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Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 3547 (Obsoleted by RFC 6407) -- Obsolete informational reference (is this intentional?): RFC 4346 (Obsoleted by RFC 5246) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 IPDVB Working Group H. Cruickshank 2 Internet-Draft University of Surrey, UK 3 Intended status: Informational P. Pillai 4 Expires: Jan 13, 2009 University of Bradford, UK 5 M. Noisternig 6 University of Salzburg, Austria 7 S. Iyengar 8 Logica, UK 9 14 July, 2008 11 Security requirements for the Unidirectional Lightweight 12 Encapsulation (ULE) protocol 13 draft-ietf-ipdvb-sec-req-08.txt 15 Status of this Draft 17 By submitting this Internet-Draft, each author represents that 18 any applicable patent or other IPR claims of which he or she is 19 aware have been or will be disclosed, and any of which he or she 20 becomes aware will be disclosed, in accordance with Section 6 of 21 BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF), its areas, and its working groups. Note that 25 other groups may also distribute working documents as Internet- 26 Drafts. 28 Internet-Drafts are draft documents valid for a maximum of six 29 months and may be updated, replaced, or obsoleted by other 30 documents at any time. It is inappropriate to use Internet- 31 Drafts as reference material or to cite them other than as "work 32 in progress." 34 The list of current Internet-Drafts can be accessed at 35 http://www.ietf.org/ietf/1id-abstracts.txt 37 The list of Internet-Draft Shadow Directories can be accessed at 38 http://www.ietf.org/shadow.html 40 This Internet-Draft will expire on January 13, 2009. 42 Abstract 44 The MPEG-2 standard defined by ISO 13818-1 supports a range of 45 transmission methods for a range of services. This document 46 provides a threat analysis and derives the security requirements 47 when using the Transport Stream, TS, to support an Internet 48 network-layer using Unidirectional Lightweight Encapsulation 49 (ULE) defined in RFC4326. The document also provides the 50 motivation for link-layer security for a ULE Stream. A ULE Stream 51 may be used to send IPv4 packets, IPv6 packets, and other 52 Protocol Data Units (PDUs) to an arbitrarily large number of 53 Receivers supporting unicast and/or multicast transmission. 55 The analysis also describes applicability to the Generic Stream 56 Encapsulation (GSE) defined by the Digital Video Broadcasting 57 (DVB) Project. 59 Table of Contents 61 1. Introduction .............................................. 2 62 2. Requirements Notation ..................................... 4 63 3. Threat Analysis ........................................... 7 64 3.1. System Components .................................... 7 65 3.2. Threats .............................................. 9 66 3.3. Threat Cases ........................................ 10 67 4. Security Requirements for IP over MPEG-2 TS .............. 11 68 5. Design recommendations for ULE Security Extension Header . 14 69 6. Compatibility with Generic Stream Encapsulation .......... 15 70 7. Summary .................................................. 15 71 8. Security Considerations .................................. 15 72 9. IANA Considerations ...................................... 16 73 10. Acknowledgments ......................................... 16 74 11. References .............................................. 16 75 11.1. Normative References ............................... 16 76 11.2. Informative References ............................. 17 77 12. Author's Addresses ...................................... 18 78 13. Intellectual Property Statement ......................... 19 79 14. Full Copyright Statement ................................ 20 80 Appendix A: ULE Security Framework .......................... 20 81 Appendix B: Motivation for ULE link-layer security .......... 24 82 Document History ............................................ 28 84 1. Introduction 86 The MPEG-2 Transport Stream (TS) has been widely accepted not 87 only for providing digital TV services, but also as a subnetwork 88 technology for building IP networks. RFC 4326 [RFC4326] describes 89 the Unidirectional Lightweight Encapsulation (ULE) mechanism for 90 the transport of IPv4 and IPv6 Datagrams and other network 91 protocol packets directly over the ISO MPEG-2 Transport Stream as 92 TS Private Data. ULE specifies a base encapsulation format and 93 supports an Extension Header format that allows it to carry 94 additional header information to assist in network/Receiver 95 processing. The encapsulation satisfies the design and 96 architectural requirement for a lightweight encapsulation defined 97 in RFC 4259 [RFC4259]. 99 Section 3.1 of RFC 4259 presents several topological scenarios 100 for MPEG-2 Transmission Networks. A summary of these scenarios 101 are presented below (see section 3.1 of RFC 4259): 103 A. Broadcast TV and Radio Delivery. This is not within the scope 104 of this document. 106 B. Broadcast Networks used as an ISP. This resembles scenario A, 107 but includes IP services to access the public Internet. 109 C. Unidirectional Star IP Scenario. This provides a data network 110 delivering a common bit stream to typically medium-sized 111 groups of Receivers. 113 D. Datacast Overlay. This employs MPEG-2 physical and link layers 114 to provide additional connectivity such as unidirectional 115 multicast to supplement an existing IP-based Internet service. 117 E. Point-to-Point Links. This connectivity may be provided using 118 a pair of transmit and receive interfaces. 120 F. Two-Way IP Networks. 122 RFC 4259 states that ULE must be robust to errors and security 123 threats. Security must also consider both unidirectional (A, B, C 124 and D) as well as bidirectional (E and F) links for the scenarios 125 mentioned above. 127 An initial analysis of the security requirements in MPEG-2 128 transmission networks is presented in the security considerations 129 section of RFC 4259. For example, when such networks are not 130 using a wireline network, the normal security issues relating to 131 the use of wireless links for transport of Internet traffic 132 should be considered [RFC3819]. 134 The security considerations of RFC 4259 recommend that any new 135 encapsulation defined by the IETF should allow Transport Stream 136 encryption and should also support optional link-layer 137 authentication of the SNDU payload. In ULE [RFC4326], it is 138 suggested that this may be provided in a flexible way using 139 Extension Headers. This requires the definition of a mandatory 140 Extension Header, but has the advantage that it decouples 141 specification of the security functions from the encapsulation 142 functions. 144 This document extends the above analysis and derives in detail 145 the security requirements for ULE in MPEG-2 transmission 146 networks. 