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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ANIMA WG M. Pritikin 3 Internet-Draft Cisco 4 Intended status: Informational M. Richardson 5 Expires: January 1, 2017 SSW 6 M. Behringer 7 S. Bjarnason 8 Cisco 9 June 30, 2016 11 Bootstrapping Remote Secure Key Infrastructures (BRSKI) 12 draft-ietf-anima-bootstrapping-keyinfra-03 14 Abstract 16 This document specifies automated bootstrapping of a remote secure 17 key infrastructure (BRSKI) using vendor installed IEEE 802.1AR 18 manufacturing installed certificates, in combination with a vendor 19 based service on the Internet. Before being authenticated, a new 20 device has only link-local connectivity, and does not require a 21 routable address. When a vendor provides an Internet based service 22 devices can be redirected to a local service. In limited/ 23 disconnected networks or legacy environments we describe a variety of 24 options that allow bootstrapping to proceed. Support for lower 25 security models, including devices with minimal identity, is 26 described for legacy reasons but not encouraged. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on January 1, 2017. 45 Copyright Notice 47 Copyright (c) 2016 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 64 1.2. Scope of solution . . . . . . . . . . . . . . . . . . . . 6 65 1.3. Trust bootstrap . . . . . . . . . . . . . . . . . . . . . 7 66 2. Architectural Overview . . . . . . . . . . . . . . . . . . . 7 67 3. Functional Overview . . . . . . . . . . . . . . . . . . . . . 9 68 3.1. Behavior of a New Entity . . . . . . . . . . . . . . . . 11 69 3.1.1. Discovery . . . . . . . . . . . . . . . . . . . . . . 13 70 3.1.2. Identity . . . . . . . . . . . . . . . . . . . . . . 14 71 3.1.3. Request Join . . . . . . . . . . . . . . . . . . . . 15 72 3.1.4. Imprint . . . . . . . . . . . . . . . . . . . . . . . 15 73 3.1.5. Lack of realtime clock . . . . . . . . . . . . . . . 16 74 3.1.6. Enrollment . . . . . . . . . . . . . . . . . . . . . 17 75 3.1.7. Being Managed . . . . . . . . . . . . . . . . . . . . 18 76 3.2. Behavior of a Proxy . . . . . . . . . . . . . . . . . . . 18 77 3.2.1. CoAP connection to Registrar . . . . . . . . . . . . 19 78 3.2.2. HTTPS proxy connection to Registrar . . . . . . . . . 19 79 3.3. Behavior of the Registrar (Bootstrap Server) . . . . . . 20 80 3.3.1. Entity Authentication . . . . . . . . . . . . . . . . 21 81 3.3.2. Entity Authorization . . . . . . . . . . . . . . . . 21 82 3.3.3. Claiming the New Entity . . . . . . . . . . . . . . . 22 83 3.3.4. Log Verification . . . . . . . . . . . . . . . . . . 23 84 3.4. Behavior of the MASA Service . . . . . . . . . . . . . . 24 85 3.4.1. Issue Authorization Token and Log the event . . . . . 24 86 3.4.2. Retrieve Audit Entries from Log . . . . . . . . . . . 24 87 3.5. Leveraging the new key infrastructure / next steps . . . 24 88 3.5.1. Network boundaries . . . . . . . . . . . . . . . . . 25 89 3.6. Interactions with Network Access Control . . . . . . . . 25 90 4. Domain Operator Activities . . . . . . . . . . . . . . . . . 25 91 4.1. Instantiating the Domain Certification Authority . . . . 25 92 4.2. Instantiating the Registrar . . . . . . . . . . . . . . . 25 93 4.3. Accepting New Entities . . . . . . . . . . . . . . . . . 26 94 4.4. Automatic Enrollment of Devices . . . . . . . . . . . . . 27 95 4.5. Secure Network Operations . . . . . . . . . . . . . . . . 27 96 5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 27 97 5.1. Request Audit Token from the Registrar . . . . . . . . . 30 98 5.2. Request Audit Token from MASA . . . . . . . . . . . . . . 32 99 5.3. Audit Token Response . . . . . . . . . . . . . . . . . . 33 100 5.3.1. Completing authentication of Provisional TLS 101 connection . . . . . . . . . . . . . . . . . . . . . 34 102 5.4. Audit Token Status Telemetry . . . . . . . . . . . . . . 35 103 5.5. MASA authorization log Request . . . . . . . . . . . . . 36 104 5.6. MASA authorization log Response . . . . . . . . . . . . . 36 105 5.7. EST Integration for PKI bootstrapping . . . . . . . . . . 37 106 5.7.1. EST Distribution of CA Certificates . . . . . . . . . 37 107 5.7.2. EST CSR Attributes . . . . . . . . . . . . . . . . . 38 108 5.7.3. EST Client Certificate Request . . . . . . . . . . . 38 109 5.7.4. Enrollment Status Telemetry . . . . . . . . . . . . . 38 110 5.7.5. EST over CoAP . . . . . . . . . . . . . . . . . . . . 39 111 6. Reduced security operational modes . . . . . . . . . . . . . 40 112 6.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 40 113 6.2. New Entity security reductions . . . . . . . . . . . . . 41 114 6.3. Registrar security reductions . . . . . . . . . . . . . . 41 115 6.4. MASA security reductions . . . . . . . . . . . . . . . . 42 116 7. Security Considerations . . . . . . . . . . . . . . . . . . . 42 117 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 44 118 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 44 119 9.1. Normative References . . . . . . . . . . . . . . . . . . 44 120 9.2. Informative References . . . . . . . . . . . . . . . . . 45 121 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46 123 1. Introduction 125 To literally "pull yourself up by the bootstraps" is an impossible 126 action. Similarly the secure establishment of a key infrastructure 127 without external help is also an impossibility. Today it is accepted 128 that the initial connections between nodes are insecure, until key 129 distribution is complete, or that domain-specific keying material is 130 pre-provisioned on each new device in a costly and non-scalable 131 manner. This document describes a zero-touch approach to 132 bootstrapping an entity by securing the initial distribution of key 133 material using third-party generic keying material, such as a 134 manufacturer installed IEEE 802.1AR certificate [IDevID], and a 135 corresponding third-party service on the Internet. 137 The two sides of an association being bootstrapped authenticate each 138 other and then determine appropriate authorization. This process is 139 described as four distinct steps between the existing domain and the 140 new entity being added: 142 o New entity authentication: "Who is this? What is its identity?" 144 o New entity authorization: "Is it mine? Do I want it? What are 145 the chances it has been compromised?" 147 o Domain authentication: "What is this domain's claimed identity?" 149 o Domain authorization: "Should I join it?" 151 A precise answer to these questions can not be obtained without 152 leveraging some established key infrastructure(s). A complexity that 153 this protocol deals with are dealing with devices from a variety of 154 vendors, and a network infrastructure (the domain) that is operated 155 by parties that do not have any priviledged relationship with the 156 device vendors. The domain's decisions are based on the new entity's 157 authenticated identity, as established by verification of previously 158 installed credentials such as a manufacturer installed IEEE 802.1AR 159 certificate, and verified back-end information such as a configured 160 list of purchased devices or communication with a (unidirectionally) 161 trusted third-party. The new entity's decisions are made according 162 to verified communication with a trusted third-party or in a strictly 163 auditable fashion. 165 Optimal security is achieved with IEEE 802.1AR certificates on each 166 new entity, accompanied by a third-party Internet based service for 167 verification. Bootstrapping concepts run to completion with less 168 requirements, but are then less secure. A domain can choose to 169 accept lower levels of security when a trusted third-party is not 170 available so that bootstrapping proceeds even at the risk of reduced 171 security. Only the domain can make these decisions based on 172 administrative input and known behavior of the new entity. 174 The result of bootstrapping is that a domain specific key 175 infrastructure is deployed. Since IEEE 802.1AR PKI certificates are 176 used for identifying the new entity, and the public key of the domain 177 identity is leveraged during communications with an Internet based 178 service, which is itself authenticated using HTTPS, bootstrapping of 179 a domain specific Public Key Infrastructure (PKI) is described. 180 Sufficient agility to support bootstrapping alternative key 181 infrastructures (such as symmetric key solutions) is considered 182 although no such alternate key infrastructure is described. 184 1.1. Terminology 186 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 187 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 188 "OPTIONAL" in this document are to be interpreted as described in 189 [RFC2119]. 191 The following terms are defined for clarity: 193 DomainID: The domain identity is the 160-bit SHA-1 hash of the BIT 194 STRING of the subjectPublicKey of the domain trust anchor that is 195 stored by the Domain CA. This is consistent with the RFC5280 196 Certification Authority subject key identifier of the Domain CA's 197 self signed root certificate. (A string value bound to the Domain 198 CA's self signed root certificate subject and issuer fields is 199 often colloquially used as a humanized identity value but during 200 protocol discussions the more exact term as defined here is used). 202 drop ship: The physical distribution of equipment containing the 203 "factory default" configuration to a final destination. In zero- 204 touch scenarios there is no staging or pre-configuration during 205 drop-ship. 207 imprint: the process where a device obtains the cryptographic key 208 material to identity and trust future interactions with a network. 209 This term is taken from Konrad Lorenz's work in biology with new 210 ducklings: during a critical period, the duckling would assume 211 that anything that looks like a mother duck is in fact their 212 mother. An equivalent for a device is to obtain the fingerprint 213 of the network's root certification authority certificate. A 214 device that imprints on an attacker suffers a similar fate to a 215 duckling that imprints on a hungry wolf. Securely imprinting is a 216 primary focus of this document.[imprinting]. 218 enrollment: the process where a device presents key material to a 219 network and acquires a network specific identity. For example 220 when a certificate signing request is presented to a certification 221 authority and a certificate is obtained in response. 223 pledge: the prospective device, which has the identity provided to 224 at the factory. Neither the device nor the network knows if the 225 device yet knows if this device belongs with this network. This 226 is definition 6, according to [pledge] 228 Audit Token: A signed token from the manufacturer authorized signing 229 authority indicating that the bootstrapping event has been 230 successfully logged. This has been referred to as an 231 "authorization token" indicating that it authorizes bootstrapping 232 to proceed. 234 Ownership Voucher: A signed voucher from the vendor vouching that a 235 specific domain "owns" the new entity as defined in 236 [I-D.ietf-netconf-zerotouch]. 238 1.2. Scope of solution 240 Questions have been posed as to whether this solution is suitable in 241 general for Internet of Things (IoT) networks. In general the answer 242 is no, but the terminology of [RFC7228] is best used to describe the 243 boundaries. 245 The entire solution described in this document is aimed in general at 246 non-constrained (i.e. class 2+) devices operating on a non-Challenged 247 network. The entire solution described here is not intended to be 248 useable as-is by constrained devices operating on challenged networks 249 (such as 802.15.4 LLNs). 