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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 TCPM WG J. Touch 2 Internet Draft USC/ISI 3 Expires: December 2006 A. Mankin 4 June 9, 2006 6 The TCP Simple Authentication Option 7 draft-touch-tcpm-tcp-simple-auth-00.txt 9 Status of this Memo 11 By submitting this Internet-Draft, each author represents that 12 any applicable patent or other IPR claims of which he or she is 13 aware have been or will be disclosed, and any of which he or she 14 becomes aware will be disclosed, in accordance with Section 6 of 15 BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html 33 This Internet-Draft will expire on December 9, 2006. 35 Abstract 37 This document specifies a TCP Simple Authentication Option (TCP-SA) 38 which is intended to replace the TCP MD5 Signature option of RFC-2385 39 (TCP/MD5). TCP-SA specifies the use of stronger HMAC-based hashes and 40 provides more details on the association of security associations 41 with TCP connections. TCP-SA assumes that rekeying is supported by 42 restarting the TCP connection, and so omits in-band parameter 43 negotiation, session key establishment, and rekeying support; where 44 such features are desired, use of the IPsec suite is recommended. 46 The result is intended to be a simple modification to support current 47 infrastructure uses of TCP/MD5, such as to protect BGP and LDP, to 48 support a larger set of hashes with minimal other system and 49 operational changes. TCP-SA requires no new option identifier, though 50 it is intended to be mutually exclusive with TCP/MD5 on a given TCP 51 connection. 53 Conventions used in this document 55 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 56 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 57 document are to be interpreted as described in RFC 2119 [RFC2119]. 59 Table of Contents 61 1. Introduction...................................................3 62 1.1. Executive Summary.........................................3 63 1.2. Summary of RFC-2119 Requirements..........................4 64 2. The TCP Simple Authentication Option...........................5 65 2.1. Review of TCP/MD5 Option..................................5 66 2.2. TCP-SA Option.............................................5 67 3. Security Association Management................................7 68 4. TCP-SA Interaction with TCP....................................9 69 4.1. User Interface............................................9 70 4.2. TCP States and Transitions................................9 71 4.3. TCP Segments.............................................10 72 4.4. Sending TCP Segments.....................................10 73 4.5. Receiving TCP Segments...................................11 74 4.6. Impact on TCP Header Size................................12 75 5. Key Establishment and Duration Issues.........................12 76 6. Use of TCP-SA with Routing Protocols..........................13 77 7. Interactions with TCP/MD5.....................................13 78 8. Security Considerations.......................................14 79 9. IANA Considerations...........................................15 80 10. Conclusions..................................................15 81 11. Acknowledgments..............................................15 82 12. References...................................................15 83 12.1. Normative References....................................15 84 12.2. Informative References..................................16 85 Author's Addresses...............................................17 86 Intellectual Property Statement..................................17 87 Disclaimer of Validity...........................................18 88 Copyright Statement..............................................18 89 Acknowledgment...................................................18 91 1. Introduction 93 The TCP MD5 Signature (TCP/MD5) is a TCP option that authenticates 94 TCP segments, including the TCP pseudo-header, TCP header, and TCP 95 data. It was developed to protect BGP sessions from spoofed TCP 96 segments which could affect BGP data or the robustness of the TCP 97 connection itself. 99 There have been many recently-documented concerns about TCP/MD5. Its 100 use of a simple keyed hash for authentication is problematic because 101 there have been escalating attacks on the algorithm itself [Be05] 102 [Bu06]. TCP/MD5 also lacks both key management and algorithm 103 agility. This document proposes to add the latter, but suggests that 104 TCP should not be the framework for cryptographic key management. 