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'FIPS-186-4' == Outdated reference: A later version (-21) exists of draft-ietf-6lo-rfc6775-update-13 == Outdated reference: A later version (-20) exists of draft-ietf-6lo-backbone-router-05 == Outdated reference: A later version (-02) exists of draft-struik-lwig-curve-representations-00 Summary: 1 error (**), 0 flaws (~~), 6 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6lo P. Thubert, Ed. 3 Internet-Draft Cisco 4 Updates: 6775 (if approved) B. Sarikaya 5 Intended status: Standards Track 6 Expires: August 27, 2018 M. Sethi 7 Ericsson 8 February 23, 2018 10 Address Protected Neighbor Discovery for Low-power and Lossy Networks 11 draft-ietf-6lo-ap-nd-06 13 Abstract 15 This document defines an extension to 6LoWPAN Neighbor Discovery (ND) 16 [RFC6775][I-D.ietf-6lo-rfc6775-update] called Address Protected ND 17 (AP-ND); AP-ND protects the owner of an address against address theft 18 and impersonation inside a low-power and lossy network (LLN). Nodes 19 supporting this extension compute a cryptographic Owner Unique 20 Interface ID and associate it with one or more of their Registered 21 Addresses. The Cryptographic ID uniquely identifies the owner of the 22 Registered Address and can be used for proof-of-ownership. It is 23 used in 6LoWPAN ND in place of the EUI-64-based unique ID that is 24 associated with the registration. Once an address is registered with 25 a Cryptographic ID, only the owner of that ID can modify the anchor 26 state information of the Registered Address, and Source Address 27 Validation can be enforced. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on August 27, 2018. 46 Copyright Notice 48 Copyright (c) 2018 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (https://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5 66 4. New Fields and Options . . . . . . . . . . . . . . . . . . . 5 67 4.1. Encoding the Public Key . . . . . . . . . . . . . . . . . 5 68 4.2. New Crypto-ID . . . . . . . . . . . . . . . . . . . . . . 6 69 4.3. Updated EARO . . . . . . . . . . . . . . . . . . . . . . 6 70 4.4. Crypto-ID Parameters Option . . . . . . . . . . . . . . . 8 71 4.5. Nonce Option . . . . . . . . . . . . . . . . . . . . . . 9 72 4.6. NDP Signature Option . . . . . . . . . . . . . . . . . . 9 73 5. Protocol Scope . . . . . . . . . . . . . . . . . . . . . . . 9 74 6. Protocol Flows . . . . . . . . . . . . . . . . . . . . . . . 10 75 6.1. First Exchange with a 6LR . . . . . . . . . . . . . . . . 11 76 6.2. Multihop Operation . . . . . . . . . . . . . . . . . . . 13 77 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15 78 7.1. Inheriting from RTC 3971 . . . . . . . . . . . . . . . . 15 79 7.2. Related to 6LoWPAN ND . . . . . . . . . . . . . . . . . . 16 80 7.3. OUID Collisions . . . . . . . . . . . . . . . . . . . . . 16 81 8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 17 82 8.1. CGA Message Type . . . . . . . . . . . . . . . . . . . . 17 83 8.2. Crypto-Type Subregistry . . . . . . . . . . . . . . . . . 17 84 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 85 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 86 10.1. Normative References . . . . . . . . . . . . . . . . . . 18 87 10.2. Informative references . . . . . . . . . . . . . . . . . 19 88 Appendix A. Requirements Addressed in this Document . . . . . . 21 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 91 1. Introduction 93 "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775] 94 (6LoWPAN ND) adapts the classical IPv6 ND protocol [RFC4861][RFC4862] 95 (IPv6 ND) for operations over a constrained low-power and lossy 96 network (LLN). In particular, 6LoWPAN ND introduces a unicast host 97 address registration mechanism that contributes to reduce the use of 98 multicast messages that are present in the classical IPv6 ND 99 protocol. 6LoWPAN ND defines a new Address Registration Option (ARO) 100 that is carried in the unicast Neighbor Solicitation (NS) and 101 Neighbor Advertisement (NA) messages between the 6LoWPAN Node (6LN) 102 and the 6LoWPAN Router (6LR). Additionally, it also defines the 103 Duplicate Address Request (DAR) and Duplicate Address Confirmation 104 (DAC) messages between the 6LR and the 6LoWPAN Border Router (6LBR). 105 In LLN networks, the 6LBR is the central repository of all the 106 registered addresses in its domain. 108 The registration mechanism in 6LoWPAN ND [RFC6775] prevents the use 109 of an address if that address is already present in the subnet (first 110 come first serve). In order to validate address ownership, the 111 registration mechanism enables the 6LR and 6LBR to validate claims 112 for a registered address with an associated Owner Unique Interface 113 IDentifier (OUID). 6LoWPAN ND specifies that the OUID is derived from 114 the MAC address of the device (using the 64-bit Extended Unique 115 Identifier EUI-64 address format specified by IEEE), which can be 116 spoofed. Therefore, any node connected to the subnet and aware of a 117 registered-address-to-OUID mapping could effectively fake the OUID, 118 steal the address and redirect traffic for that address towards a 119 different 6LN. The "Update to 6LoWPAN ND" 120 [I-D.ietf-6lo-rfc6775-update] defines an Extended ARO (EARO) option 121 that allows to transport alternate forms of OUIDs, and is a 122 prerequisite for this specification. 