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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: 8505 (if approved) B.S. Sarikaya 5 Intended status: Standards Track 6 Expires: 3 August 2020 M.S. Sethi 7 Ericsson 8 R.S. Struik 9 Struik Security Consultancy 10 31 January 2020 12 Address Protected Neighbor Discovery for Low-power and Lossy Networks 13 draft-ietf-6lo-ap-nd-15 15 Abstract 17 This document updates the 6LoWPAN Neighbor Discovery (ND) protocol 18 defined in RFC 6775 and RFC 8505. The new extension is called 19 Address Protected Neighbor Discovery (AP-ND) and it protects the 20 owner of an address against address theft and impersonation attacks 21 in a low-power and lossy network (LLN). Nodes supporting this 22 extension compute a cryptographic identifier (Crypto-ID) and use it 23 with one or more of their Registered Addresses. The Crypto-ID 24 identifies the owner of the Registered Address and can be used to 25 provide proof of ownership of the Registered Addresses. Once an 26 address is registered with the Crypto-ID and a proof-of-ownership is 27 provided, only the owner of that address can modify the registration 28 information, thereby enforcing Source Address Validation. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on 3 August 2020. 47 Copyright Notice 49 Copyright (c) 2020 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 54 license-info) in effect on the date of publication of this document. 55 Please review these documents carefully, as they describe your rights 56 and restrictions with respect to this document. Code Components 57 extracted from this document must include Simplified BSD License text 58 as described in Section 4.e of the Trust Legal Provisions and are 59 provided without warranty as described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4 67 2.3. Additional References . . . . . . . . . . . . . . . . . . 5 68 3. Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . . 5 69 4. New Fields and Options . . . . . . . . . . . . . . . . . . . 6 70 4.1. New Crypto-ID . . . . . . . . . . . . . . . . . . . . . . 6 71 4.2. Updated EARO . . . . . . . . . . . . . . . . . . . . . . 6 72 4.3. Crypto-ID Parameters Option . . . . . . . . . . . . . . . 7 73 4.4. NDP Signature Option . . . . . . . . . . . . . . . . . . 9 74 5. Protocol Scope . . . . . . . . . . . . . . . . . . . . . . . 11 75 6. Protocol Flows . . . . . . . . . . . . . . . . . . . . . . . 11 76 6.1. First Exchange with a 6LR . . . . . . . . . . . . . . . . 12 77 6.2. NDPSO generation and verification . . . . . . . . . . . . 14 78 6.3. Multihop Operation . . . . . . . . . . . . . . . . . . . 15 79 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 80 7.1. Inheriting from RFC 3971 . . . . . . . . . . . . . . . . 17 81 7.2. Related to 6LoWPAN ND . . . . . . . . . . . . . . . . . . 18 82 7.3. ROVR Collisions . . . . . . . . . . . . . . . . . . . . . 18 83 7.4. Implementation Attacks . . . . . . . . . . . . . . . . . 18 84 7.5. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . 19 85 7.6. Compromised 6LR . . . . . . . . . . . . . . . . . . . . . 19 86 8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 19 87 8.1. CGA Message Type . . . . . . . . . . . . . . . . . . . . 19 88 8.2. IPv6 ND option types . . . . . . . . . . . . . . . . . . 19 89 8.3. Crypto-Type Subregistry . . . . . . . . . . . . . . . . . 20 90 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 91 10. Normative References . . . . . . . . . . . . . . . . . . . . 21 92 11. Informative references . . . . . . . . . . . . . . . . . . . 22 93 Appendix A. Requirements Addressed in this Document . . . . . . 24 94 Appendix B. Representation Conventions . . . . . . . . . . . . . 24 95 B.1. Signature Schemes . . . . . . . . . . . . . . . . . . . . 24 96 B.2. Integer Representation for ECDSA signatures . . . . . . . 25 97 B.3. Alternative Representations of Curve25519 . . . . . . . . 25 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 100 1. Introduction 102 Neighbor Discovery Optimizations for 6LoWPAN networks [RFC6775] 103 (6LoWPAN ND) adapts the original IPv6 Neighbor Discovery (IPv6 ND) 104 protocols defined in [RFC4861] and [RFC4862] for constrained low- 105 power and lossy network (LLN). In particular, 6LoWPAN ND introduces 106 a unicast host Address Registration mechanism that reduces the use of 107 multicast compared to the Duplicate Address Detection (DAD) mechanism 108 defined in IPv6 ND. 6LoWPAN ND defines a new Address Registration 109 Option (ARO) that is carried in the unicast Neighbor Solicitation 110 (NS) and Neighbor Advertisement (NA) messages exchanged between a 111 6LoWPAN Node (6LN) and a 6LoWPAN Router (6LR). It also defines the 112 Duplicate Address Request (DAR) and Duplicate Address Confirmation 113 (DAC) messages between the 6LR and the 6LoWPAN Border Router (6LBR). 114 In LLN networks, the 6LBR is the central repository of all the 115 registered addresses in its domain. 117 The registration mechanism in "Neighbor Discovery Optimization for 118 Low-power and Lossy Networks" [RFC6775] (aka 6LoWPAN ND) prevents the 119 use of an address if that address is already registered in the subnet 120 (first come first serve). In order to validate address ownership, 121 the registration mechanism enables the 6LR and 6LBR to validate the 122 association between the registered address of a node, and its 123 Registration Ownership Verifier (ROVR). The ROVR is defined in 124 "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505] 125 and it can be derived from the MAC address of the device (using the 126 64-bit Extended Unique Identifier EUI-64 address format specified by 127 IEEE). However, the EUI-64 can be spoofed, and therefore, any node 128 connected to the subnet and aware of a registered-address-to-ROVR 129 mapping could effectively fake the ROVR. This would allow the an 130 attacker to steal the address and redirect traffic for that address. 131 [RFC8505] defines an Extended Address Registration Option (EARO) 132 option that allows to transport alternate forms of ROVRs, and is a 133 pre-requisite for this specification. 135 In this specification, a 6LN generates a cryptographic ID (Crypto-ID) 136 and places it in the ROVR field during the registration of one (or 137 more) of its addresses with the 6LR(s). Proof of ownership of the 138 Crypto-ID is passed with the first registration exchange to a new 139 6LR, and enforced at the 6LR. The 6LR validates ownership of the 140 cryptographic ID before it creates any new registration state, or 141 changes existing information. 