148 A security framework for deployment of secure ULE networks 149 describing the different building blocks and the interface 150 definitions is presented in Appendix A. 152 2. Requirements Notation 154 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 155 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and 156 "OPTIONAL" in this document are to be interpreted as described in 157 RFC2119 [RFC2119]. 159 Other terms used in this document are defined below: 161 ATSC: Advanced Television Systems Committee. A framework and a 162 set of associated standards for the transmission of video, audio, 163 and data using the ISO MPEG-2 standard. 165 DVB: Digital Video Broadcast. A framework and set of associated 166 standards published by the European Telecommunications Standards 167 Institute (ETSI) for the transmission of video, audio, and data 168 using the ISO MPEG-2 Standard [ISO-MPEG2]. 170 Encapsulator: A network device that receives PDUs and formats 171 these into Payload Units (known here as SNDUs) for output as a 172 stream of TS Packets. 174 LLC: Logical Link Control [ISO-8802], [IEEE-802]. A link-layer 175 protocol defined by the IEEE 802 standard, which follows the 176 Ethernet Medium Access Control Header. 178 MAC: Message Authentication Code. 180 MPE: Multiprotocol Encapsulation [ETSI-DAT]. A scheme that 181 encapsulates PDUs, forming a DSM-CC Table Section. Each Section 182 is sent in a series of TS Packets using a single TS Logical 183 Channel. 185 MPEG-2: A set of standards specified by the Motion Picture 186 Experts Group (MPEG) and standardized by the International 187 Standards Organisation (ISO/IEC 13818-1) [ISO-MPEG2], and ITU-T 188 (in H.222 [ITU-H222]). 190 NPA: Network Point of Attachment. In this document, refers to a 191 6-byte destination address (resembling an IEEE Medium Access 192 Control address) within the MPEG-2 transmission network that is 193 used to identify individual Receivers or groups of Receivers. 195 PDU: Protocol Data Unit. Examples of a PDU include Ethernet 196 frames, IPv4 or IPv6 datagrams, and other network packets. 198 PID: Packet Identifier [ISO-MPEG2]. A 13-bit field carried in 199 the header of TS Packets. This is used to identify the TS 200 Logical Channel to which a TS Packet belongs [ISO-MPEG2]. The TS 201 Packets forming the parts of a Table Section, PES, or other 202 Payload Unit must all carry the same PID value. The all-zeros 203 PID 0x0000 as well as other PID values is reserved for specific 204 PSI/SI Tables [ISO-MPEG2]. The all-ones PID value 0x1FFF 205 indicates a Null TS Packet introduced to maintain a constant bit 206 rate of a TS Multiplex. There is no required relationship 207 between the PID values used for TS Logical Channels transmitted 208 using different TS Multiplexes. 210 Receiver: Equipment that processes the signal from a TS Multiplex 211 and performs filtering and forwarding of encapsulated PDUs to the 212 network-layer service (or bridging module when operating at the 213 link layer). 215 SI Table: Service Information Table [ISO-MPEG2]. In this 216 document, this term describes a table that is defined by another 217 standards body to convey information about the services carried 218 in a TS Multiplex. A Table may consist of one or more Table 219 Sections; however, all sections of a particular SI Table must be 220 carried over a single TS Logical Channel [ISO-MPEG2]. 222 SNDU: SubNetwork Data Unit. An encapsulated PDU sent as an MPEG-2 223 Payload Unit. 225 TS: Transport Stream [ISO-MPEG2], a method of transmission at the 226 MPEG-2 layer using TS Packets; it represents layer 2 of the 227 ISO/OSI reference model. See also TS Logical Channel and TS 228 Multiplex. 230 TS Multiplex: In this document, this term defines a set of MPEG-2 231 TS Logical Channels sent over a single lower-layer connection. 232 This may be a common physical link (i.e., a transmission at a 233 specified symbol rate, FEC setting, and transmission frequency) 234 or an encapsulation provided by another protocol layer (e.g., 235 Ethernet, or RTP over IP). The same TS Logical Channel may be 236 repeated over more than one TS Multiplex (possibly associated 237 with a different PID value) [RFC4259]; for example, to 238 redistribute the same multicast content to two terrestrial TV 239 transmission cells. 241 TS Packet: A fixed-length 188B unit of data sent over a TS 242 Multiplex [ISO-MPEG2]. Each TS Packet carries a 4B header, plus 243 optional overhead including an Adaptation Field, encryption 244 details, and time stamp information to synchronise a set of 245 related TS Logical Channels. 247 ULE Stream: An MPEG-2 TS Logical Channel that carries only ULE 248 encapsulated PDUs. ULE Streams may be identified by definition of 249 a stream_type in SI/PSI [ISO-MPEG2]. 251 3. Threat Analysis 253 3.1. System Components 255 +------------+ +------------+ 256 | IP | | IP | 257 | End Host | | End Host | 258 +-----+------+ +------------+ 259 | ^ 260 +------------>+---------------+ | 261 + ULE | | 262 +-------------+ Encapsulator | | 263 SI-Data | +------+--------+ | 264 +-------+-------+ |MPEG-2 TS Logical Channel | 265 | MPEG-2 | | | 266 | SI Tables | | | 267 +-------+-------+ ->+------+--------+ | 268 | -->| MPEG-2 | . . . 269 +------------>+ Multiplexer | | 270 MPEG-2 TS +------+--------+ | 271 Logical Channel |MPEG-2 TS Mux | 272 | | 273 Other ->+------+--------+ | 274 MPEG-2 -->+ MPEG-2 | | 275 TS --->+ Multiplexer | | 276 ---->+------+--------+ | 277 |MPEG-2 TS Mux | 278 | | 279 +------+--------+ +------+-----+ 280 |Physical Layer | | MPEG-2 | 281 |Modulator +---------->+ Receiver | 282 +---------------+ MPEG-2 +------------+ 283 TS Mux 284 Figure 1: An example configuration for a unidirectional service 285 for IP transport over MPEG-2 (adapted from [RFC4259]). 287 As shown in Figure 1 above (from section 3.3 of [RFC4259]), there 288 are several entities within the MPEG-2 transmission network 289 architecture. These include: 291 o ULE Encapsulation Gateways (the ULE Encapsulator) 293 o SI-Table signalling generator (input to the multiplexer) 295 o Receivers (the endpoints for ULE Streams) 296 o TS multiplexers (including re-multiplexers) 298 o Modulators 300 The TS Packets are carried to the Receiver over a physical layer 301 that usually includes Forward Error Correction (FEC) coding that 302 interleaves the bytes of several consecutive, but unrelated, TS 303 Packets. FEC-coding and synchronisation processing makes 304 injection of single TS Packets very difficult. Replacement of a 305 sequence of packets is also difficult, but possible (see section 306 3.2). 