124 According to this specification, a 6LN generates a cryptographic ID 125 (Crypto-ID) and places it in the OUID field in the registration of 126 one (or more) of its addresses with the 6LR(s) that the 6LN uses as 127 default router(s). Proof of ownership of the cryptographic ID 128 (Crypto-ID) is passed with the first registration exchange to a new 129 6LR, and enforced at the 6LR. The 6LR validates ownership of the 130 cryptographic ID before it can create a registration state, or a 131 change the anchor information, that is the Link-Layer Address and 132 associated parameters, in an existing registration state. 134 The protected address registration protocol proposed in this document 135 enables the enforcement of Source Address Validation (SAVI) 136 [RFC7039], which ensures that only the correct owner uses a 137 registered address in the source address field in IPv6 packets. 138 Consequently, a 6LN that sources a packet has to use a 6LR to which 139 the source address of the packet is registered to forward the packet. 140 The 6LR maintains state information for the registered addressed, 141 including the MAC address, and a link-layer cryptographic key 142 associated with the 6LN. In SAVI-enforcement mode, the 6LR allows 143 only packets from a connected Host if the connected Host owns the 144 registration of the source address of the packet. 146 The 6lo adaptation layer framework ([RFC4944], [RFC6282]) expects 147 that a device forms its IPv6 addresses based on Layer-2 address, so 148 as to enable a better compression. This is incompatible with "Secure 149 Neighbor Discovery (SeND)" [RFC3971] and "Cryptographically Generated 150 Addresses (CGAs)" [RFC3972], which derive the Interface ID (IID) in 151 the IPv6 addresses from cryptographic material. "Privacy 152 Considerations for IPv6 Address Generation Mechanisms" [RFC7721] 153 places additional recommendations on the way addresses should be 154 formed and renewed. 156 This document specifies that a device may form and register addresses 157 at will, without a constraint on the way the address is formed or the 158 number of addresses that are registered in parallel. It enables to 159 protect multiple addresses with a single cryptographic material and 160 to send the proof only once to a given 6LR for multiple addresses and 161 refresher registrations. 163 2. Terminology 165 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 166 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 167 document are to be interpreted as described in [RFC2119]. 169 Readers are expected to be familiar with all the terms and concepts 170 that are discussed in [RFC3971], [RFC3972], [RFC4861], [RFC4919], 171 [RFC6775], and [I-D.ietf-6lo-backbone-router] which proposes an 172 evolution of [RFC6775] for wider applicability. 174 This document defines Crypto-ID as an identifier of variable size 175 which in most cases is 64 bits long. It is generated using 176 cryptographic means explained later in this document Section 4.2. 177 "Elliptic Curves for Security" [RFC7748] and "Edwards-Curve Digital 178 Signature Algorithm (EdDSA)" [RFC8032] provides information on 179 Elliptic Curve Cryptography (ECC) and a (twisted) Edwards curve, 180 Ed25519, which can be used with this specification. "Alternative 181 Elliptic Curve Representations" 182 [I-D.struik-lwig-curve-representations] provides additional 183 information on how to represent Montgomery curves and (twisted) 184 Edwards curves as curves in short-Weierstrass form and illustrates 185 how this can be used to implement elliptic curve computations using 186 existing implementations that already implement, e.g., ECDSA and ECDH 187 using NIST [FIPS-186-4] prime curves. 189 The document also conforms to the terms and models described in 190 [RFC5889] and uses the vocabulary and the concepts defined in 191 [RFC4291] for the IPv6 Architecture. Finally, common terminology 192 related to Low power And Lossy Networks (LLN) defined in [RFC7102] is 193 also used. 195 3. Updating RFC 6775 197 This specification defines a cryptographic identifier (Crypto-ID) 198 that can be used as a replacement to the MAC address in the OUID 199 field of the EARO option; the computation of the Crypto-ID is 200 detailed in Section 4.2. A node in possession of the necessary 201 cryptographic material SHOULD use Crypto-ID by default as OUID in its 202 registration. Whether a OUID is a Crypto-ID is indicated by a new 203 "C" flag in the NS(EARO) message. 205 In order to prove its ownership of a Crypto-ID, the registering node 206 needs to produce the parameters that where used to build it, as well 207 as a nonce and a signature that will prove that it has the private 208 key that corresponds to the public key that was used to build the 209 Crypto-ID. This specification adds the capability to carry new 210 options in the NS(EARO) and the NBA(EARO). These options are a 211 variation of the CGA Option Section 4.4, a Nonce option and a 212 variation of the RSA Signature option Section 4.6 in the NS(EARO) and 213 a Nonce option in the NA(EARO). 