251 In many target applications, the systems involved are large router 252 platforms with multi-gigabit inter-connections, mounted in controlled 253 access data centers. But this solution is not exclusive to the 254 large, it is intended to scale to thousands of devices located in 255 hostile environments, such as ISP provided CPE devices which are 256 drop-shipped to the end user. The situation where an order is 257 fulfilled from distributed warehouse from a common stock and shipped 258 directly to the target location at the request of the domain owner is 259 explicitly supported. That stock ("SKU") could be provided to a 260 number of potential domain owners, and the eventual domain owner will 261 not know a-priori which device will go to which location. 263 The bootstraping process can take minutes to complete depending on 264 the network infrastructure and device processing speed. The network 265 communication itself is not "chatty" but there can be delays for 266 privacy reasons. This protocol is not intended for low latency 267 handoffs. 269 Specifically, there are protocol aspects described here which might 270 result in congestion collapse or energy-exhaustion of intermediate 271 battery powered routers in an LLN. Those types of networks SHOULD 272 NOT use this solution. These limitations are predominately related 273 to the large credential and key sizes required for device 274 authentication. Defining symmetric key techniques that meet the 275 operational requirements is out-of-scope but the underlying protocol 276 operations (TLS handshake and signing structures) have sufficient 277 algorithm agility to support such techniques when defined. 279 The imprint protocol described here could, however, be used by non- 280 energy constrained devices joining a non-constrained network (for 281 instance, smart light bulbs are usually mains powered, and speak 282 802.11). It could also be used by non-constrained devices across a 283 non-energy constrained, but challenged network (such as 802.15.4). 285 Some aspects are in scope for constrained devices on challenged 286 networks: the certificate contents, and the process by which the four 287 questions above are resolved is in scope. It is simply the actual 288 on-the-wire imprint protocol which is likely inappropriate. 290 1.3. Trust bootstrap 292 The imprint protocol results in a secure relationship between the 293 domain registrar and the new device. If the new device is 294 sufficiently constrained that the ACE protocol should be leveraged 295 for operation, (see [I-D.ietf-ace-actors]), and the domain registrar 296 is also the Client Authorization Server or the Authorization Server, 297 then it may be appropriate to use this secure channel to exchange ACE 298 tokens. 300 2. Architectural Overview 302 The logical elements of the bootstrapping framework are described in 303 this section. Figure 1 provides a simplified overview of the 304 components. Each component is logical and may be combined with other 305 components as necessary. 307 . 308 .+------------------------+ 309 +--------------Drop Ship-------------->.| Vendor Service | 310 | .+------------------------+ 311 | .| M anufacturer| | 312 | .| A uthorized |Ownership| 313 | .| S igning |Tracker | 314 | .| A uthority | | 315 | .+--------------+---------+ 316 | .............. ^ 317 V | 318 +-------+ ............................................|... 319 | | . | . 320 | | . +------------+ +-----------+ | . 321 | | . | | | | | . 322 | | . | | | <-------+ . 323 | | . | Proxy | | Registrar | . 324 | <--------> <-------> | . 325 | New | . | | | | . 326 | Entity| . +------------+ +-----+-----+ . 327 | | . | . 328 | | . +-----------------+----------+ . 329 | | . | Domain Certification | . 330 | | . | Authority | . 331 +-------+ . | Management and etc | . 332 . +----------------------------+ . 333 . . 334 ................................................ 335 "Domain" components 337 Figure 1 339 Domain: The set of entities that trust a common key infrastructure 340 trust anchor. This includes the Proxy, Registrar, Domain 341 Certificate Authority, Management components and any existing 342 entity that is already a member of the domain. 344 Domain CA: The domain Certification Authority (CA) provides 345 certification functionalities to the domain. At a minimum it 346 provides certification functionalities to the Registrar and stores 347 the trust anchor that defines the domain. Optionally, it 348 certifies all elements. 350 Registrar: A representative of the domain that is configured, 351 perhaps autonomically, to decide whether a new device is allowed 352 to join the domain. The administrator of the domain interfaces 353 with a Registrar to control this process. Typically a Registrar 354 is "inside" its domain. 356 New Entity: A new device or virtual machine or software component 357 that is not yet part of the domain. 359 Proxy: A domain entity that helps the New Entity join the domain. A 360 Proxy facilitates communication for devices that find themselves 361 in an environment where they are not provided connectivity until 362 after they are validated as members of the domain. The New Entity 363 is unaware that they are communicating with a proxy rather than 364 directly with the Registrar. 366 MASA Service: A Manufacturer Authorized Signing Authority (MASA) 367 service on the global Internet. The MASA provides a repository 368 for audit log information concerning privacy protected 369 bootstrapping events. 371 Ownership Tracker An Ownership Tracker service on the global 372 internet. The Ownership Tracker uses business processes to 373 accurately track ownership of all devices shipped against domains 374 that have purchased them. Although optional this component allows 375 vendors to provide additional value in cases where their sales and 376 distribution channels allow for accurately tracking of such 377 ownership. 379 We assume a multi-vendor network. In such an environment there could 380 be a MASA or Ownership Tracker for each vendor that supports devices 381 following this document's specification, or an integrator could 382 provide a MASA service for all devices. It is unlikely that an 383 integrator could provide Ownership Tracking services for multiple 384 vendors. 386 This document describes a secure zero-touch approach to bootstrapping 387 a key infrastructure; if certain devices in a network do not support 388 this approach, they can still be bootstrapped manually. Although 389 manual deployment is not scalable and is not a focus of this document 390 the necessary mechanisms are called out in this document to ensure 391 such edge conditions are covered by the architectural and protocol 392 models. 394 3. Functional Overview 396 Entities behave in an autonomic fashion. They discover each other 397 and autonomically bootstrap into a key infrastructure delineating the 398 autonomic domain. See [I-D.irtf-nmrg-autonomic-network-definitions] 399 for more information. 401 This section details the state machine and operational flow for each 402 of the main three entities. The New Entity, the Domain (primarily 403 the Registrar) and the MASA service. 405 A representative flow is shown in Figure 2: 407 +--------+ +---------+ +------------+ +------------+ 408 | New | | Circuit | | Domain | | Vendor | 409 | Entity | | Proxy | | Registrar | | Service | 410 | | | | | | | (Internet | 411 +--------+ +---------+ +------------+ +------------+ 412 | | | | 413 |<-RFC3927 IPv4 adr | | | 414 or|<-RFC4862 IPv6 adr | | | 415 | | | | 416 |-------------------->| | | 417 | optional: mDNS query| | | 418 | RFC6763/RFC6762 | | | 419 | | | | 420 |<--------------------| | | 421 | mDNS broadcast | | | 422 | response or periodic| | | 423 | | | | 424 |<------------------->C<----------------->| | 425 | TLS via the Circuit Proxy | | 426 |<--Registrar TLS server authentication---| | 427 [PROVISIONAL accept of server cert] | | 428 P---IEEE 802.1AR client authentication--->| | 429 P | | | 430 P---Request Audit Token (include nonce)-->| | 431 P | | | 432 P | /---> | | 433 P | | [accept device?] | 434 P | | [contact Vendor] | 435 P | | |--New Entity ID---->| 436 P | | |--Domain ID-------->| 437 P | | |--optional:nonce--->| 438 P | | | [extract DomainID] 439 P | | | | 440 P | optional: | [update audit log] 441 P | |can | | 442 P | |occur | optional: is | 443 P | |in | an ownership | 444 P | |advance | voucher available? 445 P | | | | 446 P | | |<-device audit log--| 447 P | | | | 448 P | | | choice: | 449 P | | |<-audit token-------| 450 P | | |<-or: ownership-----| 451 P | \----> | voucher | 452 P | | | 453 P | [verify audit log or voucher] | 454 P | | | 455 P<--Audit token and/or ownership voucher--| | 456 [verify response ]| | | 457 [verify provisional cert ]| | | 458 | | | | 459 |---------------------------------------->| | 460 | Continue with RFC7030 enrollment | | 461 | using now bidirectionally authenticated | | 462 | TLS session. | | | 463 | | | | 464 | | | | 465 | | | | 467 Figure 2 469 3.1. Behavior of a New Entity 471 A New Entity that has not yet been bootstrapped attempts to find a 472 local domain and join it. A New Entity MUST NOT automatically 473 initiate bootstrapping if it has already been configured. 475 States of a New Entity are as follows: 477 +--------------+ 478 | Start | 479 | | 480 +------+-------+ 481 | 482 +------v-------+ 483 | Discover | 484 +------------> | 485 | +------+-------+ 486 | | 487 | +------v-------+ 488 | | Identity | 489 ^------------+ | 490 | rejected +------+-------+ 491 | | 492 | +------v-------+ 493 | | Request | 494 | | Join | 495 | +------+-------+ 496 | | 497 | +------v-------+ 498 | | Imprint | Optional 499 ^------------+ <--+Manual input 500 | Bad Vendor +------+-------+ 501 | response | 502 | +------v-------+ 503 | | Enroll | 504 ^------------+ | 505 | Enroll +------+-------+ 506 | Failure | 507 | +------v-------+ 508 | | Being | 509 ^------------+ Managed | 510 Factory +--------------+ 511 reset 513 Figure 3 515 State descriptions for the New Entity are as follows: 517 1. Discover a communication channel to the "closest" Registrar. 519 2. Identify itself. This is done by presenting an IEEE 802.1AR 520 credentials to the discovered Registrar (via the Proxy) in a TLS 521 handshake. (Although the Registrar is also authenticated these 522 credentials are only provisionally accepted at this time). 524 3. Requests to Join the discovered Registrar. A unique nonce is 525 included ensuring that any responses can be associated with this 526 particular bootstrapping attempt. 528 4. Imprint on the Registrar. This requires verification of the 529 vendor service "Audit Token" or the validation of the vendor 530 service "Ownership Voucher". Either of these responses contains 531 sufficient information for the New Entity to complete 532 authentication of the Registrar. (The New Entity can now finish 533 authentication of the Registrar TLS server certificate) 535 5. Enroll by accepting the domain specific information from the 536 Registrar, and by obtaining a domain certificate from the 537 Registrar using a standard enrollment protocol, e.g. Enrollment 538 over Secure Transport (EST) [RFC7030]. 540 6. The New Entity is now a member of, and can be managed by, the 541 domain and will only repeat the discovery aspects of 542 bootstrapping if it is returned to factory default settings. 544 The following sections describe each of these steps in more detail. 