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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: May 4, 2017 SSW 6 M. Behringer 7 S. Bjarnason 8 Cisco 9 K. Watsen 10 Juniper Networks 11 October 31, 2016 13 Bootstrapping Remote Secure Key Infrastructures (BRSKI) 14 draft-ietf-anima-bootstrapping-keyinfra-04 16 Abstract 18 This document specifies automated bootstrapping of a remote secure 19 key infrastructure (BRSKI) using vendor installed X.509 certificate, 20 in combination with a vendor authorized service on the Internet. 21 Bootstrapping a new device can occur using a routable address and a 22 cloud service, or using only link-local connectivity, or on limited/ 23 disconnected networks. Support for lower security models, including 24 devices with minimal identity, is described for legacy reasons but 25 not encouraged. Bootstrapping is complete when the cryptographic 26 identity of the new key infrastructure is successfully deployed to 27 the device but the established secure connection can be used to 28 deploy a locally issued certificate to the device as well. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on May 4, 2017. 47 Copyright Notice 49 Copyright (c) 2016 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 66 1.2. Scope of solution . . . . . . . . . . . . . . . . . . . . 7 67 1.3. Trust bootstrap . . . . . . . . . . . . . . . . . . . . . 8 68 2. Architectural Overview . . . . . . . . . . . . . . . . . . . 8 69 3. Functional Overview . . . . . . . . . . . . . . . . . . . . . 10 70 3.1. Behavior of a Pledge . . . . . . . . . . . . . . . . . . 11 71 3.1.1. Discovery . . . . . . . . . . . . . . . . . . . . . . 13 72 3.1.2. Identity . . . . . . . . . . . . . . . . . . . . . . 14 73 3.1.3. Request Join . . . . . . . . . . . . . . . . . . . . 15 74 3.1.4. Imprint . . . . . . . . . . . . . . . . . . . . . . . 15 75 3.1.5. Lack of realtime clock . . . . . . . . . . . . . . . 16 76 3.1.6. Enrollment . . . . . . . . . . . . . . . . . . . . . 17 77 3.1.7. Being Managed . . . . . . . . . . . . . . . . . . . . 18 78 3.2. Behavior of a Proxy . . . . . . . . . . . . . . . . . . . 18 79 3.2.1. CoAP connection to Registrar . . . . . . . . . . . . 19 80 3.2.2. HTTPS proxy connection to Registrar . . . . . . . . . 19 81 3.3. Behavior of the Registrar . . . . . . . . . . . . . . . . 20 82 3.3.1. Pledge Authentication . . . . . . . . . . . . . . . . 21 83 3.3.2. Pledge Authorization . . . . . . . . . . . . . . . . 22 84 3.3.3. Claiming the New Entity . . . . . . . . . . . . . . . 23 85 3.3.4. Log Verification . . . . . . . . . . . . . . . . . . 23 86 3.4. Behavior of the MASA Service . . . . . . . . . . . . . . 24 87 3.4.1. Issue Audit Voucher and Log the event . . . . . . . . 24 88 3.4.2. Retrieve Audit Entries from Log . . . . . . . . . . . 24 89 3.5. Leveraging the new key infrastructure / next steps . . . 25 90 3.5.1. Network boundaries . . . . . . . . . . . . . . . . . 25 91 3.6. Interactions with Network Access Control . . . . . . . . 25 92 4. Domain Operator Activities . . . . . . . . . . . . . . . . . 25 93 4.1. Instantiating the Domain Certification Authority . . . . 26 94 4.2. Instantiating the Registrar . . . . . . . . . . . . . . . 26 95 4.3. Accepting New Entities . . . . . . . . . . . . . . . . . 26 96 4.4. Automatic Enrollment of Devices . . . . . . . . . . . . . 27 97 4.5. Secure Network Operations . . . . . . . . . . . . . . . . 27 98 5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 28 99 5.1. Request Voucher from the Registrar . . . . . . . . . . . 30 100 5.2. Request Voucher from MASA . . . . . . . . . . . . . . . . 32 101 5.3. Audit Voucher Response . . . . . . . . . . . . . . . . . 33 102 5.3.1. Completing authentication of Provisional TLS 103 connection . . . . . . . . . . . . . . . . . . . . . 34 104 5.4. Voucher Status Telemetry . . . . . . . . . . . . . . . . 35 105 5.5. MASA authorization log Request . . . . . . . . . . . . . 36 106 5.6. MASA authorization log Response . . . . . . . . . . . . . 36 107 5.7. EST Integration for PKI bootstrapping . . . . . . . . . . 37 108 5.7.1. EST Distribution of CA Certificates . . . . . . . . . 37 109 5.7.2. EST CSR Attributes . . . . . . . . . . . . . . . . . 37 110 5.7.3. EST Client Certificate Request . . . . . . . . . . . 38 111 5.7.4. Enrollment Status Telemetry . . . . . . . . . . . . . 38 112 5.7.5. EST over CoAP . . . . . . . . . . . . . . . . . . . . 39 113 6. Reduced security operational modes . . . . . . . . . . . . . 39 114 6.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 40 115 6.2. New Entity security reductions . . . . . . . . . . . . . 40 116 6.3. Registrar security reductions . . . . . . . . . . . . . . 41 117 6.4. MASA security reductions . . . . . . . . . . . . . . . . 42 118 7. Security Considerations . . . . . . . . . . . . . . . . . . . 42 119 7.1. Security concerns with discovery process . . . . . . . . 44 120 7.1.1. Discovery of Registrar by Proxy . . . . . . . . . . . 44 121 7.1.2. Discovery of Proxy by New Entity . . . . . . . . . . 44 122 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 44 123 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 44 124 9.1. Normative References . . . . . . . . . . . . . . . . . . 44 125 9.2. Informative References . . . . . . . . . . . . . . . . . 46 126 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47 128 1. Introduction 130 To literally "pull yourself up by the bootstraps" is an impossible 131 action. Similarly the secure establishment of a key infrastructure 132 without external help is also an impossibility. Today it is accepted 133 that the initial connections between nodes are insecure, until key 134 distribution is complete, or that domain-specific keying material is 135 pre-provisioned on each new device in a costly and non-scalable 136 manner. This document describes a zero-touch approach to 137 bootstrapping an entity by securing the initial distribution of key 138 material using third-party issued X.509 certificates and 139 cryptographically signed "vouchers" issued by a new form of cloud 140 service. 142 The two sides of an association being bootstrapped authenticate each 143 other and then determine appropriate authorization. This process is 144 described as four distinct steps between the existing domain and the 145 device, or "pledge", being added: 147 o Pledge authentication: "Who is this? What is its identity?" 149 o Pledge authorization: "Is it mine? Do I want it? What are the 150 chances it has been compromised?" 152 o Domain authentication: "What is this domain's claimed identity?" 154 o Domain authorization: "Should I join it?" 156 A precise answer to these questions can not be obtained without 157 leveraging an established key infrastructure(s). The pledge's 158 decisions are made according to verified communication with a trusted 159 third-party. The domain's decisions are made by comparing the 160 pledge's authenticated identity against domain information such as a 161 configured list of purchased devices supplimented by information 162 provided by a trusted third-party. The third-party is not required 163 to provide sales channel ownership tracking nor is it required to 164 authenticate the domain. 166 Optimal security is achieved with X.509 certificates on each Pledge, 167 accompanied by a third-party (e.g., vendor, manufacturer or 168 integrator) Internet based service for verification. Bootstrapping 169 concepts run to completion with less requirements, but are then less 170 secure. A domain can choose to accept lower levels of security when 171 a trusted third-party is not available so that bootstrapping proceeds 172 even at the risk of reduced security. Only the domain can make these 173 decisions based on administrative input and known behavior of the 174 pledge. 176 The result of bootstrapping is that a domain specific key 177 infrastructure is deployed. Since X.509 PKI certificates are used 178 for identifying the pledge, and the public key of the domain identity 179 is leveraged during communications with an Internet based service, 180 which is itself authenticated using HTTPS, bootstrapping of a domain 181 specific Public Key Infrastructure (PKI) is described. Sufficient 182 agility to support bootstrapping alternative key infrastructures 183 (such as symmetric key solutions) is considered although no such 184 alternate key infrastructure is described. 186 1.1. Terminology 188 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 189 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 190 "OPTIONAL" in this document are to be interpreted as described in 191 [RFC2119]. 193 The following terms are defined for clarity: 195 DomainID: The domain identity is the 160-bit SHA-1 hash of the BIT 196 STRING of the subjectPublicKey of the domain trust anchor that is 197 stored by the Domain CA. This is consistent with the 198 Certification Authority subject key identifier (Section 4.2.1.2 199 [RFC5280]) of the Domain CA's self signed root certificate. (A 200 string value bound to the Domain CA's self signed root certificate 201 subject and issuer fields is often colloquially used as a 202 humanized identity value but during protocol discussions the more 203 exact term as defined here is used). 205 drop ship: The physical distribution of equipment containing the 206 "factory default" configuration to a final destination. In zero- 207 touch scenarios there is no staging or pre-configuration during 208 drop-ship. 210 imprint: The process where a device obtains the cryptographic key 211 material to identify and trust future interactions with a network. 212 This term is taken from Konrad Lorenz's work in biology with new 213 ducklings: during a critical period, the duckling would assume 214 that anything that looks like a mother duck is in fact their 215 mother. An equivalent for a device is to obtain the fingerprint 216 of the network's root certification authority certificate. A 217 device that imprints on an attacker suffers a similar fate to a 218 duckling that imprints on a hungry wolf. Securely imprinting is a 219 primary focus of this document.[imprinting]. The analogy to 220 Lorenz's work was first noted in [Stajano99theresurrecting]. 222 enrollment: The process where a device presents key material to a 223 network and acquires a network specific identity. For example 224 when a certificate signing request is presented to a certification 225 authority and a certificate is obtained in response. 227 Pledge: The prospective device, which has an identity installed by a 228 third-party (e.g., vendor, manufacturer or integrator). 230 Voucher A signed statement from the MASA service that indicates to a 231 Pledge the cryptographic identity of the Registrar it should 232 trust. There are different types of vouchers depending on how 233 that trust verified. 235 Audit Voucher: A voucher from the MASA service that indicates that 236 the bootstrapping event has been successfully logged. The 237 Registrar is primarily responsible for verifying the logs and 238 ensuring domain network security. 240 Ownership Voucher: A voucher from the MASA service that indicates 241 the explicit owner identity. The MASA is primarily responsible 242 for tracking ownership using out-of-band sales channel integration 243 (the definition of which is out-of-scope of this document). It is 244 defined in [I-D.ietf-netconf-zerotouch]. 246 Domain: The set of entities that trust a common key infrastructure 247 trust anchor. This includes the Proxy, Registrar, Domain 248 Certificate Authority, Management components and any existing 249 entity that is already a member of the domain. 251 Domain CA: The domain Certification Authority (CA) provides 252 certification functionalities to the domain. At a minimum it 253 provides certification functionalities to a Registrar and stores 254 the trust anchor that defines the domain. Optionally, it 255 certifies all elements. 257 Registrar: A representative of the domain that is configured, 258 perhaps autonomically, to decide whether a new device is allowed 259 to join the domain. The administrator of the domain interfaces 260 with a Registrar to control this process. Typically a Registrar 261 is "inside" its domain. 