215 4. New Fields and Options 217 In order to avoid an inflation of ND option types, this specification 218 reuses / extends options defined in SEND [RFC3971] and 6LoWPAN ND 219 [RFC6775][I-D.ietf-6lo-rfc6775-update]. This applies in particular 220 to the CGA option and the RSA Signature Option. This specification 221 provides aliases for the specific variations of those options as used 222 in AP-ND. The presence of the EARO option in the NS/NA messages 223 indicates that the options are to be understood as specified in this 224 document. A router that would receive a NS(EARO) and try to process 225 it as a SEND message will find that the signature does not match and 226 drop the packet. 228 4.1. Encoding the Public Key 230 Public Key is the most important parameter in CGA Parameters (sent by 231 6LN in an NS message). ECC Public Key could be in uncompressed form 232 or in compressed form where the first octet of the OCTET STRING is 233 0x04 and 0x02 or 0x03, respectively. Point compression can further 234 reduce the key size by about 32 octets. 236 4.2. New Crypto-ID 238 Elliptic Curve Cryptography (ECC) is used to calculate the Crypto-ID. 239 Each 6LN using a Crypto-ID for registration MUST have a public/ 240 private key pair. The digital signature is constructed by using the 241 6LN's private key over its EUI-64 (MAC) address. The signature value 242 is computed using the ECDSA signature algorithm and the hash function 243 used is SHA-256 [RFC6234]. 245 NIST P-256 [FIPS186-4] that MUST be supported by all implementations. 246 To support cryptographic algorithm agility [RFC7696], Edwards-Curve 247 Digital Signature Algorithm (EdDSA) curve Ed25519ph (pre-hashing) 248 [RFC8032] MAY be supported as an alternate. 250 The Crypto-ID is computed as follows: 252 1. An 8-bits modifier is selected, for instance, but not 253 necessarily, randomly; the modifier enables a device to form 254 multiple Crypto-IDs with a single key pair. This may be useful 255 for privacy reasons in order to avoid the correlation of 256 addresses based on their Crypto-ID; 258 2. the modifier value and the DER-encoded public key (Section 4.1) 259 are concatenated from left to right; 261 3. Digital signature (SHA-256 then either NIST P-256 or EdDSA) is 262 executed on the concatenation 264 4. the leftmost bits of the resulting signature are used as the 265 Crypto-ID; 267 With this specification, only 64 bits are retained, but it could be 268 expanded to more bits in the future by increasing the size of the 269 OUID field. 271 4.3. Updated EARO 273 This specification updates the EARO option as follows: 275 0 1 2 3 276 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 278 | Type | Length | Status | Reserved | 279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 280 | Reserved|C|R|T| TID | Registration Lifetime | 281 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 282 | | 283 + Owner Unique ID (EUI-64 or Crypto-ID) + 284 | | 285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 287 Figure 1: Enhanced Address Registration Option 289 Type: 33 291 Length: 8-bit unsigned integer. The length of the option 292 (including the type and length fields) in units of 8 293 bytes. 295 Status: 8-bit unsigned integer. Indicates the status of a 296 registration in the NA response. MUST be set to 0 in 297 NS messages. This specification uses values 298 introduced in the update to 6LoWPAN ND 299 [I-D.ietf-6lo-rfc6775-update], such as "Validation 300 Requested" and "Validation Failed". No additional 301 value is defined. 303 Reserved: This field is unused. It MUST be initialized to zero 304 by the sender and MUST be ignored by the receiver. 306 C: This "C" flag is set to indicate that the Owner 307 Unique ID field contains a Crypto-ID and that the 6LN 308 MAY be challenged for ownership as specified in this 309 document. 311 R: Defined in [I-D.ietf-6lo-rfc6775-update]. 313 T and TID: Defined in [I-D.ietf-6lo-rfc6775-update]. 315 Owner Unique ID: When the "C" flag is set, this field contains a 316 Crypto-ID. 318 4.4. Crypto-ID Parameters Option 320 This specification defines the Crypto-ID Parameters Option (CIPO), as 321 a variation of the CGA Option that carries the parameters used to 322 form a Crypto-ID. In order to provide cryptographic agility, AP-ND 323 supports two possible signature algorithms, indicated by a Crypto- 324 Type field. A value of 0 indicates that NIST P-256 is used for the 325 signature operation and SHA-256 as the hash algorithm. NIST P-256 326 MUST be supported by all implement A value of 1 indicates that 327 Ed25519ph is used for the signature operation and SHA-256 as the hash 328 algorithm. 330 0 1 2 3 331 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 | Type | Length | Pad Length | Reserved | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 | Crypto-Type | Modifier | Reserved | 336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 337 | | 338 | | 339 . . 