrDiscard  [0] BypassOrDiscardEntry } -- DISCARD/BYPASS     IPsecEntry ::= SEQUENCE {       -- Each entry consists of         name        NameSets OPTIONAL,         pFPs        PacketFlags,    -- Populate from packet flags                           -- Applies to ALL of the corresponding                           -- traffic selectors in the SelectorLists         direction   DirectionFlags, -- SA directionality         condition   SelectorLists,  -- Policy "condition"         processing  Processing      -- Policy "action"         }     BypassOrDiscardEntry ::= SEQUENCE {         bypass      BOOLEAN,        -- TRUE BYPASS, FALSE DISCARD         condition   InOutBound }     InOutBound ::= CHOICE {         outbound    [0] SelectorLists,         inbound     [1] SelectorLists,         bothways    [2] BothWays }Weis, et al.                Standards Track                    [Page 31]

RFC 5374            Multicast Extensions toRFC 4301       November 2008     BothWays ::= SEQUENCE {         inbound     SelectorLists,         outbound    SelectorLists }     NameSets ::= SEQUENCE {         passed      SET OF Names-R,  -- Matched to IKE ID by                                      -- responder         local       SET OF Names-I } -- Used internally by IKE                                      -- initiator     Names-R ::= CHOICE {                   -- IKEv2 IDs         dName       RDNSequence,           -- ID_DER_ASN1_DN         fqdn        FQDN,                  -- ID_FQDNrfc822      [0] RFC822Name,        -- ID_RFC822_ADDR         keyID       OCTET STRING }         -- KEY_ID     Names-I ::= OCTET STRING       -- Used internally by IKE                                    -- initiator     FQDN ::= IA5String     RFC822Name ::= IA5String     PacketFlags ::= BIT STRING {                 -- if set, take selector value from packet                 -- establishing SA                 -- else use value in SPD entry         localAddr  (0),         remoteAddr (1),         protocol   (2),         localPort  (3),         remotePort (4)  }     DirectionFlags ::= BIT STRING {                 -- if set, install SA in the specified                 -- direction. symmetric policy is                 -- represented by setting both bits         inbound   (0),         outbound  (1)  }     SelectorLists ::= SET OF SelectorList     SelectorList ::= SEQUENCE {         localAddr   AddrList,         remoteAddr  AddrList,         protocol    ProtocolChoice,         noswap      BOOLEAN }  -- Do not swap local and remote                                -- addresses and ports on incomingWeis, et al.                Standards Track                    [Page 32]

RFC 5374            Multicast Extensions toRFC 4301       November 2008                                -- SPD-S and SPD-I checks     Processing ::= SEQUENCE {         extSeqNum   BOOLEAN, -- TRUE 64 bit counter, FALSE 32 bit         seqOverflow BOOLEAN, -- TRUE rekey, FALSE terminate & audit         fragCheck   BOOLEAN, -- TRUE stateful fragment checking,                              -- FALSE no stateful fragment checking         lifetime    SALifetime,         spi         ManualSPI,         algorithms  ProcessingAlgs,         tunnel      TunnelOptions OPTIONAL } -- if absent, use                                              -- transport mode     SALifetime ::= SEQUENCE {         seconds   [0] INTEGER OPTIONAL,         bytes     [1] INTEGER OPTIONAL }     ManualSPI ::= SEQUENCE {         spi     INTEGER,         keys    KeyIDs }     KeyIDs ::= SEQUENCE OF OCTET STRING     ProcessingAlgs ::= CHOICE {         ah          [0] IntegrityAlgs,  -- AH         esp         [1] ESPAlgs}        -- ESP     ESPAlgs ::= CHOICE {         integrity       [0] IntegrityAlgs,       -- integrity only         confidentiality [1] ConfidentialityAlgs, -- confidentiality                                                  -- only         both            [2] IntegrityConfidentialityAlgs,         combined        [3] CombinedModeAlgs }     IntegrityConfidentialityAlgs ::= SEQUENCE {         integrity       IntegrityAlgs,         confidentiality ConfidentialityAlgs }     -- Integrity Algorithms, ordered by decreasing preference     IntegrityAlgs ::= SEQUENCE OF IntegrityAlg     -- Confidentiality Algorithms, ordered by decreasing preference     ConfidentialityAlgs ::= SEQUENCE OF ConfidentialityAlgWeis, et al.                Standards Track                    [Page 33]

RFC 5374            Multicast Extensions toRFC 4301       November 2008     -- Integrity Algorithms     IntegrityAlg ::= SEQUENCE {         algorithm   IntegrityAlgType,         parameters  ANY -- DEFINED BY algorithm -- OPTIONAL }     IntegrityAlgType ::= INTEGER {         none              (0),         auth-HMAC-MD5-96  (1),         auth-HMAC-SHA1-96 (2),         auth-DES-MAC      (3),         auth-KPDK-MD5     (4),         auth-AES-XCBC-96  (5)     --  tbd (6..65535)         }     -- Confidentiality Algorithms     ConfidentialityAlg ::= SEQUENCE {         algorithm   ConfidentialityAlgType,         parameters  ANY -- DEFINED BY algorithm -- OPTIONAL }     ConfidentialityAlgType ::= INTEGER {         encr-DES-IV64   (1),         encr-DES        (2),         encr-3DES       (3),         encr-RC5        (4),         encr-IDEA       (5),         encr-CAST       (6),         encr-BLOWFISH   (7),         encr-3IDEA      (8),         encr-DES-IV32   (9),         encr-RC4       (10),         encr-NULL      (11),         encr-AES-CBC   (12),         encr-AES-CTR   (13)     --  tbd (14..65535)         }     CombinedModeAlgs ::= SEQUENCE OF CombinedModeAlg     CombinedModeAlg ::= SEQUENCE {         algorithm   CombinedModeType,         parameters  ANY -- DEFINED BY algorithm -- }                         -- defined outside                         -- of this document for AES modes.Weis, et al.                Standards Track                    [Page 34]