263 Proxy: A domain entity that helps the pledge join the domain. A 264 Proxy facilitates communication for devices that find themselves 265 in an environment where they are not provided connectivity until 266 after they are validated as members of the domain. The pledge is 267 unaware that they are communicating with a proxy rather than 268 directly with a Registrar. 270 MASA Service: A third-party Manufacturer Authorized Signing 271 Authority (MASA) service on the global Internet. The MASA 272 provides a repository for audit log information concerning privacy 273 protected bootstrapping events. It does not track ownership. 275 Ownership Tracker An Ownership Tracker service on the global 276 internet. The Ownership Tracker uses business processes to 277 accurately track ownership of all devices shipped against domains 278 that have purchased them. Although optional this component allows 279 vendors to provide additional value in cases where their sales and 280 distribution channels allow for accurately tracking of such 281 ownership. 283 IDevID An Initial Device Identity X.509 certificate installed by the 284 vendor on new equipment. The [IDevID] certificate format is the 285 primary example. In particular the X.509 certificate needs to 286 contain the device's serial number in a well known location in 287 order to perform white list operations and in order to extract it 288 for inclusion in messages to the MASA service. The subject 289 field's DN encoding MUST include the "serialNumber" attribute with 290 the device's unique serial number. 292 1.2. Scope of solution 294 Questions have been posed as to whether this solution is suitable in 295 general for Internet of Things (IoT) networks. This depends on the 296 capabilities of the devices in question. The terminology of 297 [RFC7228] is best used to describe the boundaries. 299 The entire solution described in this document is aimed in general at 300 non-constrained (i.e. class 2+) devices operating on a non-Challenged 301 network. The entire solution described here is not intended to be 302 useable as-is by constrained devices operating on challenged networks 303 (such as 802.15.4 LLNs). 305 In many target applications, the systems involved are large router 306 platforms with multi-gigabit inter-connections, mounted in controlled 307 access data centers. But this solution is not exclusive to the 308 large, it is intended to scale to thousands of devices located in 309 hostile environments, such as ISP provided CPE devices which are 310 drop-shipped to the end user. The situation where an order is 311 fulfilled from distributed warehouse from a common stock and shipped 312 directly to the target location at the request of the domain owner is 313 explicitly supported. That stock ("SKU") could be provided to a 314 number of potential domain owners, and the eventual domain owner will 315 not know a-priori which device will go to which location. 317 The bootstraping process can take minutes to complete depending on 318 the network infrastructure and device processing speed. The network 319 communication itself is not optimized for speed; the discovery 320 process allows for the Pledge to avoid broadcasting for privacy 321 reasons. This protocol is not intended for low latency handoffs. 323 Specifically, there are protocol aspects described here which might 324 result in congestion collapse or energy-exhaustion of intermediate 325 battery powered routers in an LLN. Those types of networks SHOULD 326 NOT use this solution. These limitations are predominately related 327 to the large credential and key sizes required for device 328 authentication. Defining symmetric key techniques that meet the 329 operational requirements is out-of-scope but the underlying protocol 330 operations (TLS handshake and signing structures) have sufficient 331 algorithm agility to support such techniques when defined. 333 The imprint protocol described here could, however, be used by non- 334 energy constrained devices joining a non-constrained network (for 335 instance, smart light bulbs are usually mains powered, and speak 336 802.11). It could also be used by non-constrained devices across a 337 non-energy constrained, but challenged network (such as 802.15.4). 339 The use of an IDevID that is consistant with [IDevID] allows for 340 alignment with 802.1X network access control methods which could need 341 to complete before bootstrapping can be initiated. This document 342 presumes that network access control has either already occured, is 343 not required, or is integrated by the proxy and registrar in such a 344 way that the device itself does not need to be aware of the details. 345 Further integration is not in scope. 347 Some aspects are in scope for constrained devices on challenged 348 networks: the certificate contents, and the process by which the four 349 questions above are resolved is in scope. It is simply the actual 350 on-the-wire imprint protocol which is likely inappropriate. 352 1.3. Trust bootstrap 354 The imprint protocol results in a secure relationship between a 355 domain Registrar and the Pledge. If the new device is sufficiently 356 constrained that the ACE protocol should be leveraged for operation, 357 (see [I-D.ietf-ace-actors]), and the domain registrar is also the 358 Client Authorization Server or the Authorization Server, then it may 359 be appropriate to use this secure channel to exchange ACE tokens. 361 2. Architectural Overview 363 The logical elements of the bootstrapping framework are described in 364 this section. Figure 1 provides a simplified overview of the 365 components. Each component is logical and may be combined with other 366 components as necessary. 368 . 369 .+------------------------+ 370 +--------------Drop Ship-------------->.| Vendor Service | 371 | .+------------------------+ 372 | .| M anufacturer| | 373 | .| A uthorized |Ownership| 374 | .| S igning |Tracker | 375 | .| A uthority | | 376 | .+--------------+---------+ 377 | .............. ^ 378 V | 379 +-------+ ............................................|... 380 | | . | . 381 | | . +------------+ +-----------+ | . 382 | | . | | | | | . 383 | | . | | | <-------+ . 384 | | . | Proxy | | Registrar | . 385 | <--------> <-------> | . 386 | New | . | | | | . 387 | Entity| . +------------+ +-----+-----+ . 388 | | . | . 389 | | . +-----------------+----------+ . 390 | | . | Domain Certification | . 391 | | . | Authority | . 392 +-------+ . | Management and etc | . 393 . +----------------------------+ . 394 . . 395 ................................................ 396 "Domain" components 398 Figure 1 400 We assume a multi-vendor network. In such an environment there could 401 be a MASA or Ownership Tracker for each vendor that supports devices 402 following this document's specification, or an integrator could 403 provide a MASA service for all devices. It is unlikely that an 404 integrator could provide Ownership Tracking services for multiple 405 vendors. 407 This document describes a secure zero-touch approach to bootstrapping 408 a key infrastructure; if certain devices in a network do not support 409 this approach, they can still be bootstrapped manually. Although 410 manual deployment is not scalable and is not a focus of this document 411 the necessary mechanisms are called out in this document to ensure 412 such edge conditions are covered by the architectural and protocol 413 models. 415 3. Functional Overview 417 Entities behave in an autonomic fashion. They discover each other 418 and autonomically bootstrap into a key infrastructure delineating the 419 autonomic domain. See [RFC7575] for more information. 421 This section details the state machine and operational flow for each 422 of the main three entities. The pledge, the domain (primarily a 423 Registrar) and the MASA service. 425 A representative flow is shown in Figure 2: 427 +--------+ +---------+ +------------+ +------------+ 428 | Pledge | | Circuit | | Domain | | Vendor | 429 | | | Proxy | | Registrar | | Service | 430 | | | | | | | (Internet | 431 +--------+ +---------+ +------------+ +------------+ 432 | | | | 433 |<-RFC3927 IPv4 adr | | | 434 or|<-RFC4862 IPv6 adr | | | 435 | | | | 436 |-------------------->| | | 437 | optional: mDNS query| | | 438 | RFC6763/RFC6762 | | | 439 | | | | 440 |<--------------------| | | 441 | mDNS broadcast | | | 442 | response or periodic| | | 443 | | | | 444 |<------------------->C<----------------->| | 445 | TLS via the Circuit Proxy | | 446 |<--Registrar TLS server authentication---| | 447 [PROVISIONAL accept of server cert] | | 448 P---X.509 client authentication---------->| | 449 P | | | 450 P---Request Voucher (include nonce)------>| | 451 P | | | 452 P | /---> | | 453 P | | [accept device?] | 454 P | | [contact Vendor] | 455 P | | |--Pledge ID-------->| 456 P | | |--Domain ID-------->| 457 P | | |--optional:nonce--->| 458 P | | | [extract DomainID] 459 P | | | | 460 P | optional: | [update audit log] 461 P | |can | | 462 P | |occur | | 463 P | |in | | 464 P | |advance | | 465 P | | | | 466 P | | |<-device audit log--| 467 P | | |<- voucher ---------| 468 P | \----> | | 469 P | | | 470 P | [verify audit log and voucher] | 471 P | | | 472 P<------voucher---------------------------| | 473 [verify voucher ] | | | 474 [verify provisional cert ]| | | 475 | | | | 476 |---------------------------------------->| | 477 | Continue with RFC7030 enrollment | | 478 | using now bidirectionally authenticated | | 479 | TLS session. | | | 480 | | | | 481 | | | | 482 | | | | 484 Figure 2 486 3.1. Behavior of a Pledge 488 A pledge that has not yet been bootstrapped attempts to find a local 489 domain and join it. A pledge MUST NOT automatically initiate 490 bootstrapping if it has already been configured or is in the process 491 of being configured. 493 States of a pledge are as follows: 495 +--------------+ 496 | Start | 497 | | 498 +------+-------+ 499 | 500 +------v-------+ 501 | Discover | 502 +------------> | 503 | +------+-------+ 504 | | 505 | +------v-------+ 506 | | Identity | 507 ^------------+ | 508 | rejected +------+-------+ 509 | | 510 | +------v-------+ 511 | | Request | 512 | | Join | 513 | +------+-------+ 514 | | 515 | +------v-------+ 516 | | Imprint | Optional 517 ^------------+ <--+Manual input 518 | Bad Vendor +------+-------+ 519 | response | 520 | +------v-------+ 521 | | Enroll | 522 ^------------+ | 523 | Enroll +------+-------+ 524 | Failure | 525 | +------v-------+ 526 | | Being | 527 ^------------+ Managed | 528 Factory +--------------+ 529 reset 531 Figure 3 533 State descriptions for the pledge are as follows: 535 1. Discover a communication channel to a Registrar. 537 2. Identify itself. This is done by presenting an IDevID X.509 538 credential to the discovered Registrar (via the Proxy) in a TLS 539 handshake. (The Registrar credentials are only provisionally 540 accepted at this time). 542 3. Requests to Join the discovered Registrar. A unique nonce is 543 included ensuring that any responses can be associated with this 544 particular bootstrapping attempt. 546 4. Imprint on the Registrar. This requires verification of the 547 vendor service provided "Audit" or "Ownership" Voucher. Either 548 of these responses contains sufficient information for the pledge 549 to complete authentication of a Registrar. (The pledge can now 550 finish authentication of the Registrar TLS server certificate) 552 5. Enroll by accepting the domain specific information from a 553 Registrar, and by obtaining a domain certificate from a Registrar 554 using a standard enrollment protocol, e.g. Enrollment over 555 Secure Transport (EST) [RFC7030]. 557 6. The Pledge is now a member of, and can be managed by, the domain 558 and will only repeat the discovery aspects of bootstrapping if it 559 is returned to factory default settings. 561 The following sections describe each of these steps in more detail. 