340 . Public Key (variable length) . 341 . . 342 | | 343 | | 344 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 345 | | 346 . . 347 . Padding . 348 . . 349 | | 350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 352 Figure 2: Crypto-ID Parameters Option 354 Type: 11. This is the same value as the CGA Option, CIPO 355 is a particular case of the CGA option 357 Length: 8-bit unsigned integer. The length of the option in 358 units of 8 octets. 360 Modifier: 8-bit unsigned integer. 362 Pad Length: 8-bit unsigned integer. The length of the Padding 363 field. 365 Crypto-Type: The type of cryptographic algorithm used in 366 calculation Crypto-ID. Default value of all zeros 367 indicate NIST P-256. A value of 1 is assigned for 368 Ed25519ph. New values may be defined later. 370 Public Key: Public Key of 6LN. 372 Padding: A variable-length field making the option length a 373 multiple of 8, containing as many octets as specified 374 in the Pad Length field. 376 4.5. Nonce Option 378 This document reuses the Nonce Option defined in section 5.3.2. of 379 SEND [RFC3971] without a change. 381 4.6. NDP Signature Option 383 This document reuses the RSA Signature Option (RSAO) defined in 384 section 5.2. of SEND [RFC3971]. Admittedly, the name is ill-chosen 385 since the option is extended for non-RSA Signatures and this 386 specification defines an alias to avoid the confusion. 388 The description of the operation on the option detailed in section 389 5.2. of SEND [RFC3971] apply, but for the following changes: 391 o The 128-bit CGA Message Type tag [RFC3972] for AP-ND is 0x8701 392 55c8 0cca dd32 6ab7 e415 f148 84d0. (The tag value has been 393 generated by the editor of this specification on random.org). 395 o The signature is computed using the hash algorithm and the digital 396 signature indicated in the Crypto-Type field of the CIPO option 397 using the private key associated with the public key in the CIPO. 399 o The alias NDP Signature Option (NDPSO) can be used to refer to the 400 RSAO when used as described in this specification. 402 5. Protocol Scope 404 The scope of the present work is a 6LoWPAN Low Power Lossy Network 405 (LLN), typically a stub network connected to a larger IP network via 406 a Border Router called a 6LBR per [RFC6775]. 408 The 6LBR maintains a registration state for all devices in the 409 attached LLN, and, in conjunction with the first-hop router (the 410 6LR), is in a position to validate uniqueness and grant ownership of 411 an IPv6 address before it can be used in the LLN. This is a 412 fundamental difference with a classical network that relies on IPv6 413 address auto-configuration [RFC4862], where there is no guarantee of 414 ownership from the network, and any IPv6 Neighbor Discovery packet 415 must be individually secured [RFC3971]. 417 ---+-------- ............ 418 | External Network 419 | 420 +-----+ 421 | | 6LBR 422 +-----+ 423 o o o 424 o o o o 425 o o LLN o o o 426 o o o (6LR) 427 o (6LN) 429 Figure 3: Basic Configuration 431 In a mesh network, the 6LR is directly connected to the host device. 432 This specification expects that the peer-wise layer-2 security is 433 deployed so that all the packets from a particular host are securely 434 identifiable by the 6LR. The 6LR may be multiple hops away from the 435 6LBR. Packets are routed between the 6LR and the 6LBR via other 436 6LRs. This specification expects that a chain of trust is 437 established so that a packet that was validated by the first 6LR can 438 be safely routed by the next 6LRs to the 6LBR. 440 6. Protocol Flows 442 The 6LR/6LBR ensures first-come/first-serve by storing the EARO 443 information including the Crypto-ID correlated to the node being 444 registered. The node is free to claim any address it likes as long 445 as it is the first to make such a claim. After a successful 446 registration, the node becomes the owner of the registered address 447 and the address is bound to the Crypto-ID in the 6LR/6LBR registry. 449 This specification enables to verify the ownership of the binding at 450 any time assuming that the "C" flag is set. If it is not set, then 451 the verification methods presented in this specification cannot be 452 applied. The verification prevents other nodes from stealing the 453 address and trying to attract traffic for that address or use it as 454 their source address. 456 A node may use multiple IPv6 addresses at the same time. The node 457 may use a same Crypto-ID, or multiple crypto-IDs derived from a same 458 key pair, to protect multiple IPv6 addresses. The separation of the 459 address and the cryptographic material avoids the constrained device 460 to compute multiple keys for multiple addresses. The registration 461 process allows the node to bind all of its addresses to the same 462 Crypto-ID. 464 6.1. First Exchange with a 6LR 466 A 6LN registers to a 6LR that is one hop away from it with the "C" 467 flag set in the EARO, indicating that the Owner Unique ID field 468 contains a Crypto-ID. The on-link (local) protocol interactions are 469 shown in Figure 4 If the 6LR does not have a state with the 6LN that 470 is consistent with the NS(EARO), then it replies with a challenge NA 471 (EARO, status=Validation Requested) that contains a Nonce Option. 