105 This document updates the TCP/MD5 option to become a more general TCP 106 Simple Authentication Option (TCP-SA), to support the use of other, 107 stronger hash functions and to provide a more structured 108 recommendation on external key management. 110 This document is not intended to replace the use of the IPsec suite 111 (IPsec and IKE) to protect TCP connections [RFC4301][RFC4306]. In 112 fact, we recommend the use of IPsec and IKE, especially where 113 parameter negotiation, session key negotiation, or intra-connection 114 rekeying are desired. 116 1.1. Executive Summary 118 This document updates TCP/MD5 as follows [RFC2385]: 120 o Reuses TCP/MD5's option Kind (=19), but allows TCP/MD5 to continue 121 to be used for other connections. 123 o Replaces signed MD5 with HMAC-MD5-96, and allows other MACs at the 124 implementer's discretion. 126 o Does not allow rekeying during a TCP connection (although how to 127 achieve this is not specified in RFC2385, notably in its impact to 128 TCP windowing). 130 o Provides more detail in how this option interacts with TCP's 131 states, event processing, and user interface. 133 o Proposed option is 4 bytes shorter (14 bytes overall, rather than 134 18) in the default case (HMAC-MD5-96). 136 This document differs from currently competing proposals to update 137 TCP/MD5 as follows [Bo05][We06]: 139 o Does not require a new TCP option Kind value. 141 o Does not support rekeying during a connection. 143 o Does not support dynamic parameter negotiation. 145 o Does not require additional timers. 147 o Always authenticates the TCP options as well as the segment 148 pseudoheader, header, and data. 150 o Provides more detail in how this option interacts with TCP's 151 states, event processing, and user interface. 153 o Proposed option is 2 bytes shorter (14 bytes overall, rather than 154 16) in the default case (HMAC-MD5-96) 156 o Does not expose the MAC algorithm in the header. 158 o Does not require a key ID. 160 This document differs from an IPsec/IKE solution as follows 161 [RFC4301][RFC4306] 163 o Does not support rekeying during a connection. 165 o Does not support dynamic parameter negotiation. 167 o Does not support establishment of a per-connection key. 169 o Does not require a key ID (SPI). 171 o Does not protect from replay attacks. 173 o Forces a change of connection key when a connection restarts, even 174 when reusing a TCP socket pair (IP addresses and port numbers). 176 o Does not support encryption. 178 o Does not authenticate ICMP messages (some may be authenticated in 179 IPsec, depending on the configuration). 181 1.2. Summary of RFC-2119 Requirements 183 [NOTE: a summary will be placed here prior to last call] 185 2. The TCP Simple Authentication Option 187 The TCP Simple Authentication Option (TCP-SA) re-uses the Kind value 188 currently assigned to TCP/MD5. 190 2.1. Review of TCP/MD5 Option 192 For review, the TCP/MD5 option is shown in Figure 1. 194 +---------+---------+-------------------+ 195 | Kind=19 |Length=18| MD5 digest... | 196 +---------+---------+-------------------+ 197 | | 198 +---------------------------------------+ 199 | | 200 +---------------------------------------+ 201 | | 202 +-------------------+-------------------+ 203 | | 204 +-------------------+ 206 Figure 1 Current TCP MD5 Option [RFC2385] 208 In the current TCP/MD5 option, the length is fixed, and the MD5 209 digest occupies 16 bytes following the Kind and Length fields, using 210 the full MD5 digest of 128 bits [RFC1321]. 212 The current TCP/MD5 option specifies the use of the MD5 digest 213 calculation over the following values in the following order: 215 1. the TCP pseudoheader (IP source and destination addresses, 216 protocol number, and segment length) 218 2. TCP header excluding options and checksum 220 3. TCP data 222 4. connection key 224 2.2. TCP-SA Option 226 The new TCP-SA option is intended to be a superset of the TCP/MD5 227 option. TCP-SA reuses the same Kind and Length fields, and is shown 228 in Figure 2. 230 +---------+---------+-----------------... 231 | Kind=19 | Len=var | MAC... ... 232 +---------+---------+-----------------... 234 Figure 2 Proposed TCP-SA Option 236 The TCP-SA defines the following fields: 238 o Kind: An unsigned field indicating the TCP Option. TCP-SA reuses 239 the Kind value=19. Because of how keys are managed (see Section 240 3), an endpoint will not use TCP-SA for the same connection where 241 TCP/MD5 is used, and so there would be no confusion as to how to 242 interpret incoming Kind=19 segments. 