308 A Receiver in an MPEG-2 TS transmission network needs to identify 309 a TS Logical Channel (or MPEG-2 Elementary Stream) to reassemble 310 the fragments of PDUs sent by a L2 source [RFC4259]. In an MPEG-2 311 TS, this association is made via the Packet Identifier, PID [ISO- 312 MPEG2]. At the sender, each source associates a locally unique 313 set of PID values with each stream it originates. However, there 314 is no required relationship between the PID value used at the 315 sender and that received at the Receiver. Network devices may re- 316 number the PID values associated with one or more TS Logical 317 Channels (e.g. ULE Streams) to prevent clashes at a multiplexer 318 between input streams with the same PID carried on different 319 input multiplexes (updating entries in the PMT [ISO-MPEG2], and 320 other SI tables that reference the PID value). A device may also 321 modify and/or insert new SI data into the control plane (also 322 sent as TS Packets identified by their PID value). However, there 323 is only one valid source of data for each MPEG-2 Elementary 324 Stream, bound to a PID value. (This observation could simplify 325 the requirement for authentication of the source of a ULE 326 Stream.) 328 In an MPEG-2 network a set of signalling messages [RFC4947] may 329 need to be broadcast (e.g. by an Encapsulation Gateway or other 330 device) to form the L2 control plane. Examples of signalling 331 messages include the Program Association Table (PAT), Program Map 332 Table (PMT) and Network Information Table (NIT). In existing 333 MPEG-2 transmission networks, these messages are broadcast in the 334 clear (no encryption or integrity checks). The integrity as well 335 as authenticity of these messages is important for correct 336 working of the ULE network, i.e. supporting its security 337 objectives in the area of availability, in addition to 338 confidentiality and integrity. One method recently proposed 339 [RFC5163] encapsulates these messages using ULE. In such cases 340 all the security requirements of this document apply in securing 341 these signalling messages. 343 ULE Stream security only concerns the security between the ULE 344 Encapsulation Gateway (ULE Encapsulator) and the Receiver. In 345 many deployment scenarios the user of a ULE Stream has to secure 346 communications beyond the link since other network links are 347 utilised in addition to the ULE link. Therefore, if 348 authentication of the end-points, i.e. the IP Sources is 349 required, or users are concerned about loss of confidentiality, 350 integrity, or authenticity of their communication data, they will 351 have to employ end-to-end network security mechanisms, e.g. IPsec 352 or Transport Layer Security (TLS). Governmental users may be 353 forced by regulations to employ specific approved implementations 354 of those mechanisms. Hence for such cases, the requirements for 355 confidentiality and integrity of the user data will be met by the 356 end-to-end security mechanism and the ULE security measures would 357 focus on either providing traffic flow confidentiality for user 358 data that has already been encrypted or for users who choose not 359 to implement end-to-end security mechanisms. 361 ULE links may also be used for communications where the two IP 362 end-points are not under central control (e.g., when browsing a 363 public web site). In these cases, it may be impossible to enforce 364 any end-to-end security mechanisms. Yet, a common objective is 365 that users may make the same security assumptions as for wired 366 links [RFC3819]. ULE security could achieve this by protecting 367 the vulnerable (in terms of passive attacks) ULE Stream. 369 In contrast to the above, a ULE Stream can be used to link 370 networks such as branch offices to a central office. ULE link- 371 layer security could be the sole provider of confidentiality and 372 integrity. In this scenario, users requiring high assurance of 373 security (e.g. government use) will need to employ approved 374 cryptographic equipment (e.g. at the network layer). An 375 implementation of ULE Link Security equipment could also be 376 certified for use by specific user communities. 378 3.2. Threats 380 The simplest type of network threat is a passive threat. This 381 includes eavesdropping or monitoring of transmissions, with a 382 goal to obtain information that is being transmitted. In 383 broadcast networks (especially those utilising widely available 384 low-cost physical layer interfaces, such as DVB) passive threats 385 are the major threats. One example is an intruder monitoring the 386 MPEG-2 transmission broadcast and then extracting the data 387 carried within the link. Another example is an intruder trying to 388 determine the identity of the communicating parties and the 389 volume of their traffic by sniffing (L2) addresses. This is a 390 well-known issue in the security field; however it is more of a 391 problem in the case of broadcast networks such as MPEG-2 392 transmission networks because of the easy availability of 393 Receiver hardware and the wide geographical span of the networks. 395 Active threats (or attacks) are, in general, more difficult to 396 implement successfully than passive threats, and usually require 397 more sophisticated resources and may require access to the 398 transmitter. Within the context of MPEG-2 transmission networks, 399 examples of active attacks are: 401 o Masquerading: An entity pretends to be a different entity. 402 This includes masquerading other users and subnetwork control 403 plane messages. 405 o Modification of messages in an unauthorised manner. 407 o Replay attacks: When an intruder sends some old (authentic) 408 messages to the Receiver. In the case of a broadcast link, 409 access to previous broadcast data is easy. 411 o Denial-of-Service (DoS) attacks: When an entity fails to 412 perform its proper function or acts in a way that prevents 413 other entities from performing their proper functions. 415 The active threats mentioned above are major security concerns 416 for the Internet community [BELLOVIN]. Masquerading and 417 modification of IP packets are comparatively easy in an Internet 418 environment, whereas such attacks are in fact much harder for 419 MPEG-2 broadcast links. This could for instance motivate the 420 mandatory use of sequence numbers in IPsec, but not for 421 synchronous links. This is further reflected in the security 422 requirements for Case 2 and 3 in section 4 below. 424 As explained in section 3.1, the PID associated with an 425 Elementary Stream can be modified (e.g. in some systems by 426 reception of an updated SI table, or in other systems until the 427 next announcement/discovery data is received). An attacker that 428 is able to modify the content of the received multiplex (e.g. 429 replay data and/or control information) could inject data locally 430 into the received stream with an arbitrary PID value. 432 3.3. Threat Cases 434 Analysing the topological scenarios for MPEG-2 Transmission 435 Networks in section 1, the security threats can be abstracted 436 into three cases: 438 o Case 1: Monitoring (passive threat). Here the intruder 439 monitors the ULE broadcasts to gain information about the ULE 440 data and/or tracking the communicating parties identities (by 441 monitoring the destination NPA). In this scenario, measures 442 must be taken to protect the ULE payload data and the identity 443 of ULE Receivers. 