143 The protected address registration protocol proposed in this document 144 enables Source Address Validation (SAVI) [RFC7039]. This ensures 145 that only the actual owner uses a registered address in the IPv6 146 source address field. A 6LN can only use a 6LR for forwarding 147 packets only if it has previously registered the address used in the 148 source field of the IPv6 packet. 150 The 6lo adaptation layer in [RFC4944] and [RFC6282] requires a device 151 to form its IPv6 addresses based on its Layer-2 address to enable a 152 better compression. This is incompatible with Secure Neighbor 153 Discovery (SeND) [RFC3971] and Cryptographically Generated Addresses 154 (CGAs) [RFC3972], since they derive the Interface ID (IID) in IPv6 155 addresses with cryptographic keys. 157 2. Terminology 159 2.1. BCP 14 161 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 162 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 163 "OPTIONAL" in this document are to be interpreted as described in BCP 164 14 [RFC2119] [RFC8174] when, and only when, they appear in all 165 capitals, as shown here. 167 2.2. Abbreviations 169 This document uses the following abbreviations: 171 6BBR: 6LoWPAN Backbone Router 172 6LBR: 6LoWPAN Border Router 173 6LN: 6LoWPAN Node 174 6LR: 6LoWPAN Router 175 ARO: Address Registration Option 176 EARO: Extended Address Registration Option 177 CIPO: Crypto-ID Parameters Option 178 LLN: Low-Power and Lossy Network 179 NA: Neighbor Advertisement 180 ND: Neighbor Discovery 181 NDP: Neighbor Discovery Protocol 182 NDPSO: NDP Signature Option 183 NS: Neighbor Solicitation 184 ROVR: Registration Ownership Verifier 185 RA: Router Advertisement 186 RS: Router Solicitation 187 RSAO: RSA Signature Option 188 TID: Transaction ID 190 2.3. Additional References 192 The reader may get additional context for this specification from the 193 following references: 195 * "SEcure Neighbor Discovery (SEND)" [RFC3971], 197 * "Cryptographically Generated Addresses (CGA)" [RFC3972], 199 * "Neighbor Discovery for IP version 6" [RFC4861] , 201 * "IPv6 Stateless Address Autoconfiguration" [RFC4862], and 203 * "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 204 Overview, Assumptions, Problem Statement, and Goals " [RFC4919]. 206 3. Updating RFC 8505 208 Section 5.3 of [RFC8505] introduces the ROVR as a generic object that 209 is designed for backward compatibility with the capability to 210 introduce new computation methods in the future. Section 7.3 211 discusses collisions when heterogeneous methods to compute the ROVR 212 field coexist inside a same network. 214 [RFC8505] was designed in preparation for this specification, which 215 is the RECOMMENDED method for building a ROVR field. 217 This specification introduces a new token called a cryptographic 218 identifier (Crypto-ID) that is transported in the ROVR field and used 219 to prove indirectly the ownership of an address that is being 220 registered by means of [RFC8505]. The Crypto-ID is derived from a 221 cryptographic public key and additional parameters. 223 The proof requires the support of Elliptic Curve Cryptography (ECC) 224 and that of a hash function as detailed in Section 6.2. To enable 225 the verification of the proof, the registering node needs to supply 226 certain parameters including a Nonce and a signature that will 227 demonstrate that the node has the private-key corresponding to the 228 public-key used to build the Crypto-ID. 230 The elliptic curves and the hash functions that can be used with this 231 specification are listed in Table 2 in Section 8.3. The signature 232 scheme that specifies which combination is used is signaled by a 233 Crypto-Type in a new IPv6 ND Crypto-ID Parameters Option (CIPO, see 234 Section 4.3) that contains the parameters that are necessary for the 235 proof, a Nonce option ([RFC3971]) and a NDP Signature option 236 (Section 4.4). The NA(EARO) is modified to enable a challenge and 237 transport a Nonce option as well. 239 4. New Fields and Options 241 4.1. New Crypto-ID 243 The Crypto-ID is transported in the ROVR field of the EARO option and 244 the EDAR message, and is associated with the Registered Address at 245 the 6LR and the 6LBR. The ownership of a Crypto-ID can be 246 demonstrated by cryptographic mechanisms, and by association, the 247 ownership of the Registered Address can be acertained. 249 A node in possession of the necessary cryptographic primitives SHOULD 250 use Crypto-ID by default as ROVR in its registrations. Whether a 251 ROVR is a Crypto-ID is indicated by a new "C" flag in the NS(EARO) 252 message. 254 The Crypto-ID is derived from the public key and a modifier as 255 follows: 257 1. The hash function indicated by the Crypto-Type is applied to the 258 CIPO. Note that all the reserved and padding bits MUST be set to 259 zero. 260 2. The leftmost bits of the resulting hash, up to the size of the 261 ROVR field, are used as the Crypto-ID. 263 4.2. Updated EARO 265 This specification updates the EARO option to enable the use of the 266 ROVR field to transport the Crypto-ID. 268 The resulting format is as follows: 270 0 1 2 3 271 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 1 272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 273 | Type | Length | Status | Opaque | 274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 275 |Rsvd |C| I |R|T| TID | Registration Lifetime | 276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 | | 278 ... Registration Ownership Verifier (ROVR) ... 279 | | 280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 282 Figure 1: Enhanced Address Registration Option 284 Type: 33 286 Length: 8-bit unsigned integer. The length of the option (including 287 the type and length fields) in units of 8 bytes. 289 Status: 8-bit unsigned integer. Indicates the status of a 290 registration in the NA response. In NS messages it MUST be set to 291 0 by the sender and ignored by the receiver. 293 Opaque: Defined in [RFC8505]. 295 Rsvd (Reserved): 3-bit unsigned integer. It MUST be set to zero by 296 the sender and MUST be ignored by the receiver. 298 C: This "C" flag is set to indicate that the ROVR field contains a 299 Crypto-ID and that the 6LN MAY be challenged for ownership as 300 specified in this document. 302 I, R, T, and TID: Defined in [RFC8505]. 304 Registration Ownership Verifier (ROVR): When the "C" flag is set, 305 this field contains a Crypto-ID. 307 This specification uses Status values "Validation Requested" and 308 "Validation Failed", which are defined in [RFC8505]. No other new 309 Status values are defined. 