244 o Length: An unsigned 8-bit field indicating the length of the TCP- 245 SA option in bytes, including the Kind and Length fields. 247 >> The Length MUST be greater than or equal to 2. 249 >> The Length value MUST be consistent with the TCP header length. 251 Values of 2 and other small values are of dubious utility but not 252 specifically prohibited. 254 o MAC: The MAC is a message authentication code. Typical MACs are 255 96-128 bits (12-16 bytes), but any length that fits in the header 256 of the segment being authenticated is allowed. 258 >> TCP-SA MUST support HMAC-MD5-96; other MACs MAY be supported 259 [RFC2403]. 261 >> A single TCP segment MUST NOT have more than one TCP-SA option. 263 The MAC is defined over the following fields in the following order: 265 1. the TCP pseudoheader: IP source and destination addresses, zero- 266 padded protocol number and segment length, all in network byte 267 order, i.e., exactly as used for the TCP checksum [RFC793]: 269 +--------+--------+--------+--------+ 270 | Source Address | 271 +--------+--------+--------+--------+ 272 | Destination Address | 273 +--------+--------+--------+--------+ 274 | zero | PTCL | TCP Length | 275 +--------+--------+--------+--------+ 277 Figure 3 TCP pseudoheader [RFC793] 279 2. TCP header, including options, and where the checksum and TCP-SA 280 MAC fields are set to zero, all in network byte order 282 3. TCP data 284 4. Connection key: a key to be used to in the MAC algorithm, as 285 required by the particular MAC algorithm used 287 TCP-SA includes the TCP options because these options are intended to 288 be end-to-end and some are required for proper TCP operation (e.g., 289 SACK, timestamp). Middleboxes may alter TCP options en-route are a 290 kind of attack and would be successfully detected by TCP-SA. 292 The TCP-SA option does not indicate the MAC algorithm either 293 implicitly (as with TCP/MD5) or explicitly (as with some proposed 294 alternatives) [RFC2385][Bo05][We05]. The particular algorithm used is 295 considered part of the configuration state of the security 296 association of the connection and is managed separately (see Section 297 3). 299 3. Security Association Management 301 TCP-SA relies on a TCP Security Association Database (TSAD). TSAD 302 entries are assumed to be shared at the endpoints where TCP-SA is 303 used, in advance of the connection: 305 1. TCP connection identifier (ID), i.e., socket pair - IP source 306 address, IP destination address, TCP source port, and TCP 307 destination address [RFC793]. TSAD entries are uniquely determined 308 by their TCP connection ID. 310 2. For each of inbound (received TCP segments) and outbound (sent TCP 311 segments) on this connection: 313 a. MAC type for this connection. This includes the MAC algorithm 314 (e.g., HMAC-MD5, HMAC-SHA1, UMAC, etc.) and the length of the 315 MAC stored in the option (e.g., 96, 128, etc.). Also, a 316 setting of NONE must be supported, to indicate that 317 authentication is not used in this direction; this allows 318 asymmetric use of TCP-SA. At least one direction 319 (inbound/outbound) SHOULD have a non-NONE MAC in practice, but 320 this is not strictly required. 322 >> When the outbound MAC is set to values other than NONE, 323 TCP-SA MUST occur in every outbound TCP segment for that 324 connection; when set to NONE, TCP-SA MUST NOT occur in those 325 segments. 327 >> When the inbound MAC is set to values other than NONE, TCP- 328 SA MUST occur in every inbound TCP segment for that 329 connection; when set to NONE, TCP-SA MUST NOT occur in those 330 segments. 332 b. Connection key. A byte sequence used for connection keying, 333 this is intended to be a per-connection key, and may be 334 derived from a separate shared key by an external protocol 335 over a separate channel. 337 It is anticipated that TSAD entries for active or opening TCP 338 connections can be stored in the TCP Control Block (TCB); TSAD 339 entries for pending connections (in passive or active OPEN) may be 340 stored in a separate database. This means that in a single host there 341 should be only a single database which is consulted by all pending 342 connections, the same way that there is only one set of TCBs. 343 Multiple databases could be used to support virtual hosts, i.e., 344 groups of interfaces. 