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If it is intended as a requirements expression, it should be rewritten using one of the combinations defined in RFC 2119; otherwise it should not be all-uppercase. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: o An OSB definition MAY NOT require any behavior of a BPSEC-BPA that is in conflict with the behavior identified in this specification. In particular, the security processing requirements imposed by this specification MUST be consistent across all BPSEC-BPAs in a network. -- The document date (July 1, 2017) is 2490 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-31) exists of draft-ietf-dtn-bpbis-06 ** Downref: Normative reference to an Informational RFC: RFC 6255 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Delay-Tolerant Networking E. Birrane 3 Internet-Draft K. McKeever 4 Intended status: Standards Track JHU/APL 5 Expires: January 2, 2018 July 1, 2017 7 Bundle Protocol Security Specification 8 draft-ietf-dtn-bpsec-05 10 Abstract 12 This document defines a security protocol providing end to end data 13 integrity and confidentiality services for the Bundle Protocol. 15 Status of This Memo 17 This Internet-Draft is submitted in full conformance with the 18 provisions of BCP 78 and BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF). Note that other groups may also distribute 22 working documents as Internet-Drafts. The list of current Internet- 23 Drafts is at http://datatracker.ietf.org/drafts/current/. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 This Internet-Draft will expire on January 2, 2018. 32 Copyright Notice 34 Copyright (c) 2017 IETF Trust and the persons identified as the 35 document authors. All rights reserved. 37 This document is subject to BCP 78 and the IETF Trust's Legal 38 Provisions Relating to IETF Documents 39 (http://trustee.ietf.org/license-info) in effect on the date of 40 publication of this document. Please review these documents 41 carefully, as they describe your rights and restrictions with respect 42 to this document. Code Components extracted from this document must 43 include Simplified BSD License text as described in Section 4.e of 44 the Trust Legal Provisions and are provided without warranty as 45 described in the Simplified BSD License. 47 Table of Contents 49 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 50 1.1. Supported Security Services . . . . . . . . . . . . . . . 3 51 1.2. Specification Scope . . . . . . . . . . . . . . . . . . . 4 52 1.3. Related Documents . . . . . . . . . . . . . . . . . . . . 5 53 1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 54 2. Design Decisions . . . . . . . . . . . . . . . . . . . . . . 6 55 2.1. Block-Level Granularity . . . . . . . . . . . . . . . . . 6 56 2.2. Multiple Security Sources . . . . . . . . . . . . . . . . 7 57 2.3. Mixed Security Policy . . . . . . . . . . . . . . . . . . 7 58 2.4. User-Selected Cipher Suites . . . . . . . . . . . . . . . 8 59 2.5. Deterministic Processing . . . . . . . . . . . . . . . . 8 60 3. Security Blocks . . . . . . . . . . . . . . . . . . . . . . . 8 61 3.1. Block Definitions . . . . . . . . . . . . . . . . . . . . 8 62 3.2. Uniqueness . . . . . . . . . . . . . . . . . . . . . . . 9 63 3.3. Target Multiplicity . . . . . . . . . . . . . . . . . . . 9 64 3.4. Target Identification . . . . . . . . . . . . . . . . . . 10 65 3.5. Block Representation . . . . . . . . . . . . . . . . . . 10 66 3.6. Abstract Security Block . . . . . . . . . . . . . . . . . 11 67 3.7. Block Integrity Block . . . . . . . . . . . . . . . . . . 14 68 3.8. Block Confidentiality Block . . . . . . . . . . . . . . . 15 69 3.9. Block Interactions . . . . . . . . . . . . . . . . . . . 16 70 3.10. Cipher Suite Parameter and Result Identification . . . . 17 71 3.11. BSP Block Example . . . . . . . . . . . . . . . . . . . . 18 72 4. Canonical Forms . . . . . . . . . . . . . . . . . . . . . . . 19 73 5. Security Processing . . . . . . . . . . . . . . . . . . . . . 20 74 5.1. Bundles Received from Other Nodes . . . . . . . . . . . . 20 75 5.1.1. Receiving BCB Blocks . . . . . . . . . . . . . . . . 20 76 5.1.2. Receiving BIB Blocks . . . . . . . . . . . . . . . . 21 77 5.2. Bundle Fragmentation and Reassembly . . . . . . . . . . . 22 78 6. Key Management . . . . . . . . . . . . . . . . . . . . . . . 22 79 7. Security Policy Considerations . . . . . . . . . . . . . . . 23 80 8. Security Considerations . . . . . . . . . . . . . . . . . . . 24 81 8.1. Attacker Capabilities and Objectives . . . . . . . . . . 24 82 8.2. Attacker Behaviors and BPSec Mitigations . . . . . . . . 25 83 8.2.1. Eavesdropping Attacks . . . . . . . . . . . . . . . . 25 84 8.2.2. Modification Attacks . . . . . . . . . . . . . . . . 26 85 8.2.3. Topology Attacks . . . . . . . . . . . . . . . . . . 27 86 8.2.4. Message Injection . . . . . . . . . . . . . . . . . . 27 87 9. Cipher Suite Authorship Considerations . . . . . . . . . . . 28 88 10. Defining Other Security Blocks . . . . . . . . . . . . . . . 29 89 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 90 11.1. Bundle Block Types . . . . . . . . . . . . . . . . . . . 30 91 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 92 12.1. Normative References . . . . . . . . . . . . . . . . . . 30 93 12.2. Informative References . . . . . . . . . . . . . . . . . 31 94 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 31 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 97 1. Introduction 99 This document defines security features for the Bundle Protocol (BP) 100 [BPBIS] and is intended for use in Delay Tolerant Networks (DTNs) to 101 provide end-to-end security services. 103 The Bundle Protocol specification [BPBIS] defines DTN as referring to 104 "a networking architecture providing communications in and/or through 105 highly stressed environments" where "BP may be viewed as sitting at 106 the application layer of some number of constituent networks, forming 107 a store-carry-forward overlay network". The term "stressed" 108 environment refers to multiple challenging conditions including 109 intermittent connectivity, large and/or variable delays, asymmetric 110 data rates, and high bit error rates. 112 The BP might be deployed such that portions of the network cannot be 113 trusted, posing the usual security challenges related to 114 confidentiality and integrity. However, the stressed nature of the 115 BP operating environment imposes unique conditions where usual 116 transport security mechanisms may not be sufficient. For example, 117 the store-carry-forward nature of the network may require protecting 118 data at rest, preventing unauthorized consumption of critical 119 resources such as storage space, and operating without regular 120 contact with a centralized security oracle (such as a certificate 121 authority). 123 An end-to-end security service is needed that operates in all of the 124 environments where the BP operates. 126 1.1. Supported Security Services 128 BPSec provides end-to-end integrity and confidentiality services for 129 BP bundles. 131 Integrity services ensure that protected data within a bundle are not 132 changed from the time they are provided to the network to the time 133 they are delivered at their destination. Data changes may be caused 134 by processing errors, environmental conditions, or intentional 135 manipulation. 137 Confidentiality services ensure that protected data is unintelligible 138 to nodes in the DTN, except for authorized nodes possessing special 139 information. Confidentiality, in this context, applies to the 140 contents of protected data and does not extend to hiding the fact 141 that protected data exist in the bundle. 143 NOTE: Hop-by-hop authentication is NOT a supported security service 144 in this specification, for three reasons. 146 1. The term "hop-by-hop" is ambiguous in a BP overlay, as nodes that 147 are adjacent in the overlay may not be adjacent in physical 148 connectivity. This condition is difficult or impossible to 149 detect and therefore hop-by-hop authentication is difficult or 150 impossible to enforce. 152 2. Networks in which BPSec may be deployed may have a mixture of 153 security-aware and not-security-aware nodes. Hop-by-hop 154 authentication cannot be deployed in a network if adjacent nodes 155 in the network have different security capabilities. 157 3. Hop-by-hop authentication is a special case of data integrity and 158 can be achieved with the integrity mechanisms defined in this 159 specification. Therefore, a separate authentication service is 160 not necessary. 162 1.2. Specification Scope 164 This document defines the security services provided by the BPSec. 