445 o Case 2: Locally conduct active attacks on the MPEG-TS 446 multiplex. Here an intruder is assumed to be sufficiently 447 sophisticated to over-ride the original transmission from the 448 ULE Encapsulation Gateway and deliver a modified version of 449 the MPEG-TS transmission to a single ULE Receiver or a small 450 group of Receivers (e.g. in a single company site). The MPEG-2 451 transmission network operator might not be aware of such 452 attacks. Measures must be taken to ensure ULE data integrity 453 and authenticity and preventing replay of old messages. 455 o Case 3: Globally conduct active attacks on the MPEG-TS 456 multiplex. This assumes a sophisticated intruder able to over- 457 ride the whole MPEG-2 transmission multiplex. The requirements 458 are similar to scenario 2. The MPEG-2 transmission network 459 operator can usually identify such attacks and provide 460 corrective action to restore the original transmission. 462 For both Cases 2 and 3, there can be two sub-cases: 464 o Insider attacks, i.e. active attacks from adversaries within 465 the network with knowledge of the secret material. 467 o Outsider attacks, i.e. active attacks from outside of a 468 virtual private network. 470 In terms of priority, Case 1 is considered the major threat in 471 MPEG-2 transmission systems. Case 2 is considered a lesser 472 threat, appropriate to specific network configurations, 473 especially when vulnerable to insider attacks. Case 3 is less 474 likely to be found in an operational network, and is expected to 475 be noticed by the MPEG-2 transmission operator. It will require 476 restoration of the original transmission. The assumption being 477 that physical access to the network components (multiplexers, 478 etc) and/or connecting physical media is secure. Therefore Case 3 479 is not considered further in this document. 481 4. Security Requirements for IP over MPEG-2 TS 483 From the threat analysis in section 3, the following security 484 requirements can be derived: 486 Req 1. Data confidentiality MUST be provided by a link that 487 supports ULE Stream Security to prevent passive attacks and 488 reduce the risk of active threats. 490 Req 2. Protection of L2 NPA address is OPTIONAL. In broadcast 491 networks this protection can be used to prevent an intruder 492 tracking the identity of ULE Receivers and the volume of their 493 traffic. 495 Req 3. Integrity protection and source authentication of ULE 496 Stream data are OPTIONAL. These can be used to prevent active 497 attacks described in section 3.2. 499 Req 4. Protection against replay attacks is OPTIONAL. This is 500 used to counter active attacks described in section 3.2. 502 Req 5. L2 ULE Source and Receiver authentication is OPTIONAL. 503 This can be performed during the initial key exchange and 504 authentication phase, before the ULE Receiver can join a 505 secure session with the ULE Encapsulator (ULE source). This 506 could be either unidirectional or bidirectional authentication 507 based on the underlying key management protocol. 509 Other general requirements for all threat cases for link-layer 510 security are: 512 GReq (a) ULE key management functions MUST be decoupled from ULE 513 security services such as encryption and source authentication. 514 This allows the independent development of both systems. 516 GReq (b) Support SHOULD be provided for automated as well as 517 manual insertion of keys and policy into the relevant 518 databases. 520 GReq (c) Algorithm agility MUST be supported. It should be 521 possible to update the crypto algorithms and hashes when they 522 become obsolete without affecting the overall security of the 523 system. 525 GReq (d) The security extension header MUST be compatible with 526 other ULE extension headers. The method must allow other 527 extension headers (either mandatory or optional) to be used in 528 combination with a security extension. It is RECOMMENDED that 529 these are placed after the security extension header. This 530 permits full protection for all headers. It also avoids 531 situations where the SNDU has to be discarded on processing the 532 security extension header, while preceding headers have already 533 been evaluated. One exception is the Timestamp extension which 534 SHOULD precede the security extension header [RFC5163]. In this 535 case, the timestamp will be unaffected by security services 536 such as data confidentiality and can be decoded without the 537 need for key material. 539 Examining the threat cases in section 3.3, the security 540 requirements for each case can be summarised as: 542 o Case 1: Data confidentiality (Req 1) MUST be provided to 543 prevent monitoring of the ULE data (such as user information 544 and IP addresses). Protection of NPA addresses (Req 2) MAY be 545 provided to prevent tracking ULE Receivers and their 546 communications. 548 o Case 2: In addition to Case 1 requirements, new measures MAY 549 be implemented such as authentication schemes using Message 550 Authentication Codes, digital signatures, or TESLA [RFC4082] 551 in order to provide integrity protection and source 552 authentication (Req 2, Req 3 and Req 5). In addition, sequence 553 numbers (Req 4) MAY be used to protect against replay attacks. 554 In terms of outsider attacks, group authentication using 555 Message Authentication Codes should provide the same level of 556 security (Req 3 and 5). This will significantly reduce the 557 ability of intruders to successfully inject their own data 558 into the MPEG-TS stream. However, scenario 2 threats apply 559 only in specific service cases, and therefore authentication 560 and protection against replay attacks are OPTIONAL. Such 561 measures incur additional transmission as well as processing 562 overheads. Moreover, intrusion detection systems may also be 563 needed by the MPEG-2 network operator. These should best be 564 coupled with perimeter security policy to monitor common DoS 565 attacks. 567 o Case 3: As stated in section 3.3, the requirements here are 568 similar to Case 2, but since the MPEG-2 transmission network 569 operator can usually identify such attacks, the constraints on 570 intrusion detections are less than in Case 2. 572 Table 1 below shows the threats that are applicable to ULE 573 networks, and the relevant security mechanisms to mitigate those 574 threats. 576 Mitigation of Threat 577 ----------------------------------------------- 578 |Data |Data |Source |Data |Intru |Iden | 579 |Privacy |fresh |Authent|Integ |sion |tity | 580 | |ness |ication|rity |Dete |Prote | 581 | | | | |ction |ction | 582 Attack | | | | | | | 583 ---------------|--------|-------|-------|-------|-------|------| 584 | Monitoring | X | - | - | - | - | X | 585 |---------------------------------------------------------------| 586 | Masquerading | X | - | X | X | - | X | 587 |---------------------------------------------------------------| 588 | Replay Attacks| - | X | X | X | X | - | 589 |---------------------------------------------------------------| 590 | DoS Attacks | - | X | X | X | X | - | 591 |---------------------------------------------------------------| 592 | Modification | - | - | X | X | X | - | 593 | of Messages | | | | | | | 594 --------------------------------------------------------------- 595 Table 1: Security techniques to mitigate network threats 596 in ULE Networks. 