546 3.1.1. Discovery 548 The result of discovery is logically communication with a Proxy 549 instead of a Domain Registrar but in such a case the proxy 550 facilitates communication with the actual Domain Registrar in a 551 manner that is transparent to the New Entity. Therefore or clarity a 552 Proxy is always assumed. 554 To discover the Domain Bootstrap Server the New Entity performs the 555 following actions: 557 a. MUST: Obtains a local address using either IPv4 or IPv6 methods 558 as described in [RFC4862] IPv6 Stateless Address 559 AutoConfiguration or [RFC3927] Dynamic Configuration of IPv4 560 Link-Local Addresses. 562 b. MUST: Performs DNS-based Service Discovery [RFC6763] over 563 Multicast DNS [RFC6762] searching for the service 564 "_bootstrapks._tcp.local.". To prevent unaccceptable levels of 565 network traffic the congestion avoidance mechanisms specified in 566 [RFC6762] section 7 MUST be followed. The New Entity SHOULD 567 listen for an unsolicited broadcast response as described in 568 [RFC6762]. This allows devices to avoid announcing their 569 presence via mDNS broadcasts and instead silently join a network 570 by watching for periodic unsolicited broadcast responses. 572 c. MAY: Performs DNS-based Service Discovery [RFC6763] over normal 573 DNS operations. The service searched for is 574 "_bootstrapks._tcp.example.net". In this case the domain 575 "example.net" is discovered as described in [RFC6763] section 11. 577 d. MAY: If no local bootstrapks service is located using the DNS- 578 based Service Discovery methods the New Entity contacts a well 579 known vendor provided bootstrapping server by performing a DNS 580 lookup using a well known URI such as "bootstrapks.vendor- 581 example.com". The details of the URI are vendor specific. 582 Vendors that leverage this method SHOULD provision appropriately. 584 DNS-based service discovery communicates the local proxy IPv4 or IPv6 585 address and port to the New Entity. Once a proxy is discovered the 586 New Entity communicates with the Registrar through the proxy using 587 the bootstrapping protocol defined in Section 5. The current DNS 588 services returned during each query is maintained until bootstrapping 589 is completed. If bootstrapping fails and the New Entity returns to 590 the Discovery state it picks up where it left off and continues 591 attempting bootstrapping. For example if the first Multicast DNS 592 _bootstrapks._tcp.local response doesn't work then the second and 593 third responses are tried. If these fail the New Entity moves on to 594 normal DNS-based Service Discovery. 596 Each discovery method attempted SHOULD exponentially back-off 597 attempts (to a maximum of one hour) to avoid overloading that 598 discovery methods network infrastructure. The back-off timer for 599 each method MUST be independent of other methods. Methods SHOULD be 600 run in parallel to avoid head of queue problems. Once a connection 601 to a Registrar is established (e.g. establishment of a TLS session 602 key) there are expectations of more timely responses, see 603 Section 5.1. 605 Once all discovered services are attempted the device SHOULD return 606 to Multicast DNS. It should periodically retry the vendor specific 607 mechanisms. The New Entity may prioritize selection order as 608 appropriate for the anticipated environment. 610 3.1.2. Identity 612 The New Entity identifies itself during the communication protocol 613 handshake. If the client identity is rejected the New Entity repeats 614 the Discovery process using the next proxy or discovery method 615 available. 617 The bootstrapping protocol server is not initially authenticated. 618 Thus the connection is provisional and all data received is untrusted 619 until sufficiently validated even though it is over a TLS connection. 621 This is aligned with the existing provisional mode of EST [RFC7030] 622 during s4.1.1 "Bootstrap Distribution of CA Certificates". See 623 Section 5.3 for more information about when the TLS connection 624 authenticated is completed. 626 All security associations established are between the new device and 627 the Bootstrapping server regardless of proxy operations. 629 3.1.3. Request Join 631 The New Entity POSTs a request to join the domain to the 632 Bootstrapping server. This request contains a New Entity generated 633 nonce and informs the Bootstrapping server which imprint methods the 634 New Entity will accept. 636 As indicated in EST [RFC7030] the bootstrapping server MAY redirect 637 the client to an alternate server. This is most useful in the case 638 where the New Entity has resorted to a well known vendor URI and is 639 communicating with the vendor's Registrar directly. In this case the 640 New Entity has authenticated the Registrar using the local Implicit 641 Trust Anchor database and can therefore treat the redirect URI as a 642 trusted URI which can also be validated using the Implicit Trust 643 Anchor database. Since client authentication occurs during the TLS 644 handshake the bootstrapping server has sufficient information to 645 apply appropriate policy concerning which server to redirect to. 647 The nonce ensures the New Entity can verify that responses are 648 specific to this bootstrapping attempt. This minimizes the use of 649 global time and provides a substantial benefit for devices without a 650 valid clock. 652 3.1.4. Imprint 654 The domain trust anchor is received by the New Entity during the 655 bootstrapping protocol methods in the form of either an Audit Token 656 containing the domain CA cert or an explicit ownership voucher. The 657 goal of the imprint state is to securely obtain a copy of this trust 658 anchor without involving human interaction. 660 The enrollment protocol EST [RFC7030] details a set of non-autonomic 661 bootstrapping methods such as: 663 o using the Implicit Trust Anchor database (not an autonomic 664 solution because the URL must be securely distributed), 666 o engaging a human user to authorize the CA certificate using out- 667 of-band data (not an autonomic solution because the human user is 668 involved), 670 o using a configured Explicit TA database (not an autonomic solution 671 because the distribution of an explicit TA database is not 672 autonomic), 674 o and using a Certificate-Less TLS mutual authentication method (not 675 an autonomic solution because the distribution of symmetric key 676 material is not autonomic). 678 This document describes additional autonomic methods: 680 MASA audit token Audit tokens are obtained by the Registrar from the 681 MASA service and presented to the New Entity for validation. 682 These indicate to the New Entity that joining the domain has been 683 logged by a logging service. 685 Ownership Voucher Ownership Vouchers are obtained by the Registrar 686 from the MASA service and explicitly indicate the fully qualified 687 domain name of the domain the new entity currently belongs to. 688 The Ownership Voucher is defined in [I-D.ietf-netconf-zerotouch]. 690 Since client authentication occurs during the TLS handshake the 691 bootstrapping server has sufficient information to apply appropriate 692 policy concerning which method to use. 694 The audit token contains the domain's public key material as provided 695 to the MASA service by the Registrar. This provides sufficient 696 information to the client to complete automated bootstrapping with 697 the local key infrastructure. 699 If the autonomic methods fail the New Entity returns to discovery 700 state and attempts bootstrapping with the next available discovered 701 Registrar. 703 3.1.5. Lack of realtime clock 705 Many devices when bootstrapping do not have knowledge of the current 706 time. Mechanisms like Network Time Protocols can not be secured 707 until bootstrapping is complete. Therefore bootstrapping is defined 708 in a method that does not require knowledge of the current time. 710 Unfortunately there are moments during bootstrapping when 711 certificates are verified, such as during the TLS handshake, where 712 validity periods are confirmed. This paradoxical "catch-22" is 713 resolved by the New Entity maintaining a concept of the current 714 "window" of presumed time validity that is continually refined 715 throughout the bootstrapping process as follows: 717 o Initially the New Entity does not know the current time. The 718 nonce included in join attempts provides an alternate mechanism 719 for the New Entity to ensure responses are associated with a 720 particular bootstrapping attempt. Nonceless audit tokens from the 721 MASA server are always valid and thus time is not needed. 723 o In accordance with IEEE 802.1AR and RFC5280 all manufacturing 724 installed certificates and trust anchors are assumed to have 725 infinite lifetimes. All such certificates "SHOULD be assigned the 726 GeneralizedTime value of 99991231235959Z" [RFC5280]. The New 727 Entity, Registrar and MASA server MUST ignore any other validity 728 period information in these credentials and treat the effective 729 lifetime as 99991231235959Z. This ensures that client 730 authentication (see Section 3.3.1) and the audit token signature 731 (see Section 5.3) can always be verified during RFC5280 path 732 validation. 734 o Once the audit token is accepted the validity period of the 735 domainCAcert in the token (see Section 5.3) now describes a valid 736 time window. Any subsequent certificate validity periods checked 737 during RFC5280 path validation MUST occur within this window. 739 o When accepting an enrollment certificate the validity period 740 within the new end entity certificate is assumed to be valid by 741 the New Entity. The New Entity is now willing to use this 742 credential for client authentication. 744 Once in this state the New Entity has a valid trust anchor with the 745 local domain and has a locally issued credential. These MAY be used 746 to secure distribution of more accurate time information although 747 specification of such a protocol is out-of-scope of this document. 749 3.1.6. Enrollment 751 As the final step of bootstrapping a Registrar helps to issue a 752 domain specific credential to the New Entity. For simplicity in this 753 document, a Registrar primarily facilitates issuing a credential by 754 acting as an RFC5280 Registration Authority for the Domain 755 Certification Authority. 757 Enrollment proceeds as described in Enrollment over Secure Transport 758 (EST) [RFC7030]. The New Entity contacts the Registrar using EST as 759 indicated: 761 o The New Entity is authenticated using the IEEE 802.1AR 762 credentials. 764 o The EST section 4.1.3 CA Certificates Response is verified using 765 either the Audit Token which provided the domain identity -or- 767 o The EST server is authenticated by using the Ownership Voucher 768 indicated fully qualified domain name to build the EST URI such 769 that EST section 4.1.1 bootstrapping using the New Entity implicit 770 Trust Anchor database can be used. 772 Once the Audit Token is received, as specified in this document, the 773 client has sufficient information to leverage the existing 774 communication channel with the Registrar to continue an EST RFC7030 775 enrollment. Enrollment picks up at RFC7030 section 4.1.1. 776 bootstrapping where the audit token provides the "out-of-band" CA 777 certificate fingerprint (in this case the full CA certificate) such 778 that the client can now complete the TLS server authentication. At 779 this point the client continues with EST enrollment operations 780 including "CA Certificates Request", "CSR Attributes" and "Client 781 Certificate Request" or "Server-Side Key Generation". 