472 The Nonce option MUST contain a Nonce value that was never used with 473 this device. 475 The 6LN replies to the challenge with a proof-of-ownership NS(EARO) 476 that includes the echoed Nonce option, the CIPO with all the 477 parameters that where used to build EARO with a Crypto-ID, and as the 478 last option the NDPSO with the signature. The information associated 479 to a crypto-ID is passed to and stored by the 6LR on the first NS 480 exchange where it appears. The 6LR SHOULD store the CIPO information 481 associated with the crypto-ID so it can be used for more than one 482 address. 484 6LN 6LR 485 | | 486 |<------------------------- RA -------------------------| 487 | | ^ 488 |---------------- NS with EARO (Crypto-ID) ------------>| | 489 | | option 490 |<- NA with EARO (status=Validation Requested), Nonce --| | 491 | | v 492 |-------- NS with EARO, CIPO, Nonce and NDPSO --------->| 493 | | 494 |<------------------- NA with EARO ---------------------| 495 | | 496 ... 497 | | 498 |--------------- NS with EARO (Crypto-ID) ------------->| 499 | | 500 |<------------------- NA with EARO ---------------------| 501 | | 502 ... 503 | | 504 |--------------- NS with EARO (Crypto-ID) ------------->| 505 | | 506 |<------------------- NA with EARO ---------------------| 507 | | 509 Figure 4: On-link Protocol Operation 511 The steps for the registration to the 6LR are as follows: 513 o Upon the first exchange with a 6LR, a 6LN may be challenged and 514 have to produce the proof of ownership of the Crypto-ID. However, 515 it is not expected that the proof is needed again in the periodic 516 refresher registrations for that address, or when registering 517 other addresses with the same OUID. When a 6LR receives a 518 NS(EARO) registration with a new Crypto-ID as a OUID, it SHOULD 519 challenge by responding with a NA(EARO) with a status of 520 "Validation Requested". This process of validation MAY be skipped 521 in networks where there is no mobility. 523 o The challenge MUST also be triggered in the case of a registration 524 for which the Source Link-Layer Address is not consistent with a 525 state that already exists either at the 6LR or the 6LBR. In the 526 latter case, the 6LBR returns a status of "Validation Requested" 527 in the DAR/DAC exchange, which is echoed by the 6LR in the NA 528 (EARO) back to the registering node. This flow should not alter a 529 preexisting state in the 6LR or the 6LBR. 531 o Upon receiving a NA(EARO) with a status of "Validation Requested", 532 the registering node SHOULD retry its registration with a Crypto- 533 ID Parameters Option (CIPO) Section 4.4 that contains all the 534 necessary material for building the Crypto-ID, the Nonce and the 535 NDP signature Section 4.6 options that prove its ownership of the 536 Crypto-ID. 538 o In order to validate the ownership, the 6LR performs the same 539 steps as the 6LN and rebuilds the Crypto-ID based on the 540 parameters in the CIPO. If the result is different then the 541 validation fails. Else, the 6LR checks the signature in the NDPSO 542 using the public key in the CIPO. If it is correct then the 543 validation passes, else it fails. 545 o If the 6LR fails to validate the signed NS(EARO), it responds with 546 a status of "Validation Failed". After receiving a NA(EARO) with 547 a status of "Validation Failed", the registering node SHOULD try 548 an alternate Signature Algorithm and Crypto-ID. In any case, it 549 MUST NOT use this Crypto-ID for registering with that 6LR again. 551 6.2. Multihop Operation 553 In a multihop 6LoWPAN, the registration with Crypto-ID is propagated 554 to 6LBR as described in Section 6.2. If a chain of trust is present 555 between the 6LR and the 6LBR, then there is no need to propagate the 556 proof of ownership to the 6LBR. All the 6LBR needs to know is that 557 this particular OUID is randomly generated, so as to enforce that any 558 update via a different 6LR is also random. 560 A new device that joins the network auto-configures an address and 561 performs an initial registration to an on-link 6LR with an NS message 562 that carries an Address Registration Option (EARO) [RFC6775]. The 563 6LR validates the address with the central 6LBR using a DAR/DAC 564 exchange, and the 6LR confirms (or denies) the address ownership with 565 an NA message that also carries an Address Registration Option. 567 Figure 5 illustrates a registration flow all the way to a 6LowPAN 568 Backbone Router (6BBR). 570 6LN 6LR 6LBR 6BBR 571 | | | | 572 | NS(EARO) | | | 573 |--------------->| | | 574 | | Extended DAR | | 575 | |-------------->| | 576 | | | | 577 | | | proxy NS(EARO) | 578 | | |--------------->| 579 | | | | NS(DAD) 580 | | | | ------> 581 | | | | 582 | | | | 583 | | | | 584 | | | proxy NA(EARO) | 585 | | |<---------------| 586 | | Extended DAC | | 587 | |<--------------| | 588 | NA(EARO) | | | 589 |<---------------| | | 590 | | | | 592 Figure 5: (Re-)Registration Flow 594 In a multihop 6LoWPAN, a 6LBR sends RAs with prefixes downstream and 595 the 6LR receives and relays them to the nodes. 