311 4.3. Crypto-ID Parameters Option 313 This specification defines the Crypto-ID Parameters Option (CIPO). 314 The CIPO carries the parameters used to form a Crypto-ID. 316 In order to provide cryptographic agility [RFC7696], this 317 specification supports different elliptic curves, indicated by a 318 Crypto-Type field: 320 * NIST P-256 [FIPS186-4] MUST be supported by all implementations. 322 * The Edwards-Curve Digital Signature Algorithm (EdDSA) curve 323 Ed25519 (PureEdDSA) [RFC8032] MAY be supported as an alternate. 325 * the specification is open to future extensions for different 326 cryptographic algorithms and longer keys. 328 0 1 2 3 329 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 1 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | Type | Length |Reserved1| Public Key Length | 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 | Crypto-Type | Modifier | Reserved2 | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 | | 336 | | 337 . . 338 . Public Key (variable length) . 339 . . 340 | | 341 | | 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 343 | | 344 . . 345 . Padding . 346 . . 347 | | 348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 350 Figure 2: Crypto-ID Parameters Option 352 Type: 8-bit unsigned integer. to be assigned by IANA, see Table 1. 354 Length: 8-bit unsigned integer. The length of the option in units 355 of 8 octets. 357 Reserved1: 5-bit unsigned integer. It MUST be set to zero by the 358 sender and MUST be ignored by the receiver. 360 Public Key Length: 13-bit unsigned integer. The length of the 361 Public Key field in bytes. 363 Crypto-Type: 8-bit unsigned integer. The type of cryptographic 364 algorithm used in calculation Crypto-ID (see Table 2 in 365 Section 8.3). Although the different signature schemes target 366 similar cryptographic strength, they rely on different curves, 367 hash functions, signature algorithms, and/or representation 368 conventions. 370 Modifier: 8-bit unsigned integer. Set to an arbitrary value by the 371 creator of the Crypto-ID. The role of the modifier is to enable 372 the formation of multiple Crypto-IDs from a same key pair, which 373 reduces the traceability and thus improves the privacy of a 374 constrained node that could not maintain many key-pairs. 376 Reserved2: 16-bit unsigned integer. It MUST be set to zero by the 377 sender and MUST be ignored by the receiver. 379 Public Key: A variable-length field, size indicated in the Public 380 Key Length field. JWK-Encoded Public Key [RFC7517]. 382 Padding: A variable-length field completing the Public Key field to 383 align to the next 8-bytes boundary. 385 The implementation of multiple hash functions in a constrained 386 devices may consume excessive amounts of program memory. 388 [CURVE-REPRESENTATIONS] provides information on how to represent 389 Montgomery curves and (twisted) Edwards curves as curves in short- 390 Weierstrass form and illustrates how this can be used to implement 391 elliptic curve computations using existing implementations that 392 already provide, e.g., ECDSA and ECDH using NIST [FIPS186-4] prime 393 curves. 395 For more details on representation conventions, we refer to 396 Appendix B. 398 4.4. NDP Signature Option 400 The format of the NDP Signature Option (NDPSO) is illustrated in 401 Figure 3. 403 As opposed to the RSA Signature Option (RSAO) defined in section 5.2. 404 of SEND [RFC3971], the NDPSO does not have a key hash field. The 405 hash that can be used as index is the 128 leftmost bits of the ROVR 406 field in the EARO. 408 The CIPO may be present in the same message as the NDPSO. If not, it 409 can be found in an abstract table that was created by a previous 410 message and indexed by the hash. 412 0 1 2 3 413 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 1 414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 415 | Type | Length | Pad Length | | 416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 417 | Reserved | 418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 419 | | 420 | | 421 . . 422 . Digital Signature . 423 . . 424 | | 425 | | 426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 427 | | 428 . . 429 . Padding . 430 . . 431 | | 432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 434 Figure 3: NDP signature Option 436 Type: to be assigned by IANA, see Table 1. 438 Length: 8-bit unsigned integer. The length of the option in units 439 of 8 octets. 441 Pad Length: 8-bit unsigned integer. The length of the Padding 442 field. 444 Reserved: 40-bit unsigned integer. It MUST be set to zero by the 445 sender and MUST be ignored by the receiver. 447 Digital Signature: A variable-length field containing a digital 448 signature. The computation of the digital signature depends on 449 the Crypto-Type which is found in the associated CIPO. For the 450 values of the Crypto-Type that are defined in ths specification, 451 the signature is computed as detailed in Section 6.2. 453 Padding: A variable-length field making the option length a multiple 454 of 8, containing as many octets as specified in the Pad Length 455 field. Typically there is no need of a padding and the field is 456 NULL. 458 5. Protocol Scope 460 The scope of the protocol specified here is a 6LoWPAN LLN, typically 461 a stub network connected to a larger IP network via a Border Router 462 called a 6LBR per [RFC6775]. A 6LBR has sufficient capability to 463 satisfy the needs of duplicate address detection. 465 The 6LBR maintains registration state for all devices in its attached 466 LLN. Together with the first-hop router (the 6LR), the 6LBR assures 467 uniqueness and grants ownership of an IPv6 address before it can be 468 used in the LLN. This is in contrast to a traditional network that 469 relies on IPv6 address auto-configuration [RFC4862], where there is 470 no guarantee of ownership from the network, and each IPv6 Neighbor 471 Discovery packet must be individually secured [RFC3971]. 473 ---+-------- ............ 474 | External Network 475 | 476 +-----+ 477 | | 6LBR 478 +-----+ 479 o o o 480 o o o o 481 o o LLN o o o 482 o o o (6LR) 483 o (6LN) 485 Figure 4: Basic Configuration 487 In a mesh network, the 6LR is directly connected to the host device. 