563 3.1.1. Discovery 565 The result of discovery is a logical communication with a Registrar, 566 through a Proxy. The Proxy is transparent to the Pledge but is 567 always assumed to exist. 569 To discover the Registrar the Pledge performs the following actions: 571 a. MUST: Obtains a local address using either IPv4 or IPv6 methods 572 as described in [RFC4862] IPv6 Stateless Address 573 AutoConfiguration or [RFC3927] Dynamic Configuration of IPv4 574 Link-Local Addresses. The Plege MAY obtain an IP address via 575 DHCP [RFC2131]. The DHCP provided parameters for the Domain Name 576 System can be used to perform step (d) DNS operations if all 577 local discovery attempts fail (see below). 579 b. MUST: Performs DNS-based Service Discovery [RFC6763] over 580 Multicast DNS [RFC6762] searching for the service 581 "_bootstrapks._tcp.local.". To prevent unaccceptable levels of 582 network traffic the congestion avoidance mechanisms specified in 583 [RFC6762] section 7 MUST be followed. The Pledge SHOULD listen 584 for an unsolicited broadcast response as described in [RFC6762]. 585 This allows devices to avoid announcing their presence via mDNS 586 broadcasts and instead silently join a network by watching for 587 periodic unsolicited broadcast responses. 589 c. MAY: Performs DNS-based Service Discovery [RFC6763] over normal 590 DNS operations. The service searched for is 591 "_bootstrapks._tcp.example.com". In this case the domain 592 "example.com" is discovered as described in [RFC6763] section 11. 594 d. MAY: If no local bootstrapks service is located using the DNS- 595 based Service Discovery methods the Pledge contacts a well known 596 vendor provided bootstrapping server by performing a DNS lookup 597 using a well known URI such as "bootstrapks.vendor-example.com". 598 The details of the URI are vendor specific. Vendors that 599 leverage this method on the Pledge are responsible for providing 600 the bootstrapks service. 602 DNS-based service discovery communicates the local proxy IPv4 or IPv6 603 address and port to the Pledge. Once a proxy is discovered the 604 Pledge communicates with a Registrar through the proxy using the 605 bootstrapping protocol defined in Section 5. The current DNS 606 services returned during each query is maintained until bootstrapping 607 is completed. If bootstrapping fails and the Pledge returns to the 608 Discovery state it picks up where it left off and continues 609 attempting bootstrapping. For example if the first Multicast DNS 610 _bootstrapks._tcp.local response doesn't work then the second and 611 third responses are tried. If these fail the Pledge moves on to 612 normal DNS-based Service Discovery. 614 Each discovery method attempted SHOULD exponentially back-off 615 attempts (to a maximum of one hour) to avoid overloading the network 616 infrastructure with discovery. The back-off timer for each method 617 MUST be independent of other methods. Methods SHOULD be run in 618 parallel to avoid head of queue problems. Once a connection to a 619 Registrar is established (e.g. establishment of a TLS session key) 620 there are expectations of more timely responses, see Section 5.1. 622 Once all discovered services are attempted the device SHOULD return 623 to Multicast DNS. It should periodically retry the vendor specific 624 mechanisms. The Pledge may prioritize selection order as appropriate 625 for the anticipated environment. 627 3.1.2. Identity 629 The Pledge identifies itself during the communication protocol 630 handshake. If the client identity is rejected the Pledge repeats the 631 Discovery process using the next proxy or discovery method available. 633 The bootstrapping protocol server is not initially authenticated. 634 Thus the connection is provisional and all data received is untrusted 635 until sufficiently validated even though it is over a TLS connection. 636 This is aligned with the existing provisional mode of EST [RFC7030] 637 during s4.1.1 "Bootstrap Distribution of CA Certificates". See 638 Section 5.3 for more information about when the TLS connection 639 authenticated is completed. 641 All security associations established are between the new device and 642 the Bootstrapping server regardless of proxy operations. 644 3.1.3. Request Join 646 The Pledge POSTs a request to join the domain to the Bootstrapping 647 server. This request contains a Pledge generated nonce and informs 648 the Bootstrapping server which imprint methods the Pledge will 649 accept. 651 As indicated in EST [RFC7030] the bootstrapping server MAY redirect 652 the client to an alternate server. This is most useful in the case 653 where the Pledge has resorted to a well known vendor URI and is 654 communicating with the vendor's Registrar directly. In this case the 655 Pledge has authenticated the Registrar using the local Implicit Trust 656 Anchor database and can therefore treat the redirect URI as a trusted 657 URI which can also be validated using the Implicit Trust Anchor 658 database. Since client authentication occurs during the TLS 659 handshake the bootstrapping server has sufficient information to 660 apply appropriate policy concerning which server to redirect to. 662 The nonce ensures the Pledge can verify that responses are specific 663 to this bootstrapping attempt. This minimizes the use of global time 664 and provides a substantial benefit for devices without a valid clock. 666 3.1.4. Imprint 668 The domain trust anchor is received by the Pledge during the 669 bootstrapping protocol methods in the form of a voucher. The goal of 670 the imprint state is to securely obtain a copy of this trust anchor 671 without involving human interaction. 673 The enrollment protocol EST [RFC7030] details a set of non-autonomic 674 bootstrapping methods such as: 676 o using the Implicit Trust Anchor database (not an autonomic 677 solution because the URL must be securely distributed), 679 o engaging a human user to authorize the CA certificate using out- 680 of-band data (not an autonomic solution because the human user is 681 involved), 683 o using a configured Explicit TA database (not an autonomic solution 684 because the distribution of an explicit TA database is not 685 autonomic), 687 o and using a Certificate-Less TLS mutual authentication method (not 688 an autonomic solution because the distribution of symmetric key 689 material is not autonomic). 691 This document describes autonomic methods that MUST be supported by 692 the Pledge: 694 Audit Voucher Audit Vouchers are obtained by a Registrar from the 695 MASA service and presented to the Pledge for validation. These 696 indicate to the Pledge that joining the domain has been logged by 697 a logging service. 699 Ownership Voucher Ownership Vouchers are obtained by a Registrar 700 from the MASA service and explicitly indicate the owner of the 701 Pledge. The Ownership Voucher is defined in 702 [I-D.ietf-netconf-zerotouch]. 704 Since client authentication occurs during the TLS handshake the 705 bootstrapping server has sufficient information to apply appropriate 706 policy concerning which method to use. 708 The Audit Voucher contains the domain's public key material as 709 provided to the MASA service by a Registrar. This provides 710 sufficient information to the client to complete automated 711 bootstrapping with the local key infrastructure. The Ownership 712 Voucher contains the Owner Certificate which the Pledge uses to 713 authenticate the TLS connection. 715 If the autonomic methods fail the Pledge returns to discovery state 716 and attempts bootstrapping with the next available discovered 717 Registrar. 719 3.1.5. Lack of realtime clock 721 Many devices when bootstrapping do not have knowledge of the current 722 time. Mechanisms like Network Time Protocols can not be secured 723 until bootstrapping is complete. Therefore bootstrapping is defined 724 in a method that does not require knowledge of the current time. 726 Unfortunately there are moments during bootstrapping when 727 certificates are verified, such as during the TLS handshake, where 728 validity periods are confirmed. This paradoxical "catch-22" is 729 resolved by the Pledge maintaining a concept of the current "window" 730 of presumed time validity that is continually refined throughout the 731 bootstrapping process as follows: 733 o Initially the Pledge does not know the current time. 735 o During Pledge authentiation by the Registrar a realtime clock can 736 be used by the Registrar. This bullet expands on a closely 737 related issue regarding Pledge lifetimes. RFC5280 indicates that 738 long lived Pledge certifiates "SHOULD be assigned the 739 GeneralizedTime value of 99991231235959Z" [RFC5280] so the 740 Registrar MUST support such lifetimes and SHOULD support ignoring 741 Pledge lifetimes if they did not follow the RFC5280 742 recommendations. 744 o Once the Audit Voucher is accepted the validity period of the 745 domainCAcert in the voucher (see Section 5.3) now describes a 746 valid time window. Any subsequent certificate validity periods 747 checked during RFC5280 path validation MUST occur within this 748 window. 750 o When accepting an enrollment certificate the validity period 751 within the new certificate is assumed to be valid by the Pledge. 752 The Pledge is now willing to use this credential for client 753 authentication. 755 Once in this state the Pledge has a valid trust anchor with the local 756 domain and has a locally issued credential. These MAY be used to 757 secure distribution of more accurate time information although 758 specification of such a protocol is out-of-scope of this document. 760 The nonce included in join attempts provides an alternate mechanism 761 for the Pledge to ensure Audit Voucher responses are associated with 762 a particular bootstrapping attempt. Nonceless Audit Vouchers from 763 the MASA server are always valid and thus time is not needed. 765 Ownership Vouchers include time information and MUST be validated 766 using a realtime clock. 768 3.1.6. Enrollment 770 As the final step of bootstrapping a Registrar helps to issue a 771 domain specific credential to the Pledge. For simplicity in this 772 document, a Registrar primarily facilitates issuing a credential by 773 acting as an RFC5280 Registration Authority for the Domain 774 Certification Authority. 776 Enrollment proceeds as described in [RFC7030]. Authentication of the 777 EST server is done using the Voucher rather than the methods defined 778 in EST. 780 Once the Audit or Ownership Voucher is received, as specified in this 781 document, the client has sufficient information to leverage the 782 existing communication channel with a Registrar to continue an EST 783 RFC7030 enrollment. Enrollment picks up at RFC7030 section 4.1.1. 784 bootstrapping where the Audit Voucher provides the "out-of-band" CA 785 certificate fingerprint (in this case the full CA certificate) such 786 that the client can now complete the TLS server authentication. At 787 this point the client continues with EST enrollment operations 788 including "CA Certificates Request", "CSR Attributes" and "Client 789 Certificate Request" or "Server-Side Key Generation". 791 3.1.7. Being Managed 793 Functionality to provide generic "configuration" information is 794 supported. The parsing of this data and any subsequent use of the 795 data, for example communications with a Network Management System is 796 out of scope but is expected to occur after bootstrapping enrollment 797 is complete. This ensures that all communications with management 798 systems which can divulge local security information (e.g. network 799 topology or raw key material) is secured using the local credentials 800 issued during enrollment. 802 The Pledge uses bootstrapping to join only one domain. Management by 803 multiple domains is out-of-scope of bootstrapping. After the device 804 has successfully joined a domain and is being managed it is plausible 805 that the domain can insert credentials for other domains depending on 806 the device capabilities. 808 See Section 3.5. 