165 This includes the data specification for representing these services 166 as BP extension blocks, and the rules for adding, removing, and 167 processing these blocks at various points during the bundle's 168 traversal of the DTN. 170 BPSec applies only to those nodes that implement it, known as 171 "security-aware" nodes. There might be other nodes in the DTN that 172 do not implement BPSec. While all nodes in a BP overlay can exchange 173 bundles, BPSec security operations can only happen at BPSec security- 174 aware nodes. 176 This specification does not address individual cipher suite 177 implementations. Different networking conditions and operational 178 considerations require varying strengths of security mechanism such 179 that mandating a cipher suite in this specification may result in too 180 much security for some networks and too little security in others. 181 It is expected that separate documents will be standardized to define 182 cipher suites compatible with BPSec, to include operational cipher 183 suites and interoperability cipher suites. 185 This specification does not address the implementation of security 186 policy and does not provide a security policy for the BPSec. Similar 187 to cipher suites, security policies are based on the nature and 188 capabilities of individual networks and network operational concepts. 189 This specification does provide policy considerations when building a 190 security policy. 192 This specification does not address how to combine the BPSec security 193 blocks with other protocols, other BP extension blocks, or other best 194 practices to achieve security in any particular network 195 implementation. 197 1.3. Related Documents 199 This document is best read and understood within the context of the 200 following other DTN documents: 202 "Delay-Tolerant Networking Architecture" [RFC4838] defines the 203 architecture for DTNs and identifies certain security assumptions 204 made by existing Internet protocols that are not valid in a DTN. 206 The Bundle Protocol [BPBIS] defines the format and processing of 207 bundles, defines the extension block format used to represent BPSec 208 security blocks, and defines the canonicalization algorithms used by 209 this specification. 211 The Bundle Security Protocol [RFC6257] and Streamlined Bundle 212 Security Protocol [SBSP] documents introduced the concepts of using 213 BP extension blocks for security services in a DTN. The BPSec is a 214 continuation and refinement of these documents. 216 1.4. Terminology 218 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 219 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 220 "OPTIONAL" in this document are to be interpreted as described in 221 [RFC2119]. 223 This section defines terminology either unique to the BPSec or 224 otherwise necessary for understanding the concepts defined in this 225 specification. 227 o Bundle Source - the node which originates a bundle. The Node ID 228 of the BPA originating the bundle. 230 o Forwarder - any node that transmits a bundle in the DTN. The Node 231 ID of the Bundle Protocol Agent (BPA) that sent the bundle on its 232 most recent hop. 234 o Intermediate Receiver, Waypoint, or "Next Hop" - any node that 235 receives a bundle from a Forwarder that is not the Destination. 236 The Node ID of the BPA at any such node. 238 o Path - the ordered sequence of nodes through which a bundle passes 239 on its way from Source to Destination. The path is not 240 necessarily known in advance by the bundle or any BPAs in the DTN. 242 o Security Block - a BPSec extension block in a bundle. 244 o Security Operation - the application of a security service to a 245 security target, notated as OP(security service, security target). 246 For example, OP(confidentiality, payload). Every security 247 operation in a bundle MUST be unique, meaning that a security 248 service can only be applied to a security target once in a bundle. 249 A security operation is implemented by a security block. 251 o Security Service - the security features supported by this 252 specification: integrity and confidentiality. 254 o Security Source - a bundle node that adds a security block to a 255 bundle. The Node ID of that node. 257 o Security Target - the block within a bundle that receives a 258 security-service as part of a security-operation. 260 2. Design Decisions 262 The application of security services in a DTN is a complex endeavor 263 that must consider physical properties of the network, policies at 264 each node, and various application security requirements. This 265 section identifies those desirable properties that guide design 266 decisions for this specification and are necessary for understanding 267 the format and behavior of the BPSec protocol. 269 2.1. Block-Level Granularity 271 Security services within this specification MUST allow different 272 blocks within a bundle to have different security services applied to 273 them. 275 Blocks within a bundle represent different types of information. The 276 primary block contains identification and routing information. The 277 payload block carries application data. Extension blocks carry a 278 variety of data that may augment or annotate the payload, or 279 otherwise provide information necessary for the proper processing of 280 a bundle along a path. Therefore, applying a single level and type 281 of security across an entire bundle fails to recognize that blocks in 282 a bundle may represent different types of information with different 283 security needs. 285 For example, a payload block might be encrypted to protect its 286 contents and an extension block containing summary information 287 related to the payload might be integrity signed but unencrypted to 288 provide waypoints access to payload-related data without providing 289 access to the payload. 291 2.2. Multiple Security Sources 293 A bundle MAY have multiple security blocks and these blocks MAY have 294 different security sources. 296 The Bundle Protocol allows extension blocks to be added to a bundle 297 at any time during its existence in the DTN. When a waypoint adds a 298 new extension block to a bundle, that extension block may have 299 security services applied to it by that waypoint. Similarly, a 300 waypoint may add a security service to an existing extension block, 301 consistent with its security policy. For example, a node 302 representing a boundary between a trusted part of the network and an 303 untrusted part of the network may wish to apply payload encryption 304 for bundles leaving the trusted portion of the network. 306 When a waypoint adds a security service to the bundle, the waypoint 307 is the security source for that service. The security block(s) which 308 represent that service in the bundle may need to record this security 309 source as the bundle destination might need this information for 310 processing. For example, a destination node might interpret policy 311 as it related to security blocks as a function of the security source 312 for that block. 314 2.3. Mixed Security Policy 316 The security policy enforced by nodes in the DTN MAY differ. 318 Some waypoints may not be security aware and will not be able to 319 process security blocks. Therefore, security blocks MUST have their 320 processing flags set such that the block will be treated 321 appropriately by non-security-aware waypoints 323 Some waypoints will have security policies that require evaluating 324 security services even if they are not the bundle destination or the 325 final intended destination of the service. For example, a waypoint 326 may choose to verify an integrity service even though the waypoint is 327 not the bundle destination and the integrity service will be needed 328 by other node along the bundle's path. 330 Some waypoints will determine, through policy, that they are the 331 intended recipient of the security service and terminate the security 332 service in the bundle. For example, a gateway node may determine 333 that, even though it is not the destination of the bundle, it should 334 verify and remove a particular integrity service or attempt to 335 decrypt a confidentiality service, before forwarding the bundle along 336 its path. 338 Some waypoints may understand security blocks but refuse to process 339 them unless they are the bundle destination. 341 2.4. User-Selected Cipher Suites 343 The security services defined in this specification rely on a variety 344 of cipher suites providing integrity signatures, cipher-text, and 345 other information necessary to populate security blocks. Users MAY 346 select different cipher suites to implement security services. For 347 example, some users might prefer a SHA2 hash function for integrity 348 whereas other users may prefer a SHA3 hash function instead. The 349 security services defined in this specification MUST provide a 350 mechanism for identifying what cipher suite has been used to populate 351 a security block. 