783 3.1.7. Being Managed 785 Functionality to provide generic "configuration" information is 786 supported. The parsing of this data and any subsequent use of the 787 data, for example communications with a Network Management System is 788 out of scope but is expected to occur after bootstrapping enrollment 789 is complete. This ensures that all communications with management 790 systems which can divulge local security information (e.g. network 791 topology or raw key material) is secured using the local credentials 792 issued during enrollment. 794 The New Entity uses bootstrapping to join only one domain. 795 Management by multiple domains is out-of-scope of bootstrapping. 796 After the device has successfully joined a domain and is being 797 managed it is plausible that the domain can insert credentials for 798 other domains depending on the device capabilities. 800 See Section 3.5. 802 3.2. Behavior of a Proxy 804 The role of the Proxy is to facilitate communications. The Proxy 805 forwards packets between the New Entity and the Registrar that has 806 been configured on the Proxy. The Proxy does not terminate the TLS 807 handshake. 809 In order to permit the proxy functionality to be implemented on the 810 maximum variety of devices the chosen mechanism SHOULD use the 811 minimum amount of state on the proxy device. While many devices in 812 the ANIMA target space will be rather large routers, the proxy 813 function is likely to be implemented in the control plane CPU such a 814 device, with available capabilities for the proxy function similar to 815 many class 2 IoT devices. 817 The document [I-D.richardson-anima-state-for-joinrouter] provides a 818 more extensive analysis of the alternative proxy methods. 820 3.2.1. CoAP connection to Registrar 822 The proxy MUST implement an IPIP (protocol 41) encapsulation function 823 for CoAP traffic to the configured UDP port on the registrar. The 824 proxy does not terminate the CoAP DTLS connection. [[EDNOTE: The 825 choice of CoAP as the mandatory to implement protocol rather than 826 HTTP maximizes code reuse on the smallest of devices. Unfortunately 827 this means this document will have to include the EST over CoAP 828 details as additional sections. The alternative is to make 'HTTPS 829 proxy' method the mandatory to implement and provide a less friendly 830 environment for the smallest of devices. This is a decision we'll 831 have to see addressed by the broader team.]] 833 As a result of the Proxy Discovery process in section Section 3.1.1, 834 the port number exposed by the proxy does not need to be well known, 835 or require an IANA allocation. 837 The address and port of the Registrar to which the packets will be 838 forwarded will be discovered by the GRASP protocol inside the ACP. 839 For the IPIP encapsulation methods, the port announced by the Proxy 840 MUST be the same as on the registrar in order for the proxy to remain 841 stateless. 843 The IPIP encapsulation allows the proxy to forward traffic which is 844 otherwise not to be forwarded, as the traffic between New Node and 845 Proxy use IPv6 Link Local addresses. 847 If the Proxy device has more than one interface on which it offers 848 the proxy function, then it must select a unique (ACP) IP address per 849 interface in order so that the proxy can stateless return the reply 850 packets to the correct link. 852 3.2.2. HTTPS proxy connection to Registrar 854 The proxy SHOULD also provide one of: an IPIP encapsulation of HTTP 855 traffic on TCP port TBD to the registrar, or a TCP circuit proxy that 856 connects the New Node to the Registrar. 858 When the Proxy provides a circuit proxy to the Registrar the 859 Registrar MUST accept HTTPS connections. 861 When the Proxy provides a stateless IPIP encapsulation to the 862 Registrar, then the Registrar will have to perform IPIP 863 decapsulation, remembering the originating outer IPIP source address 864 in order to qualify the inner link-local address. This is a kind of 865 encapsulation and processing which is similar in many ways to how 866 mobile IP works. 868 Being able to connect a TCP (HTTP) or UDP (CoAP) socket to a link- 869 local address with an encapsulated IPIP header requires API 870 extensions beyond [RFC3542] for UDP use, and requires a form of 871 connection latching (see section 4.1 of [RFC5386] and all of 872 [RFC5660], except that a simple IPIP tunnel is used rather than an 873 IPsec tunnel). 875 3.3. Behavior of the Registrar (Bootstrap Server) 877 Once a Registrar is established it listens for new entities and 878 determines if they can join the domain. The registrar delivers any 879 necessary authorization information to the new device and facilitates 880 enrollment with the domain PKI. 882 Registrar behavior is as follows: 884 Contacted by New Entity 885 + 886 | 887 +-------v----------+ 888 | Entity | fail? 889 | Authentication +---------+ 890 +-------+----------+ | 891 | | 892 +-------v----------+ | 893 | Entity | fail? | 894 | Authorization +---------> 895 +-------+----------+ | 896 | | 897 +-------v----------+ | 898 | Claiming the | fail? | 899 | Entity +---------> 900 +-------+----------+ | 901 | | 902 +-------v----------+ | 903 | Log Verification | fail? | 904 | +---------> 905 +-------+----------+ | 906 | | 907 +-------v----------+ +----v-------+ 908 | Forward | | | 909 | Audit | | Reject | 910 | token + config | | Device | 911 | to the Entity | | | 912 +------------------+ +------------+ 914 Figure 4 916 3.3.1. Entity Authentication 918 The applicable authentication methods detailed in EST [RFC7030] are: 920 o the use of an IEEE 802.1AR IDevID credential during the TLS client 921 authentication, 923 o or the use of a secret that is transmitted out of band between the 924 New Entity and the Registrar (this use case is not autonomic). 926 3.3.2. Entity Authorization 928 In a fully automated network all devices must be securely identified 929 and authorized to join the domain. 931 A Registrar accepts or declines a request to join the domain, based 932 on the authenticated identity presented. Automated acceptance 933 criteria include: 935 o allow any device of a specific type (as determined by the IEEE 936 802.1AR device identity), 938 o allow any device from a specific vendor (as determined by the IEEE 939 802.1AR identity), 941 o allow a specific device from a vendor (as determined by the IEEE 942 802.1AR identity) 944 Since all New Entities accept Audit Tokens the Registrar MUST use the 945 vendor provided MASA service to verify that the device's history log 946 does not include unexpected Registrars. If a device had previously 947 registered with another domain, the Registrar of that domain would 948 show in the log. 950 In order to validate the IEEE 802.1AR device identity the Registrar 951 maintains a database of vendor trust anchors (e.g. vendor root 952 certificates or keyIdentifiers for vendor root public keys). For 953 user interface purposes this database can be mapped to colloquial 954 vendor names. Registrars can be shipped with the trust anchors of a 955 significant number of third-party vendors within the target market. 957 If a device is accepted into the domain, it is expected request a 958 domain certificate through a certificate enrollment process. The 959 result is a common trust anchor and device certificates for all 960 autonomic devices in a domain (these certificates can subsequently be 961 used to determine the boundaries of the homenet, to authenticate 962 other domain nodes, and to autonomically enable services on the 963 homenet). The authorization performed during this phase MAY be 964 cached for the TLS session and applied to subsequent EST enrollment 965 requests so long as the session lasts. 967 3.3.3. Claiming the New Entity 969 Claiming an entity establishes an audit log at the MASA server and 970 provides the Registrar with proof, in the form of a MASA 971 authorization token, that the log entry has been inserted. As 972 indicated in Section 3.1.4 a New Entity will only proceed with 973 bootstrapping if a validated MASA authorization token has been 974 received. The New Entity therefore enforces that bootstrapping only 975 occurs if the claim has been logged. There is no requirement for the 976 vendor to definitively know that the device is owned by the 977 Registrar. 979 Registrar's obtain the Vendor URI via static configuration or by 980 extracting it from the IEEE 802.1AR credential. The imprint method 981 supported by the New Entity is known from the IEEE 802.1AR 982 credential. [[EDNOTE: An appropriate extension for indicating the 983 Vendor URI and imprint method could be defined using the methods 984 described in [I-D.lear-mud-framework]]]. 986 During initial bootstrapping the New Entity provides a nonce specific 987 to the particular bootstrapping attempt. The Registrar SHOULD 988 include this nonce when claiming the New Entity from the MASA 989 service. Claims from an unauthenticated Registrar are only serviced 990 by the MASA resource if a nonce is provided. 992 The Registrar can claim a New Entity that is not online by forming 993 the request using the entities unique identifier and not including a 994 nonce in the claim request. Audit Tokens obtained in this way do not 995 have a lifetime and they provide a permanent method for the domain to 996 claim the device. Evidence of such a claim is provided in the audit 997 log entries available to any future Registrar. Such claims reduce 998 the ability for future domains to secure bootstrapping and therefore 999 the Registrar MUST be authenticated by the MASA service. 1001 An ownership voucher requires the vendor to definitively know that a 1002 device is owned by a specific domain. The method used to "claim" 1003 this are out-of-scope. The Registrar simply requests an ownership 1004 validation token and the New Entity trusts the response. 1006 3.3.4. Log Verification 1008 The Registrar requests the log information for the new entity from 1009 the MASA service. The log is verified to confirm that the following 1010 is true to the satisfaction of the Registrar's configured policy: 1012 o Any nonceless entries in the log are associated with domainIDs 1013 recognized by the registrar. 1015 o Any nonce'd entries are older than when the domain is known to 1016 have physical possession of the new entity or that the domainIDs 1017 are recognized by the registrar. 1019 If any of these criteria are unacceptable to the registrar the entity 1020 is rejected. The Registrar MAY be configured to ignore the history 1021 of the device but it is RECOMMENDED that this only be configured if 1022 hardware assisted NEA [RFC5209] is supported. 1024 This document specifies a simple log format as provided by the MASA 1025 service to the registar. This format could be improved by 1026 distributed consensus technologies that integrate the audit token 1027 with a current technologies such as block-chain or hash trees or the 1028 like. Doing so is out of the scope of this document but are 1029 anticipated improvements for future work. 1031 3.4. Behavior of the MASA Service 1033 The MASA service is provided by the Factory provider on the global 1034 Internet. The URI of this service is well known. The URI SHOULD 1035 also be provided as an IEEE 802.1AR IDevID X.509 extension (a "MASA 1036 Audit Token Distribution Point" extension). 1038 The MASA service provides the following functionalities to 1039 Registrars: 1041 3.4.1. Issue Authorization Token and Log the event 1043 A Registrar POSTs a claim message optionally containing the bootstrap 1044 nonce to the MASA server. 1046 If a nonce is provided the MASA service responds to all requests. 