598 5. Design recommendations for ULE Security Extension Header 600 Table 1 may assist in selecting fields within a ULE Security 601 Extension Header framework. 603 Security services may be grouped into profiles based on security 604 requirements, e.g. a base profile (with payload encryption and 605 identity protection), and a second profile that extends this to 606 also provide source authentication and protection against replay 607 attacks. 609 A modular design of ULE security may allow it to use and benefit 610 from existing key management protocols, such as GSAKMP [RFC4535] 611 and GDOI [RFC3547] defined by the IETF Multicast Security (MSEC) 612 working group. This does not preclude the use of other key 613 management methods in scenarios where this is more appropriate. 615 IPsec [RFC4301] and TLS [RFC4346] also provide a proven security 616 architecture defining key exchange mechanisms and the ability to 617 use a range of cryptographic algorithms. ULE security can make 618 use of these established mechanisms and algorithms. See appendix 619 A for more details. 621 6. Compatibility with Generic Stream Encapsulation 623 RFC 5163 [RFC5163] describes three new Extension Headers that may 624 be used with Unidirectional Link Encapsulation, ULE, [RFC4326] 625 and the Generic Stream Encapsulation (GSE) that has been designed 626 for the Generic Mode (also known as the Generic Stream (GS)), 627 offered by second-generation DVB physical layers [GSE]. 629 The security threats and requirement presented in this document 630 are applicable to ULE and GSE encapsulations. 632 7. Summary 634 This document analyses a set of threats and security 635 requirements. It defines the requirements for ULE security and 636 states the motivation for link security as a part of the 637 Encapsulation layer. 639 ULE security must provide link-layer encryption and ULE Receiver 640 identity protection. The framework must support the optional 641 ability to provide for link-layer authentication and integrity 642 assurance, as well as protection against insertion of old 643 (duplicated) data into the ULE Stream (i.e. replay protection). 644 This set of features is optional to reduce encapsulation overhead 645 when not required. 647 ULE Stream security between a ULE Encapsulation Gateway and the 648 corresponding Receiver(s) is considered an additional security 649 mechanism to IPsec, TLS, and application layer end-to-end 650 security, and not as a replacement. It allows a network operator 651 to provide similar functions to that of IPsec, but in addition 652 provides MPEG-2 transmission link confidentiality and protection 653 of ULE Receiver identity (NPA). 655 Annexe 1 describes a set of building blocks that may be used to 656 realise a framework that provides ULE security functions. 658 8. Security Considerations 660 Link-layer (L2) encryption of IP traffic is commonly used in 661 broadcast/radio links to supplement end-to-end security (e.g. 662 provided by TLS [RFC4346], SSH [RFC4251], IPsec [RFC4301). 664 A common objective is to provide the same level of privacy as 665 wired links. It is recommended that an ISP or user provide end- 666 to-end security services based on well known mechanisms such as 667 IPsec or TLS. 669 This document provides a threat analysis and derives the security 670 requirements to provide link encryption and optional link-layer 671 integrity / authentication of the SNDU payload. 673 There are some security issues that were raised in RFC 4326 674 [RFC4326] that are not addressed in this document (i.e. are out 675 of scope), e.g.: 677 o The security issue with un-initialised stuffing bytes. In ULE, 678 these bytes are set to 0xFF (normal practice in MPEG-2). 680 o Integrity issues related to the removal of the LAN FCS in a 681 bridged networking environment. The removal for bridged frames 682 exposes the traffic to potentially undetected corruption while 683 being processed by the Encapsulator and/or Receiver. 685 o There is a potential security issue when a Receiver receives a 686 PDU with two Length fields: The Receiver would need to 687 validate the actual length and the Length field and ensure 688 that inconsistent values are not propagated by the network. 690 9. IANA Considerations 692 There are no IANA actions defined in this document. 694 10. Acknowledgments 696 The authors acknowledge the help and advice from Gorry Fairhurst 697 (University of Aberdeen). The authors also acknowledge 698 contributions from Laurence Duquerroy and Stephane Coombes (ESA), 699 and Yim Fun Hu (University of Bradford). 701 11. References 703 11.1. Normative References 705 [ISO-MPEG2] "Information technology -- generic coding of moving 706 pictures and associated audio information systems, 707 Part I", ISO 13818-1, International Standards 708 Organisation (ISO), 2000. 710 [RFC2119] Bradner, S., "Key Words for Use in RFCs to Indicate 711 Requirement Levels", BCP 14, RFC 2119, 1997. 713 [RFC4326] Fairhurst, G. and B. Collini-Nocker, "Unidirectional 714 Lightweight Encapsulation (ULE) for Transmission of 715 IP Datagrams over an MPEG-2 Transport Stream (TS)", 716 IETF RFC 4326, December 2005. 718 11.2. Informative References 720 [RFC4947] G. Fairhurst, M.-J. Montpetit, "Address Resolution 721 Mechanisms for IP Datagrams over MPEG-2 Networks", 722 IETF RFC 4947, July 2007. 724 [RFC5163] G. Fairhurst and B. Collini-Nocker, "Extension Header 725 formats for Unidirectional Lightweight Encapsulation 726 (ULE) and the Generic Stream Encapsulation (GSE)", 727 IETF RFC 5163, April 2008. 729 [IEEE-802] "Local and metropolitan area networks-Specific 730 requirements Part 2: Logical Link Control", IEEE 731 802.2, IEEE Computer Society, (also ISO/IEC 8802-2), 732 1998. 734 [ISO-8802] ISO/IEC 8802.2, "Logical Link Control", International 735 Standards Organisation (ISO), 1998. 737 [ITU-H222] H.222.0, "Information technology, Generic coding of 738 moving pictures and associated audio information 739 Systems", International Telecommunication Union, 740 (ITU-T), 1995. 742 [RFC4259] M.-J. Montpetit, G. Fairhurst, H. Clausen, B. 743 Collini-Nocker, and H. Linder, "A Framework for 744 Transmission of IP Datagrams over MPEG-2 Networks", 745 IETF RFC 4259, November 2005. 747 [ETSI-DAT] EN 301 192, "Digital Video Broadcasting (DVB); DVB 748 Specifications for Data Broadcasting", European 749 Telecommunications Standards Institute (ETSI). 751 [BELLOVIN] S. Bellovin, "Problem Area for the IP Security 752 protocols", Computer Communications Review 2:19, pp. 753 32-48, April 989. http://www.cs.columbia.edu/~smb/ 755 [GSE] TS 102 606, "Digital Video Broadcasting (DVB); 756 Generic Stream Encapsulation (GSE) Protocol, 757 "European Telecommunication Standards, Institute 758 (ETSI), 2007. 