488 This specification mandates that the peer-wise layer-2 security is 489 deployed so that all the packets from a particular host are securely 490 identifiable by the 6LR. The 6LR may be multiple hops away from the 491 6LBR. Packets are routed between the 6LR and the 6LBR via other 492 6LRs. This specification mandates that a chain of trust is 493 established so that a packet that was validated by the first 6LR can 494 be safely routed by other on-path 6LRs to the 6LBR. 496 6. Protocol Flows 498 The 6LR/6LBR ensures first-come/first-serve by storing the EARO 499 information including the Crypto-ID associated to the node being 500 registered. The node can claim any address as long as it is the 501 first to make such a claim. After a successful registration, the 502 node becomes the owner of the registered address and the address is 503 bound to the Crypto-ID in the 6LR/6LBR registry. 505 This specification enables the 6LR to verify the ownership of the 506 binding at any time assuming that the "C" flag is set. The 507 verification prevents other nodes from stealing the address and 508 trying to attract traffic for that address or use it as their source 509 address. 511 A node may use multiple IPv6 addresses at the same time. The node 512 MAY use the same Crypto-ID, to prove the ownership of multiple IPv6 513 addresses. The separation of the address and the cryptographic 514 material avoids the constrained device to compute multiple keys for 515 multiple addresses. The registration process allows the node to use 516 the same Crypto-ID for all of its addresses. 518 6.1. First Exchange with a 6LR 520 A 6LN registers to a 6LR that is one hop away from it with the "C" 521 flag set in the EARO, indicating that the ROVR field contains a 522 Crypto-ID. The Target Address in the NS message indicates the IPv6 523 address that the 6LN is trying to register. The on-link (local) 524 protocol interactions are shown in Figure 5. If the 6LR does not 525 have a state with the 6LN that is consistent with the NS(EARO), then 526 it replies with a challenge NA (EARO, status=Validation Requested) 527 that contains a Nonce Option (shown as NonceLR in Figure 5). The 528 Nonce option contains a Nonce value that, to the extent possible for 529 the implementation, was never employed in association with the key 530 pair used to generate the ROVR. This specification inherits from 531 [RFC3971] that simply indicates that the nonce is a random value. 532 Ideally, an implementation would use an unpredictable 533 cryptographically random value [RFC4086]. But that may be 534 impractical in some LLN scenarios where the devices do not have a 535 guaranteed sense of time and for which computing complex hashes is 536 detrimental to the battery lifetime. Alternatively, the device may 537 use an always-incrementing value saved in the same stable storage as 538 the key, so they are lost together, and starting at a best effort 539 random value, either as Nonce value or as a component to its 540 computation. 542 The 6LN replies to the challenge with an NS(EARO) that includes a new 543 Nonce option (shown as NonceLN in Figure 5), the CIPO (Section 4.3), 544 and the NDPSO containing the signature. The information associated 545 to a Crypto-ID stored by the 6LR on the first NS exchange where it 546 appears. The 6LR MUST store the CIPO parameters associated with the 547 Crypto-ID so it can be used for more than one address. 549 6LN 6LR 550 | | 551 |<------------------------- RA -------------------------| 552 | | ^ 553 |---------------- NS with EARO (Crypto-ID) ------------>| | 554 | | option 555 |<- NA with EARO (status=Validation Requested), NonceLR-| | 556 | | v 557 |------- NS with EARO, CIPO, NonceLN and NDPSO -------->| 558 | | 559 |<------------------- NA with EARO ---------------------| 560 | | 561 ... 562 | | 563 |--------------- NS with EARO (Crypto-ID) ------------->| 564 | | 565 |<------------------- NA with EARO ---------------------| 566 | | 567 ... 568 | | 569 |--------------- NS with EARO (Crypto-ID) ------------->| 570 | | 571 |<------------------- NA with EARO ---------------------| 572 | | 574 Figure 5: On-link Protocol Operation 576 The steps for the registration to the 6LR are as follows: 578 * Upon the first exchange with a 6LR, a 6LN will be challenged to 579 prove ownership of the Crypto-ID and the Target Address being 580 registered in the Neighbor Solicitation message. When a 6LR 581 receives a NS(EARO) registration with a new Crypto-ID as a ROVR, 582 and unless the registration is rejected for another reason, it 583 MUST challenge by responding with a NA(EARO) with a status of 584 "Validation Requested". 586 * The challenge is triggered when the registration for a Source 587 Link-Layer Address is not verifiable either at the 6LR or the 588 6LBR. In the latter case, the 6LBR returns a status of 589 "Validation Requested" in the DAR/DAC exchange, which is echoed by 590 the 6LR in the NA (EARO) back to the registering node. The 591 challenge MUST NOT alter a valid registration in the 6LR or the 592 6LBR. 594 * Upon receiving a first NA(EARO) with a status of "Validation 595 Requested" from a 6LR, the registering node SHOULD retry its 596 registration with a Crypto-ID Parameters Option (CIPO) 597 (Section 4.3) that contains all the necessary material for 598 building the Crypto-ID, the NonceLN that it generated, and the NDP 599 signature (Section 4.4) option that proves its ownership of the 600 Crypto-ID and intent of registering the Target Address. In 601 subsequent revalidation with the same 6LR, the 6LN MAY try to omit 602 the CIPO to save bandwidth, with the expectation that the 6LR 603 saved it. If the validation fails and it gets challenged again, 604 then it SHOULD add the CIPO again. 606 * In order to validate the ownership, the 6LR performs the same 607 steps as the 6LN and rebuilds the Crypto-ID based on the 608 parameters in the CIPO. If the rebuilt Crypto-ID matches the 609 ROVR, the 6LN also verifies the signature contained in the NDPSO 610 option. If at that point the signature in the NDPSO option can be 611 verified, then the validation succeeds. Otherwise the validation 612 fails. 614 * If the 6LR fails to validate the signed NS(EARO), it responds with 615 a status of "Validation Failed". After receiving a NA(EARO) with 616 a status of "Validation Failed", the registering node SHOULD try 617 to register an alternate target address in the NS message. 619 6.2. NDPSO generation and verification 621 The signature generated by the 6LN to provide proof-of-ownership of 622 the private-key is carried in the NDP Signature Option (NDPSO). It 623 is generated by the 6LN in a fashion that depends on the Crypto-Type 624 (see Table 2 in Section 8.3) chosen by the 6LN as follows: 626 * Concatenate the following in the order listed: 628 1. The 128-bit Message Type tag [RFC3972] (in network byte order). 