353 2.5. Deterministic Processing 355 Whenever a node determines that it must process more than one 356 security block in a received bundle (either because the policy at a 357 waypoint states that it should process security blocks or because the 358 node is the bundle destination) the order in which security blocks 359 are processed MUST be deterministic. All nodes MUST impose this same 360 deterministic processing order for all security blocks. This 361 specification provides determinism in the application and evaluation 362 of security services, even when doing so results in a loss of 363 flexibility. 365 3. Security Blocks 367 3.1. Block Definitions 369 This specification defines two types of security block: the Block 370 Integrity Block (BIB) and the Block Confidentiality Block (BCB). 372 The BIB is used to ensure the integrity of its security target(s). 373 The integrity information in the BIB MAY be verified by any node 374 in between the BIB security source and the bundle destination. 375 Security-aware waypoints may add or remove BIBs from bundles in 376 accordance with their security policy. 378 The BCB indicates that the security target(s) have been encrypted 379 at the BCB security source in order to protect its content while 380 in transit. The BCB may be decrypted by security-aware nodes in 381 the network, up to and including the bundle destination, as a 382 matter of security policy. 384 3.2. Uniqueness 386 Security operations in a bundle MUST be unique - the same security 387 service MUST NOT be applied to a security target more than once in a 388 bundle. Since a security operation is represented as a security 389 block, this limits what security blocks may be added to a bundle: if 390 adding a security block to a bundle would cause some other security 391 block to no longer represent a unique security operation then the new 392 block MUST NOT be added. 394 If multiple security blocks representing the same security operation 395 were allowed in a bundle at the same time, there would exist 396 ambiguity regarding block processing order and the property of 397 deterministic processing blocks would be lost. 399 Using the notation OP(service,target), several examples illustrate 400 this uniqueness requirement. 402 o Signing the payload twice: The two operations OP(integrity, 403 payload) and OP(integrity, payload) are redundant and MUST NOT 404 both be present in the same bundle at the same time. 406 o Signing different blocks: The two operations OP(integrity, 407 payload) and OP(integrity, extension_block_1) are not redundant 408 and both may be present in the same bundle at the same time. 409 Similarly, the two operations OP(integrity, extension_block_1) and 410 OP(integrity,extension_block_2) are also not redundant and may 411 both be present in the bundle at the same time. 413 o Different Services on same block: The two operations 414 OP(integrity,payload) and OP(confidentiality, payload) are not 415 inherently redundant and may both be present in the bundle at the 416 same time, pursuant to other processing rules in this 417 specification. 419 3.3. Target Multiplicity 421 Under special circumstances, a single security block may represent 422 multiple security operations as a way of reducing the overall number 423 of security blocks present in a bundle. In these circumstances, 424 reducing the number of security blocks in the bundle reduces the 425 amount of redundant information in the bundle. 427 A set of security operations may be represented by a single security 428 block if and only if the following conditions are true. 430 o The security operations apply the same security service. For 431 example, they are all integrity operations or all confidentiality 432 operations. 434 o The cipher suite parameters and key information for the security 435 operations are identical. 437 o The security source for the security operations is the same. 438 Meaning the set of operations are being added/removed by the same 439 node. 441 o No security operations have the same security target, as that 442 would violate the need for security operations to be unique. 444 o None of the security operations conflict with security operations 445 already present in the bundle. 447 When representing multiple security operations in a single security 448 block, the information that is common across all operations is 449 represented once in the security block, and the information which is 450 different (e.g., the security targets) are represented individually. 451 When the security block is processed all security operations 452 represented by the security block MUST be applied/evaluated at that 453 time. 455 3.4. Target Identification 457 A security target is a block in the bundle to which a security 458 service applies. This target MUST be uniquely and unambiguously 459 identifiable when processing a security block. The definition of the 460 extension block header from [BPBIS] provides a "Block Number" field 461 suitable for this purpose. Therefore, a security target in a 462 security block MUST be represented as the Block Number of the target 463 block. 465 3.5. Block Representation 467 Each security block uses the Canonical Bundle Block Format as defined 468 in [BPBIS]. That is, each security block is comprised of the 469 following elements: 471 o Block Type Code 473 o Block Number 475 o Block Processing Control Flags 477 o CRC Type and CRC Field (if present) 478 o Block Data Length 480 o Block Type Specific Data Fields 482 Security-specific information for a security block is captured in the 483 "Block Type Specific Data Fields". 485 3.6. Abstract Security Block 487 The structure of the security-specific portions of a security block 488 is identical for both the BIB and BCB Block Types. Therefore, this 489 section defines an Abstract Security Block (ASB) data structure and 490 discusses the definition, processing, and other constraints for using 491 this structure. An ASB is never directly instantiated within a 492 bundle, it is only a mechanism for discussing the common aspects of 493 BIB and BCB security blocks. 495 The fields of the ASB SHALL be as follows, listed in the order in 496 which they MUST appear. 498 Security Targets: 499 This field identifies the block(s) targetted by the security 500 operation(s) represented by this security block. Each target 501 block is represented by its unique Block Number. This field 502 SHALL be represented by a CBOR array of data items. Each 503 target within this CBOR array SHALL be represented by a CBOR 504 unsigned integer. This array MUST have at least 1 entry and 505 each entry MUST represent the Block Number of a block that 506 exists in the bundle. There MUST NOT be duplicate entries in 507 this array. 509 Cipher Suite Id: 510 This field identifies the cipher suite used to implement the 511 security service represented by this block and applied to each 512 security target. This field SHALL be represented by a CBOR 513 unsigned integer. 515 Cipher Suite Flags: 516 This field identifies which optional fields are present in the 517 security block. This field SHALL be represented as a CBOR 518 unsigned integer containing a bit field of 5 bits indicating 519 the presence or absence of other security block fields, as 520 follows. 522 Bit 1 (the most-significant bit, 0x10): reserved. 524 Bit 2 (0x08): reserved. 526 Bit 3 (0x04): reserved. 528 Bit 4 (0x02): Security Source Present Flag. 530 Bit 5 (the least-significant bit, 0x01): Cipher Suite 531 Parameters Present Flag. 533 In this field, a value of 1 indicates that the associated 534 security block field MUST be included in the security block. A 535 value of 0 indicates that the associated security block field 536 MUST NOT be in the security block. 538 Security Source (Optional Field): 539 This field identifies the Endpoint that inserted the security 540 block in the bundle. If the security source field is not 541 present then the source MAY be inferred from other information, 542 such as the bundle source or the previous hop, as defined by 543 security policy. This field SHALL be represented by a CBOR 544 array in accordance with [BPBIS] rules for representing 545 Endpoint Identifiers (EIDs). 547 Cipher Suite Parameters (Optional Field): 548 This field captures one or more cipher suite parameters that 549 should be provided to security-aware nodes when processing the 550 security service described by this security block. This field 551 SHALL be represented by a CBOR array. Each entry in this array 552 is a single cipher suite parameter. A single cipher suite 553 parameter SHALL also be represented as a CBOR array comprising 554 a 2-tuple of the id and value of the parameter, as follows. 