760 [RFC4082] A. Perrig, D. Song, "Timed Efficient Stream Loss- 761 Tolerant Authentication (TESLA): Multicast Source 762 Authentication Transform Introduction", IETF RFC 763 4082, June 2005. 765 [RFC4535] H. Harney, et al, "GSAKMP: Group Secure Association 766 Group Management Protocol", IETF RFc 4535, June 2006. 768 [RFC3547] M. Baugher, et al, "GDOI: The Group Domain of 769 Interpretation", IETF RFC 3547. 771 [WEIS08] B. Weis, et al, "Multicast Extensions to the Security 772 Architecture for the Internet", , June 2008, IETF Work in 774 Progress. 776 [RFC3715] B. Aboba, W. Dixson, "IPsec-Network Address 777 Translation (NAT) Compatibility Requirements" IETF 778 RFC 3715, March 2004. 780 [RFC4346] T. Dierks, E. Rescorla, "The Transport Layer Security 781 (TLS) Protocol Version 1.1", IETF RFC 4346, April 782 2006. 784 [RFC3135] J. Border, M. Kojo, eyt. al., "Performance Enhancing 785 Proxies Intended to Mitigate Link-Related 786 Degradations", IETF RFC 3135, June 2001. 788 [RFC4301] S. Kent, K. Seo, "Security Architecture for the 789 Internet Protocol", IETF RFC 4301, December 2006. 791 [RFC3819] P. Karn, C. Bormann, G. Fairhurst, D. Grossman, R. 792 Ludwig, J. Mahdavi, G. Montenegro, J. Touch, and L. 793 Wood, "Advice for Internet Subnetwork Designers", BCP 794 89, IETF RFC 3819, July 2004. 796 [RFC4251] T. Ylonen, C. Lonvick, Ed., "The Secure Shell (SSH) 797 Protocol Architecture", IETF RFC 4251, January 2006. 799 12. Author's Addresses 801 Haitham Cruickshank 802 Centre for Communications System Research (CCSR) 803 University of Surrey 804 Guildford, Surrey, GU2 7XH 805 UK 806 Email: h.cruickshank@surrey.ac.uk 807 Prashant Pillai 808 Mobile and Satellite Communications Research Centre (MSCRC) 809 School of Engineering, Design and Technology 810 University of Bradford 811 Richmond Road, Bradford BD7 1DP 812 UK 813 Email: p.pillai@bradford.ac.uk 815 Michael Noisternig 816 Multimedia Comm. Group, Dpt. of Computer Sciences 817 University of Salzburg 818 Jakob-Haringer-Str. 2 819 5020 Salzburg 820 Austria 821 Email: mnoist@cosy.sbg.ac.at 823 Sunil Iyengar 824 Space & Defence 825 Logica 826 Springfield Drive 827 Leatherhead 828 Surrey KT22 7LP 829 UK 830 Email: sunil.iyengar@logica.com 832 13. Intellectual Property Statement 834 The IETF takes no position regarding the validity or scope of any 835 Intellectual Property Rights or other rights that might be 836 claimed to pertain to the implementation or use of the technology 837 described in this document or the extent to which any license 838 under such rights might or might not be available; nor does it 839 represent that it has made any independent effort to identify any 840 such rights. Information on the procedures with respect to 841 rights in RFC documents can be found in BCP 78 and BCP 79. 843 Copies of IPR disclosures made to the IETF Secretariat and any 844 assurances of licenses to be made available, or the result of an 845 attempt made to obtain a general license or permission for the 846 use of such proprietary rights by implementers or users of this 847 specification can be obtained from the IETF on-line IPR 848 repository at http://www.ietf.org/ipr. 850 The IETF invites any interested party to bring to its attention 851 any copyrights, patents or patent applications, or other 852 proprietary rights that may cover technology that may be required 853 to implement this standard. Please address the information to 854 the IETF at ietf-ipr@ietf.org. 856 14. Full Copyright Statement 858 Copyright (C) The IETF Trust (2008). 860 This document is subject to the rights, licenses and restrictions 861 contained in BCP 78, and except as set forth therein, the authors 862 retain all their rights. 864 This document and the information contained herein are provided 865 on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 866 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE 867 IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL 868 WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY 869 WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE 870 ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR 871 FITNESS FOR A PARTICULAR PURPOSE. 873 Appendix A: ULE Security Framework 875 This section describes a security framework for the deployment of 876 secure ULE networks. 878 A.1 Building Blocks 880 This ULE Security framework describes the following building 881 blocks as shown in figure 2 below: 883 o The Key Management Block 885 o The ULE Security Extension Header Block 887 o The ULE Databases Block 889 Within the Key Management Block the communication between the 890 Group Member entity and the Group Server entity happens in the 891 control plane. The ULE Security Header Block applies security to 892 the ULE SNDU and this happens in the ULE data plane. The ULE 893 Security Databases Block acts as the interface between the Key 894 Management Block (control plane) and the ULE Security Header 895 Block (ULE data plane) as shown in figure 2. 897 ----- 898 +------+----------+ +----------------+ / \ 899 | Key Management |/---------\| Key Management | | 900 | Block |\---------/| Block | | 901 | Group Member | | Group Server | Control 902 +------+----------+ +----------------+ Plane 903 | | | 904 | | | 905 | | \ / 906 ----------- Key management <-> ULE Security databases ----- 907 | | 908 \ / 909 +------+----------+ 910 | ULE | 911 | SAD / SPD | 912 | Databases | 913 | Block | 914 +------+-+--------+ 915 / \ 916 | | 917 ----------- ULE Security databases <-> ULE Security Header ---- 918 | | / \ 919 | | | 920 | | | 921 +------+-+--------+ ULE Data 922 | ULE Security | Plane 923 | Extension Header| | 924 | Block | | 925 +-----------------+ \ / 926 ----- 928 Figure 2: Secure ULE Framework Building Blocks 930 A.1.1 Key Management Block 932 A key management framework is required to provide security at the 933 ULE level using extension headers. This key management framework 934 is responsible for user authentication, access control, and 935 Security Association negotiation (which include the negotiations 936 of the security algorithms to be used and the generation of the 937 different session keys as well as policy material). The key 938 management framework can be either automated or manual. Hence 939 this key management client entity (shown as the Key Management 940 Group Member Block in figure 2) will be present in all ULE 941 Receivers as well as at the ULE Encapsulators. The ULE 942 Encapsulator could also be the Key Management Group Server Entity 943 (shown as the Key Management Group Server Block in figure 2. This 944 happens when the ULE Encapsulator also acts as the Key Management 945 Group Server. Deployment may use either automated key management 946 protocols (e.g. GSAKMP [RFC4535]) or manual insertion of keying 947 material. 949 A.1.2 ULE Extension Header Block 951 A new security extension header for the ULE protocol is required 952 to provide the security features of data confidentiality, data 953 integrity, data authentication, and mechanisms to prevent replay 954 attacks. Security keying material will be used for the different 955 security algorithms (for encryption/decryption, MAC generation, 956 etc.), which are used to meet the security requirements, 957 described in detail in Section 4 of this document. 