629 For this specification the tag is 0x8701 55c8 0cca dd32 6ab7 e415 630 f148 84d0. (The tag value has been generated by the editor of 631 this specification on random.org). 632 2. JWK-encoded public key 633 3. the 16-byte Target Address (in network byte order) sent in the 634 Neighbor Solicitation (NS) message. It is the address which the 635 6LN is registering with the 6LR and 6LBR. 636 4. NonceLR received from the 6LR (in network byte order) in the 637 Neighbor Advertisement (NA) message. The Nonce is at least 6 638 bytes long as defined in [RFC3971]. 639 5. NonceLN sent from the 6LN (in network byte order). The Nonce is 640 at least 6 bytes long as defined in [RFC3971]. 641 6. The length of the ROVR field in the NS message containing the 642 Crypto-ID that was sent. 644 7. 1-byte (in network byte order) Crypto-Type value sent in the CIPO 645 option. 647 * Depending on the Crypto-Type, apply the hash function on this 648 concatenation. 650 * Depending on the Crypto-Type, sign the hash output with ECDSA (if 651 curve P-256 is used) or sign the hash with EdDSA (if curve Ed25519 652 (PureEdDSA)). 654 The 6LR on receiving the NDPSO and CIPO options first regenerates the 655 Crypto-ID based on the CIPO option to make sure that the leftmost 656 bits up to the size of the ROVR match. If and only if the check is 657 successful, it tries to verify the signature in the NDPSO option 658 using the following: 660 * Concatenate the following in the order listed: 662 1. 128-bit type tag (in network byte order) 663 2. JWK-encoded public key received in the CIPO option 664 3. the 16-byte Target Address (in network byte order) received in 665 the Neighbor Solicitation (NS) message. It is the address which 666 the 6LN is registering with the 6LR and 6LBR. 667 4. NonceLR sent in the Neighbor Advertisement (NA) message. The 668 Nonce is at least 6 bytes long as defined in [RFC3971]. 669 5. NonceLN received from the 6LN (in network byte order) in the NS 670 message. The Nonce is at least 6 bytes long as defined in 671 [RFC3971]. 672 6. The length of the ROVR field in the NS message containing the 673 Crypto-ID that was received. 674 7. 1-byte (in network byte order) Crypto-Type value received in the 675 CIPO option. 677 * Depending on the Crypto-Type indicated by the (6LN) in the CIPO, 678 apply the hash function on this concatenation. 680 * Verify the signature with the public-key received and the locally 681 computed values. If the verification succeeds, the 6LR and 6LBR 682 add the state information about the Crypto-ID, public-key and 683 Target Address being registered to their database. 685 6.3. Multihop Operation 687 In a multihop 6LoWPAN, the registration with Crypto-ID is propagated 688 to 6LBR as described in this section. If the 6LR and the 6LBR 689 maintain a security association, then there is no need to propagate 690 the proof of ownership to the 6LBR. 692 A new device that joins the network auto-configures an address and 693 performs an initial registration to a neighboring 6LR with an NS 694 message that carries an Address Registration Option (EARO) [RFC8505]. 695 The 6LR validates the address with an 6LBR using a DAR/DAC exchange, 696 and the 6LR confirms (or denies) the address ownership with an NA 697 message that also carries an Address Registration Option. 699 Figure 6 illustrates a registration flow all the way to a 6LowPAN 700 Backbone Router (6BBR) [BACKBONE-ROUTER]. 702 6LN 6LR 6LBR 6BBR 703 | | | | 704 | NS(EARO) | | | 705 |--------------->| | | 706 | | Extended DAR | | 707 | |-------------->| | 708 | | | | 709 | | | proxy NS(EARO) | 710 | | |--------------->| 711 | | | | NS(DAD) 712 | | | | ------> 713 | | | | 714 | | | | 715 | | | | 716 | | | proxy NA(EARO) | 717 | | |<---------------| 718 | | Extended DAC | | 719 | |<--------------| | 720 | NA(EARO) | | | 721 |<---------------| | | 722 | | | | 724 Figure 6: (Re-)Registration Flow 726 In a multihop 6LoWPAN, a 6LBR sends RAs with prefixes downstream and 727 the 6LR receives and relays them to the nodes. 6LR and 6LBR 728 communicate using ICMPv6 Duplicate Address Request (DAR) and 729 Duplicate Address Confirmation (DAC) messages. The DAR and DAC use 730 the same message format as NS and NA, but have different ICMPv6 type 731 values. 733 In AP-ND we extend DAR/DAC messages to carry cryptographically 734 generated ROVR. In a multihop 6LoWPAN, the node exchanges the 735 messages shown in Figure 6. The 6LBR must identify who owns an 736 address (EUI-64) to defend it, if there is an attacker on another 737 6LR. 739 7. Security Considerations 741 7.1. Inheriting from RFC 3971 743 Observations regarding the following threats to the local network in 744 [RFC3971] also apply to this specification. 746 Neighbor Solicitation/Advertisement Spoofing: Threats in section 747 9.2.1 of RFC3971 apply. AP-ND counters the threats on NS(EARO) 748 messages by requiring that the NDP Signature and CIPO options be 749 present in these solicitations. 751 Duplicate Address Detection DoS Attack: Inside the LLN, Duplicate 752 Addresses are sorted out using the ROVR, which differentiates it 753 from a movement. DAD coming from the backbone are not forwarded 754 over the LLN, which provides some protection against DoS attacks 755 inside the resource-constrained part of the network. Over the 756 backbone, the EARO option is present in NS/NA messages. This 757 protects against misinterpreting a movement for a duplication, and 758 enables the backbone routers to determine which one has the 759 freshest registration and is thus the best candidate to validate 760 the registration for the device attached to it. But this 761 specification does not guarantee that the backbone router claiming 762 an address over the backbone is not an attacker. 764 Router Solicitation and Advertisement Attacks: This specification 765 does not change the protection of RS and RA which can still be 766 protected by SEND. 768 Replay Attacks Using Nonces (NonceLR and NonceLN) generated by both 769 the 6LR and 6LN provides an efficient protection against replay 770 attacks of challenge response flow. The quality of the protection 771 still depends on the quality of the Nonce, in particular of a 772 random generator if they are computed that way. 774 Neighbor Discovery DoS Attack: A rogue node that managed to access 775 the L2 network may form many addresses and register them using AP- 776 ND. The perimeter of the attack is all the 6LRs in range of the 777 attacker. The 6LR MUST protect itself against overflows and 778 reject excessive registration with a status 2 "Neighbor Cache 779 Full". This effectively blocks another (honest) 6LN from 780 registering to the same 6LR, but the 6LN may register to other 781 6LRs that are in its range but not in that of the rogue. 