556 * Parameter Id. This field identifies which cipher suite 557 parameter is being specified. This field SHALL be 558 represented as a CBOR unsigned integer. Parameter ids are 559 selected as described in Section 3.10. 561 * Parameter Value. This field captures the value associated 562 with this parameter. This field SHALL be represented by the 563 applicable CBOR representation of the parameter, in 564 accordance with Section 3.10. 566 The logical layout of the cipher suite parameters array is 567 illustrated in Figure 1. 569 +----------------+----------------+ +----------------+ 570 | Parameter 1 | Parameter 2 | ... | Parameter N | 571 +------+---------+------+---------+ +------+---------+ 572 | Id | Value | Id | Value | | Id | Value | 573 +------+---------+------+---------+ +------+---------+ 575 Figure 1: Cipher Suite Parameters 577 Security Results: 578 This field captures the results of applying a security service 579 to the security targets of the security block. This field 580 SHALL be represented as a CBOR array of target results. Each 581 entry in this array represents the set of security results for 582 a specific security target. The target results MUST be ordered 583 identically to the Security Targets field of the security 584 block. This means that the first set of target results in this 585 array corresponds to the first entry in the Security Targets 586 field of the security block, and so on. There MUST be one 587 entry in this array for each entry in the Security Targets 588 field of the security block. 590 The set of security results for a target is also represented as 591 a CBOR array of individual results. An individual result is 592 represented as a 2-tuple of a result id and a result value, 593 defined as follows. 595 * Result Id. This field identifies which security result is 596 being specified. Some security results capture the primary 597 output of a cipher suite. Other security results contain 598 additional annotative information from cipher suite 599 processing. This field SHALL be represented as a CBOR 600 unsigned integer. Security result ids will be as specified 601 in Section 3.10. 603 * Result Value. This field captures the value associated with 604 the result. This field SHALL be represented by the 605 applicable CBOR representation of the result value, in 606 accordance with Section 3.10. 608 The logical layout of the security results array is illustrated 609 in Figure 2. In this figure there are N security targets for 610 this security block. The first security target contains M 611 results and the Nth security target contains K results. 613 +------------------------------+ +------------------------------+ 614 | Target 1 | | Target N | 615 +------------+----+------------+ +------------------------------+ 616 | Result 1 | | Result M | ... | Result 1 | | Result K | 617 +----+-------+ .. +----+-------+ +----+-------+ .. +----+-------+ 618 | Id | Value | | Id | Value | | Id | Value | | Id | Value | 619 +----+-------+ +----+-------+ +----+-------+ +----+-------+ 621 Figure 2: Security Results 623 3.7. Block Integrity Block 625 A BIB is a bundle extension block with the following characteristics. 627 o The Block Type Code value is as specified in Section 11.1. 629 o The Block Type Specific Data Fields follow the structure of the 630 ASB. 632 o A security target listed in the Security Targets field MUST NOT 633 reference a security block defined in this specification (e.g., a 634 BIB or a BCB). 636 o The Cipher Suite Id MUST be documented as an end-to-end 637 authentication-cipher suite or as an end-to-end error-detection- 638 cipher suite. 640 o An EID-reference to the security source MAY be present. If this 641 field is not present, then the security source of the block SHOULD 642 be inferred according to security policy and MAY default to the 643 bundle source. The security source may also be specified as part 644 of key information described in Section 3.10. 646 Notes: 648 o It is RECOMMENDED that cipher suite designers carefully consider 649 the effect of setting flags that either discard the block or 650 delete the bundle in the event that this block cannot be 651 processed. 653 o Since OP(integrity, target) is allowed only once in a bundle per 654 target, it is RECOMMENDED that users wishing to support multiple 655 integrity signatures for the same target define a multi-signature 656 cipher suite. 658 o For some cipher suites, (e.g., those using asymmetric keying to 659 produce signatures or those using symmetric keying with a group 660 key), the security information MAY be checked at any hop on the 661 way to the destination that has access to the required keying 662 information, in accordance with Section 3.9. 664 o The use of a generally available key is RECOMMENDED if custodial 665 transfer is employed and all nodes SHOULD verify the bundle before 666 accepting custody. 668 3.8. Block Confidentiality Block 670 A BCB is a bundle extension block with the following characteristics. 672 The Block Type Code value is as specified in Section 11.1. 674 The Block Processing Control flags value can be set to whatever 675 values are required by local policy, except that this block MUST 676 have the "replicate in every fragment" flag set if the target of 677 the BCB is the Payload Block. Having that BCB in each fragment 678 indicates to a receiving node that the payload portion of each 679 fragment represents cipher-text. 681 The Block Type Specific Data Fields follow the structure of the 682 ASB. 684 A security target listed in the Security Targets field MAY 685 reference the payload block, a non-security extension block, or a 686 BIB block. A BCB MUST NOT include another BCB as a security 687 target. A BCB MUST NOT target the primary block. 689 The Cipher Suite Id MUST be documented as a confidentiality cipher 690 suite. 692 Any additional bytes generated from applying the cipher suite to a 693 security target (such as additional authenticated text) MAY be 694 placed in an appropriate security result (e.g., an Integrity Check 695 Value) in accordance with cipher suite and security policy. 697 An EID-reference to the security source MAY be present. If this 698 field is not present, then the security source of the block SHOULD 699 be inferred according to security policy and MAY default to the 700 bundle source. The security source may also be specified as part 701 of key information described in Section 3.10. 703 The BCB modifies the contents of its security target(s). When a BCB 704 is applied, the security target body data are encrypted "in-place". 705 Following encryption, the security target Block Type Specific Data 706 Fields contains cipher-text, not plain-text. Other block fields 707 remain unmodified, with the exception of the Block Data Length field, 708 which may be changed if the BCB is allowed to change the length of 709 the block (see below). 711 Fragmentation, reassembly, and custody transfer are adversely 712 affected by a change in size of the payload block due to ambiguity 713 about what byte range of the block is actually in any particular 714 fragment. Therefore, when the security target of a BCB is the bundle 715 payload, the BCB MUST NOT alter the size of the payload block body 716 data. This "in-place" encryption allows fragmentation, reassembly, 717 and custody transfer to operate without knowledge of whether or not 718 encryption has occurred. 720 If a BCB cannot alter the size of the security target (e.g., the 721 security target is the payload block or block length modifications 722 are disallowed by policy) then differences in the size of the cipher- 723 text and plain-text MUST be handled in the following way. If the 724 cipher-text is shorter in length than the plain-text, padding must be 725 used in accordance with the cipher suite policy. If the cipher-text 726 is larger than the plain-text, overflow bytes MUST be placed in 727 overflow parameters in the Security Result field. 729 Notes: 731 o It is RECOMMENDED that cipher suite designers carefully consider 732 the effect of setting flags that either discard the block or 733 delete the bundle in the event that this block cannot be 734 processed. 736 o The BCB block processing control flags MAY be set independently 737 from the processing control flags of the security target(s). The 738 setting of such flags SHOULD be an implementation/policy decision 739 for the encrypting node. 741 o A BCB MAY include information as part of additional authenticated 742 data to address parts of the target block that are not converted 743 to cipher-text. 745 3.9. Block Interactions 747 The security block types defined in this specification are designed 748 to be as independent as possible. However, there are some cases 749 where security blocks may share a security target creating processing 750 dependencies. 