346 Note that TSAD and the TCP-SA fields omit a key ID; the TCP 347 connection ID already uniquely specifies the TSAD entry, so a 348 separate ID is not needed. The TCP-SA fields omit an explicit 349 algorithm ID; that algorithm is already specified by the TCP 350 connection ID and stored in the TSAD. 352 Also note that this document does not address how TSAD entries are 353 created or destroyed. It is presumed that a TSAD entry affecting 354 particular connection cannot be destroyed during an active connection 355 - or, equivalently, that its parameters are copied local to the 356 connection and so changes would affect only new connections. The TSAD 357 could be managed by a separate application protocol if desired. 359 4. TCP-SA Interaction with TCP 361 The following is a description of how various TCP states, segments, 362 events, and interfaces. This description is intended to augment the 363 description of TCP as provided in RFC793 [RFC793]. 365 4.1. User Interface 367 The TCP user interface supports active and passive OPEN, SEND, 368 RECEIVE, CLOSE, STATUS and ABORT. 370 >> TCP OPEN, or the sequence of commands that configure a connection 371 to be in the active or passive OPEN state, MUST be augmented so that 372 a TSAD entry can be configured. 374 >> New TSAD entries MUST be checked against a cache of previously 375 used TSAD entries. 377 Users are advised to not inappropriately reuse keys [RFC3562]. 379 >> TCP STATUS SHOULD be augmented to allow the TSAD entry of a 380 current or pending connection to be read (for confirmation). 382 >> TCP STATUS MUST NOT allow TSAD entries for ongoing TCP connections 383 (i.e., not in the CLOSED state) to be modified. 385 TSAD entries for TCP connections not in the CLOSED state are deleted 386 indirectly using the CLOSE or ABORT commands. 388 >> Use of CLOSE or ABORT MUST retain the TSAD entry in a cache to 389 assist with checking for key reuse. 391 This entry may correspond to one of the wait states of TCP (FINE- 392 WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, or TIME-WAIT), or 393 may be stored separately (for connections proceeding rapidly to 394 CLOSED). The size of this cache and duration of retained entries is 395 up to the user, where we again advise the application of known key 396 management principles [RFC3562]. 398 TCP SEND and RECEIVE are not affected by TCP-SA. 400 4.2. TCP States and Transitions 402 TCP includes the states LISTEN, SYN-SENT, SYN-RECEIVED, ESTABLISHED, 403 FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT, and 404 CLOSED. 406 >> A TSAD entry MAY be associated with any TCP state. 408 >> A TSAD entry MAY underspecify the TCP connection for the LISTEN 409 state. Such an entry MUST NOT be used for more than one connection 410 progressing out of the LISTEN state. 412 4.3. TCP Segments 414 TCP includes control (at least one of SYN, FIN, RST flags set) and 415 data (none of SYN, FIN, or RST flags set) segments. 417 >> All TCP segments MUST be checked against the TSAD for matching TCP 418 connection IDs. 420 >> TCP segments matching TSAD entries with non-NULL MACs without TCP- 421 SA, or with TCP-SA and whose MACs do not validate MUST be silently 422 discarded. 424 >> TCP segments with TCP-SA but not matching TSAD entries MUST be 425 silently accepted. 427 >> Silent discard events SHOULD be signaled to the user as a warning, 428 and silent accept events MAY be signaled to the user as a warning. 429 Both warnings, if available, MUST be accessible via the STATUS 430 interface. Either signal MAY be asynchronous, but if so they MUST be 431 rate-limited. Either signal MAY be logged; logging SHOULD allow rate- 432 limiting as well. 434 All TCP-SA processing occurs between the interface of TCP and IP; for 435 incoming segments, this occurs after validation of the TCP checksum. 436 For outgoing segments, this occurs before computation of the TCP 437 checksum. 439 Note that the TCP-SA option is not negotiated. It is the 440 responsibility of the receiver to determine when TCP-SA is required 441 and to enforce that requirement. 443 >> Receivers MAY silently accept TCP segments with the TCP-SA option. 445 4.4. Sending TCP Segments 447 The following procedure describes the modifications to TCP to support 448 TCP-SA when a segment departs. 450 1. Check the segment's TCP connection ID against the TSAD 451 2. If there is NO TSAD entry, omit the TCP-SA option. Proceed with 452 computing the TCP checksum and transmit the segment. 