783 7.2. Related to 6LoWPAN ND 785 The threats discussed in 6LoWPAN ND [RFC6775][RFC8505] also apply 786 here. Compared with SeND, this specification saves about 1Kbyte in 787 every NS/NA message. Also, this specification separates the 788 cryptographic identifier from the registered IPv6 address so that a 789 node can have more than one IPv6 address protected by the same 790 cryptographic identifier. SeND forces the IPv6 address to be 791 cryptographic since it integrates the CGA as the IID in the IPv6 792 address. This specification frees the device to form its addresses 793 in any fashion, thereby enabling not only 6LoWPAN compression which 794 derives IPv6 addresses from Layer-2 addresses but also privacy 795 addresses. 797 7.3. ROVR Collisions 799 A collision of Registration Ownership Verifiers (ROVR) (i.e., the 800 Crypto-ID in this specification) is possible, but it is a rare event. 801 The formula for calculating the probability of a collision is 1 - 802 e^{-k^2/(2n)} where n is the maximum population size (2^64 here, 803 1.84E19) and K is the actual population (number of nodes). If the 804 Crypto-ID is 64-bits (the least possible size allowed), the chance of 805 a collision is 0.01% when the network contains 66 million nodes. 806 Moreover, the collision is only relevant when this happens within one 807 stub network (6LBR). In the case of such a collision, an attacker 808 may be able to claim the registered address of an another legitimate 809 node. However for this to happen, the attacker would also need to 810 know the address which was registered by the legitimate node. This 811 registered address is never broadcasted on the network and therefore 812 providing an additional 64-bits that an attacker must correctly 813 guess. To prevent address disclosure, it is RECOMMENDED that nodes 814 derive the address being registered independently of the ROVR. 816 7.4. Implementation Attacks 818 The signature schemes referenced in this specification comply with 819 NIST [FIPS186-4] or Crypto Forum Research Group (CFRG) standards 820 [RFC8032] and offer strong algorithmic security at roughly 128-bit 821 security level. These signature schemes use elliptic curves that 822 were either specifically designed with exception-free and constant- 823 time arithmetic in mind [RFC7748] or where one has extensive 824 implementation experience of resistance to timing attacks 825 [FIPS186-4]. However, careless implementations of the signing 826 operations could nevertheless leak information on private keys. For 827 example, there are micro-architectural side channel attacks that 828 implementors should be aware of [breaking-ed25519]. Implementors 829 should be particularly aware that a secure implementation of Ed25519 830 requires a protected implementation of the hash function SHA-512, 831 whereas this is not required with implementations of SHA-256 used 832 with ECDSA. 834 7.5. Cross-Protocol Attacks 836 The same private key MUST NOT be reused with more than one signature 837 scheme in this specification. 839 7.6. Compromised 6LR 841 This specification distributes the challenge and its validation at 842 the edge of the network, between the 6LN and its 6LR. The central 843 6LBR is offloaded, which avoids DOS attacks targeted at that central 844 entity. This also saves back and forth exchanges across a 845 potentially large and constrained network. 847 The downside is that the 6LBR needs to trust the 6LR for performing 848 the checking adequately, and the communication between the 6LR and 849 the 6LBR must be protected to avoid tempering with the result of the 850 test. 852 If a 6LR is compromised, it may pretend that it owns any address and 853 defeat the protection. It may also admit any rogue and let it take 854 ownership of any address in the network, provided that the 6LR knows 855 the ROVR field used by the real owner of the address. 857 8. IANA considerations 859 8.1. CGA Message Type 861 This document defines a new 128-bit value under the CGA Message Type 862 [RFC3972] name space: 0x8701 55c8 0cca dd32 6ab7 e415 f148 84d0. 864 8.2. IPv6 ND option types 866 This document registers two new ND option types under the subregistry 867 "IPv6 Neighbor Discovery Option Formats": 869 +------------------------------+-----------------+---------------+ 870 | Option Name | Suggested Value | Reference | 871 +==============================+=================+===============+ 872 | NDP Signature Option (NDPSO) | 38 | This document | 873 +------------------------------+-----------------+---------------+ 874 | Crypto-ID Parameters Option | 39 | This document | 875 | (CIPO) | | | 876 +------------------------------+-----------------+---------------+ 878 Table 1: New ND options 880 8.3. Crypto-Type Subregistry 882 IANA is requested to create a new subregistry "Crypto-Type 883 Subregistry" in the "Internet Control Message Protocol version 6 884 (ICMPv6) Parameters". The registry is indexed by an integer in the 885 interval 0..255 and contains an Elliptic Curve, a Hash Function, a 886 Signature Algorithm, and Representation Conventions, as shown in 887 Table 2, which together specify a signature scheme. The following 888 Crypto-Type values are defined in this document: 890 +----------------+-----------------+-------------+-----------------+ 891 | Crypto-Type | 0 (ECDSA256) | 1 (Ed25519) | 2 (ECDSA25519) | 892 | value | | | | 893 +================+=================+=============+=================+ 894 | Elliptic curve | NIST P-256 | Curve25519 | Curve25519 | 895 | | [FIPS186-4] | [RFC7748] | [RFC7748] | 896 +----------------+-----------------+-------------+-----------------+ 897 | Hash function | SHA-256 | SHA-512 | SHA-256 | 898 | | [RFC6234] | [RFC6234] | [RFC6234] | 899 +----------------+-----------------+-------------+-----------------+ 900 | Signature | ECDSA | Ed25519 | ECDSA | 901 | algorithm | [FIPS186-4] | [RFC8032] | [FIPS186-4] | 902 +----------------+-----------------+-------------+-----------------+ 903 | Representation | Weierstrass, | Edwards, | Weierstrass, | 904 | conventions | (un)compressed, | compressed, | (un)compressed, | 905 | | MSB/msb first | LSB/lsb | MSB/msb first | 906 | | | first | | 907 +----------------+-----------------+-------------+-----------------+ 908 | Defining | This document | This | This document | 909 | specification | | document | | 910 +----------------+-----------------+-------------+-----------------+ 912 Table 2: Crypto-Types 914 New Crypto-Type values providing similar or better security (with 915 less code) may be defined in the future. 