752 If confidentiality is being applied to a target that already has 753 integrity applied to it, then an undesirable condition occurs where a 754 security aware waypoint would be unable to check the integrity result 755 of a block because the block contents have been encrypted after the 756 integrity signature was generated. To address this concern, the 757 following processing rules MUST be followed. 759 o If confidentiality is to be applied to a target, it MUST also be 760 applied to any integrity operation already defined for that 761 target. This means that if a BCB is added to encrypt a block, 762 another BCB MUST also be added to encrypt a BIB also targeting 763 that block. 765 o An integrity operation MUST NOT be applied to a security target if 766 a BCB in the bundle shares the same security target. This 767 prevents ambiguity in the order of evaluation when receiving a BIB 768 and a BCB for a given security target. 770 o An integrity value MUST NOT be evaluated if the BIB providing the 771 integrity value is the security target of an existing BCB block in 772 the bundle. In such a case, the BIB data contains cipher-text as 773 it has been encrypted. 775 o An integrity value MUST NOT be evaluated if the security target of 776 the BIB is also the security target of a BCB in the bundle. In 777 such a case, the security target data contains cipher-text as it 778 has been encrypted. 780 o As mentioned in Section 3.7, a BIB MUST NOT have a BCB as its 781 security target. BCBs may embed integrity results as part of 782 security results. 784 These restrictions on block interactions impose a necessary ordering 785 when applying security operations within a bundle. Specifically, for 786 a given security target, BIBs MUST be added before BCBs. This 787 ordering MUST be preserved in cases where the current BPA is adding 788 all of the security blocks for the bundle or whether the BPA is a 789 waypoint adding new security blocks to a bundle that already contains 790 security blocks. 792 3.10. Cipher Suite Parameter and Result Identification 794 Cipher suite parameters and security results each represent multiple 795 distinct pieces of information in a security block. Each piece of 796 information is assigned an identifier and a CBOR encoding. 797 Identifiers MUST be unique for a given cipher suite but do not need 798 to be unique across all cipher suites. Therefore, parameter ids and 799 security result ids are specified in the context of a cipher suite 800 definition. 802 Individual BPSec cipher suites SHOULD use existing registries of 803 identifiers and CBOR encodings, such as those defined in [COSE], 804 whenever possible. Cipher suites MAY define their own identifiers 805 and CBOR encodings when necessary. 807 A cipher suite MAY include multiple instances of the same identifier 808 for a parameter or result in a security block. Parameters and 809 results are represented using CBOR, and any identification of a new 810 parameter or result MUST include how the value will be represented 811 using the CBOR specification. Ids themselves are always represented 812 as a CBOR unsigned integer. 814 3.11. BSP Block Example 816 An example of BPSec blocks applied to a bundle is illustrated in 817 Figure 3. In this figure the first column represents blocks within a 818 bundle and the second column represents the Block Number for the 819 block, using the terminology B1...Bn for the purpose of illustration. 821 Block in Bundle ID 822 +===================================+====+ 823 | Primary Block | B1 | 824 +-----------------------------------+----+ 825 | BIB | B2 | 826 | OP(integrity, target=B1) | | 827 +-----------------------------------+----+ 828 | BCB | B3 | 829 | OP(confidentiality, target=B4) | | 830 +-----------------------------------+----+ 831 | Extension Block | B4 | 832 +-----------------------------------+----+ 833 | BIB | B5 | 834 | OP(integrity, target=B6) | | 835 +-----------------------------------+----+ 836 | Extension Block | B6 | 837 +-----------------------------------+----+ 838 | BCB | B7 | 839 | OP(confidentiality,targets=B8,B9) | | 840 +-----------------------------------+----+ 841 | BIB (encrypted by B7) | B8 | 842 | OP(integrity, target=B9) | | 843 +-----------------------------------+----| 844 | Payload Block | B9 | 845 +-----------------------------------+----+ 847 Figure 3: Sample Use of BPSec Blocks 849 In this example a bundle has four non-security-related blocks: the 850 primary block (B1), two extension blocks (B4,B6), and a payload block 851 (B9). The following security applications are applied to this 852 bundle. 854 o An integrity signature applied to the canonicalized primary block. 855 This is accomplished by a single BIB (B2). 857 o Confidentiality for the first extension block (B4). This is 858 accomplished by a BCB block (B3). 860 o Integrity for the second extension block (B6). This is 861 accomplished by a BIB block (B5). NOTE: If the extension block B6 862 contains a representation of the serialized bundle (such as a hash 863 over all blocks in the bundle at the time of its last 864 transmission) then the BIB block is also providing an 865 authentication service. 867 o An integrity signature on the payload (B10). This is accomplished 868 by a BIB block (B8). 870 o Confidentiality for the payload block and it's integrity 871 signature. This is accomplished by a BCB block, B7, encrypting B8 872 and B9. In this case, the security source, key parameters, and 873 service are identical, so a single security block MAY be used for 874 this purpose, rather than requiring two BCBs one to encrypt B8 and 875 one to encrypt B9. 877 4. Canonical Forms 879 Security services require consistency and determinism in how 880 information is presented to cipher suites at the security source and 881 at a receiving node. For example, integrity services require that 882 the same target information (e.g., the same bits in the same order) 883 is provided to the cipher suite when generating an original signature 884 and when generating a comparison signature. Canonicalization 885 algorithms are used to construct a stable, end-to-end bit 886 representation of a target block. 888 Canonical forms are not transmitted, they are used to generate input 889 to a cipher suite for security processing at a security-aware node. 891 The canonicalization of the primary block is as specified in [BPBIS]. 893 All non-primary blocks share the same block structure and are 894 canonicalized as specified in [BPBIS] with the following exception. 896 o If the service being applied is a confidentiality service, then 897 the Block Type Code, Block Number, Block Processing Control Flags, 898 CRC Type and CRC Field (if present), and Block Data Length fields 899 MUST NOT be included in the canonicalization. Confidentiality 900 services are used solely to convert the Block Type Specific Data 901 Fields from plain-text to cipher-text. 903 o Reserved flags MUST NOT be included in any canonicalization as it 904 is not known if those flags will change in transit. 906 These canonicalization algorithms assume that Endpoint IDs do not 907 change from the time at which a security source adds a security block 908 to a bundle and the time at which a node processes that security 909 block. 911 Cipher suites MAY define their own canonicalization algorithms and 912 require the use of those algorithms over the ones provided in this 913 specification. In the event of conflicting canonicalization 914 algorithms, cipher suite algorithms take precedence over this 915 specification. 917 5. Security Processing 919 This section describes the security aspects of bundle processing. 921 5.1. Bundles Received from Other Nodes 923 Security blocks MUST be processed in a specific order when received 924 by a security-aware node. The processing order is as follows. 926 o All BCB blocks in the bundle MUST be evaluated prior to evaluating 927 any BIBs in the bundle. When BIBs and BCBs share a security 928 target, BCBs MUST be evaluated first and BIBs second. 930 5.1.1. Receiving BCB Blocks 932 If a received bundle contains a BCB, the receiving node MUST 933 determine whether it has the responsibility of decrypting the BCB 934 security target and removing the BCB prior to delivering data to an 935 application at the node or forwarding the bundle. 937 If the receiving node is the destination of the bundle, the node MUST 938 decrypt any BCBs remaining in the bundle. If the receiving node is 939 not the destination of the bundle, the node MAY decrypt the BCB if 940 directed to do so as a matter of security policy. 