6LR and 6LBR 596 communicate using ICMPv6 Duplicate Address Request (DAR) and 597 Duplicate Address Confirmation (DAC) messages. The DAR and DAC use 598 the same message format as NS and NA, but have different ICMPv6 type 599 values. 601 In AP-ND we extend DAR/DAC messages to carry cryptographically 602 generated OUID. In a multihop 6LoWPAN, the node exchanges the 603 messages shown in Figure 5. The 6LBR must identify who owns an 604 address (EUI-64) to defend it, if there is an attacker on another 605 6LR. 607 Occasionally, a 6LR might miss the node's OUID (that it received in 608 ARO). 6LR should be able to ask for it again. This is done by 609 restarting the exchanges shown in Figure 4. The result enables 6LR 610 to refresh the information that was lost. The 6LR MUST send DAR 611 message with ARO to 6LBR. The 6LBR replies with a DAC message with 612 the information copied from the DAR, and the Status field is set to 613 zero. With this exchange, the 6LBR can (re)validate and store the 614 information to make sure that the 6LR is not a fake. 616 In some cases, the 6LBR may use a DAC message to solicit a Crypto-ID 617 from a 6LR and also requests 6LR to verify the EUI-64 6LR received 618 from 6LN. This may happen when a 6LN node is compromised and a fake 619 node is sending the Crypto-ID as if it is the node's EUI-64. Note 620 that the detection in this case can only be done by 6LBR not by 6LR. 622 7. Security Considerations 624 7.1. Inheriting from RTC 3971 626 The observations regarding the threats to the local network in 627 [RFC3971] also apply to this specification. Considering RFC3971 628 security section subsection by subsection: 630 Neighbor Solicitation/Advertisement Spoofing Threats in section 631 9.2.1 of RFC3971 apply. AP-ND counters the threats on NS(EARO) 632 messages by requiring that the NDP Signature and CIPO options be 633 present in these solicitations. 635 Neighbor Unreachability Detection Failure With RFC6775, a NUD can 636 still be used by the endpoint to assess the liveliness of a 637 device. The NUD request may be protected by SEND in which case 638 the provision in section 92.2. of RFC 3972 applies. The response 639 to the NUD may be proxied by a backbone router only if it has a 640 fresh registration state for it. The registration being protected 641 by this specification, the proxied NUD response provides a 642 truthful information on the original owner of the address but it 643 cannot be proven using SEND. If the NUD response is not proxied, 644 the 6LR will pass the lookup to the end device which will respond 645 with a traditional NA. If the 6LR does not have a cache entry 646 associated for the device, it can issue a NA with EARO 647 (status=Validation Requested) upon the NA from the device, which 648 will trigger a NS that will recreate and revalidate the ND cache 649 entry. 651 Duplicate Address Detection DoS Attack Inside the LLN, Duplicate 652 Addresses are sorted out using the OUID, which differentiates it 653 from a movement. DAD coming from the backbone are not forwarded 654 over the LLN so the LLN is protected by the backbone routers. 655 Over the backbone, the EARO option is present in NS/NA messages. 656 This protects against misinterpreting a movement for a 657 duplication, and enables to decide which backbone router has the 658 freshest registration and thus most possibly the device attached 659 to it. But this specification does not guarantee that the 660 backbone router claiming an address over the backbone is not an 661 attacker. 663 Router Solicitation and Advertisement Attacks This specification 664 does not change the protection of RS and RA which can still be 665 protected by SEND. 667 Replay Attacks A Nonce given by the 6LR in the NA with EARO 668 (status=Validation Requested) and echoed in the signed NS 669 guarantees against replay attacks of the NS(EARO). The NA(EARO) 670 is not protected and can be forged by a rogue node that is not the 671 6LR in order to force the 6LN to rebuild a NS(EARO) with the proof 672 of ownership, but that rogue node must have access to the L2 radio 673 network next to the 6LN to perform the attack. 675 Neighbor Discovery DoS Attack A rogue node that managed to access 676 the L2 network may form many addresses and register them using AP- 677 ND. The perimeter of the attack os all the 6LRs in range of the 678 attacker. The 6LR must protect itself against overflows and 679 reject excessive registration with a status 2 "Neighbor Cache 680 Full". This effectively blocks another (honest) 6LN from 681 registering to the same 6LR, but the 6LN may register to other 682 6LRs that are in its range but not in that of the rogue. 