454 3. If there is a TSAD entry and the outgoing MAC is NONE, omit the 455 TCP-SA option. Proceed with computing the TCP checksum and 456 transmit the segment. 458 4. If there is a TSAD entry and the outgoing MAC is not NONE: 460 a. Augment the TCP header with the TCP-SA, inserting the 461 appropriate Length based on the indexed TSAD entry. Update the 462 TCP header length accordingly. 464 b. Compute the MAC using the indexed TSAD connection key, MAC, 465 and data from the segment as specified in Section 2.2. 467 c. Insert the MAC in the TCP-SA field. 469 d. Proceed with computing the TCP checksum and transmit the 470 segment. 472 4.5. Receiving TCP Segments 474 The following procedure describes the modifications to TCP to support 475 TCP-SA when a segment arrives. 477 1. Check the segments TCP connection ID against the TSAD 479 2. If there is NO TSAD entry, proceed with TCP processing. 481 3. If there is a TSAD entry and the incoming MAC is NONE, proceed 482 with TCP processing. 484 4. If there is a TSAD entry and the incoming MAC is not NONE: 486 a. Check that the segment's TCP-SA Length matches the indexed 487 TSAD Length. 489 i. If Lengths differ, silently discard the segment. Log 490 and/or signal the event as indicated in Section 4.3. 492 b. Compute the segment's MAC using the indexed TSAD MAC algorithm 493 and connection key, and portions of the segment as indicated 494 in Section 2.2. 496 i. If the computed MAC differs from the TCP-SA MAC field 497 value, silently discard the segment. Log and/or signal 498 the event as indicated in Section 4.3. 500 c. Proceed with TCP processing of the segment. 502 It is suggested that TCP-SA implementations validate a segment's 503 Length field before computing a MAC, to reduce the overhead incurred 504 by spoofed segments with invalid TCP-SA fields. 506 4.6. Impact on TCP Header Size 508 The TCP-SA option typically uses a total of 16-18 bytes of TCP header 509 space. TCP-SA is no larger than and typically 2 bytes smaller than 510 the TCP/MD5 option. Although TCP option space is limited, we believe 511 TCP-SA is consistent with the desire to authenticate TCP at the 512 connection level for similar uses as were intended by TCP/MD5. 514 5. Key Establishment and Duration Issues 516 The TCP-SA option does not provide connection key negotiation, 517 parameter negotiation (MAC algorithm, length, or use of the TCP-SA 518 option), or rekeying during a connection. We assume out-of-band 519 mechanisms for key establishment and parameter negotiation. 520 Deployments desiring more dynamic key and/or parameter management are 521 encouraged to use the IPsec security suite [RFC4301][RFC4306]. 523 We encourage users of TCP-SA to apply known techniques for generating 524 appropriate keys, including the use of reasonable connection key 525 lengths, limited connection key sharing, and limiting the duration of 526 connection key use [RFC3562]. 528 TCP-SA does not support rekeying as such. Connections needing 529 rekeying would close the existing connection using the old connection 530 key and start a new connection using a new connection key. 531 Applications using TCP-SA will work more efficiently if they support 532 graceful transition between sequences of such connections, either by 533 handoff between the two connections while both are open or by 534 limiting the impact of the first connection closing. Such support is 535 already being developed for Internet routing protocols, as discussed 536 in Section 6. 538 Implementations are encouraged to keep keys in a suitably private 539 area. Users of TCP-SA are encouraged to use different keys for 540 inbound and outbound MACs on a given TCP connection. 542 6. Use of TCP-SA with Routing Protocols 544 TCP-SA assumes that applications requiring rekeying are not 545 significantly affected by TCP connection reestablishment, because 546 that is the only method for changing keys. Some current routing 547 protocols, notably BGP, may be affected because they interpret the 548 stability of TCP connections to indicate the stability of the 549 communication path to its peers (or of the peers themselves). 551 This problem has already been addressed in extensions to BGP and BGP 552 for MPLS, in a mechanism known as "graceful restart" [Re05][Sa04]. 553 Without graceful restart, when a TCP connection is interrupted - 554 either deliberately (shutdown BGP client) or otherwise (via an 555 attack) - BGP flushes the routes of that peer from its tables, 556 causing substantial service interruption, and taking a long time to 557 reestablish [To06]. In graceful restart, BGP signals its peer in-band 558 that a connection is to be closed, and the routes are not flushed. 