917 Assignment of new values for new Crypto-Type MUST be done through 918 IANA with either "Specification Required" or "IESG Approval" as 919 defined in [RFC8126]. 921 9. Acknowledgments 923 Many thanks to Charlie Perkins for his in-depth review and 924 constructive suggestions. The authors are also especially grateful 925 to Robert Moskowitz for his comments that led to many improvements. 926 The authors wish to thank Mirja Kuhlewind, Eric Vyncke, Vijay 927 Gurbani, Al Morton and Adam Montville for their constructive reviews 928 during the IESG process. 930 10. Normative References 932 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 933 Requirement Levels", BCP 14, RFC 2119, 934 DOI 10.17487/RFC2119, March 1997, 935 . 937 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 938 Bormann, "Neighbor Discovery Optimization for IPv6 over 939 Low-Power Wireless Personal Area Networks (6LoWPANs)", 940 RFC 6775, DOI 10.17487/RFC6775, November 2012, 941 . 943 [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, 944 DOI 10.17487/RFC7517, May 2015, 945 . 947 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 948 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 949 May 2017, . 951 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 952 "SEcure Neighbor Discovery (SEND)", RFC 3971, 953 DOI 10.17487/RFC3971, March 2005, 954 . 956 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 957 Perkins, "Registration Extensions for IPv6 over Low-Power 958 Wireless Personal Area Network (6LoWPAN) Neighbor 959 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 960 . 962 [FIPS186-4] 963 FIPS 186-4, "Digital Signature Standard (DSS), Federal 964 Information Processing Standards Publication 186-4", US 965 Department of Commerce/National Institute of Standards and 966 Technology , July 2013. 968 [SEC1] SEC1, "SEC 1: Elliptic Curve Cryptography, Version 2.0", 969 Standards for Efficient Cryptography , June 2009. 971 11. Informative references 973 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 974 RFC 3972, DOI 10.17487/RFC3972, March 2005, 975 . 977 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 978 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 979 DOI 10.17487/RFC4861, September 2007, 980 . 982 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 983 Address Autoconfiguration", RFC 4862, 984 DOI 10.17487/RFC4862, September 2007, 985 . 987 [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves 988 for Security", RFC 7748, DOI 10.17487/RFC7748, January 989 2016, . 991 [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital 992 Signature Algorithm (EdDSA)", RFC 8032, 993 DOI 10.17487/RFC8032, January 2017, 994 . 996 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 997 "Transmission of IPv6 Packets over IEEE 802.15.4 998 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 999 . 1001 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1002 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1003 DOI 10.17487/RFC6282, September 2011, 1004 . 1006 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 1007 over Low-Power Wireless Personal Area Networks (6LoWPANs): 1008 Overview, Assumptions, Problem Statement, and Goals", 1009 RFC 4919, DOI 10.17487/RFC4919, August 2007, 1010 . 1012 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 1013 "Randomness Requirements for Security", BCP 106, RFC 4086, 1014 DOI 10.17487/RFC4086, June 2005, 1015 . 1017 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1018 Writing an IANA Considerations Section in RFCs", BCP 26, 1019 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1020 . 1022 [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms 1023 (SHA and SHA-based HMAC and HKDF)", RFC 6234, 1024 DOI 10.17487/RFC6234, May 2011, 1025 . 1027 [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., 1028 "Source Address Validation Improvement (SAVI) Framework", 1029 RFC 7039, DOI 10.17487/RFC7039, October 2013, 1030 . 1032 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 1033 Interface Identifiers with IPv6 Stateless Address 1034 Autoconfiguration (SLAAC)", RFC 7217, 1035 DOI 10.17487/RFC7217, April 2014, 1036 . 1038 [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm 1039 Agility and Selecting Mandatory-to-Implement Algorithms", 1040 BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, 1041 . 1043 [BACKBONE-ROUTER] 1044 Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 1045 Backbone Router", Work in Progress, Internet-Draft, draft- 1046 ietf-6lo-backbone-router-13, 26 September 2019, 1047 . 1050 [CURVE-REPRESENTATIONS] 1051 Struik, R., "Alternative Elliptic Curve Representations", 1052 Work in Progress, Internet-Draft, draft-ietf-lwig-curve- 1053 representations-08, 24 July 2019, 1054 . 1057 [breaking-ed25519] 1058 Samwel, N., Batina, L., Bertoni, G., Daemen, J., and R. 1059 Susella, "Breaking Ed25519 in WolfSSL", Cryptographers' 1060 Track at the RSA Conference , 2018, 1061 . 1064 Appendix A. Requirements Addressed in this Document 1066 In this section we state requirements of a secure neighbor discovery 1067 protocol for low-power and lossy networks. 1069 * The protocol MUST be based on the Neighbor Discovery Optimization 1070 for Low-power and Lossy Networks protocol defined in [RFC6775]. 1071 RFC6775 utilizes optimizations such as host-initiated interactions 1072 for sleeping resource-constrained hosts and elimination of 1073 multicast address resolution. 1074 * New options to be added to Neighbor Solicitation messages MUST 1075 lead to small packet sizes, especially compared with existing 1076 protocols such as SEcure Neighbor Discovery (SEND). Smaller 1077 packet sizes facilitate low-power transmission by resource- 1078 constrained nodes on lossy links. 1079 * The support for this registration mechanism SHOULD be extensible 1080 to more LLN links than IEEE 802.15.4 only. Support for at least 1081 the LLN links for which a 6lo "IPv6 over foo" specification 1082 exists, as well as Low-Power Wi-Fi SHOULD be possible. 1083 * As part of this extension, a mechanism to compute a unique 1084 Identifier should be provided with the capability to form a Link 1085 Local Address that SHOULD be unique at least within the LLN 1086 connected to a 6LBR. 1087 * The Address Registration Option used in the ND registration SHOULD 1088 be extended to carry the relevant forms of Unique Interface 1089 Identifier. 1090 * The Neighbor Discovery should specify the formation of a site- 1091 local address that follows the security recommendations from 1092 [RFC7217]. 