684 7.2. Related to 6LoWPAN ND 686 The threats discussed in 6LoWPAN ND [RFC6775] and its update 687 [I-D.ietf-6lo-rfc6775-update] also apply here. Compared with SeND, 688 this specification saves about 1Kbyte in every NS/NA message. Also, 689 this specification separates the cryptographic identifier from the 690 registered IPv6 address so that a node can have more than one IPv6 691 address protected by the same cryptographic identifier. SeND forces 692 the IPv6 address to be cryptographic since it integrates the CGA as 693 the IID in the IPv6 address. This specification frees the device to 694 form its addresses in any fashion, so as to enable the classical 695 6LoWPAN compression which derives IPv6 addresses from Layer-2 696 addresses, as well as privacy addresses. The threats discussed in 697 Section 9.2 of [RFC3971] are countered by the protocol described in 698 this document as well. 700 7.3. OUID Collisions 702 Collisions of Owner Unique Interface IDentifier (OUID) (which is the 703 Crypto-ID in this specification) is a possibility that needs to be 704 considered. The formula for calculating the probability of a 705 collision is 1 - e^{-k^2/(2n)} where n is the maximum population size 706 (2^64 here, 1.84E19) and K is the actual population (number of 707 nodes). If the Crypto-ID is 64-bit long, then the chance of finding 708 a collision is 0.01% when the network contains 66 million nodes. It 709 is important to note that the collision is only relevant when this 710 happens within one stub network (6LBR). A collision of Crypto-ID is 711 a rare event. In the case of a collision, an attacker may be able to 712 claim the registered address of an another legitimate node. However 713 for this to happen, the attacker would also need to know the address 714 which was registered by the legitimate node. This registered address 715 is however never broadcasted on the network and therefore it provides 716 an additional entropy of 64-bits that an attacker must correctly 717 guess. To prevent such a scenario, it is RECOMMENDED that nodes 718 derive the address being registered independently of the OUID. 720 8. IANA considerations 722 8.1. CGA Message Type 724 This document defines a new 128-bit value under the CGA Message Type 725 [RFC3972] namespace, 0x8701 55c8 0cca dd32 6ab7 e415 f148 84d0. 727 8.2. Crypto-Type Subregistry 729 IANA is requested to create a new subregistry "Crypto-Type 730 Subregistry" in the "Internet Control Message Protocol version 6 731 (ICMPv6) Parameters". The registry is indexed by an integer 0..255 732 and contains a Signature Algorithm and a Hash Function as shown in 733 Table 1. The following Crypto-Type values are defined in this 734 document: 736 +--------------+-----------------+---------------+------------------+ 737 | Crypto-Type | Signature | Hash Function | Defining | 738 | value | Algorithm | | Specification | 739 +--------------+-----------------+---------------+------------------+ 740 | 0 | NIST P-256 | SHA-256 | RFC THIS | 741 | | [FIPS186-4] | [RFC6234] | | 742 | 1 | Ed25519ph | SHA-256 | RFC THIS | 743 | | [RFC8032] | [RFC6234] | | 744 +--------------+-----------------+---------------+------------------+ 746 Table 1: Crypto-Types 748 Assignment of new values for new Crypto-Type MUST be done through 749 IANA with "Specification Required" and "IESG Approval" as defined in 750 [RFC8126]. 752 9. Acknowledgments 754 Many thanks to Charlie Perkins for his in-depth review and 755 constructive suggestions. We are also especially grateful to Rene 756 Struik and Robert Moskowitz for their comments that lead to many 757 improvements to this document, in particular WRT ECC computation and 758 references. 760 10. References 762 10.1. Normative References 764 [FIPS-186-4] 765 FIPS 186-4, "Digital Signature Standard (DSS), Federal 766 Information Processing Standards Publication 186-4", US 767 Department of Commerce/National Institute of Standards and 768 Technology Gaithersburg, MD, July 2013. 770 [I-D.ietf-6lo-rfc6775-update] 771 Thubert, P., Nordmark, E., Chakrabarti, S., and C. 772 Perkins, "An Update to 6LoWPAN ND", draft-ietf-6lo- 773 rfc6775-update-13 (work in progress), February 2018. 775 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 776 Requirement Levels", BCP 14, RFC 2119, 777 DOI 10.17487/RFC2119, March 1997, 778 . 780 [RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and 781 Identifiers for the Internet X.509 Public Key 782 Infrastructure Certificate and Certificate Revocation List 783 (CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April 784 2002, . 786 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 787 "SEcure Neighbor Discovery (SEND)", RFC 3971, 788 DOI 10.17487/RFC3971, March 2005, 789 . 791 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 792 RFC 3972, DOI 10.17487/RFC3972, March 2005, 793 . 795 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 796 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 797 2006, . 799 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 800 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 801 DOI 10.17487/RFC4861, September 2007, 802 . 804 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 805 Address Autoconfiguration", RFC 4862, 806 DOI 10.17487/RFC4862, September 2007, 807 . 