942 If the security policy of a security-aware node specifies that a 943 bundle should have applied confidentiality to a specific security 944 target and no such BCB is present in the bundle, then the node MUST 945 process this security target in accordance with the security policy. 946 This MAY involve removing the security target from the bundle. If 947 the removed security target is the payload block, the bundle MAY be 948 discarded. 950 If an encrypted payload block cannot be decrypted (i.e., the 951 decryption key cannot be deduced or decryption fails), then the 952 bundle MUST be discarded and processed no further. If an encrypted 953 security target other than the payload block cannot be decrypted then 954 the associated security target and all security blocks associated 955 with that target MUST be discarded and processed no further. In both 956 cases, requested status reports (see [BPBIS]) MAY be generated to 957 reflect bundle or block deletion. 959 When a BCB is decrypted, the recovered plain-text MUST replace the 960 cipher-text in the security target Block Type Specific Data Fields. 961 If the Block Data Length field was modified at the time of encryption 962 it MUST be updated to reflect the decrypted block length. 964 If a BCB contains multiple security targets, all security targets 965 MUST be processed when the BCB is processed. Errors and other 966 processing steps SHALL be made as if each security target had been 967 represented by an individual BCB with a single security target. 969 5.1.2. Receiving BIB Blocks 971 If a received bundle contains a BIB, the receiving node MUST 972 determine whether it has the final responsibility of verifying the 973 BIB security target and removing it prior to delivering data to an 974 application at the node or forwarding the bundle. If a BIB check 975 fails, the security target has failed to authenticate and the 976 security target SHALL be processed according to the security policy. 977 A bundle status report indicating the failure MAY be generated. 978 Otherwise, if the BIB verifies, the security target is ready to be 979 processed for delivery. 981 A BIB MUST NOT be processed if the security target of the BIB is also 982 the security target of a BCB in the bundle. Given the order of 983 operations mandated by this specification, when both a BIB and a BCB 984 share a security target, it means that the security target MUST have 985 been encrypted after it was integrity signed and, therefore, the BIB 986 cannot be verified until the security target has been decrypted by 987 processing the BCB. 989 If the security policy of a security-aware node specifies that a 990 bundle should have applied integrity to a specific security target 991 and no such BIB is present in the bundle, then the node MUST process 992 this security target in accordance with the security policy. This 993 MAY involve removing the security target from the bundle. If the 994 removed security target is the payload or primary block, the bundle 995 MAY be discarded. This action may occur at any node that has the 996 ability to verify an integrity signature, not just the bundle 997 destination. 999 If a receiving node does not have the final responsibility of 1000 verifying the BIB it MAY still attempt to verify the BIB to prevent 1001 the needless forwarding of corrupt data. If the check fails, the 1002 node SHALL process the security target in accordance to local 1003 security policy. It is RECOMMENDED that if a payload integrity check 1004 fails at a waypoint that it is processed in the same way as if the 1005 check fails at the destination. If the check passes, the node MUST 1006 NOT remove the BIB prior to forwarding. 1008 If a BIB contains multiple security targets, all security targets 1009 MUST be processed if the BIB is processed by the Node. Errors and 1010 other processing steps SHALL be made as if each security target had 1011 been represented by an individual BIB with a single security target. 1013 5.2. Bundle Fragmentation and Reassembly 1015 If it is necessary for a node to fragment a bundle payload, and 1016 security services have been applied to that bundle, the fragmentation 1017 rules described in [BPBIS] MUST be followed. As defined there and 1018 summarized here for completeness, only the payload block may be 1019 fragmented; security blocks, like all extension blocks, can never be 1020 fragmented. 1022 Due to the complexity of payload block fragmentation, including the 1023 possibility of fragmenting payload block fragments, integrity and 1024 confidentiality operations are not to be applied to a bundle 1025 representing a fragment. Specifically, a BCB or BIB MUST NOT be 1026 added to a bundle if the "Bundle is a Fragment" flag is set in the 1027 Bundle Processing Control Flags field. 1029 Security processing in the presence of payload block fragmentation 1030 MAY be handled by other mechanisms outside of the BPSec protocol or 1031 by applying BPSec blocks in coordination with an encapsulation 1032 mechanism. 1034 6. Key Management 1036 There exist a myriad of ways to establish, communicate, and otherwise 1037 manage key information in a DTN. Certain DTN deployments might 1038 follow established protocols for key management whereas other DTN 1039 deployments might require new and novel approaches. BPSec assumes 1040 that key management is handled as a separate part of network 1041 management and this specification neither defines nor requires a 1042 specific key management strategy. 1044 7. Security Policy Considerations 1046 When implementing BPSec, several policy decisions must be considered. 1047 This section describes key policies that affect the generation, 1048 forwarding, and receipt of bundles that are secured using this 1049 specification. No single set of policy decisions is envisioned to 1050 work for all secure DTN deployments. 1052 o If a bundle is received that contains more than one security 1053 operation, in violation of BPSec, then the BPA must determine how 1054 to handle this bundle. The bundle may be discarded, the block 1055 affected by the security operation may be discarded, or one 1056 security operation may be favored over another. 1058 o BPAs in the network MUST understand what security operations they 1059 should apply to bundles. This decision may be based on the source 1060 of the bundle, the destination of the bundle, or some other 1061 information related to the bundle. 1063 o If a waypoint has been configured to add a security operation to a 1064 bundle, and the received bundle already has the security operation 1065 applied, then the receiver MUST understand what to do. The 1066 receiver may discard the bundle, discard the security target and 1067 associated BPSec blocks, replace the security operation, or some 1068 other action. 1070 o It is recommended that security operations only be applied to the 1071 blocks that absolutely need them. If a BPA were to apply security 1072 operations such as integrity or confidentiality to every block in 1073 the bundle, regardless of need, there could be downstream errors 1074 processing blocks whose contents must be inspected or changed at 1075 every hop along the path. 1077 o Adding a BIB to a security target that has already been encrypted 1078 by a BCB is not allowed. If this condition is likely to be 1079 encountered, there are (at least) three possible policies that 1080 could handle this situation. 1082 1. At the time of encryption, an integrity signature may be 1083 generated and added to the BCB for the security target as 1084 additional information in the security result field. 1086 2. The encrypted block may be replicated as a new block and 1087 integrity signed. 1089 3. An encapsulation scheme may be applied to encapsulate the 1090 security target (or the entire bundle) such that the 1091 encapsulating structure is, itself, no longer the security 1092 target of a BCB and may therefore be the security target of a 1093 BIB. 1095 8. Security Considerations 1097 Given the nature of DTN applications, it is expected that bundles may 1098 traverse a variety of environments and devices which each pose unique 1099 security risks and requirements on the implementation of security 1100 within BPSec. For these reasons, it is important to introduce key 1101 threat models and describe the roles and responsibilities of the 1102 BPSec protocol in protecting the confidentiality and integrity of the 1103 data against those threats. This section provides additional 1104 discussion on security threats that BPSec will face and describes how 1105 BPSec security mechanisms operate to mitigate these threats. 