1047 The MASA service verifies the Registrar is representative of the 1048 domain and generates a privacy protected log entry before responding 1049 with the Audit Token. 1051 If a nonce is not provided then the MASA service MUST authenticate 1052 the Registrar as a valid customer. This prevents denial of service 1053 attacks. 1055 3.4.2. Retrieve Audit Entries from Log 1057 When determining if a New Entity should be accepted into a domain the 1058 Registrar retrieves a copy of the audit log from the MASA service. 1059 This contains a list of privacy protected domain identities that have 1060 previously claimed the device. Included in the list is an indication 1061 of the time the entry was made and if the nonce was included. 1063 3.5. Leveraging the new key infrastructure / next steps 1065 As the devices have a common trust anchor, device identity can be 1066 securely established, making it possible to automatically deploy 1067 services across the domain in a secure manner. 1069 Examples of services: 1071 o Device management. 1073 o Routing authentication. 1075 o Service discovery. 1077 3.5.1. Network boundaries 1079 When a device has joined the domain, it can validate the domain 1080 membership of other devices. This makes it possible to create trust 1081 boundaries where domain members have higher level of trusted than 1082 external devices. Using the autonomic User Interface, specific 1083 devices can be grouped into to sub domains and specific trust levels 1084 can be implemented between those. 1086 3.6. Interactions with Network Access Control 1088 The assumption is that Network Access Control (NAC) completes using 1089 the New Entity 802.1AR credentials and results in the device having 1090 sufficient connectivity to discovery and communicate with the proxy. 1091 Any additional connectivity or quarantine behavior by the NAC 1092 infrastructure is out-of-scope. After the devices has completed 1093 bootstrapping the mechanism to trigger NAC to re-authenticate the 1094 device and provide updated network privileges is also out-of-scope. 1096 This achieves the goal of a bootstrap architecture that can integrate 1097 with NAC but does not require NAC within the network where it wasn't 1098 previously required. Future optimizations can be achieved by 1099 integrating the bootstrapping protocol directly into an initial EAP 1100 exchange. 1102 4. Domain Operator Activities 1104 This section describes how an operator interacts with a domain that 1105 supports the bootstrapping as described in this document. 1107 4.1. Instantiating the Domain Certification Authority 1109 This is a one time step by the domain administrator. This is an "off 1110 the shelf" CA with the exception that it is designed to work as an 1111 integrated part of the security solution. This precludes the use of 1112 3rd party certification authority services that do not provide 1113 support for delegation of certificate issuance decisions to a domain 1114 managed Registration Authority. 1116 4.2. Instantiating the Registrar 1118 This is a one time step by the domain administrator. One or more 1119 devices in the domain are configured take on a Registrar function. 1121 A device can be configured to act as a Registrar or a device can 1122 auto-select itself to take on this function, using a detection 1123 mechanism to resolve potential conflicts and setup communication with 1124 the Domain Certification Authority. Automated Registrar selection is 1125 outside scope for this document. 1127 4.3. Accepting New Entities 1129 For each New Entity the Registrar is informed of the unique 1130 identifier (e.g. serial number) along with the manufacturer's 1131 identifying information (e.g. manufacturer root certificate). This 1132 can happen in different ways: 1134 1. Default acceptance: In the simplest case, the new device asserts 1135 its unique identity to the registrar. The registrar accepts all 1136 devices without authorization checks. This mode does not provide 1137 security against intruders and is not recommended. 1139 2. Per device acceptance: The new device asserts its unique identity 1140 to the registrar. A non-technical human validates the identity, 1141 for example by comparing the identity displayed by the registrar 1142 (for example using a smartphone app) with the identity shown on 1143 the packaging of the device. Acceptance may be triggered by a 1144 click on a smartphone app "accept this device", or by other forms 1145 of pairing. See also [I-D.behringer-homenet-trust-bootstrap] for 1146 how the approach could work in a homenet. 1148 3. Whitelist acceptance: In larger networks, neither of the previous 1149 approaches is acceptable. Default acceptance is not secure, and 1150 a manual per device methods do not scale. Here, the registrar is 1151 provided a priori with a list of identifiers of devices that 1152 belong to the network. This list can be extracted from an 1153 inventory database, or sales records. If a device is detected 1154 that is not on the list of known devices, it can still be 1155 manually accepted using the per device acceptance methods. 1157 4. Automated Whitelist: an automated process that builds the 1158 necessary whitelists and inserts them into the larger network 1159 domain infrastructure is plausible. Once set up, no human 1160 intervention is required in this process. Defining the exact 1161 mechanisms for this is out of scope although the registrar 1162 authorization checks is identified as the logical integration 1163 point of any future work in this area. 1165 None of these approaches require the network to have permanent 1166 Internet connectivity. Even when the Internet based MASA service is 1167 used, it is possible to pre-fetch the required information from the 1168 MASA a priori, for example at time of purchase such that devices can 1169 enroll later. This supports use cases where the domain network may 1170 be entirely isolated during device deployment. 1172 Additional policy can be stored for future authorization decisions. 1173 For example an expected deployment time window or that a certain 1174 Proxy must be used. 1176 4.4. Automatic Enrollment of Devices 1178 The approach outlined in this document provides a secure zero-touch 1179 method to enroll new devices without any pre-staged configuration. 1180 New devices communicate with already enrolled devices of the domain, 1181 which proxy between the new device and a Registrar. As a result of 1182 this completely automatic operation, all devices obtain a domain 1183 based certificate. 1185 4.5. Secure Network Operations 1187 The certificate installed in the previous step can be used for all 1188 subsequent operations. For example, to determine the boundaries of 1189 the domain: If a neighbor has a certificate from the same trust 1190 anchor it can be assumed "inside" the same organization; if not, as 1191 outside. See also Section 3.5.1. The certificate can also be used 1192 to securely establish a connection between devices and central 1193 control functions. Also autonomic transactions can use the domain 1194 certificates to authenticate and/or encrypt direct interactions 1195 between devices. The usage of the domain certificates is outside 1196 scope for this document. 1198 5. Protocol Details 1200 A bootstrapping protocol could be implemented as an independent 1201 protocol from EST, but for simplicity and to reduce the number of TLS 1202 connections and crypto operations required on the New Entity, it is 1203 described specifically as extensions to EST. These extensions MUST 1204 be supported by the Registrar EST server within the same .well-known 1205 URI tree as the existing EST URIs as described in [RFC7030] section 1206 3.2.2. 1208 The new entity establishes a TLS connection with the Registrar 1209 through the circuit proxy (see Section 3.2) but the TLS connection is 1210 with the Registar; so for this section the "New Entity" is the TLS 1211 client and the "Registrar" is the TLS server. 1213 Establishment of the TLS connection for bootstrapping is as specified 1214 for EST [RFC7030]. In particular server identity and client identity 1215 are as described in EST [RFC7030] section 3.3. In EST [RFC7030] 1216 provisional server authentication for bootstrapping is described in 1217 section 4.1.1 wherein EST clients can "engage a human user to 1218 authorize the CA certificate using out-of-band data such as a CA 1219 certificate" or wherein a human user configures the URI of the EST 1220 server for Implicit TA based authentication. As described in this 1221 document, Section 5.3.1, a new method of bootstrapping now provides a 1222 completely automating method of bootstrapping PKI. 1224 The extensions for the New Entity client are as follows: 1226 o The New Entity provisionally accept the EST server certificate 1227 during the TLS handshake as detailed in Section 5.3.1. 1229 o The New Entity requests and validates the Audit Token as described 1230 below. At this point the New Entity has sufficient information to 1231 validate domain credentials. 1233 o The New Entity calls the EST defined /cacerts method to obtain the 1234 current CA certificate. These are validated using the Audit 1235 Token. 1237 o The New Entity completes bootstrapping as detailed in EST section 1238 4.1.1. 1240 In order to obtain a validated Audit Token and Audit Log the 1241 Registrar contacts the MASA service Service using REST calls: 1243 +-----------+ +----------+ +-----------+ +----------+ 1244 | New | | Circuit | | | | | 1245 | Entity | | Proxy | | Registrar | | Vendor | 1246 | | | | | | | | 1247 ++----------+ +--+-------+ +-----+-----+ +--------+-+ 1248 | | | | 1249 | | | | 1250 | TLS hello | TLS hello | | 1251 Establish +---------------C---------------> | 1252 TLS | | | | 1253 connection | | Server Cert | | 1254 <---------------C---------------+ | 1255 | Client Cert | | | 1256 +---------------C---------------> | 1257 | | | | 1258 HTTP REST | POST /requestaudittoken | | 1259 Data +--------------------nonce------> | 1260 | . | /requestaudittoken 1261 | . +----------------> 1262 | <----------------+ 1263 | | /requestauditlog 1264 | +----------------> 1265 | audit token or owner voucher <----------------+ 1266 <-------------------------------+ | 1267 | (optional config information) | | 1268 | . | | 1269 | . | | 1271 Figure 5 1273 In some use cases the Registrar may need to contact the Vendor in 1274 advanced, for example when the target network is air-gapped. The 1275 nonceless request format is provided for this and the resulting flow 1276 is slightly different. The security differences associated with not 1277 knowing the nonce are discussed below: 1279 +-----------+ +----------+ +-----------+ +----------+ 1280 | New | | Circuit | | | | | 1281 | Entity | | Proxy | | Registrar | | Vendor | 1282 | | | | | | | | 1283 ++----------+ +--+-------+ +-----+-----+ +--------+-+ 1284 | | | | 1285 | | | | 1286 | | | /requestaudittoken 1287 | | (nonce +----------------> 1288 | | unknown) <----------------+ 1289 | | | /requestauditlog 1290 | | +----------------> 1291 | | <----------------+ 1292 | TLS hello | TLS hello | | 1293 Establish +---------------C---------------> | 1294 TLS | | | | 1295 connection | | Server Cert | | 1296 <---------------C---------------+ | 1297 | Client Cert | | | 1298 | | | | 1299 HTTP REST | POST /requestaudittoken | | 1300 Data +----------------------nonce----> (discard | 1301 | audit token or owner Voucher | nonce) | 1302 <-------------------------------+ | 1303 | (optional config information) | | 1304 | . | | 1305 | . | | 1307 Figure 6 1309 The extensions for the Registrar server are as follows: 1311 o The Registrar requests and validates the Audit Token from the 1312 vendor authorized MASA service. 