810 3.2. Behavior of a Proxy 812 The role of the Proxy is to facilitate communications. The Proxy 813 forwards packets between the Pledge and a Registrar that has been 814 configured on the Proxy. The Proxy does not terminate the TLS 815 handshake. A Proxy is always assumed even if directly integrated 816 into a Registrar. 818 As a result of the Proxy Discovery process in section Section 3.1.1, 819 the port number exposed by the proxy does not need to be well known, 820 or require an IANA allocation. 822 If the Proxy joins an Autonomic Control Plane 823 ([I-D.ietf-anima-autonomic-control-plane]) it SHOULD use Autonomic 824 Control Plane secured GRASP ([I-D.ietf-anima-grasp]) to discovery the 825 Registrar address and port. For the IPIP encapsulation methods, the 826 port announced by the Proxy MUST be the same as on the registrar in 827 order for the proxy to remain stateless. 829 In order to permit the proxy functionality to be implemented on the 830 maximum variety of devices the chosen mechanism SHOULD use the 831 minimum amount of state on the proxy device. While many devices in 832 the ANIMA target space will be rather large routers, the proxy 833 function is likely to be implemented in the control plane CPU such a 834 device, with available capabilities for the proxy function similar to 835 many class 2 IoT devices. 837 The document [I-D.richardson-anima-state-for-joinrouter] provides a 838 more extensive analysis of the alternative proxy methods. 840 3.2.1. CoAP connection to Registrar 842 The proxy MUST implement an IPIP (protocol 41) encapsulation function 843 for CoAP traffic to the configured UDP port on the registrar. The 844 proxy does not terminate the CoAP DTLS connection. [[EDNOTE: The 845 choice of CoAP as the mandatory to implement protocol rather than 846 HTTP maximizes code reuse on the smallest of devices. Unfortunately 847 this means this document will have to include the EST over CoAP 848 details as additional sections. The alternative is to make 'HTTPS 849 proxy' method the mandatory to implement and provide a less friendly 850 environment for the smallest of devices. This is a decision we'll 851 have to see addressed by the broader team.]] 853 The IPIP encapsulation allows the proxy to forward traffic which is 854 otherwise not to be forwarded, as the traffic between New Node and 855 Proxy use IPv6 Link Local addresses. 857 If the Proxy device has more than one interface on which it offers 858 the proxy function, then it must select a unique (ACP) IP address per 859 interface in order so that the proxy can stateless return the (link- 860 local) reply packets to the correct link. 862 3.2.2. HTTPS proxy connection to Registrar 864 The proxy SHOULD also provide one of: an IPIP encapsulation of HTTP 865 traffic on TCP port TBD to the registrar, or a TCP circuit proxy that 866 connects the Pledge to a Registrar. 868 When the Proxy provides a circuit proxy to a Registrar the Registrar 869 MUST accept HTTPS connections. 871 When the Proxy provides a stateless IPIP encapsulation to a 872 Registrar, then the Registrar will have to perform IPIP 873 decapsulation, remembering the originating outer IPIP source address 874 in order to qualify the inner link-local address. This is a kind of 875 encapsulation and processing which is similar in many ways to how 876 mobile IP works. 878 Being able to connect a TCP (HTTP) or UDP (CoAP) socket to a link- 879 local address with an encapsulated IPIP header requires API 880 extensions beyond [RFC3542] for UDP use, and requires a form of 881 connection latching (see section 4.1 of [RFC5386] and all of 882 [RFC5660], except that a simple IPIP tunnel is used rather than an 883 IPsec tunnel). 885 3.3. Behavior of the Registrar 887 A Registrar listens for Pledges and determines if they can join the 888 domain. A Registrar obtains a Voucher from the MASA service and 889 delivers them to the Pledge as well as facilitating enrollment with 890 the domain PKI. 892 A Registrar is typically configured manually. If the Registrar joins 893 an Autonomic Control Plane ([I-D.ietf-anima-autonomic-control-plane]) 894 it MUST use Autonomic Control Plane secured GRASP 895 ([I-D.ietf-anima-grasp]) to broadcast the Registrar's address and 896 port to potential Proxies. 898 Registrar behavior is as follows: 900 Contacted by Pledge 901 + 902 | 903 +-------v----------+ 904 | Entity | fail? 905 | Authentication +---------+ 906 +-------+----------+ | 907 | | 908 +-------v----------+ | 909 | Entity | fail? | 910 | Authorization +---------> 911 +-------+----------+ | 912 | | 913 +-------v----------+ | 914 | Claiming the | fail? | 915 | Entity +---------> 916 +-------+----------+ | 917 | | 918 +-------v----------+ | 919 | Log Verification | fail? | 920 | +---------> 921 +-------+----------+ | 922 | | 923 +-------v----------+ +----v-------+ 924 | Forward | | | 925 | Audit | | Reject | 926 | voucher + config | | Device | 927 | to the Entity | | | 928 +------------------+ +------------+ 930 Figure 4 932 3.3.1. Pledge Authentication 934 The applicable authentication methods detailed in EST [RFC7030] are: 936 o the use of an IDevID X.509 credential during the TLS client 937 authentication, 939 o or the use of a secret that is transmitted out of band between the 940 Pledge and a Registrar (this use case is not autonomic). 942 In order to validate the IDevID X.509 credential a Registrar 943 maintains a database of vendor trust anchors (e.g. vendor root 944 certificates or keyIdentifiers for vendor root public keys). For 945 user interface purposes this database can be mapped to colloquial 946 vendor names. Registrars can be shipped with the trust anchors of a 947 significant number of third-party vendors within the target market. 949 3.3.2. Pledge Authorization 951 In a fully automated network all devices must be securely identified 952 and authorized to join the domain. 954 A Registrar accepts or declines a request to join the domain, based 955 on the authenticated identity presented. Automated acceptance 956 criteria include: 958 o allow any device of a specific type (as determined by the X.509 959 IDevID), 961 o allow any device from a specific vendor (as determined by the 962 X.509 IDevID), 964 o allow a specific device from a vendor (as determined by the X.509 965 IDevID) against a domain white list. (The mechanism for checking 966 a shared white list potentiatlly used by multiple Registrars is 967 out of scope). 969 To look the Pledge up in a domain white list a consistent method for 970 extracting device identity from the X.509 certificate is required. 971 RFC6125 describes Domain-Based Application Service identity but here 972 we require Vendor Device-Based identity. The subject field's DN 973 encoding MUST include the "serialNumber" attribute with the device's 974 unique serial number. In the language of RFC6125 this provides for a 975 SERIALNUM-ID category of identifier that can be included in a 976 certificate and therefore that can also be used for matching 977 purposes. The SERIALNUM-ID whitelist is collated according to vendor 978 trust anchor since serial numbers are not globally unique. 980 Since all Pledges accept Audit Vouchers a Registrar MUST use the 981 vendor provided MASA service to verify that the device's history log 982 does not include unexpected Registrars. If a device had previously 983 registered with another domain, a Registrar of that domain would show 984 in the log. 986 If a Pledge is accepted into the domain, it is expected to request a 987 domain certificate through a certificate enrollment process. The 988 result is a common trust anchor and device certificates for all 989 autonomic devices in a domain (these certificates can be used for 990 other methods, for example boundary detection, auto-securing 991 protocols, etc.). The authorization performed during this phase is 992 used for EST enrollment requests. 994 3.3.3. Claiming the New Entity 996 Claiming an entity establishes an audit log at the MASA server and 997 provides a Registrar with proof, in the form of a MASA Audit Voucher, 998 that the log entry has been inserted. As indicated in Section 3.1.4 999 a Pledge will only proceed with bootstrapping if a validated MASA 1000 Audit Voucher has been received. The Pledge therefore enforces that 1001 bootstrapping only occurs if the claim has been logged. There is no 1002 requirement for the vendor to definitively know that the device is 1003 owned by the Registrar. 1005 Registrar's obtain the Vendor URI via static configuration or by 1006 extracting it from the X.509 IDevID credential. The imprint method 1007 supported by the Pledge is known from the X.509 IDevID credential. 1008 [[EDNOTE: An appropriate extension for indicating the Vendor URI and 1009 imprint method could be defined using the methods described in 1010 [I-D.lear-mud-framework]]]. 1012 During initial bootstrapping the Pledge provides a nonce specific to 1013 the particular bootstrapping attempt. The Registrar SHOULD include 1014 this nonce when claiming the Pledge from the MASA service. Claims 1015 from an unauthenticated Registrar are only serviced by the MASA 1016 resource if a nonce is provided. 1018 The Registrar can claim a Pledge that is not online by forming the 1019 request using the entities unique identifier and not including a 1020 nonce in the claim request. Audit Voucher obtained in this way do 1021 not have a lifetime and they provide a permanent method for the 1022 domain to claim the device. Evidence of such a claim is provided in 1023 the audit log entries available to any future Registrar. Such claims 1024 reduce the ability for future domains to secure bootstrapping and 1025 therefore the Registrar MUST be authenticated by the MASA service 1026 although no requirement is implied that the MASA associates this 1027 authentication with ownership. 1029 An Ownership Voucher requires the vendor to definitively know that a 1030 device is owned by a specific domain. The method used to "claim" 1031 this are out-of-scope. A MASA ignores or reports failures when an 1032 attempt is made to claim a device that has a an Ownership Voucher. 1034 3.3.4. Log Verification 1036 A Registrar requests the log information for the Pledge from the MASA 1037 service. The log is verified to confirm that the following is true 1038 to the satisfaction of a Registrar's configured policy: 1040 o Any nonceless entries in the log are associated with domainIDs 1041 recognized by the registrar. 1043 o Any nonce'd entries are older than when the domain is known to 1044 have physical possession of the Pledge or that the domainIDs are 1045 recognized by the registrar. 1047 If any of these criteria are unacceptable to a Registrar the entity 1048 is rejected. A Registrar MAY be configured to ignore the history of 1049 the device but it is RECOMMENDED that this only be configured if 1050 hardware assisted NEA [RFC5209] is supported. 1052 This document specifies a simple log format as provided by the MASA 1053 service to the registar. This format could be improved by 1054 distributed consensus technologies that integrate the Audit Voucher 1055 with a current technologies such as block-chain or hash trees or the 1056 like. Doing so is out of the scope of this document but are 1057 anticipated improvements for future work. 1059 3.4. Behavior of the MASA Service 1061 The MASA service is provided by the Factory provider on the global 1062 Internet. The URI of this service is well known. The URI SHOULD 1063 also be provided as an X.509 IDevID extension (a "MASA Audit Voucher 1064 Distribution Point" extension). 1066 The MASA service provides the following functionalities to 1067 Registrars: 1069 3.4.1. Issue Audit Voucher and Log the event 1071 A Registrar POSTs a claim message optionally containing the bootstrap 1072 nonce to the MASA server. 1074 If a nonce is provided the MASA service responds to all requests. 1075 The MASA service verifies the Registrar is representative of the 1076 domain and generates a privacy protected log entry before responding 1077 with the Audit Voucher. For the simple log format defined in this 1078 document using the DomainID is considered sufficient privacy. Future 1079 work to improve the logging mechanism could include additional 1080 privacy protections. 