560 Although TCP/MD5 is used for other routing protocols besides BGP, 561 notably LDP, PCEP, and MSDP, it is not known whether these protocols 562 support similar graceful restart or other handoff mechanisms. 563 Further, the cost of restarting these protocols is nonzero; some 564 protocols, notably BGP, exchange their entire routing tables upon 565 restart rather than only their updates. This can result in longer 566 convergence time and increased bandwidth utilization. 568 In cases where graceful restart is not feasible or efficient, it may 569 be necessary to support secure associations with dynamic rekeying. In 570 those cases, a true key management protocol - such as IKE - is 571 recommended. Such a mechanism is not included in TCP-AO for 572 simplicity, notably to avoid complex interactions between key 573 activity periods and TCP's windowing algorithm. 575 [can anyone suggest what LDP, PCEP, or MSDP do?] 577 [is there a citation for BGP restart time/cost?] 579 7. Interactions with TCP/MD5 581 TCP-SA is intended to be deployed without regard for existing TCP/MD5 582 option support. 584 >> A TCP implementation MUST NOT use both TCP-SA and TCP/MD5 for a 585 particular TCP connection, but MAY support TCP-SA and TCP/MD5 586 simultaneously for different connections. 588 There is no need to explicitly indicate which of TCP-SA or TCP/MD5 is 589 used for a particular connection in the TCP segments. Even where the 590 two used the same hash (e.g., if TCP-SA were to use MD5 rather than 591 HMAC-MD5) and the same length (128 bits), TCP-SA computes its MAC 592 over different data (including the TCP-SA option, notably, with the 593 MAC zeroed) than TCP/MD5. The probability of a TCP-SA segment being 594 validated by TCP/MD5 or the converse is roughly equivalent to that of 595 a random party guessing a valid MAC. 597 8. Security Considerations 599 Use of TCP-SA, like use of TCP/MD5 or IPsec, will impact host 600 performance. Connections that are known to use TCP-SA can be attacked 601 by transmitting segments with invalid MACs. Attackers would need to 602 know only the TCP connection ID and TCP-SA Length value to 603 substantially impact the host's processing capacity. This is similar 604 to the susceptibility of IPsec to on-path attacks, where the IP 605 addresses and SPI would be visible. For IPsec, the entire SPI space 606 (32 bits) is arbitrary, whereas for routing protocols typically only 607 the source port (16 bits) is arbitrary. As a result, it would be 608 easier for an off-path attacker to spoof a TCP-SA segment that could 609 cause receiver validation effort. However, we note that between 610 Internet routers both ports could be arbitrary (i.e., determined a- 611 priori out of band), which would constitute roughly the same off-path 612 antispoofing protection of an arbitrary SPI. 614 TCP-SA, like TCP/MD5, may inhibit connectionless resets. Such resets 615 typically occur after peer crashes, either in response to new 616 connection attempts or when data is sent on stale connections; in 617 either case, the recovering endpoint may lack the connection key 618 required (e.g., if lost during the crash). This may result in time- 619 outs, rather than more responsive recovery after such a crash. 621 TCP-SA does not expose the MAC algorithm used to authenticate a 622 particular connection; that information is kept in the TSAD at the 623 endpoints, and is not indicated in the header. 625 TCP-SA is intended to provide similar protections to IPsec, but is 626 not intended to replace the use of IPsec or IKE either for more 627 robust security or more sophisticated security management. 629 TCP-SA does not address the issue of ICMP attacks on TCP. IPsec makes 630 recommendations regarding dropping ICMPs in certain contexts, or 631 requiring that they are endpoint authenticated in others [RFC4301]. 632 There are other mechanisms proposed to reduce the impact of ICMP 633 attacks by further validating ICMP contents and changing the effect 634 of some messages based on TCP state, but these do not provide the 635 level of authentication for ICMP that TCP-SA provides for TCP [Go06]. 637 >> A TCP-SA implementation MUST allow the system administrator to 638 configure whether TCP will ignore incoming ICMP messages of Type 3 639 Codes 2-4 intended for connections that match TSAD entries with non- 640 NONE inbound MACs. An implementation SHOULD allow ignored ICMPs to be 641 logged. 