1314 o The Registrar forwards the Audit Token to the New Entity when 1315 requested. 1317 o The Registar performs log verifications in addition to local 1318 authorization checks before accepting the New Entity device. 1320 5.1. Request Audit Token from the Registrar 1322 When the New Entity reaches the EST section 4.1.1 "Bootstrap 1323 Distribution of CA Certificates" state but wishes to proceed in a 1324 fully automated fashion it makes a request for a MASA authorization 1325 token from the Registrar. 1327 This is done with an HTTPS POST using the operation path value of 1328 "/requestaudittoken". 1330 The request format is JSON object containing a 64bit nonce generated 1331 by the client for each request. This nonce MUST be a 1332 cryptographically strong random or pseudo-random number that can not 1333 be easily predicted. The nonce MUST NOT be reused for multiple 1334 attempts to join a network domain. The nonce assures the New Entity 1335 that the audit token response is associated with this bootstrapping 1336 attempt and is not a replay. 1338 Request media type: application/auditnonce 1340 Request format: a JSON file with the following: 1342 { 1343 "version":"1", 1344 "nonce":"<64bit nonce value>", 1345 } 1347 [[EDNOTE: Even if the nonce was signed it would provide no defense 1348 against rogue registrars; although it would assure the MASA that a 1349 certified new entity exists. To protect against rogue registrars a 1350 nonce component generated by the MASA (a new round trip) would be 1351 required). Instead this is addressed by requiring MASA & Registrar 1352 authentications but it is worth exploring additional protections. 1353 This to be explored more at IETF96.]] 1355 The Registrar validates the client identity as described in EST 1356 [RFC7030] section 3.3.2. The registrar performs authorization as 1357 detailed in Section 3.3.2. If authorization is successful the 1358 Registrar obtains an Audit Token from the MASA service (see 1359 Section 5.2). 1361 The received MASA authorization token is returned to the New Entity. 1363 As indicated in EST [RFC7030] the bootstrapping server can redirect 1364 the client to an alternate server. If the New Entity authenticated 1365 the Registrar using the well known URI method then the New Entity 1366 MUST follow the redirect automatically and authenticate the new 1367 Registrar against the redirect URI provided. If the New Entity had 1368 not yet authenticated the Registrar because it was discovered and was 1369 not a known-to-be-valid URI then the new Registrar must be 1370 authenticated using one of the two autonomic methods described in 1371 this document. Similarly the Registar MAY respond with an HTTP 202 1372 ("the request has been accepted for processing, but the processing 1373 has not been completed") as described in EST [RFC7030] section 4.2.3. 1375 Recall that during this communication with the Registar the TLS 1376 authentication is only provisional. The New Entity client MUST 1377 handle all data from the Registrar with upmost care. In particular 1378 the New Entity MUST only allow a single redirection and MUST only 1379 support a delay of five seconds before declaring the Registrar a 1380 failure and moving on to the next discovered Registrar. As detailed 1381 in Section 3.1.1 if no suitable Registrar is found the New Entity 1382 restarts the state machine and tries again. So a Registrar that is 1383 unable to complete the transaction the first time will have future 1384 chances. 1386 5.2. Request Audit Token from MASA 1388 The Registrar requests the Audit Token from the MASA service using a 1389 REST interface. For simplicity this is defined as an optional EST 1390 message between the Registrar and an EST server running on the MASA 1391 service although the Registrar is not required to make use of any 1392 other EST functionality when communicating with the MASA service. 1393 (The MASA service MUST properly reject any EST functionality requests 1394 it does not wish to service; a requirement that holds for any REST 1395 interface). 1397 This is done with an HTTP POST using the operation path value of 1398 "/requestaudittoken". 1400 The request format is a JSON object optionally containing the nonce 1401 value (as obtained from the bootstrap request) and the IEEE 802.1AR 1402 identity of the device as a serial number (the full certificate is 1403 not needed and no proof-of-possession information for the device 1404 identity is included). The AuthorityKeyIdentifier value from the 1405 certificate is included to ensure a statistically unique identity. 1406 The New Entity's serial number is extracted from the IEEE 802.1AR 1407 subject name id-at-serialNumber or it is the base64 encoded RFC4108 1408 hardwareModuleName hwSerialNum: 1410 { 1411 "version":"1", 1412 "nonce":"<64bit nonce value>", 1413 "IDevIDAuthorityKeyIdentifier":", 1414 "DevIDSerialNumber":"", 1416 } 1418 The Registrar MAY exclude the nonce from the request. Doing so 1419 allows the Registrar to request an authorization token when the New 1420 Entity is not online, or when the target bootstrapping environment is 1421 not on the same network as the MASA server (this requires the 1422 Registrar to learn the appropriate DevIDSerialNumber field from the 1423 physical device labeling or from the sales channel -- how this occurs 1424 is out-of-scope of this document). If a nonce is not provided the 1425 MASA server MUST authenticate the client as described in EST 1426 [RFC7030] section 3.3.2 to reduce the risk of DDoS attacks. The 1427 registrar performs authorization as detailed in Section 3.3.2. If 1428 authorization is successful the Registrar obtains an Audit Token from 1429 the MASA service (see Section 5.2). 1431 The JSON message information is encapsulated in a [RFC5652] Signed- 1432 data that is signed by the Registrar. The entire certificate chain, 1433 up to and including the Domain CA, MUST be included in the 1434 CertificateSet structure. The MASA service checks the internal 1435 consistency of the CMS but does not authenticate the domain identity 1436 information. The domain is not know to the MASA server in advance 1437 and a shared trust anchor is not implied. The MASA server MUST 1438 verify that the CMS is signed by a Registrar certificate (by checking 1439 for the cmc-idRA field) that was issued by a the root certificate 1440 included in the CMS. This ensures that the Registrar making the 1441 claim is an authorized Registrar of the unauthenticated domain. The 1442 EST style client authentication (TLS and HTTP) is used to provide a 1443 DDoS prevention strategy. 1445 The domain ID (e.g. hash of the public key of the domain) is 1446 extracted from the root certificate and is used to populate the MASA 1447 authorization token and to update the audit log. 1449 5.3. Audit Token Response 1451 The authorization token response to requests from the device and 1452 requests from the Registrar are in the same format. The Registrar 1453 either caches prior MASA responses or dynamically requests a new 1454 Audit Token based on local policy. 1456 If the the join operation is successful, the server response MUST 1457 contain an HTTP 200 response code with a content-type of 1458 "application/authorization-token". The server MUST answer with a 1459 suitable 4xx or 5xx HTTP [RFC2616] error code when a problem occurs. 1460 The response data from the MASA server MUST be a plaintext human- 1461 readable error message containing explanatory information describing 1462 why the request was rejected. 1464 The authorization token consists of the nonce, if supplied, the 1465 serial number information identifying the device and the domain CA 1466 certificate extracted from the request: 1468 { 1469 "version":"1", 1470 "nonce":"<64bit nonce value>", 1471 "IDevIDAuthorityKeyIdentifier":"", 1472 "DevIDSerialNumber":"", 1473 "domainCAcert":"" 1474 } 1476 The audit token response is encapsulated in a [RFC5652] Signed-data 1477 that is signed by the MASA server. The New Entity verifies this 1478 signed message using the IEEE 802.1AR manufacturer installed trust 1479 anchor. 1481 [[EDNOTE: Using CMS is consistent with the alignment of this 1482 bootstrapping document with EST, a PKIX enrollment protocol that 1483 includes Certificate Management over CMS. An alternative format 1484 would be the RFC7515 JSON Web Signature (JWS), which would allow 1485 clients that do not use fullCMC messages to avoid CMS entirely. Use 1486 of JWS would likely include a discussion of CBOR in order ensure the 1487 base64 expansions of the certs and signatures within the JWS message 1488 are of minimal size -- it is not yet clear to this author how that 1489 would work out]] 1491 The 'domainCAcert' element of this message contains the domain CA's 1492 public key. This is specific to bootstrapping a public key 1493 infrastructure. To support bootstrapping other key infrastructures 1494 additional domain identity types might be defined in the future. 1495 Clients MUST be prepared to ignore additional fields they do not 1496 recognize. Clients MUST be prepared to parse and fail gracefully 1497 from an audit token response that does not contain a 'domainCAcert' 1498 field at all. 1500 To minimize the size of the audit token response message the 1501 domainCAcert is not a complete distribution of the EST section 4.1.3 1502 CA Certificate Response. 1504 The New Entity installs the domainCAcert trust anchor. As indicated 1505 in Section 3.1.2 the newly installed trust anchor is used as an EST 1506 RFC7030 Explicit Trust Anchor. The New Entity MUST use the 1507 domainCAcert trust anchor to immediately validate the currently 1508 provisional TLS connection to the Registrar. 1510 5.3.1. Completing authentication of Provisional TLS connection 1512 If the Registrar's credential can not be verified using the 1513 domainCAcert trust anchor the TLS connection is immediately discarded 1514 and the New Entity abandons attempts to bootstrap with this 1515 discovered registrar. 1517 The following behaviors on the Registrar and New Entity are in 1518 addition to normal PKIX operations: 1520 o The EST server MUST use a certificate that chains to the 1521 domainCAcert. This means that when the EST server obtains renewed 1522 credentials the credentials included in the Section 5.2 request 1523 match the chain used in the current provisional TLS connection. 1525 o The New Entity PKIX path validation of the Registrar validity 1526 period information is as described in Section 3.1.5. 1528 Because the domainCAcert trust anchor is installed as an Explicit 1529 Trust Anchor it can be used to authenticate any dynamically 1530 discovered EST server that contain the id-kp-cmcRA extended key usage 1531 extension as detailed in EST RFC7030 section 3.6.1; but to reduce 1532 system complexity the New Entity SHOULD avoid additional discovery 1533 operations. Instead the New entity SHOULD communicate directly with 1534 the Registrar as the EST server to complete PKI local certificate 1535 enrollment. Additionally the New Entity SHOULD use the existing TLS 1536 connection to proceed with EST enrollment, thus reducing the total 1537 amount of cryptographic and round trip operations required during 1538 bootstrapping. [[EDNOTE: It is reasonable to mandate that the 1539 existing TLS connection be re-used? e.g. MUST >> SHOULD?]] 1541 5.4. Audit Token Status Telemetry 1543 For automated bootstrapping of devices the adminstrative elements 1544 providing bootstrapping also provide indications to the system 1545 administrators concerning device lifecycle status. To facilitate 1546 this those elements need telemetry information concerning the 1547 device's status. 