1082 If a nonce is not provided then the MASA service MUST authenticate 1083 the Registrar as a valid customer. This prevents denial of service 1084 attacks. 1086 3.4.2. Retrieve Audit Entries from Log 1088 When determining if a Pledge should be accepted into a domain the 1089 Registrar retrieves a copy of the audit log from the MASA service. 1090 This contains a list of privacy protected domain identities that have 1091 previously claimed the device. Included in the list is an indication 1092 of the time the entry was made and if the nonce was included. 1094 3.5. Leveraging the new key infrastructure / next steps 1096 As the devices have a common trust anchor, device identity can be 1097 securely established, making it possible to automatically deploy 1098 services across the domain in a secure manner. 1100 Examples of services: 1102 o Device management. 1104 o Routing authentication. 1106 o Service discovery. 1108 3.5.1. Network boundaries 1110 When a device has joined the domain, it can validate the domain 1111 membership of other devices. This makes it possible to create trust 1112 boundaries where domain members have higher level of trusted than 1113 external devices. Using the autonomic User Interface, specific 1114 devices can be grouped into to sub domains and specific trust levels 1115 can be implemented between those. 1117 3.6. Interactions with Network Access Control 1119 The assumption is that Network Access Control (NAC) completes using 1120 the Pledge 's X.509 IDevID credentials and results in the device 1121 having sufficient connectivity to discovery and communicate with the 1122 proxy. Any additional connectivity or quarantine behavior by the NAC 1123 infrastructure is out-of-scope. After the devices has completed 1124 bootstrapping the mechanism to trigger NAC to re-authenticate the 1125 device and provide updated network privileges is also out-of-scope. 1127 This achieves the goal of a bootstrap architecture that can integrate 1128 with NAC but does not require NAC within the network where it wasn't 1129 previously required. Future optimizations can be achieved by 1130 integrating the bootstrapping protocol directly into an initial EAP 1131 exchange. 1133 4. Domain Operator Activities 1135 This section describes how an operator interacts with a domain that 1136 supports the bootstrapping as described in this document. 1138 4.1. Instantiating the Domain Certification Authority 1140 This is a one time step by the domain administrator. This is an "off 1141 the shelf" CA with the exception that it is designed to work as an 1142 integrated part of the security solution. This precludes the use of 1143 3rd party certification authority services that do not provide 1144 support for delegation of certificate issuance decisions to a domain 1145 managed Registration Authority. 1147 4.2. Instantiating the Registrar 1149 This is a one time step by the domain administrator. One or more 1150 devices in the domain are configured take on a Registrar function. 1152 A device can be configured to act as a Registrar or a device can 1153 auto-select itself to take on this function, using a detection 1154 mechanism to resolve potential conflicts and setup communication with 1155 the Domain Certification Authority. Automated Registrar selection is 1156 outside scope for this document. 1158 4.3. Accepting New Entities 1160 For each Pledge the Registrar is informed of the unique identifier 1161 (e.g. serial number) along with the manufacturer's identifying 1162 information (e.g. manufacturer root certificate). This can happen in 1163 different ways: 1165 1. Default acceptance: In the simplest case, the new device asserts 1166 its unique identity to a Registrar. The registrar accepts all 1167 devices without authorization checks. This mode does not provide 1168 security against intruders and is not recommended. 1170 2. Per device acceptance: The new device asserts its unique identity 1171 to a Registrar. A non-technical human validates the identity, 1172 for example by comparing the identity displayed by the registrar 1173 (for example using a smartphone app) with the identity shown on 1174 the packaging of the device. Acceptance may be triggered by a 1175 click on a smartphone app "accept this device", or by other forms 1176 of pairing. See also [I-D.behringer-homenet-trust-bootstrap] for 1177 how the approach could work in a homenet. 1179 3. Whitelist acceptance: In larger networks, neither of the previous 1180 approaches is acceptable. Default acceptance is not secure, and 1181 a manual per device methods do not scale. Here, the registrar is 1182 provided a priori with a list of identifiers of devices that 1183 belong to the network. This list can be extracted from an 1184 inventory database, or sales records. If a device is detected 1185 that is not on the list of known devices, it can still be 1186 manually accepted using the per device acceptance methods. 1188 4. Automated Whitelist: an automated process that builds the 1189 necessary whitelists and inserts them into the larger network 1190 domain infrastructure is plausible. Once set up, no human 1191 intervention is required in this process. Defining the exact 1192 mechanisms for this is out of scope although the registrar 1193 authorization checks is identified as the logical integration 1194 point of any future work in this area. 1196 None of these approaches require the network to have permanent 1197 Internet connectivity. Even when the Internet based MASA service is 1198 used, it is possible to pre-fetch the required information from the 1199 MASA a priori, for example at time of purchase such that devices can 1200 enroll later. This supports use cases where the domain network may 1201 be entirely isolated during device deployment. 1203 Additional policy can be stored for future authorization decisions. 1204 For example an expected deployment time window or that a certain 1205 Proxy must be used. 1207 4.4. Automatic Enrollment of Devices 1209 The approach outlined in this document provides a secure zero-touch 1210 method to enroll new devices without any pre-staged configuration. 1211 New devices communicate with already enrolled devices of the domain, 1212 which proxy between the new device and a Registrar. As a result of 1213 this completely automatic operation, all devices obtain a domain 1214 based certificate. 1216 4.5. Secure Network Operations 1218 The certificate installed in the previous step can be used for all 1219 subsequent operations. For example, to determine the boundaries of 1220 the domain: If a neighbor has a certificate from the same trust 1221 anchor it can be assumed "inside" the same organization; if not, as 1222 outside. See also Section 3.5.1. The certificate can also be used 1223 to securely establish a connection between devices and central 1224 control functions. Also autonomic transactions can use the domain 1225 certificates to authenticate and/or encrypt direct interactions 1226 between devices. The usage of the domain certificates is outside 1227 scope for this document. 1229 5. Protocol Details 1231 A bootstrapping protocol could be implemented as an independent 1232 protocol from EST, but for simplicity and to reduce the number of TLS 1233 connections and crypto operations required on the Pledge, it is 1234 described specifically as extensions to EST. These extensions MUST 1235 be supported by the Registrar EST server within the same .well-known 1236 URI tree as the existing EST URIs as described in [RFC7030] section 1237 3.2.2. 1239 The Pledge establishes a TLS connection with the Registrar through 1240 the circuit proxy (see Section 3.2) but the TLS connection is with 1241 the Registar; so for this section the "Pledge" is the TLS client and 1242 the "Registrar" is the TLS server. 1244 Establishment of the TLS connection for bootstrapping is as specified 1245 for EST [RFC7030]. In particular server identity and client identity 1246 are as described in EST [RFC7030] section 3.3. In EST [RFC7030] 1247 provisional server authentication for bootstrapping is described in 1248 section 4.1.1 wherein EST clients can "engage a human user to 1249 authorize the CA certificate using out-of-band data such as a CA 1250 certificate" or wherein a human user configures the URI of the EST 1251 server for Implicit TA based authentication. As described in this 1252 document, Section 5.3.1, a new method of bootstrapping now provides a 1253 completely automating method of bootstrapping PKI. 1255 The extensions for the Pledge client are as follows: 1257 o The Pledge provisionally accept the EST server certificate during 1258 the TLS handshake as detailed in Section 5.3.1. 1260 o The Pledge requests and validates the Audit Voucher as described 1261 below. At this point the Pledge has sufficient information to 1262 validate domain credentials. 1264 o The Pledge calls the EST defined /cacerts method to obtain the 1265 current CA certificate. These are validated using the Audit 1266 Voucher. 1268 o The Pledge completes bootstrapping as detailed in EST section 1269 4.1.1. 1271 In order to obtain a validated Audit Voucher and Audit Log a 1272 Registrar contacts the MASA service Service using REST calls: 1274 +-----------+ +----------+ +-----------+ +----------+ 1275 | New | | Circuit | | | | | 1276 | Entity | | Proxy | | Registrar | | Vendor | 1277 | | | | | | | | 1278 ++----------+ +--+-------+ +-----+-----+ +--------+-+ 1279 | | | | 1280 | | | | 1281 | TLS hello | TLS hello | | 1282 Establish +---------------C---------------> | 1283 TLS | | | | 1284 connection | | Server Cert | | 1285 <---------------C---------------+ | 1286 | Client Cert | | | 1287 +---------------C---------------> | 1288 | | | | 1289 HTTP REST | POST /requestvoucher | | 1290 Data +--------------------nonce------> | 1291 | . | /requestvoucher| 1292 | . +----------------> 1293 | <----------------+ 1294 | | /requestlog | 1295 | +----------------> 1296 | voucher <----------------+ 1297 <-------------------------------+ | 1298 | (optional config information) | | 1299 | . | | 1300 | . | | 1302 Figure 5 1304 In some use cases the Registrar may need to contact the Vendor in 1305 advanced, for example when the target network is air-gapped. The 1306 nonceless request format is provided for this and the resulting flow 1307 is slightly different. The security differences associated with not 1308 knowing the nonce are discussed below: 1310 +-----------+ +----------+ +-----------+ +----------+ 1311 | New | | Circuit | | | | | 1312 | Entity | | Proxy | | Registrar | | Vendor | 1313 | | | | | | | | 1314 ++----------+ +--+-------+ +-----+-----+ +--------+-+ 1315 | | | | 1316 | | | | 1317 | | | /requestvoucher| 1318 | | (nonce +----------------> 1319 | | unknown) <----------------+ 1320 | | | /requestlog | 1321 | | +----------------> 1322 | | <----------------+ 1323 | TLS hello | TLS hello | | 1324 Establish +---------------C---------------> | 1325 TLS | | | | 1326 connection | | Server Cert | | 1327 <---------------C---------------+ | 1328 | Client Cert | | | 1329 | | | | 1330 HTTP REST | POST /requestvoucher | | 1331 Data +----------------------nonce----> (discard | 1332 | voucher | nonce) | 1333 <-------------------------------+ | 1334 | (optional config information) | | 1335 | . | | 1336 | . | | 1338 Figure 6 1340 The extensions for a Registrar server are as follows: 1342 o The Registrar requests and validates the Audit Voucher from the 1343 vendor authorized MASA service. 1345 o The Registrar forwards the Audit Voucher to the Pledge when 1346 requested. 1348 o The Registar performs log verifications in addition to local 1349 authorization checks before accepting the Pledge device. 1351 5.1. Request Voucher from the Registrar 1353 When the Pledge bootstraps it makes a request for a Voucher from a 1354 Registrar. 1356 This is done with an HTTPS POST using the operation path value of 1357 "/requestvoucher". 