809 [RFC5758] Dang, Q., Santesson, S., Moriarty, K., Brown, D., and T. 810 Polk, "Internet X.509 Public Key Infrastructure: 811 Additional Algorithms and Identifiers for DSA and ECDSA", 812 RFC 5758, DOI 10.17487/RFC5758, January 2010, 813 . 815 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 816 Bormann, "Neighbor Discovery Optimization for IPv6 over 817 Low-Power Wireless Personal Area Networks (6LoWPANs)", 818 RFC 6775, DOI 10.17487/RFC6775, November 2012, 819 . 821 10.2. Informative references 823 [FIPS186-4] 824 "FIPS Publication 186-4: Digital Signature Standard", July 825 2013, . 828 [I-D.ietf-6lo-backbone-router] 829 Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo- 830 backbone-router-05 (work in progress), January 2018. 832 [I-D.struik-lwig-curve-representations] 833 Struik, R., "Alternative Elliptic Curve Representations", 834 draft-struik-lwig-curve-representations-00 (work in 835 progress), November 2017. 837 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 838 over Low-Power Wireless Personal Area Networks (6LoWPANs): 839 Overview, Assumptions, Problem Statement, and Goals", 840 RFC 4919, DOI 10.17487/RFC4919, August 2007, 841 . 843 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 844 "Transmission of IPv6 Packets over IEEE 802.15.4 845 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 846 . 848 [RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing 849 Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889, 850 September 2010, . 852 [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms 853 (SHA and SHA-based HMAC and HKDF)", RFC 6234, 854 DOI 10.17487/RFC6234, May 2011, 855 . 857 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 858 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 859 DOI 10.17487/RFC6282, September 2011, 860 . 862 [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., 863 "Source Address Validation Improvement (SAVI) Framework", 864 RFC 7039, DOI 10.17487/RFC7039, October 2013, 865 . 867 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 868 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 869 2014, . 871 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 872 Interface Identifiers with IPv6 Stateless Address 873 Autoconfiguration (SLAAC)", RFC 7217, 874 DOI 10.17487/RFC7217, April 2014, 875 . 877 [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm 878 Agility and Selecting Mandatory-to-Implement Algorithms", 879 BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, 880 . 882 [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy 883 Considerations for IPv6 Address Generation Mechanisms", 884 RFC 7721, DOI 10.17487/RFC7721, March 2016, 885 . 887 [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves 888 for Security", RFC 7748, DOI 10.17487/RFC7748, January 889 2016, . 891 [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital 892 Signature Algorithm (EdDSA)", RFC 8032, 893 DOI 10.17487/RFC8032, January 2017, 894 . 896 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 897 Writing an IANA Considerations Section in RFCs", BCP 26, 898 RFC 8126, DOI 10.17487/RFC8126, June 2017, 899 . 901 Appendix A. Requirements Addressed in this Document 903 In this section we state requirements of a secure neighbor discovery 904 protocol for low-power and lossy networks. 906 o The protocol MUST be based on the Neighbor Discovery Optimization 907 for Low-power and Lossy Networks protocol defined in [RFC6775]. 908 RFC6775 utilizes optimizations such as host-initiated interactions 909 for sleeping resource-constrained hosts and elimination of 910 multicast address resolution. 912 o New options to be added to Neighbor Solicitation messages MUST 913 lead to small packet sizes, especially compared with existing 914 protocols such as SEcure Neighbor Discovery (SEND). Smaller 915 packet sizes facilitate low-power transmission by resource- 916 constrained nodes on lossy links. 918 o The support for this registration mechanism SHOULD be extensible 919 to more LLN links than IEEE 802.15.4 only. Support for at least 920 the LLN links for which a 6lo "IPv6 over foo" specification 921 exists, as well as Low-Power Wi-Fi SHOULD be possible. 923 o As part of this extension, a mechanism to compute a unique 924 Identifier should be provided with the capability to form a Link 925 Local Address that SHOULD be unique at least within the LLN 926 connected to a 6LBR. 928 o The Address Registration Option used in the ND registration SHOULD 929 be extended to carry the relevant forms of Unique Interface 930 IDentifier. 932 o The Neighbour Discovery should specify the formation of a site- 933 local address that follows the security recommendations from 934 [RFC7217]. 936 Authors' Addresses 938 Pascal Thubert (editor) 939 Cisco Systems, Inc 940 Building D 941 45 Allee des Ormes - BP1200 942 MOUGINS - Sophia Antipolis 06254 943 FRANCE 945 Phone: +33 497 23 26 34 946 Email: pthubert@cisco.com 947 Behcet Sarikaya 948 Plano, TX 949 USA 951 Email: sarikaya@ieee.org 953 Mohit Sethi 954 Ericsson 955 Hirsalantie 956 Jorvas 02420 958 Email: mohit@piuha.net