1107 It should be noted that BPSEC addresses only the security of data 1108 traveling over the DTN, not the underlying DTN itself. Additionally, 1109 BPSec addresses neither the fitness of externally-defined 1110 cryptographic methods nor the security of their implementation. It 1111 is the responsibility of the BPSec implementer that appropriate 1112 algorithms and methods are chosen. Furthermore, the BPSec protocol 1113 does not address threats which share computing resources with the DTN 1114 and/or BPSec software implementations. These threats may be 1115 malicious software or compromised libraries which intend to intercept 1116 data or recover cryptographic material. Here, it is the 1117 responsibility of the BPSec implementer to ensure that any 1118 cryptographic material, including shared secret or private keys, is 1119 protected against access within both memory and storage devices. 1121 The threat model described here is assumed to have a set of 1122 capabilities identical to those described by the Internet Threat 1123 Model in [RFC3552], but the BPSec threat model is scoped to 1124 illustrate threats specific to BPSec operating within DTN 1125 environments and therefore focuses on man-in-the-middle (MITM) 1126 attackers. 1128 8.1. Attacker Capabilities and Objectives 1130 BPSec was designed to protect against MITM threats which may have 1131 access to a bundle during transit from its source, Alice, to its 1132 destination, Bob. A MITM node, Mallory, is a non-cooperative node 1133 operating on the DTN between Alice and Bob that has the ability to 1134 receive bundles, examine bundles, modify bundles, forward bundles, 1135 and generate bundles at will in order to compromise the 1136 confidentiality or integrity of data within the DTN. For the 1137 purposes of this section, any MITM node is assumed to effectively be 1138 security-aware even if it does not implement the BPSec protocol. 1140 There are three classes of MITM nodes which are differentiated based 1141 on their access to cryptographic material: 1143 o Unprivileged Node: Mallory has not been provisioned within the 1144 secure environment and only has access to cryptographic material 1145 which has been publicly-shared. 1147 o Legitimate Node: Mallory is within the secure environment and 1148 therefore has access to cryptographic material which has been 1149 provisioned to Mallory (i.e., K_M) as well as material which has 1150 been publicly-shared. 1152 o Privileged Node: Mallory is a privileged node within the secure 1153 environment and therefore has access to cryptographic material 1154 which has been provisioned to Mallory, Alice and/or Bob (i.e. 1155 K_M, K_A, and/or K_B) as well as material which has been publicly- 1156 shared. 1158 If Mallory is operating as a privileged node, this is tantamount to 1159 compromise; BPSec does not provide mechanisms to detect or remove 1160 Mallory from the DTN or BPSec secure environment. It is up to the 1161 BPSec implementer or the underlying cryptographic mechanisms to 1162 provide appropriate capabilities if they are needed. It should also 1163 be noted that if the implementation of BPSec uses a single set of 1164 shared cryptographic material for all nodes, a legitimate node is 1165 equivalent to a privileged node because K_M == K_A == K_B. 1167 A special case of the legitimate node is when Mallory is either Alice 1168 or Bob (i.e., K_M == K_A or K_M == K_B). In this case, Mallory is 1169 able to impersonate traffic as either Alice or Bob, which means that 1170 traffic to and from that node can be decrypted and encrypted, 1171 respectively. Additionally, messages may be signed as originating 1172 from one of the endpoints. 1174 8.2. Attacker Behaviors and BPSec Mitigations 1176 8.2.1. Eavesdropping Attacks 1178 Once Mallory has received a bundle, she is able to examine the 1179 contents of that bundle and attempt to recover any protected data or 1180 cryptographic keying material from the blocks contained within. The 1181 protection mechanism that BPSec provides against this action is the 1182 BCB, which encrypts the contents of its security target, providing 1183 confidentiality of the data. Of course, it should be assumed that 1184 Mallory is able to attempt offline recovery of encrypted data, so the 1185 cryptographic mechanisms selected to protect the data should provide 1186 a suitable level of protection. 1188 When evaluating the risk of eavesdropping attacks, it is important to 1189 consider the lifetime of bundles on a DTN. Depending on the network, 1190 bundles may persist for days or even years. If a bundle does persist 1191 on the network for years and the cipher suite used for a BCB provides 1192 inadequate protection, Mallory may be able to recover the protected 1193 data before that bundle reaches its intended destination. 1195 8.2.2. Modification Attacks 1197 As a node participating in the DTN between Alice and Bob, Mallory 1198 will also be able to modify the received bundle, including non-BPSec 1199 data such as the primary block, payload blocks, or block processing 1200 control flags as defined in [BPBIS]. Mallory will be able to 1201 undertake activities which include modification of data within the 1202 blocks, replacement of blocks, addition of blocks, or removal of 1203 blocks. Within BPSec, both the BIB and BCB provide integrity 1204 protection mechanisms to detect or prevent data manipulation attempts 1205 by Mallory. 1207 The BIB provides that protection to another block which is its 1208 security target. The cryptographic mechanisms used to generate the 1209 BIB should be strong against collision attacks and Mallory should not 1210 have access to the cryptographic material used by the originating 1211 node to generate the BIB (e.g., K_A). If both of these conditions 1212 are true, Mallory will be unable to modify the security target or the 1213 BIB and lead Bob to validate the security target as originating from 1214 Alice. 1216 Since BPSec security operations are implemented by placing blocks in 1217 a bundle, there is no in-band mechanism for detecting or correcting 1218 certain cases where Mallory removes blocks from a bundle. If Mallory 1219 removes a BCB block, but keeps the security target, the security 1220 target remains encrypted and there is a possibility that there may no 1221 longer be sufficient information to decrypt the block at its 1222 destination. If Mallory removes both a BCB (or BIB) and its security 1223 target there is no evidence left in the bundle of the security 1224 operation. Similarly, if Mallory removes the BIB but not the 1225 security target there is no evidence left in the bundle of the 1226 security operation. In each of these cases, the implementation of 1227 BPSec MUST be combined with policy configuration at endpoints in the 1228 network which describe the expected and required security operations 1229 that must be applied on transmission and are expected to be present 1230 on receipt. This or other similar out-of-band information is 1231 required to correct for removal of security information in the 1232 bundle. 1234 A limitation of the BIB may exist within the implementation of BIB 1235 validation at the destination node. If Mallory is a legitimate node 1236 within the DTN, the BIB generated by Alice with K_A can be replaced 1237 with a new BIB generated with K_M and forwarded to Bob. If Bob is 1238 only validating that the BIB was generated by a legitimate user, Bob 1239 will acknowledge the message as originating from Mallory instead of 1240 Alice. In order to provide verifiable integrity checks, both a BIB 1241 and BCB should be used. Alice creates a BIB with the protected data 1242 block as the security target and then creates a BCB with both the BIB 1243 and protected data block as its security targets. In this 1244 configuration, since Mallory is only a legitimate node and does not 1245 have access to Alice's key K_A, Mallory is unable to decrypt the BCB 1246 and replace the BIB. 1248 8.2.3. Topology Attacks 1250 If Mallory is in a MITM position within the DTN, she is able to 1251 influence how any bundles that come to her may pass through the 1252 network. Upon receiving and processing a bundle that must be routed 1253 elsewhere in the network, Mallory has three options as to how to 1254 proceed: not forward the bundle, forward the bundle as intended, or 1255 forward the bundle to one or more specific nodes within the network. 