1359 The request format is JSON object containing a 64bit nonce generated 1360 by the client for each request. This nonce MUST be a 1361 cryptographically strong random or pseudo-random number that can not 1362 be easily predicted. The nonce MUST NOT be reused for multiple 1363 attempts to join a network domain. The nonce assures the Pledge that 1364 the Audit Voucher response is associated with this bootstrapping 1365 attempt and is not a replay. 1367 Request media type: application/auditnonce 1369 Request format: a JSON file with the following: 1371 { 1372 "version":"1", 1373 "nonce":"<64bit nonce value>", 1374 } 1376 [[EDNOTE: Even if the nonce was signed it would provide no defense 1377 against rogue registrars; although it would assure the MASA that a 1378 certified Pledge exists. To protect against rogue registrars a nonce 1379 component generated by the MASA (a new round trip) would be 1380 required). Instead this is addressed by requiring MASA & Registrar 1381 authentications but it is worth exploring additional protections. 1382 This to be explored more at IETF96.]] 1384 The Registrar validates the client identity as described in EST 1385 [RFC7030] section 3.3.2. The registrar performs authorization as 1386 detailed in Section 3.3.2. If authorization is successful the 1387 Registrar obtains an Voucher from the MASA service (see Section 5.2). 1389 The received Voucher is forwarded to the Pledge. 1391 As indicated in EST [RFC7030] the bootstrapping server can redirect 1392 the client to an alternate server. If the Pledge authenticated a 1393 Registrar using the well known URI method then the Pledge MUST follow 1394 the redirect automatically and authenticate the new Registrar against 1395 the redirect URI provided. If the Pledge had not yet authenticated a 1396 Registrar because it was discovered and was not a known-to-be-valid 1397 URI then the new Registrar must be authenticated using one of the two 1398 autonomic methods described in this document. Similarly the Registar 1399 MAY respond with an HTTP 202 ("the request has been accepted for 1400 processing, but the processing has not been completed") as described 1401 in EST [RFC7030] section 4.2.3. 1403 Recall that during this communication with the Registar the TLS 1404 authentication is only provisional. The Pledge client MUST handle 1405 all data from the Registrar with upmost care. In particular the 1406 Pledge MUST only allow a single redirection and MUST only support a 1407 delay of five seconds before declaring the Registrar a failure and 1408 moving on to the next discovered Registrar. As detailed in 1409 Section 3.1.1 if no suitable Registrar is found the Pledge restarts 1410 the state machine and tries again. So a Registrar that is unable to 1411 complete the transaction the first time will have future chances. 1413 5.2. Request Voucher from MASA 1415 A Registrar requests a Voucher from the MASA service using a REST 1416 interface. For simplicity this is defined as an optional EST message 1417 between a Registrar and an EST server running on the MASA service 1418 although the Registrar is not required to make use of any other EST 1419 functionality when communicating with the MASA service. (The MASA 1420 service MUST properly reject any EST functionality requests it does 1421 not wish to service; a requirement that holds for any REST 1422 interface). 1424 This is done with an HTTP POST using the operation path value of 1425 "/requestvoucher". 1427 The request format is a JSON object optionally containing the nonce 1428 value (as obtained from the bootstrap request) and the X.509 IDevID 1429 extracted serial number (the full certificate is not needed and no 1430 proof-of-possession information for the device identity is included). 1431 The AuthorityKeyIdentifier value from the certificate is included to 1432 ensure a statistically unique identity. The Pledge's serial number 1433 is extracted from the X.509 IDevID subject name id-at-serialNumber or 1434 it is the base64 encoded RFC4108 hardwareModuleName hwSerialNum: 1436 { 1437 "version":"1", 1438 "nonce":"<64bit nonce value>", 1439 "IDevIDAuthorityKeyIdentifier":", 1440 "DevIDSerialNumber":"", 1442 } 1444 A Registrar MAY exclude the nonce from the request. Doing so allows 1445 the Registrar to request a Voucher when the Pledge is not online, or 1446 when the target bootstrapping environment is not on the same network 1447 as the MASA server (this requires the Registrar to learn the 1448 appropriate DevIDSerialNumber field from the physical device labeling 1449 or from the sales channel -- how this occurs is out-of-scope of this 1450 document). If a nonce is not provided the MASA server MUST 1451 authenticate the client as described in EST [RFC7030] section 3.3.2 1452 to reduce the risk of DDoS attacks. A Registrar performs 1453 authorization as detailed in Section 3.3.2. If authorization is 1454 successful the Registrar obtains an Voucher from the MASA service 1455 (see Section 5.2). 1457 The JSON message information is encapsulated in a [RFC5652] Signed- 1458 data that is signed by the Registrar. The entire certificate chain, 1459 up to and including the Domain CA, MUST be included in the 1460 CertificateSet structure. The MASA service checks the internal 1461 consistency of the CMS but does not authenticate the domain identity 1462 information. The domain is not know to the MASA server in advance 1463 and a shared trust anchor is not implied. The MASA server MUST 1464 verify that the CMS is signed by a Registrar certificate (by checking 1465 for the cmc-idRA field) that was issued by a the root certificate 1466 included in the CMS. This ensures that the Registrar making the 1467 claim is an authorized Registrar of the unauthenticated domain. The 1468 EST style client authentication (TLS and HTTP) is used to provide a 1469 DDoS prevention strategy. 1471 The root certificate is extracted and used to populate the Audit 1472 Voucher. The domain ID (e.g. hash of the public key of the domain) 1473 is extracted from the root certificate and is used to update the 1474 audit log. 1476 5.3. Audit Voucher Response 1478 The voucher response to requests from the device and requests from a 1479 Registrar are in the same format. A Registrar either caches prior 1480 MASA responses or dynamically requests a new Voucher based on local 1481 policy. 1483 If the the join operation is successful, the server response MUST 1484 contain an HTTP 200 response code with a content-type of 1485 "application/authorizationvoucher". The server MUST answer with a 1486 suitable 4xx or 5xx HTTP [RFC2616] error code when a problem occurs. 1487 The response data from the MASA server MUST be a plaintext human- 1488 readable error message containing explanatory information describing 1489 why the request was rejected. 1491 The Audit Voucher consists of the nonce, if supplied, the serial 1492 number information identifying the device and the domain CA 1493 certificate extracted from the request: 1495 { 1496 "version":"1", 1497 "nonce":"<64bit nonce value>", 1498 "IDevIDAuthorityKeyIdentifier":"", 1499 "DevIDSerialNumber":"", 1500 "domainCAcert":"" 1501 } 1502 The Audit Voucher response is encapsulated in a [RFC5652] Signed-data 1503 that is signed by the MASA server. The Pledge verifies this signed 1504 message using the manufacturer installed trust anchor assocaited with 1505 the X.509 IDevID. [[EDNOTE: As detailed in netconf-zerotouch this 1506 might be a distinct trust anchor rather than re-using the trust 1507 anchor for the IDevID. This concept will need to be detailed in this 1508 document as well.]] 1510 [[EDNOTE: Using CMS is consistent with the alignment of this 1511 bootstrapping document with EST, a PKIX enrollment protocol that 1512 includes Certificate Management over CMS. An alternative format 1513 would be the RFC7515 JSON Web Signature (JWS), which would allow 1514 clients that do not use fullCMC messages to avoid CMS entirely. Use 1515 of JWS would likely include a discussion of CBOR in order ensure the 1516 base64 expansions of the certs and signatures within the JWS message 1517 are of minimal size -- it is not yet clear to this author how that 1518 would work out]] 1520 The 'domainCAcert' element of this message contains the domain CA's 1521 public key. This is specific to bootstrapping a public key 1522 infrastructure. To support bootstrapping other key infrastructures 1523 additional domain identity types might be defined in the future. 1524 Clients MUST be prepared to ignore additional fields they do not 1525 recognize. Clients MUST be prepared to parse and fail gracefully 1526 from an Audit Voucher response that does not contain a 'domainCAcert' 1527 field at all. 1529 To minimize the size of the Audit Voucher response message the 1530 domainCAcert is not a complete distribution of the EST section 4.1.3 1531 CA Certificate Response. 1533 The Pledge installs the domainCAcert trust anchor. As indicated in 1534 Section 3.1.2 the newly installed trust anchor is used as an EST 1535 RFC7030 Explicit Trust Anchor. The Pledge MUST use the domainCAcert 1536 trust anchor to immediately validate the currently provisional TLS 1537 connection to a Registrar. 1539 5.3.1. Completing authentication of Provisional TLS connection 1541 If a Registrar's credential can not be verified using the 1542 domainCAcert trust anchor the TLS connection is immediately discarded 1543 and the Pledge abandons attempts to bootstrap with this discovered 1544 registrar. 1546 The following behaviors on a Registrar and Pledge are in addition to 1547 normal PKIX operations: 1549 o The EST server MUST use a certificate that chains to the 1550 domainCAcert. This means that when the EST server obtains renewed 1551 credentials the credentials included in the Section 5.2 request 1552 match the chain used in the current provisional TLS connection. 1554 o The Pledge PKIX path validation of a Registrar validity period 1555 information is as described in Section 3.1.5. 1557 Because the domainCAcert trust anchor is installed as an Explicit 1558 Trust Anchor it can be used to authenticate any dynamically 1559 discovered EST server that contain the id-kp-cmcRA extended key usage 1560 extension as detailed in EST RFC7030 section 3.6.1; but to reduce 1561 system complexity the Pledge SHOULD avoid additional discovery 1562 operations. Instead the Pledge SHOULD communicate directly with the 1563 Registrar as the EST server to complete PKI local certificate 1564 enrollment. Additionally the Pledge SHOULD use the existing TLS 1565 connection to proceed with EST enrollment, thus reducing the total 1566 amount of cryptographic and round trip operations required during 1567 bootstrapping. [[EDNOTE: It is reasonable to mandate that the 1568 existing TLS connection be re-used? e.g. MUST >> SHOULD?]] 1570 5.4. Voucher Status Telemetry 1572 For automated bootstrapping of devices the adminstrative elements 1573 providing bootstrapping also provide indications to the system 1574 administrators concerning device lifecycle status. To facilitate 1575 this those elements need telemetry information concerning the 1576 device's status. 1578 To indicate Pledge status regarding the Audit Voucher the client 1579 SHOULD post a status message. 1581 The client HTTP POSTs the following to the server at the EST well 1582 known URI /voucher_status. The Status field indicates if the Voucher 1583 was acceptable. If it was not acceptable the Reason string indicates 1584 why. In the failure case this message is being sent to an 1585 unauthenticated, potentially malicious Registrar and therefore the 1586 Reason string SHOULD NOT provide information beneficial to an 1587 attacker. The operational benefit of this telemetry information is 1588 balanced against the operational costs of not recording that an 1589 Voucher was ignored by a client the registar expected to continue 1590 joining the domain. 1592 { 1593 "version":"1", 1594 "Status":FALSE /* TRUE=Success, FALSE=Fail" 1595 "Reason":"Informative human readable message" 1596 } 1597 The server SHOULD respond with an HTTP 200 but MAY simply fail with 1598 an HTTP 404 error. The client ignores any response. Within the 1599 server logs the server SHOULD capture this telemetry information. 