1549 To indicate New Entity status regarding the audit token the client 1550 SHOULD post a status message. 1552 The client HTTP POSTs the following to the server at the EST well 1553 known URI /requestaudittoken_status. The Status field indicates if 1554 the audit token was acceptable. If it was not acceptable the Reason 1555 string indicates why. In the failure case this message is being sent 1556 to an unauthenticated, potentially malicious Registrar and therefore 1557 the Reason string SHOULD NOT provide information beneficial to an 1558 attacker. The operational benefit of this telemetry information is 1559 balanced against the operational costs of not recording that an audit 1560 token was ignored by a client the registar expected to continue 1561 joining the domain. 1563 { 1564 "version":"1", 1565 "Status":FALSE /* TRUE=Success, FALSE=Fail" 1566 "Reason":"Informative human readable message" 1567 } 1569 The server SHOULD respond with an HTTP 200 but MAY simply fail with 1570 an HTTP 404 error. The client ignores any response. Within the 1571 server logs the server SHOULD capture this telemetry information. 1573 5.5. MASA authorization log Request 1575 A registrar requests the MASA authorization log from the MASA service 1576 using this EST extension. 1578 This is done with an HTTP GET using the operation path value of 1579 "/requestMASAlog". 1581 The client HTTP POSTs the same Audit Token Request as for requesting 1582 an audit token but now posts it the /requestMASAlog URI instead. The 1583 IDevIDAuthorityKeyIdentifier and DevIDSerialNumber informs the MASA 1584 server which log is requested so the appropriate log can be prepared 1585 for the response. 1587 5.6. MASA authorization log Response 1589 A log data file is returned consisting of all log entries. For 1590 example: 1592 { 1593 "version":"1", 1594 "events":[ 1595 { 1596 "date":"", 1597 "domainID":"", 1599 "nonce":"" 1600 }, 1601 { 1602 "date":"", 1603 "domainID":"", 1605 "nonce":"" 1606 } 1607 ] 1608 } 1609 Distribution of a large log is less than ideal. This structure can 1610 be optimized as follows: All nonce-less entries for the same domainID 1611 MAY be condensed into the single most recent nonceless entry. 1613 The Registrar uses this log information to make an informed decision 1614 regarding the continued bootstrapping of the New Entity. For example 1615 if the log includes unexpected domainIDs this is indicative of 1616 problematic imprints by the new entity. If the log includes nonce- 1617 less entries this is indicative of the permanent ability for the 1618 indicated domain to trigger a reset of the device and take over 1619 management of it. Equipment that is purchased pre-owned can be 1620 expected to have an extensive history. 1622 Log entries containing the Domain's ID can be compared against local 1623 history logs in search of discrepancies. 1625 5.7. EST Integration for PKI bootstrapping 1627 The prior sections describe EST extensions necessary to enable fully 1628 automated bootstrapping. Although the audit token request/response 1629 structure members IDevIDAuthorityKeyIdentifier and DevIDSerialNumber 1630 are specific to PKI bootstrapping these are the only PKI specific 1631 aspects of the extensions and future work might replace them with 1632 non-PKI structures. 1634 The prior sections provide functionality for the New Entity to obtain 1635 a trust anchor representative of the Domain. The following section 1636 describe using EST to obtain a locally issued PKI certificate. The 1637 New Entity MAY perform alternative enrollment methods or proceed to 1638 use its IDevID credential indefinately, but those that leverage the 1639 discovered Registrar to proceed with certificate enrollment MUST 1640 implement the following EST choices. 1642 5.7.1. EST Distribution of CA Certificates 1644 The New Entity MUST request the full EST Distribution of CA 1645 Certificates message. See RFC7030, section 4.1. 1647 This ensures that the New Entity has the complete set of current CA 1648 certificates beyond the domainCAcert (see Section 5.3 for a 1649 discussion of the limitations). Although these restrictions are 1650 acceptable for the Registrar integrated with initial bootstrapping 1651 they are not appropriate for ongoing PKIX end entity certificate 1652 validation. 1654 5.7.2. EST CSR Attributes 1656 Automated bootstrapping occurs without local administrative 1657 configuration of the New Entity. In some deployments its plausible 1658 that the New Entity generates a certificate request containing only 1659 identity information known to the New Entity (essentially the IDevID 1660 information) and ultimately receives a certificate containing domain 1661 specific identity information. Conceptually the CA has complete 1662 control over all fields issued in the end entity certificate. 1663 Realistically this is operationally difficult with the current status 1664 of PKI certificate authority deployments where the CSR is submitted 1665 to the CA via a number of non-standard protocols. 1667 To alleviate operational difficulty the New Entity MUST request the 1668 EST "CSR Attributes" from the EST server. This allows the local 1669 infrastructure to inform the New Entity of the proper fields to 1670 include in the generated CSR. 1672 [[EDNOTE: The following is specific to anima purposes and should be 1673 moved to an appropriate anima document so as to keep bootstrapping as 1674 generic as possible: What we want are a 'domain name' stored in [TBD] 1675 and an 'ACP IPv6 address' stored in the iPAddress field as specified 1676 in RFC5208 s4.2.1.6. ref ACP draft where certificate verification 1677 [TBD]. These should go into the subjectaltname in the [TBD] 1678 fields.]]. If the hardwareModuleName in the IDevID is populated then 1679 it SHOULD by default be propagated to the LDevID along with the 1680 hwSerialNum. The registar SHOULD support local policy concerning 1681 this functionality. [[EDNOTE: extensive use of EST CSR Attributes 1682 might need an new OID definition]].]] 1684 The Registar MUST also confirm the resulting CSR is formatted as 1685 indicated before forwarding the request to a CA. If the Registar is 1686 communicating with the CA using a protocol like full CMC which 1687 provides mechanisms to override the CSR attributes, then these 1688 mechanisms MAY be used even if the client ignores CSR Attribute 1689 guidance. 1691 5.7.3. EST Client Certificate Request 1693 The New Entity MUST request a new client certificate. See RFC7030, 1694 section 4.2. 1696 5.7.4. Enrollment Status Telemetry 1698 For automated bootstrapping of devices the adminstrative elements 1699 providing bootstrapping also provide indications to the system 1700 administrators concerning device lifecycle status. This might 1701 include information concerning attempted bootstrapping messages seen 1702 by the client, MASA provides logs and status of credential 1703 enrollment. The EST protocol assumes an end user and therefore does 1704 not include a final success indication back to the server. This is 1705 insufficient for automated use cases. 1707 To indicate successful enrollment the client SHOULD re-negotiate the 1708 EST TLS session using the newly obtained credentials. This occurs by 1709 the client initiating a new TLS ClientHello message on the existing 1710 TLS connection. The client MAY simply close the old TLS session and 1711 start a new one. The server MUST support either model. 1713 In the case of a failure the Reason string indicates why the most 1714 recent enrollment failed. The SubjectKeyIdentifier field MUST be 1715 included if the enrollment attempt was for a keypair that is locally 1716 known to the client. If EST /serverkeygen was used and failed then 1717 the this field is ommited from the status telemetry. 1719 The client HTTP POSTs the following to the server at the new EST well 1720 known URI /enrollstatus. 1722 { 1723 "version":"1", 1724 "Status":TRUE /* TRUE=Success, FALSE=Fail" 1725 "Reason":"Informative human readable message" 1726 "SubjectKeyIdentifier":"" 1728 } 1730 The server SHOULD respond with an HTTP 200 but MAY simply fail with 1731 an HTTP 404 error. 1733 Within the server logs the server MUST capture if this message was 1734 recieved over an TLS session with a matching client certificate. 1735 This allows for clients that wish to minimize their crypto operations 1736 to simpy POST this response without renegotiating the TLS session - 1737 at the cost of the server not being able to accurately verify that 1738 enrollment was truly successful. 1740 5.7.5. EST over CoAP 1742 [[EDNOTE: In order to support smaller devices the above section on 1743 Proxy behavior introduces mandatory to implement support for CoAP 1744 support by the Proxy. This implies similar support by the New Entity 1745 and Registrar and means that the EST protocol operation encapsulation 1746 into CoAP needs to be described. EST is HTTP based and "CoaP is 1747 designed to easily interface with HTTP for integration" [RFC7252]. 1748 Use of CoAP implies Datagram TLS (DTLS) wherever this document 1749 describes TLS handshake specifics. A complexity is that the large 1750 message sizes necessary for bootstrapping will require support for 1751 [draft-ietf-core-block].]] 1753 6. Reduced security operational modes 1755 A common requirement of bootstrapping is to support less secure 1756 operational modes for support specific use cases. The following 1757 sections detail specific ways that the New Entity, Registrar and MASA 1758 can be configured to run in a less secure mode for the indicated 1759 reasons. 1761 6.1. Trust Model 1763 +--------+ +---------+ +------------+ +------------+ 1764 | New | | Circuit | | Domain | | Vendor | 1765 | Entity | | Proxy | | Registrar | | Service | 1766 | | | | | | | (Internet | 1767 +--------+ +---------+ +------------+ +------------+ 1769 Figure 7 1771 New Entity: The New Entity could be compromised and providing an 1772 attack vector for malware. The entity is trusted to only imprint 1773 using secure methods described in this document. Additional 1774 endpoint assessment techniques are RECOMMENDED but are out-of- 1775 scope of this document. 1777 Proxy: Provides proxy functionalities but is not involved in 1778 security considerations. 1780 Registrar: When interacting with a MASA server the Registrar makes 1781 all decisions. When ownership vouchers are involved the Registrar 1782 is only a conduit and all security decisions are made on the 1783 vendor service. 1785 Vendor Service, MASA: This form of vendor service is trusted to 1786 accurately log all claim attempts and to provide authoritative log 1787 information to Registrars. The MASA does not know which devices 1788 are associated with which domains. These claims could be 1789 strengthened by using cryptographic log techniques to provide 1790 append only, cryptographic assured, publicly auditable logs. 1791 Current text provides only for a trusted vendor. 1793 Vendor Service, Ownership Validation: This form of vendor service is 1794 trusted to accurately know which device is owned by which domain. 1796 6.2. New Entity security reductions 1798 Although New Entity can choose to run in less secure modes this is 1799 MUST NOT be the default state because it permanently degrades the 1800 security for all other uses cases. 1802 The device may have an operational mode where it skips Audit Token or 1803 Ownership Voucher validation one time. For example if a physical 1804 button is depressed during the bootstrapping operation. This can be 1805 useful if the vendor service is unavailable. This behavior SHOULD be 1806 available via local configuration or physical presence methods to 1807 ensure new entities can always be deployed even when autonomic 1808 methods fail. This allows for unsecure imprint. 