1094 Appendix B. Representation Conventions 1096 B.1. Signature Schemes 1098 The signature scheme ECDSA256 corresponding to Crypto-Type 0 is 1099 ECDSA, as specified in [FIPS186-4], instantiated with the NIST prime 1100 curve P-256, as specified in Appendix B of [FIPS186-4], and the hash 1101 function SHA-256, as specified in [RFC6234], where points of this 1102 NIST curve are represented as points of a short-Weierstrass curve 1103 (see [FIPS186-4]) and are encoded as octet strings in most- 1104 significant-bit first (msb) and most-significant-byte first (MSB) 1105 order. The signature itself consists of two integers (r and s), 1106 which are each encoded as fixed-size octet strings in most- 1107 significant-bit first and most-significant-byte first order. For 1108 details on ECDSA, see [FIPS186-4]; for details on the integer 1109 encoding, see Appendix B.2. 1111 The signature scheme Ed25519 corresponding to Crypto-Type 1 is EdDSA, 1112 as specified in [RFC8032], instantiated with the Montgomery curve 1113 Curve25519, as specified in [RFC7748], and the hash function SHA-512, 1114 as specified in [RFC6234], where points of this Montgomery curve are 1115 represented as points of the corresponding twisted Edwards curve (see 1116 Appendix B.3) and are encoded as octet strings in least-significant- 1117 bit first (lsb) and least-significant-byte first (LSB) order. The 1118 signature itself consists of a bit string that encodes a point of 1119 this twisted Edwards curve, in compressed format, and an integer 1120 encoded in least-significant-bit first and least-significant-byte 1121 first order. For details on EdDSA and on the encoding conversions, 1122 see the specification of pure Ed25519 in . [RFC8032] 1124 The signature scheme ECDSA25519 corresponding to Crypto-Type 2 is 1125 ECDSA, as specified in [FIPS186-4], instantiated with the Montgomery 1126 curve Curve25519, as specified in [RFC7748], and the hash function 1127 SHA-256, as specified in [RFC6234], where points of this Montgomery 1128 curve are represented as points of a corresponding curve in short- 1129 Weierstrass form (see Appendix B.3) and are encoded as octet strings 1130 in most-significant-bit first and most-significant-byte first order. 1131 The signature itself consists of a bit string that encodes two 1132 integers, each encoded as fixed-size octet strings in most- 1133 significant-bit first and most-significant-byte first order. For 1134 details on ECDSA, see [FIPS186-4]; for details on the integer 1135 encoding, see Appendix B.2 1137 B.2. Integer Representation for ECDSA signatures 1139 With ECDSA, each signature is a pair (r, s) of integers [FIPS186-4]. 1140 Each integer is encoded as a fixed-size 256-bit bit string, where 1141 each integer is represented according to the Field Element to Octet 1142 String and Octet String to Bit String conversion rules in [SEC1] and 1143 where the ordered pair of integers is represented as the 1144 rightconcatenation of the resulting representation values. The 1145 inverse operation follows the corresponding Bit String to Octet 1146 String and Octet String to Field Element conversion rules of [SEC1]. 1148 B.3. Alternative Representations of Curve25519 1150 The elliptic curve Curve25519, as specified in [RFC7748], is a so- 1151 called Montgomery curve. Each point of this curve can also be 1152 represented as a point of a twisted Edwards curve or as a point of an 1153 elliptic curve in short-Weierstrass form, via a coordinate 1154 transformation (a so-called isomorphic mapping). The parameters of 1155 the Montgomery curve and the corresponding isomorphic curves in 1156 twisted Edwards curve and short-Weierstrass form are as indicated 1157 below. Here, the domain parameters of the Montgomery curve 1158 Curve25519 and of the twisted Edwards curve Edwards25519 are as 1159 specified in [RFC7748]; the domain parameters of the elliptic curve 1160 Wei25519 in short-Weierstrass curve comply with Section 6.1.1 of 1161 [FIPS186-4]. For details of the coordinate transformation referenced 1162 above, see [RFC7748] and [CURVE-REPRESENTATIONS]. 1164 General parameters (for all curve models): 1166 p 2^{255}-19 1167 (=0x7fffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff 1168 ffffffed) 1169 h 8 1170 n 1171 723700557733226221397318656304299424085711635937990760600195093828 1172 5454250989 1173 (=2^{252} + 0x14def9de a2f79cd6 5812631a 5cf5d3ed) 1175 Montgomery curve-specific parameters (for Curve25519): 1177 A 486662 1178 B 1 1179 Gu 9 (=0x9) 1180 Gv 1181 147816194475895447910205935684099868872646061346164752889648818377 1182 55586237401 1183 (=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2 1184 7eced3d9) 1186 Twisted Edwards curve-specific parameters (for Edwards25519): 1188 a -1 (-0x01) 1189 d -121665/121666 1190 (=3709570593466943934313808350875456518954211387984321901638878553 1191 3085940283555) 1192 (=0x52036cee 2b6ffe73 8cc74079 7779e898 00700a4d 4141d8ab 75eb4dca 1193 135978a3) 1194 Gx 1195 151122213495354007725011514095885315114540126930418572060461132839 1196 49847762202 1197 (=0x216936d3 cd6e53fe c0a4e231 fdd6dc5c 692cc760 9525a7b2 c9562d60 1198 8f25d51a) 1199 Gy 4/5 1200 (=4631683569492647816942839400347516314130799386625622561578303360 1201 3165251855960) 1202 (=0x66666666 66666666 66666666 66666666 66666666 66666666 66666666 1203 66666658) 1205 Weierstrass curve-specific parameters (for Wei25519): 1207 a 1208 192986815395526992372618308347813179755449974442734273399095973345 1209 73241639236 1210 (=0x2aaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaa98 1211 4914a144) 1212 b 1213 557517466698189089076452890782571408182411037279010123152944008379 1214 56729358436 1215 (=0x7b425ed0 97b425ed 097b425e d097b425 ed097b42 5ed097b4 260b5e9c 1216 7710c864) 1217 GX 1218 192986815395526992372618308347813179755449974442734273399095973346 1219 52188435546 1220 (=0x2aaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa 1221 aaad245a) 1222 GY 1223 147816194475895447910205935684099868872646061346164752889648818377 1224 55586237401 1225 (=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2 1226 7eced3d9) 1228 Authors' Addresses 1230 Pascal Thubert (editor) 1231 Cisco Systems, Inc 1232 Building D 1233 45 Allee des Ormes - BP1200 1234 06254 MOUGINS - Sophia Antipolis 1235 France 1237 Phone: +33 497 23 26 34 1238 Email: pthubert@cisco.com 1240 Behcet Sarikaya 1242 Email: sarikaya@ieee.org 1244 Mohit Sethi 1245 Ericsson 1246 FI-02420 Jorvas 1247 Finland 1249 Email: mohit@piuha.net 1250 Rene Struik 1251 Struik Security Consultancy 1253 Email: rstruik.ext@gmail.com