RFC 5374            Multicast Extensions toRFC 4301       November 2008     CombinedModeType ::= INTEGER {         comb-AES-CCM    (1),         comb-AES-GCM    (2)     --  tbd (3..65535)         }     TunnelOptions ::= SEQUENCE {         dscp        DSCP,         ecn         BOOLEAN,    -- TRUE Copy CE to inner header         ap-l        BOOLEAN,    -- TRUE Copy inner IP header                                 -- source address to outer                                 -- IP header source address         ap-r        BOOLEAN,    -- TRUE Copy inner IP header                                 -- destination address to outer                                 -- IP header destination address         df          DF,         addresses   TunnelAddresses }     TunnelAddresses ::= CHOICE {         ipv4        IPv4Pair,         ipv6        [0] IPv6Pair }     IPv4Pair ::= SEQUENCE {         local       OCTET STRING (SIZE(4)),         remote      OCTET STRING (SIZE(4)) }     IPv6Pair ::= SEQUENCE {         local       OCTET STRING (SIZE(16)),         remote      OCTET STRING (SIZE(16)) }     DSCP ::= SEQUENCE {         copy      BOOLEAN, -- TRUE copy from inner header                            -- FALSE do not copy         mapping   OCTET STRING OPTIONAL} -- points to table                                          -- if no copy     DF ::= INTEGER {         clear   (0),         set     (1),         copy    (2) }     ProtocolChoice::= CHOICE {         anyProt  AnyProtocol,              -- for ANY protocol         noNext   [0] NoNextLayerProtocol,  -- has no next layer                                            -- items         oneNext  [1] OneNextLayerProtocol, -- has one next layer                                            -- itemWeis, et al.                Standards Track                    [Page 35]

RFC 5374            Multicast Extensions toRFC 4301       November 2008         twoNext  [2] TwoNextLayerProtocol, -- has two next layer                                            -- items         fragment FragmentNoNext }          -- has no next layer                                            -- info     AnyProtocol ::= SEQUENCE {         id          INTEGER (0),    -- ANY protocol         nextLayer   AnyNextLayers }     AnyNextLayers ::= SEQUENCE {      -- with either         first       AnyNextLayer,     -- ANY next layer selector         second      AnyNextLayer }    -- ANY next layer selector     NoNextLayerProtocol ::= INTEGER (2..254)     FragmentNoNext ::= INTEGER (44)   -- Fragment identifier     OneNextLayerProtocol ::= SEQUENCE {         id          INTEGER (1..254),   -- ICMP, MH, ICMPv6         nextLayer   NextLayerChoice }   -- ICMP Type*256+Code                                         -- MH   Type*256     TwoNextLayerProtocol ::= SEQUENCE {         id          INTEGER (2..254),   -- Protocol         local       NextLayerChoice,    -- Local and         remote      NextLayerChoice }   -- Remote ports     NextLayerChoice ::= CHOICE {         any         AnyNextLayer,         opaque      [0] OpaqueNextLayer,         range       [1] NextLayerRange }     -- Representation of ANY in next layer field     AnyNextLayer ::= SEQUENCE {         start       INTEGER (0),         end         INTEGER (65535) }     -- Representation of OPAQUE in next layer field.     -- Matches IKE convention     OpaqueNextLayer ::= SEQUENCE {         start       INTEGER (65535),         end         INTEGER (0) }     -- Range for a next layer field     NextLayerRange ::= SEQUENCE {         start       INTEGER (0..65535),         end         INTEGER (0..65535) }Weis, et al.                Standards Track                    [Page 36]

RFC 5374            Multicast Extensions toRFC 4301       November 2008     -- List of IP addresses     AddrList ::= SEQUENCE {         v4List      IPv4List OPTIONAL,         v6List      [0] IPv6List OPTIONAL }     -- IPv4 address representations     IPv4List ::= SEQUENCE OF IPv4Range     IPv4Range ::= SEQUENCE {    -- close, but not quite right ...         ipv4Start   OCTET STRING (SIZE (4)),         ipv4End     OCTET STRING (SIZE (4)) }     -- IPv6 address representations     IPv6List ::= SEQUENCE OF IPv6Range     IPv6Range ::= SEQUENCE {    -- close, but not quite right ...         ipv6Start   OCTET STRING (SIZE (16)),         ipv6End     OCTET STRING (SIZE (16)) }     ENDWeis, et al.                Standards Track                    [Page 37]

RFC 5374            Multicast Extensions toRFC 4301       November 2008Authors' Addresses   Brian Weis   Cisco Systems   170 W. Tasman Drive,   San Jose, CA 95134-1706   USA   Phone: +1-408-526-4796   EMail: bew@cisco.com   George Gross   Secure Multicast Networks LLC   977 Bates Road   Shoreham, VT 05770   USA   Phone: +1-802-897-5339   EMail: gmgross@securemulticast.net   Dragan Ignjatic   Polycom   Suite 200   3605 Gilmore Way   Burnaby, BC V5G 4X5   Canada   Phone: +1-604-453-9424   EMail: dignjatic@polycom.comWeis, et al.                Standards Track                    [Page 38]