1810 It is RECOMMENDED that this only be available if hardware assisted 1811 NEA [RFC5209] is supported. 1813 6.3. Registrar security reductions 1815 The Registrar can choose to accept devices using less secure methods. 1816 These methods are acceptable when low security models are needed, as 1817 the security decisions are being made by the local administrator, but 1818 they MUST NOT be the default behavior: 1820 1. The registrar MAY choose to accept all devices, or all devices of 1821 a particular type, at the administrator's discretion. This could 1822 occur when informing the Registrar of unique identifiers of new 1823 entities might be operationally difficult. 1825 2. The registrar MAY choose to accept devices that claim a unique 1826 identity without the benefit of authenticating that claimed 1827 identity. This could occur when the New Entity does not include 1828 an IEEE 802.1AR factory installed credential. New Entities 1829 without an IDevID credential MAY form the Section 5.1 request 1830 using the Section 5.2 format to ensure the New Entity's serial 1831 number information is provided to the Registar (this includes the 1832 IDevIDAuthorityKeyIdentifier value which would be statically 1833 configured on the New Entity). The New Entity MAY refused to 1834 provide a TLS client certificate (as one is not available). The 1835 New Entity SHOULD support HTTP-based or certificate-less TLS 1836 authentication as described in EST RFC7030 section 3.3.2. 1838 3. The registrar MAY request nonce-less Audit Tokens from the MASA 1839 service. These tokens can then be transmitted to the Registrar 1840 and stored until they are needed during bootstrapping operations. 1841 This is for use cases where target network is protected by an air 1842 gap and therefore can not contact the MASA service during New 1843 Entity deployment. 1845 4. The registrar MAY ignore unrecognized nonce-less Audit Log 1846 entries. This could occur when used equipment is purchased with 1847 a valid history being deployed in air gap networks that required 1848 permanent Audit Tokens. 1850 These modes are not available for devices that require a vendor 1851 Ownership Voucher. The methods vendors use to determine which 1852 devices are owned by which domains is out-of-scope. 1854 6.4. MASA security reductions 1856 Lower security modes chosen by the MASA service effect all device 1857 deployments unless bound to the specific device identities. In which 1858 case these modes can be provided as additional features for specific 1859 customers. The MASA service can choose to run in less secure modes 1860 by: 1862 1. Not enforcing that a Nonce is in the Audit Token. This results 1863 in distribution of Audit Tokens that never expire and in effect 1864 makes the Domain an always trusted entity to the New Entity 1865 during any subsequent bootstrapping attempts. That this occurred 1866 is captured in the log information so that the Domain registrar 1867 can make appropriate security decisions when a New Entity joins 1868 the Domain. This is useful to support use cases where Registrars 1869 might not be online during actual device deployment. Because 1870 this results in long lived Audit Tokens and do not require the 1871 proof that the device is online this is only accepted when the 1872 Registrar is authenticated by the MASA server and authorized to 1873 provide this functionality. The MASA server is RECOMMENDED to 1874 use this functionality only in concert with Ownership Validation 1875 tracking. 1877 2. Not verifying ownership before responding with an Audit Token. 1878 This is expected to be a common operational model because doing 1879 so relieves the vendor providing MASA services from having to 1880 tracking ownership during shipping and supply chain and allows 1881 for a very low overhead MASA service. The Registrar uses the 1882 audit log information as a defense in depth strategy to ensure 1883 that this does not occur unexpectedly (for example when 1884 purchasing new equipment the Registrar would throw an error if 1885 any audit log information is reported). 1887 7. Security Considerations 1889 In order to support a wide variety of use cases, devices can be 1890 claimed by a registrar without proving possession of the device in 1891 question. This would result in a nonceless, and thus always valid, 1892 claim. Or would result in an invalid nonce being associated with a 1893 claim. The MASA service is required to authenticate such Registrars 1894 but no programmatic method is provided to ensure good behavior by the 1895 MASA service. Nonceless entries into the audit log therefore 1896 permanently reduce the value of a device because future Registrars, 1897 during future bootstrap attempts, would now have to be configured 1898 with policy to ignore previously (and potentially unknown) domains. 1900 Future registrars are recommended to take the audit history of a 1901 device into account when deciding to join such devices into their 1902 network. If the MASA server were to have allowed a significantly 1903 large number of claims this might become onerous to the MASA server 1904 which must maintain all the extra log entries. Ensuring the 1905 Registrar is representative of a valid customer domain even without 1906 validating ownership helps to mitigate this. 1908 It is possible for an attacker to send an authorization request to 1909 the MASA service directly after the real Registrar obtains an 1910 authorization log. If the attacker could also force the 1911 bootstrapping protocol to reset there is a theoretical opportunity 1912 for the attacker to use the Audit Token to take control of the New 1913 Entity but then proceed to enroll with the target domain. Possible 1914 prevention mechanisms include: 1916 o Per device rate limits on the MASA service ensure such timing 1917 attacks are difficult. 1919 o In the advent of an unexpectedly lost bootstrapping connection the 1920 Registrar repeats the request for audit log information. 1922 To facilitate auditing the New Entity reports on audit token parsing 1923 status. In the case of a failure this information is informative to 1924 the potentially malicious Registar but this is included because the 1925 operational benefits are concidered beneficial. 1927 As indicated in EST [RFC7030] the connection is provisional and 1928 untrusted until the server is successfully authorized. If the server 1929 provides a redirect response the client MUST follow the redirect but 1930 the connection remains provisional. If the client uses a well known 1931 URI for contacting a well known Registrar the EST Implicit Trust 1932 Anchor database is used as is described in RFC6125 to authenticate 1933 the well known URI. In this case the connection is not provisional 1934 and RFC6125 methods can be used for each subsequent redirection. 1936 To facilitate truely limited clients EST RFC7030 section 3.3.2 1937 requirements that the client MUST support a client authentication 1938 model have been reduced in Section 6 to a statement that clients only 1939 "SHOULD" support such a model. This reflects current (not great) 1940 practices but is NOT RECOMMENDED. 1942 The MASA service could lock a claim and refuse to issue a new token 1943 or the MASA service could go offline (for example if a vendor went 1944 out of business). This functionality provides benefits such as theft 1945 resistance, but it also implies an operational risk to the Domain 1946 that Vendor behavior could limit future bootstrapping of the device 1947 by the Domain. This can be mitigated by Registrars that request 1948 nonce-less authorization tokens. 1950 8. Acknowledgements 1952 We would like to thank the various reviewers for their input, in 1953 particular Markus Stenberg, Brian Carpenter, Fuyu Eleven, Toerless 1954 Eckert, Eliot Lear and Sergey Kasatkin. 1956 9. References 1958 9.1. Normative References 1960 [IDevID] IEEE Standard, , "IEEE 802.1AR Secure Device Identifier", 1961 December 2009, . 1964 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1965 Requirement Levels", BCP 14, RFC 2119, 1966 DOI 10.17487/RFC2119, March 1997, 1967 . 1969 [RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei, 1970 "Advanced Sockets Application Program Interface (API) for 1971 IPv6", RFC 3542, May 2003. 1973 [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic 1974 Configuration of IPv4 Link-Local Addresses", RFC 3927, May 1975 2005. 1977 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1978 Address Autoconfiguration", RFC 4862, September 2007. 1980 [RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing 1981 Security: An Unauthenticated Mode of IPsec", RFC 5386, 1982 November 2008. 1984 [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, 1985 RFC 5652, DOI 10.17487/RFC5652, September 2009, 1986 . 1988 [RFC5660] Williams, N., "IPsec Channels: Connection Latching", 1989 RFC 5660, October 2009. 1991 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, 1992 DOI 10.17487/RFC6762, February 2013, 1993 . 1995 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 1996 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 1997 . 1999 [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., 2000 "Enrollment over Secure Transport", RFC 7030, 2001 DOI 10.17487/RFC7030, October 2013, 2002 . 2004 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 2005 Constrained-Node Networks", RFC 7228, 2006 DOI 10.17487/RFC7228, May 2014, 2007 . 2009 9.2. Informative References 2011 [I-D.behringer-homenet-trust-bootstrap] 2012 Behringer, M., Pritikin, M., and S. Bjarnason, 2013 "Bootstrapping Trust on a Homenet", draft-behringer- 2014 homenet-trust-bootstrap-02 (work in progress), February 2015 2014. 2017 [I-D.ietf-ace-actors] 2018 Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An 2019 architecture for authorization in constrained 2020 environments", draft-ietf-ace-actors-03 (work in 2021 progress), March 2016. 2023 [I-D.ietf-netconf-zerotouch] 2024 Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning 2025 for NETCONF or RESTCONF based Management", draft-ietf- 2026 netconf-zerotouch-08 (work in progress), April 2016. 2028 [I-D.irtf-nmrg-autonomic-network-definitions] 2029 Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A., 2030 Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic 2031 Networking - Definitions and Design Goals", draft-irtf- 2032 nmrg-autonomic-network-definitions-07 (work in progress), 2033 March 2015. 2035 [I-D.lear-mud-framework] 2036 Lear, E., "Manufacturer Usage Description Framework", 2037 draft-lear-mud-framework-00 (work in progress), January 2038 2016. 2040 [I-D.richardson-anima-state-for-joinrouter] 2041 Richardson, M., "Considerations for stateful vs stateless 2042 join router in ANIMA bootstrap", draft-richardson-anima- 2043 state-for-joinrouter-00 (work in progress), January 2016. 2045 [imprinting] 2046 Wikipedia, , "Wikipedia article: Imprinting", July 2015, 2047 . 2049 [pledge] Dictionary.com, , "Dictionary.com Unabridged", July 2015, 2050 . 2052 Authors' Addresses 2054 Max Pritikin 2055 Cisco 2057 Email: pritikin@cisco.com 2059 Michael C. Richardson 2060 Sandelman Software Works 2061 470 Dawson Avenue 2062 Ottawa, ON K1Z 5V7 2063 CA 2065 Email: mcr+ietf@sandelman.ca 2066 URI: http://www.sandelman.ca/ 2068 Michael H. Behringer 2069 Cisco 2071 Email: mbehring@cisco.com 2073 Steinthor Bjarnason 2074 Cisco 2076 Email: sbjarnas@cisco.com