643 This control affects only ICMPs that currently require 'hard errors' 644 which would abort the TCP connection. This recommendation is intended 645 to be similar to how IPsec would handle those messages [RFC4301]. 647 9. IANA Considerations 649 The TCP-SA option reuses the TCP MD5 Signature option (TCP/MD5), 650 where Kind=19. This document augments that use of this Kind value, 651 but there is no need to deprecate or override the use of TCP/MD5. 652 This document suggests that only one key algorithm would be 653 applicable in either case, and so there would be no confusion for a 654 given Length and key value as used for authenticating segments of a 655 given TCP connection. 657 If this document is approved as an IETF Standard, IANA is requested 658 to add a registration for TCP-SA to Kind=19, along with the existing 659 registration for TCP/MD5, and add a pointer to this document. 661 10. Conclusions 663 (to be completed) 665 11. Acknowledgments 667 This document was inspired by the revisions to TCP/MD5 suggested by 668 Brian Weis and Ron Bonica [Bo06][We05]. Russ Housley suggested 669 L4/application layer management of the TSAD. 671 12. References 673 12.1. Normative References 675 [RFC793] Postel, J., "Transmission Control Protocol," STD-007, RFC- 676 793, [Standard], Sept. 1981. 678 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 679 Requirement Levels", BCP 14, RFC 2119, [Best Current 680 Practice], March 1997. 682 [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 683 Signature Option," RFC-2385 [Proposed Standard], Aug. 1998. 685 [RFC2403] Madson, C., R. Glenn, "The Use of HMAC-MD5-96 within ESP 686 and AH," RFC-2403 [Proposed Standard], Nov. 1998. 688 [RFC4301] Kent, S., K. Seo, "Security Architecture for the Internet 689 Protocol," RFC-4301, [Proposed Standard], Dec. 2005. 691 12.2. Informative References 693 [Be05] Bellovin, S., E. Rescorla, "Deploying a New Hash 694 Algorithm," presented at the First NIST Cryptographic Hash 695 Workshop, Oct. 2005. 696 http://csrc.nist.gov/pki/HashWorkshop/2005/program.htm 698 [Bu06] Burr, B., "NIST Cryptographic Standards Status Report," 699 Invited talk at Internet 2 5th Annual PKI R&D Workshop, 700 April 2006. 701 http://middleware.internet2.edu/pki06/proceedings/ 703 [Bo06] Bonica, R., "Authentication for TCP-based Routing and 704 Management Protocols," draft-bonica-tcp-auth-04, (work in 705 progress), Jan. 2006. 707 [Go06] Gont, F., "ICMP attacks against TCP," draft-ietf-tcpm-icmp- 708 attacks-00, Feb. 2006. 710 [Re05] Rekhter, Y., R. Aggarwal, "Graceful Restart Mechanism for 711 BGP with MPLS," draft-ietf-mpls-bgp-mpls-restart-05, (work 712 in progress), Aug. 2005. 714 [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC-1321, 715 April 1992. 717 [RFC3562] Leech, M., "Key Management Considerations for the TCP MD5 718 Signature Option," RFC-3562, July 2003. 720 [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol," RFC- 721 4306, [Proposed Standard], Dec. 2005. 723 [Sa04] Sangli, S., Y. Rekhter, R. Fernando, J. Scudder, E. Chen, 724 "Graceful Restart Mechanism for BGP," draft-ietf-idr- 725 restart-10 (work in progress), June 2004. 727 [To06] Touch, J., "Defending TCP Against Spoofing Attacks," draft- 728 ietf-tcpm-tcp-antispoof-04, May 2006. 730 [We05] Weis, B., "TCP Message Authentication Code Option," draft- 731 weis-tcp-mac-option-00 (work in progress), Dec. 2005. 733 [We06] Weis, B., "Automated key selection extension for the TCP 734 Authentication Option," draft-weis-tcp-auth-auto-ks-00 735 (work in progress), Feb. 2006. 737 Author's Addresses 739 Joe Touch 740 USC/ISI 741 4676 Admiralty Way 742 Marina del Rey, CA 90292-6695 743 U.S.A. 745 Phone: +1 (310) 448-9151 746 Email: touch@isi.edu 747 URL: http://www.isi.edu/touch 749 Allison Mankin 750 Washington, DC 751 U.S.A. 753 Phone: 1 301 728 7199 754 Email: mankin@psg.com 755 URL: http://www.psg.com/~mankin/ 757 Intellectual Property Statement 759 The IETF takes no position regarding the validity or scope of any 760 Intellectual Property Rights or other rights that might be claimed to 761 pertain to the implementation or use of the technology described in 762 this document or the extent to which any license under such rights 763 might or might not be available; nor does it represent that it has 764 made any independent effort to identify any such rights. 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