1601 5.5. MASA authorization log Request 1603 A registrar requests the MASA authorization log from the MASA service 1604 using this EST extension. 1606 This is done with an HTTP GET using the operation path value of 1607 "/requestauditlog". 1609 The client HTTP POSTs the same Voucher Request as for requesting an 1610 audit token but now posts it to the /requestauditlog URI instead. 1611 The IDevIDAuthorityKeyIdentifier and DevIDSerialNumber informs the 1612 MASA server which log is requested so the appropriate log can be 1613 prepared for the response. 1615 5.6. MASA authorization log Response 1617 A log data file is returned consisting of all log entries. For 1618 example: 1620 { 1621 "version":"1", 1622 "events":[ 1623 { 1624 "date":"", 1625 "domainID":"", 1627 "nonce":"" 1628 }, 1629 { 1630 "date":"", 1631 "domainID":"", 1633 "nonce":"" 1634 } 1635 ] 1636 } 1638 Distribution of a large log is less than ideal. This structure can 1639 be optimized as follows: All nonce-less entries for the same domainID 1640 MAY be condensed into the single most recent nonceless entry. 1642 A Registrar uses this log information to make an informed decision 1643 regarding the continued bootstrapping of the Pledge. For example if 1644 the log includes unexpected domainIDs this is indicative of 1645 problematic imprints by the Pledge. If the log includes nonce-less 1646 entries this is indicative of the permanent ability for the indicated 1647 domain to trigger a reset of the device and take over management of 1648 it. Equipment that is purchased pre-owned can be expected to have an 1649 extensive history. 1651 Log entries containing the Domain's ID can be compared against local 1652 history logs in search of discrepancies. 1654 5.7. EST Integration for PKI bootstrapping 1656 The prior sections describe EST extensions necessary to enable fully 1657 automated bootstrapping. Although the Audit Voucher request/response 1658 structure members IDevIDAuthorityKeyIdentifier and DevIDSerialNumber 1659 are specific to PKI bootstrapping these are the only PKI specific 1660 aspects of the extensions and future work might replace them with 1661 non-PKI structures. 1663 The prior sections provide functionality for the Pledge to obtain a 1664 trust anchor representative of the Domain. The following section 1665 describe using EST to obtain a locally issued PKI certificate. The 1666 Pledge SHOULD leverage the discovered Registrar to proceed with 1667 certificate enrollment and, if they do, MUST implement the EST 1668 options described in this section. The Pledge MAY perform 1669 alternative enrollment methods including discovering an alternate EST 1670 server, or proceed to use its IDevID credential indefinitely. 1672 5.7.1. EST Distribution of CA Certificates 1674 The Pledge MUST request the full EST Distribution of CA Certificates 1675 message. See RFC7030, section 4.1. 1677 This ensures that the Pledge has the complete set of current CA 1678 certificates beyond the domainCAcert (see Section 5.3 for a 1679 discussion of the limitations). Although these restrictions are 1680 acceptable for a Registrar integrated with initial bootstrapping they 1681 are not appropriate for ongoing PKIX end entity certificate 1682 validation. 1684 5.7.2. EST CSR Attributes 1686 Automated bootstrapping occurs without local administrative 1687 configuration of the Pledge. In some deployments its plausible that 1688 the Pledge generates a certificate request containing only identity 1689 information known to the Pledge (essentially the IDevID information) 1690 and ultimately receives a certificate containing domain specific 1691 identity information. Conceptually the CA has complete control over 1692 all fields issued in the end entity certificate. Realistically this 1693 is operationally difficult with the current status of PKI certificate 1694 authority deployments where the CSR is submitted to the CA via a 1695 number of non-standard protocols. 1697 To alleviate operational difficulty the Pledge MUST request the EST 1698 "CSR Attributes" from the EST server. This allows the local 1699 infrastructure to inform the Pledge of the proper fields to include 1700 in the generated CSR. 1702 [[EDNOTE: The following is specific to anima purposes and should be 1703 moved to an appropriate anima document so as to keep bootstrapping as 1704 generic as possible: What we want are a 'domain name' stored in [TBD] 1705 and an 'ACP IPv6 address' stored in the iPAddress field as specified 1706 in RFC5208 s4.2.1.6. ref ACP draft where certificate verification 1707 [TBD]. These should go into the subjectaltname in the [TBD] 1708 fields.]]. If the hardwareModuleName in the IDevID is populated then 1709 it SHOULD by default be propagated to the LDevID along with the 1710 hwSerialNum. The registar SHOULD support local policy concerning 1711 this functionality. [[EDNOTE: extensive use of EST CSR Attributes 1712 might need an new OID definition]].]] 1714 The Registar MUST also confirm the resulting CSR is formatted as 1715 indicated before forwarding the request to a CA. If the Registar is 1716 communicating with the CA using a protocol like full CMC which 1717 provides mechanisms to override the CSR attributes, then these 1718 mechanisms MAY be used even if the client ignores CSR Attribute 1719 guidance. 1721 5.7.3. EST Client Certificate Request 1723 The Pledge MUST request a new client certificate. See RFC7030, 1724 section 4.2. 1726 5.7.4. Enrollment Status Telemetry 1728 For automated bootstrapping of devices the adminstrative elements 1729 providing bootstrapping also provide indications to the system 1730 administrators concerning device lifecycle status. This might 1731 include information concerning attempted bootstrapping messages seen 1732 by the client, MASA provides logs and status of credential 1733 enrollment. The EST protocol assumes an end user and therefore does 1734 not include a final success indication back to the server. This is 1735 insufficient for automated use cases. 1737 To indicate successful enrollment the client SHOULD re-negotiate the 1738 EST TLS session using the newly obtained credentials. This occurs by 1739 the client initiating a new TLS ClientHello message on the existing 1740 TLS connection. The client MAY simply close the old TLS session and 1741 start a new one. The server MUST support either model. 1743 In the case of a failure the Reason string indicates why the most 1744 recent enrollment failed. The SubjectKeyIdentifier field MUST be 1745 included if the enrollment attempt was for a keypair that is locally 1746 known to the client. If EST /serverkeygen was used and failed then 1747 the this field is ommited from the status telemetry. 1749 The client HTTP POSTs the following to the server at the new EST well 1750 known URI /enrollstatus. 1752 { 1753 "version":"1", 1754 "Status":TRUE /* TRUE=Success, FALSE=Fail" 1755 "Reason":"Informative human readable message" 1756 "SubjectKeyIdentifier":"" 1758 } 1760 The server SHOULD respond with an HTTP 200 but MAY simply fail with 1761 an HTTP 404 error. 1763 Within the server logs the server MUST capture if this message was 1764 recieved over an TLS session with a matching client certificate. 1765 This allows for clients that wish to minimize their crypto operations 1766 to simpy POST this response without renegotiating the TLS session - 1767 at the cost of the server not being able to accurately verify that 1768 enrollment was truly successful. 1770 5.7.5. EST over CoAP 1772 [[EDNOTE: In order to support smaller devices the above section on 1773 Proxy behavior introduces mandatory to implement support for CoAP 1774 support by the Proxy. This implies similar support by the Pledge and 1775 Registrar and means that the EST protocol operation encapsulation 1776 into CoAP needs to be described. EST is HTTP based and "CoaP is 1777 designed to easily interface with HTTP for integration" [RFC7252]. 1778 Use of CoAP implies Datagram TLS (DTLS) wherever this document 1779 describes TLS handshake specifics. A complexity is that the large 1780 message sizes necessary for bootstrapping will require support for 1781 [draft-ietf-core-block].]] 1783 6. Reduced security operational modes 1785 A common requirement of bootstrapping is to support less secure 1786 operational modes for support specific use cases. The following 1787 sections detail specific ways that the Pledge, Registrar and MASA can 1788 be configured to run in a less secure mode for the indicated reasons. 1790 6.1. Trust Model 1792 +--------+ +---------+ +------------+ +------------+ 1793 | New | | Circuit | | Domain | | Vendor | 1794 | Entity | | Proxy | | Registrar | | Service | 1795 | | | | | | | (Internet | 1796 +--------+ +---------+ +------------+ +------------+ 1798 Figure 7 1800 Pledge: The Pledge could be compromised and providing an attack 1801 vector for malware. The entity is trusted to only imprint using 1802 secure methods described in this document. Additional endpoint 1803 assessment techniques are RECOMMENDED but are out-of-scope of this 1804 document. 1806 Proxy: Provides proxy functionalities but is not involved in 1807 security considerations. 1809 Registrar: When interacting with a MASA server a Registrar makes all 1810 decisions. When Ownership Vouchers are involved a Registrar is 1811 only a conduit and all security decisions are made on the vendor 1812 service. 1814 Vendor Service, MASA: This form of vendor service is trusted to 1815 accurately log all claim attempts and to provide authoritative log 1816 information to Registrars. The MASA does not know which devices 1817 are associated with which domains. These claims could be 1818 strengthened by using cryptographic log techniques to provide 1819 append only, cryptographic assured, publicly auditable logs. 1820 Current text provides only for a trusted vendor. 1822 Vendor Service, Ownership Validation: This form of vendor service is 1823 trusted to accurately know which device is owned by which domain. 1825 6.2. New Entity security reductions 1827 The Pledge MAY support "trust on first use" on physical interfaces 1828 but MUST NOT support "trust on first use" on network interfaces. 1829 This is because "trust on first use" permanently degrades the 1830 security for all other use cases. 1832 The Pledge MAY have an operational mode where it skips Voucher 1833 validation one time. For example if a physical button is depressed 1834 during the bootstrapping operation. This can be useful if the vendor 1835 service is unavailable. This behavior SHOULD be available via local 1836 configuration or physical presence methods to ensure new entities can 1837 always be deployed even when autonomic methods fail. This allows for 1838 unsecured imprint. 1840 It is RECOMMENDED that this only be available if hardware assisted 1841 NEA [RFC5209] is supported. 1843 6.3. Registrar security reductions 1845 A Registrar can choose to accept devices using less secure methods. 1846 These methods are acceptable when low security models are needed, as 1847 the security decisions are being made by the local administrator, but 1848 they MUST NOT be the default behavior: 1850 1. A registrar MAY choose to accept all devices, or all devices of a 1851 particular type, at the administrator's discretion. This could 1852 occur when informing all Registrars of unique identifiers of new 1853 entities might be operationally difficult. 1855 2. A registrar MAY choose to accept devices that claim a unique 1856 identity without the benefit of authenticating that claimed 1857 identity. This could occur when the Pledge does not include an 1858 X.509 IDevID factory installed credential. New Entities without 1859 an IDevID credential MAY form the Section 5.1 request using the 1860 Section 5.2 format to ensure the Pledge's serial number 1861 information is provided to the Registar (this includes the 1862 IDevIDAuthorityKeyIdentifier value which would be statically 1863 configured on the Pledge). The Pledge MAY refused to provide a 1864 TLS client certificate (as one is not available). The Pledge 1865 SHOULD support HTTP-based or certificate-less TLS authentication 1866 as described in EST RFC7030 section 3.3.2. A Registrar MUST NOT 1867 accept unauthenticated New Entities unless it has been configured 1868 to do so by an administrator that has verified that only expected 1869 new entities can communicate with a Registrar (presumably via a 1870 physically secured perimeter). 