959 This block will use the keying material and policy information 960 from the ULE Security Database Block on the ULE payload to 961 generate the secure ULE Extension Header or to decipher the 962 secure ULE extension header to get the ULE payload. An example 963 overview of the ULE Security extension header format along with 964 the ULE header and payload is shown in figure 3 below. 966 +-------+------+-------------------------------+------+ 967 | ULE |SEC | Protocol Data Unit | | 968 |Header |Header| |CRC-32| 969 +-------+------+-------------------------------+------+ 970 Figure 3: ULE Security Extension Header Placement 972 A.1.3 ULE Security Databases Block 974 There needs to be two databases, i.e. similar to the IPsec 975 databases. 977 o ULE-SAD: ULE Security Association Database contains all the 978 Security Associations that are currently established with 979 different ULE peers. 981 o ULE-SPD: ULE Security Policy Database contains the policies as 982 described by the system manager. These policies describe the 983 security services that must be enforced. 985 The design of these two databases may be based on IPsec databases 986 as defined in RFC4301 [RFC4301]. 988 The exact details of the header patterns that the SPD and SAD 989 will have to support for all use cases will be described in a 990 separate document. This document only highlights the need for 991 such interfaces between the ULE data plane and the Key Management 992 control plane. 994 A.2 Interface definition 996 Two new interfaces have to be defined between the blocks as shown 997 in Figure 2 above. These interfaces are: 999 o Key Management Block <-> ULE Security Databases Block 1001 o ULE Security Databases Block <-> ULE Security Header Block 1003 While the first interface is used by the Key Management Block to 1004 insert keys, security associations and policies into the ULE 1005 Database Block, the second interface is used by the ULE Security 1006 Extension Header Block to get the keys and policy material for 1007 generation of the security extension header. 1009 A.2.1 Key Management <-> ULE Security databases 1011 This interface is between the Key Management Block of a group 1012 member (GM client) and the ULE Security Database Block (shown in 1013 figure 2). The Key Management GM entity will communicate with the 1014 GCKS and then get the relevant security information (keys, cipher 1015 mode, security service, ULE_Security_ID and other relevant keying 1016 material as well as policy) and insert this data into the ULE 1017 Security Database Block. The Key Management could be either 1018 automated (e.g. GSAKMP [RFC4535] or GDOI [RFC3547]), or security 1019 information could be manually inserted using this interface. 1021 Examples of interface functions are: 1023 o Insert_record_database (char * Database, char * record, char * 1024 Unique_ID); 1026 o Update_record_database (char * Database, char * record, char * 1027 Unique_ID); 1029 o Delete_record_database (char * Database, char * Unique_ID); 1031 The definitions of the variables are as follows: 1033 o Database - This is a pointer to the ULE Security databases 1035 o record - This is the rows of security attributes to be entered 1036 or modified in the above databases 1038 o Unique_ID - This is the primary key to lookup records (rows of 1039 security attributes) in the above databases 1041 A.2.2 ULE Security Databases <-> ULE Security Header 1043 This interface is between the ULE Security Database and the ULE 1044 Security Extension Header Block as shown in figure 2. When 1045 sending traffic, the ULE encapsulator uses the Destination 1046 Address, the PID, and possibly other information such as L3 1047 source and destination addresses to locate the relevant security 1048 record within the ULE Security Database. It then uses the data in 1049 the record to create the ULE security extension header. For 1050 received traffic, the ULE decapsulator on receiving the ULE SNDU 1051 will use the Destination Address, the PID, and a ULE Security ID 1052 inserted by the ULE encapsulator into the security extension to 1053 retrieve the relevant record from the Security Database. It then 1054 uses this information to decrypt the ULE extension header. For 1055 both cases (either send or receive traffic) only one interface is 1056 needed since the main difference between the sender and receiver 1057 is the direction of the flow of traffic. An example of such 1058 interface is as follows: 1060 o Get_record_database (char * Database, char * record, char * 1061 Unique_ID); 1063 Appendix B: Motivation for ULE link-layer security 1065 Examination of the threat analysis and security requirements in 1066 sections 3 and 4 has shown that there is a need to provide 1067 security in MPEG-2 transmission networks employing ULE. This 1068 section compares the placement of security functionalities in 1069 different layers. 1071 B.1 Security at the IP layer (using IPsec) 1073 The security architecture for the Internet Protocol [RFC4301] 1074 describes security services for traffic at the IP layer. This 1075 architecture primarily defines services for the Internet Protocol 1076 (IP) unicast packets, as well as manually configured IP multicast 1077 packets. 1079 It is possible to use IPsec to secure ULE Streams. The major 1080 advantage of IPsec is its wide implementation in IP routers and 1081 hosts. IPsec in transport mode can be used for end-to-end 1082 security transparently over MPEG-2 transmission links with little 1083 impact. 1085 In the context of MPEG-2 transmission links, if IPsec is used to 1086 secure a ULE Stream, then the ULE Encapsulator and Receivers are 1087 equivalent to the security gateways in IPsec terminology. A 1088 security gateway implementation of IPsec uses tunnel mode. Such 1089 usage has the following disadvantages: 1091 o There is an extra transmission overhead associated with using 1092 IPsec in tunnel mode, i.e. the extra IP header (IPv4 or IPv6). 1094 o There is a need to protect the identity (NPA) of ULE Receivers 1095 over the ULE broadcast medium; IPsec is not suitable for 1096 providing this service. In addition, the interfaces of these 1097 devices do not necessarily have IP addresses (they can be L2 1098 devices). 1100 o Multicast is considered a major service over ULE links. The 1101 current IPsec specifications [RFC4301] only define a pairwise 1102 tunnel between two IPsec devices with manual keying. Work is 1103 in progress in defining the extra detail needed for multicast 1104 and to use the tunnel mode with address preservation to allow 1105 efficient multicasting. For further details refer to [WEIS08]. 1107 B.2 Link security below the encapsulation layer 1109 Link layer security can be provided at the MPEG-2 TS layer (below 1110 ULE). MPEG-2 TS encryption encrypts all TS Packets sent with a 1111 specific PID value. However, an MPEG-2 TS may typically multiplex 1112 several IP flows, belonging to different users, using a common 1113 PID. Therefore all multiplexed traffic will share the same 1114 security keys. 1116 This has the following advantages: 1118 o The bit stream sent on the broadcast network does not expose 1119 any L2 or L3 headers, specifically all addresses, type fields, 1120 and length fields are encrypted prior to transmission. 1122 o This method does not preclude the use of IPsec, TLS, or any 1123 other form of higher-layer security. 1125 However it has the following disadvantages: 1127 o When a PID is shared between several users, each ULE Receiver 1128 needs to decrypt all MPEG-2 TS Packets with a matching PID, 1129 possibly including those that are not required to be 1130 forwarded. Therefore it does not have the flexibility to 1131 separately secure individual IP flows. 1133 o When a PID is shared between several users, the ULE Receivers 1134 will have access to private traffic destined to other ULE 1135 Receivers, since they share a common PID and key. 1137 o IETF-based key management that is very flexible and secure is 1138 not used in existing MPEG-2 based systems. Existing access 1139 control mechanisms in such systems have limited flexibility in 1140 terms of controlling the use of key and rekeying. Therefore if 1141 the key is compromised, then this will impact several ULE 1142 Receivers. 1144 Currently there are few deployed L2 security systems for MPEG-2 1145 transmission networks. Conditional access for digital TV 1146 broadcasting is one example. However, this approach is optimised 1147 for TV services and is not well-suited to IP packet transmission. 1148 Some other systems are specified in standards such as MPE [ETSI- 1149 DAT], but there are currently no known implementations and these 1150 methods are not applicable to GSE. 1152 B.3 Link security as a part of the encapsulation layer 1154 Examining the threat analysis in section 3 has shown that 1155 protection of ULE Stream from eavesdropping and ULE Receiver 1156 identity are major requirements. 1158 There are several major advantages in using ULE link layer 1159 security: 1161 o The protection of the complete ULE Protocol Data Unit (PDU) 1162 including IP addresses. The protection can be applied either 1163 per IP flow or per Receiver NPA address. 1165 o Ability to protect the identity of the Receiver within the 1166 MPEG-2 transmission network at the IP layer and also at L2. 1168 o Efficient protection of IP multicast over ULE links. 1170 o Transparency to the use of Network Address Translation (NATs) 1171 [RFC3715] and TCP Performance Enhancing Proxies (PEP) 1172 [RFC3135], which require the ability to inspect and modify the 1173 packets sent over the ULE link. 1175 This method does not preclude the use of IPsec at L3 (or TLS 1176 [RFC4346] at L4). IPsec and TLS provide strong authentication of 1177 the end-points in the communication. 1179 L3 end-to-end security would partially deny the advantage listed 1180 above (use of PEP, compression etc), since those techniques could 1181 only be applied to TCP packets bearing a TCP-encapsulated IPsec 1182 packet exchange, but not the TCP packets of the original 1183 applications, which in particular inhibits compression. 1185 End-to-end security (IPsec, TLS, etc.) may be used independently 1186 to provide strong authentication of the end-points in the 1187 communication. This authentication is desirable in many scenarios 1188 to ensure that the correct information is being exchanged between 1189 the trusted parties, whereas Layer 2 methods cannot provide this 1190 guarantee. 1192 >>> NOTE to RFC Editor: Please remove this appendix prior to 1193 publication] 1195 Document History 1197 Working Group Draft 00 1199 o Fixed editorial mistakes and ID style for WG adoption. 1201 Working Group Draft 01 1203 o Fixed editorial mistakes and added an appendix which shows the 1204 preliminary framework for securing the ULE network. 1206 Working Group Draft 02 1208 o Fixed editorial mistakes and added some important changes as 1209 pointed out by Knut Eckstein (ESA), Gorry Fairhurst and 1210 UNISAL. 1212 o Added section 4.1 on GSE. Extended the security considerations 1213 section. 1215 o Extended the appendix to show the extension header placement. 1217 o The definition of the header patterns for the ULE Security 1218 databases will be defined in a separate draft. 1220 o Need to include some words on key management transport over 1221 air interfaces, actually key management bootstrapping. 1223 Working Group Draft 03 1225 o Fixed editorial mistakes and added some important changes as 1226 pointed out by Gorry Fairhurst. 1228 o Table 1 added in Section 6.2 to list the different security 1229 techniques to mitigate the various possible network threats. 1231 o Figure 2 modified to clearly explain the different interfaces 1232 present in the framework. 1234 o New Section 7 has been added. 1236 o New Section 6 has been added. 1238 o The previous sections 5 and 6 have been combined to section 5. 1240 o Sections 3, 8 and 9 have been rearranged and updated with 1241 comments and suggestions from Michael Noisternig from 1242 University of Salzburg. 1244 o The Authors and the Acknowledgments section have been updated. 1246 Working Group Draft 04 1248 o Fixed editorial mistakes and added some important changes as 1249 pointed out by DVB-GBS group, Gorry Fairhurst and Laurence 1250 Duquerroy. 1252 o Table 1 modified to have consistent use of Security Services. 1254 o Text modified to be consistent with the draft-ietf-ipdvb-ule- 1255 ext-04.txt 1257 Working Group Draft 06 1259 o Fixed editorial mistakes and added some important changes as 1260 pointed out by Pat Cain and Gorry Fairhurst. 1262 o Figure 1 modified to have consistent use of Security Services. 1264 o Text modified in Section 4 to clearly state the requirements. 1266 o Moved Section 5 to the Appendix B 1268 o Updated IANA consideration section 1270 o Numbered the different requirements and cross referenced them 1271 within the text. 1273 Working Group Draft 07 1275 o Rephrased some sentences throughout the document to add more 1276 clarity, mainly due to suggestions by Gorry Fairhurst. 1278 o Updated section 4 to more clearly specify requirements, 1279 choosing more appropriate RFC 2119 keywords, and removed some 1280 overly general requirements. 1282 o Moved security header placement recommendation from appendix 1283 to list of general requirements in section 4, as suggested by 1284 Gorry Fairhurst. 1286 o Modified text in appendix section A.2.2 to correctly specify 1287 which information sender and receiver use to look up security 1288 information within the database. 1290 o Fixed some editorial mistakes and updated the reference list. 1292 Working Group Draft 08 1294 o Rephrased some sentences to add more clarity. 1296 o Fixed some editorial mistakes pointed out by Gorry Fairhurst. 1298 o Described the interface definitions in section A.2 as examples 1299 rather than requirements.