1872 3. A Registrar MAY request nonce-less Audit Vouchers from the MASA 1873 service (by not including a nonce in the request). These Audit 1874 Vouchers can then be transmitted to the Registrar and stored 1875 until they are needed during bootstrapping operations. This is 1876 for use cases where target network is protected by an air gap and 1877 therefore can not contact the MASA service during Pledge 1878 deployment. 1880 4. A registrar MAY ignore unrecognized nonce-less Audit Log entries. 1881 This could occur when used equipment is purchased with a valid 1882 history being deployed in air gap networks that required 1883 permanent Audit Vouchers. 1885 These modes are not available for devices that require a vendor 1886 Ownership Voucher. The methods vendors use to determine which 1887 devices are owned by which domains is out-of-scope. 1889 6.4. MASA security reductions 1891 Lower security modes chosen by the MASA service effect all device 1892 deployments unless bound to the specific device identities. In which 1893 case these modes can be provided as additional features for specific 1894 customers. The MASA service can choose to run in less secure modes 1895 by: 1897 1. Not enforcing that a Nonce is in the Audit Voucher. This results 1898 in distribution of Audit Voucher that never expire and in effect 1899 makes the Domain an always trusted entity to the Pledge during 1900 any subsequent bootstrapping attempts. That this occurred is 1901 captured in the log information so that the Domain registrar can 1902 make appropriate security decisions when a Pledge joins the 1903 Domain. This is useful to support use cases where Registrars 1904 might not be online during actual device deployment. Because 1905 this results in long lived Audit Voucher and do not require the 1906 proof that the device is online this is only accepted when the 1907 Registrar is authenticated by the MASA server and authorized to 1908 provide this functionality. The MASA server is RECOMMENDED to 1909 use this functionality only in concert with Ownership Validation 1910 tracking. 1912 2. Not verifying ownership before responding with an Audit Voucher. 1913 This is expected to be a common operational model because doing 1914 so relieves the vendor providing MASA services from having to 1915 tracking ownership during shipping and supply chain and allows 1916 for a very low overhead MASA service. A Registrar uses the audit 1917 log information as a defense in depth strategy to ensure that 1918 this does not occur unexpectedly (for example when purchasing new 1919 equipment the Registrar would throw an error if any audit log 1920 information is reported). 1922 7. Security Considerations 1924 In order to support a wide variety of use cases, devices can be 1925 claimed by a registrar without proving possession of the device in 1926 question. This would result in a nonceless, and thus always valid, 1927 claim. Or would result in an invalid nonce being associated with a 1928 claim. The MASA service is required to authenticate such Registrars 1929 but no programmatic method is provided to ensure good behavior by the 1930 MASA service. Nonceless entries into the audit log therefore 1931 permanently reduce the value of a device because future Registrars, 1932 during future bootstrap attempts, would now have to be configured 1933 with policy to ignore previously (and potentially unknown) domains. 1935 Future registrars are recommended to take the audit history of a 1936 device into account when deciding to join such devices into their 1937 network. If the MASA server were to have allowed a significantly 1938 large number of claims this might become onerous to the MASA server 1939 which must maintain all the extra log entries. Ensuring a Registrar 1940 is representative of a valid customer domain even without validating 1941 ownership helps to mitigate this. 1943 It is possible for an attacker to send an authorization request to 1944 the MASA service directly after the real Registrar obtains an 1945 authorization log. If the attacker could also force the 1946 bootstrapping protocol to reset there is a theoretical opportunity 1947 for the attacker to use the Audit Voucher to take control of the 1948 Pledge but then proceed to enroll with the target domain. Possible 1949 prevention mechanisms include: 1951 o Per device rate limits on the MASA service ensure such timing 1952 attacks are difficult. 1954 o In the advent of an unexpectedly lost bootstrapping connection the 1955 Registrar repeats the request for audit log information. 1957 To facilitate logging and administrative oversight the Pledge reports 1958 on Audit Voucher parsing status to the Registrar. In the case of a 1959 failure this information is informative to a potentially malicious 1960 Registar but this is RECOMMENDED anyway because of the operational 1961 benefits of an informed administrator in cases where the failure is 1962 indicative of a problem. 1964 As indicated in EST [RFC7030] the connection is provisional and 1965 untrusted until the server is successfully authorized. If the server 1966 provides a redirect response the client MUST follow the redirect but 1967 the connection remains provisional. If the client uses a well known 1968 URI for contacting a well known Registrar the EST Implicit Trust 1969 Anchor database is used as is described in RFC6125 to authenticate 1970 the well known URI. In this case the connection is not provisional 1971 and RFC6125 methods can be used for each subsequent redirection. 1973 To facilitate truely limited clients EST RFC7030 section 3.3.2 1974 requirements that the client MUST support a client authentication 1975 model have been reduced in Section 6 to a statement that clients only 1976 "SHOULD" support such a model. This reflects current (not great) 1977 practices but is NOT RECOMMENDED. 1979 The MASA service could lock a claim and refuse to issue a new voucher 1980 or the MASA service could go offline (for example if a vendor went 1981 out of business). This functionality provides benefits such as theft 1982 resistance, but it also implies an operational risk to the Domain 1983 that Vendor behavior could limit future bootstrapping of the device 1984 by the Domain. This can be mitigated by Registrars that request 1985 nonce-less Audit Vouchers. 1987 7.1. Security concerns with discovery process 1989 7.1.1. Discovery of Registrar by Proxy 1991 As described in section Section 3.2, the RECOMMENDED mechanism is for 1992 the proxy to discover the address of the registrar via GRASP 1993 [I-D.ietf-anima-grasp] 1995 GRASP is intended to run over a secured, and private Autonomic 1996 Control Plan [I-D.ietf-anima-autonomic-control-plane]. This 1997 discovery is between the already registered Registrar, and the 1998 already registered Proxy. There are no GRASP security issues with 1999 this part, as both entities will have already joined the secured ACP. 2001 7.1.2. Discovery of Proxy by New Entity 2003 [[EDNOTE: To be discussed]] 2005 8. Acknowledgements 2007 We would like to thank the various reviewers for their input, in 2008 particular Markus Stenberg, Brian Carpenter, Fuyu Eleven, Toerless 2009 Eckert, Eliot Lear and Sergey Kasatkin. 2011 9. References 2013 9.1. Normative References 2015 [IDevID] IEEE Standard, , "IEEE 802.1AR Secure Device Identifier", 2016 December 2009, . 2019 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2020 Requirement Levels", BCP 14, RFC 2119, 2021 DOI 10.17487/RFC2119, March 1997, 2022 . 2024 [RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei, 2025 "Advanced Sockets Application Program Interface (API) for 2026 IPv6", RFC 3542, DOI 10.17487/RFC3542, May 2003, 2027 . 2029 [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic 2030 Configuration of IPv4 Link-Local Addresses", RFC 3927, 2031 DOI 10.17487/RFC3927, May 2005, 2032 . 2034 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2035 Address Autoconfiguration", RFC 4862, 2036 DOI 10.17487/RFC4862, September 2007, 2037 . 2039 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 2040 Housley, R., and W. Polk, "Internet X.509 Public Key 2041 Infrastructure Certificate and Certificate Revocation List 2042 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 2043 . 2045 [RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing 2046 Security: An Unauthenticated Mode of IPsec", RFC 5386, 2047 DOI 10.17487/RFC5386, November 2008, 2048 . 2050 [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, 2051 RFC 5652, DOI 10.17487/RFC5652, September 2009, 2052 . 2054 [RFC5660] Williams, N., "IPsec Channels: Connection Latching", 2055 RFC 5660, DOI 10.17487/RFC5660, October 2009, 2056 . 2058 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, 2059 DOI 10.17487/RFC6762, February 2013, 2060 . 2062 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 2063 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 2064 . 2066 [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., 2067 "Enrollment over Secure Transport", RFC 7030, 2068 DOI 10.17487/RFC7030, October 2013, 2069 . 2071 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 2072 Constrained-Node Networks", RFC 7228, 2073 DOI 10.17487/RFC7228, May 2014, 2074 . 2076 9.2. Informative References 2078 [I-D.behringer-homenet-trust-bootstrap] 2079 Behringer, M., Pritikin, M., and S. Bjarnason, 2080 "Bootstrapping Trust on a Homenet", draft-behringer- 2081 homenet-trust-bootstrap-02 (work in progress), February 2082 2014. 2084 [I-D.ietf-ace-actors] 2085 Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An 2086 architecture for authorization in constrained 2087 environments", draft-ietf-ace-actors-04 (work in 2088 progress), September 2016. 2090 [I-D.ietf-anima-autonomic-control-plane] 2091 Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic 2092 Control Plane", draft-ietf-anima-autonomic-control- 2093 plane-03 (work in progress), July 2016. 2095 [I-D.ietf-anima-grasp] 2096 Bormann, C., Carpenter, B., and B. Liu, "A Generic 2097 Autonomic Signaling Protocol (GRASP)", draft-ietf-anima- 2098 grasp-08 (work in progress), October 2016. 2100 [I-D.ietf-netconf-zerotouch] 2101 Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning 2102 for NETCONF or RESTCONF based Management", draft-ietf- 2103 netconf-zerotouch-09 (work in progress), July 2016. 2105 [I-D.lear-mud-framework] 2106 Lear, E., "Manufacturer Usage Description Framework", 2107 draft-lear-mud-framework-00 (work in progress), January 2108 2016. 2110 [I-D.richardson-anima-state-for-joinrouter] 2111 Richardson, M., "Considerations for stateful vs stateless 2112 join router in ANIMA bootstrap", draft-richardson-anima- 2113 state-for-joinrouter-01 (work in progress), July 2016. 2115 [imprinting] 2116 Wikipedia, , "Wikipedia article: Imprinting", July 2015, 2117 . 2119 [pledge] Dictionary.com, , "Dictionary.com Unabridged", July 2015, 2120 . 2122 [RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A., 2123 Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic 2124 Networking: Definitions and Design Goals", RFC 7575, 2125 DOI 10.17487/RFC7575, June 2015, 2126 . 2128 [Stajano99theresurrecting] 2129 Stajano, F. and R. Anderson, "The resurrecting duckling: 2130 security issues for ad-hoc wireless networks", 1999, 2131 . 2134 Authors' Addresses 2136 Max Pritikin 2137 Cisco 2139 Email: pritikin@cisco.com 2141 Michael C. Richardson 2142 Sandelman Software Works 2144 Email: mcr+ietf@sandelman.ca 2145 URI: http://www.sandelman.ca/ 2147 Michael H. Behringer 2148 Cisco 2150 Email: mbehring@cisco.com 2152 Steinthor Bjarnason 2153 Cisco 2155 Email: sbjarnas@cisco.com 2157 Kent Watsen 2158 Juniper Networks 2160 Email: kwatsen@juniper.net