1257 Attacks that involve re-routing the packets throughout the network 1258 are essentially a special case of the modification attacks described 1259 in this section where the attacker is modifying fields within the 1260 primary block of the bundle. Given that BPSec cannot encrypt the 1261 contents of the primary block, alternate methods must be used to 1262 prevent this situation. These methods MAY include requiring BIBs for 1263 primary blocks, using encapsulation, or otherwise strategically 1264 manipulating primary block data. The specifics of any such 1265 mitigation technique are specific to the implementation of the 1266 deploying network and outside of the scope of this document. 1268 Furthermore, routing rules and policies may be useful in enforcing 1269 particular traffic flows to prevent topology attacks. While these 1270 rules and policies may utilize some features provided by BPSec, their 1271 definition is beyond the scope of this specification. 1273 8.2.4. Message Injection 1275 Mallory is also able to generate new bundles and transmit them into 1276 the DTN at will. These bundles may either be copies or slight 1277 modifications of previously-observed bundles (i.e., a replay attack) 1278 or entirely new bundles generated based on the Bundle Protocol, 1279 BPSec, or other bundle-related protocols. With these attacks 1280 Mallory's objectives may vary, but may be targeting either the bundle 1281 protocol or application-layer protocols conveyed by the bundle 1282 protocol. 1284 BPSec relies on cipher suite capabilities to prevent replay or forged 1285 message attacks. A BCB used with appropriate cryptographic 1286 mechanisms (e.g., a counter-based cipher mode) may provide replay 1287 protection under certain circumstances. Alternatively, application 1288 data itself may be augmented to include mechanisms to assert data 1289 uniqueness and then protected with a BIB, a BCB, or both along with 1290 other block data. In such a case, the receiving node would be able 1291 to validate the uniqueness of the data. 1293 9. Cipher Suite Authorship Considerations 1295 Cipher suite developers or implementers should consider the diverse 1296 performance and conditions of networks on which the Bundle Protocol 1297 (and therefore BPSec) will operate. Specifically, the delay and 1298 capacity of delay-tolerant networks can vary substantially. Cipher 1299 suite developers should consider these conditions to better describe 1300 the conditions when those suites will operate or exhibit 1301 vulnerability, and selection of these suites for implementation 1302 should be made with consideration to the reality. There are key 1303 differences that may limit the opportunity to leverage existing 1304 cipher suites and technologies that have been developed for use in 1305 traditional, more reliable networks: 1307 o Data Lifetime: Depending on the application environment, bundles 1308 may persist on the network for extended periods of time, perhaps 1309 even years. Cryptographic algorithms should be selected to ensure 1310 protection of data against attacks for a length of time reasonable 1311 for the application. 1313 o One-Way Traffic: Depending on the application environment, it is 1314 possible that only a one-way connection may exist between two 1315 endpoints, or if a two-way connection does exist, the round-trip 1316 time may be extremely large. This may limit the utility of 1317 session key generation mechanisms, such as Diffie-Hellman, as a 1318 two-way handshake may not be feasible or reliable. 1320 o Opportunistic Access: Depending on the application environment, a 1321 given endpoint may not be guaranteed to be accessible within a 1322 certain amount of time. This may make asymmetric cryptographic 1323 architectures which rely on a key distribution center or other 1324 trust center impractical under certain conditions. 1326 When developing new cipher suites for use with BPSec, the following 1327 information SHOULD be considered for inclusion in these 1328 specifications. 1330 o Cipher Suite Parameters. Cipher suites MUST define their 1331 parameter ids, the data types of those parameters, and their CBOR 1332 encoding. 1334 o Security Results. Cipher suites MUST define their security result 1335 ids, the data types of those results, and their CBOR encoding. 1337 o New Canonicalizations. Cipher suites MAY define new 1338 canonicalization algorithms as necessary. 1340 10. Defining Other Security Blocks 1342 Other security blocks (OSBs) may be defined and used in addition to 1343 the security blocks identified in this specification. Both the usage 1344 of BIB, BCB, and any future OSBs MAY co-exist within a bundle and MAY 1345 be considered in conformance with BPSec if each of the following 1346 requirements are met by any future identified security blocks. 1348 o Other security blocks (OSBs) MUST NOT reuse any enumerations 1349 identified in this specification, to include the block type codes 1350 for BIB and BCB. 1352 o An OSB definition MUST state whether it can be the target of a BIB 1353 or a BCB. The definition MUST also state whether the OSB can 1354 target a BIB or a BCB. 1356 o An OSB definition MUST provide a deterministic processing order in 1357 the event that a bundle is received containing BIBs, BCBs, and 1358 OSBs. This processing order MUST NOT alter the BIB and BCB 1359 processing orders identified in this specification. 1361 o An OSB definition MUST provide a canonicalization algorithm if the 1362 default non-primary-block canonicalization algorithm cannot be 1363 used to generate a deterministic input for a cipher suite. This 1364 requirement MAY be waived if the OSB is defined so as to never be 1365 the security target of a BIB or a BCB. 1367 o An OSB definition MAY NOT require any behavior of a BPSEC-BPA that 1368 is in conflict with the behavior identified in this specification. 1369 In particular, the security processing requirements imposed by 1370 this specification MUST be consistent across all BPSEC-BPAs in a 1371 network. 1373 o The behavior of an OSB when dealing with fragmentation MUST be 1374 specified and MUST NOT lead to ambiguous processing states. In 1375 particular, an OSB definition should address how to receive and 1376 process an OSB in a bundle fragment that may or may not also 1377 contain its security target. An OSB definition should also 1378 address whether an OSB may be added to a bundle marked as a 1379 fragment. 1381 Additionally, policy considerations for the management, monitoring, 1382 and configuration associated with blocks SHOULD be included in any 1383 OSB definition. 1385 NOTE: The burden of showing compliance with processing rules is 1386 placed upon the standards defining new security blocks and the 1387 identification of such blocks shall not, alone, require maintenance 1388 of this specification. 1390 11. IANA Considerations 1392 A registry of cipher suite identifiers will be required. 1394 11.1. Bundle Block Types 1396 This specification allocates two block types from the existing 1397 "Bundle Block Types" registry defined in [RFC6255] . 1399 Additional Entries for the Bundle Block-Type Codes Registry: 1401 +-------+-----------------------------+---------------+ 1402 | Value | Description | Reference | 1403 +-------+-----------------------------+---------------+ 1404 | TBD | Block Integrity Block | This document | 1405 | TBD | Block Confidentiality Block | This document | 1406 +-------+-----------------------------+---------------+ 1408 Table 1 1410 12. References 1412 12.1. Normative References 1414 [BPBIS] Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol", 1415 draft-ietf-dtn-bpbis-06 (work in progress), July 2016. 1417 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1418 Requirement Levels", BCP 14, RFC 2119, March 1997. 1420 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC 1421 Text on Security Considerations", BCP 72, RFC 3552, 1422 DOI 10.17487/RFC3552, July 2003, 1423 . 1425 [RFC6255] Blanchet, M., "Delay-Tolerant Networking Bundle Protocol 1426 IANA Registries", RFC 6255, May 2011. 1428 12.2. Informative References 1430 [COSE] Schaad, J., "CBOR Object Signing and Encryption (COSE)", 1431 draft-ietf-cose-msg-24 (work in progress), November 2016. 1433 [RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, 1434 R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant 1435 Networking Architecture", RFC 4838, April 2007. 1437 [RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell, 1438 "Bundle Security Protocol Specification", RFC 6257, May 1439 2011. 1441 [SBSP] Birrane, E., "Streamlined Bundle Security Protocol", 1442 draft-birrane-dtn-sbsp-01 (work in progress), October 1443 2015. 1445 Appendix A. Acknowledgements 1447 The following participants contributed technical material, use cases, 1448 and useful thoughts on the overall approach to this security 1449 specification: Scott Burleigh of the Jet Propulsion Laboratory, Amy 1450 Alford and Angela Hennessy of the Laboratory for Telecommunications 1451 Sciences, and Angela Dalton and Cherita Corbett of the Johns Hopkins 1452 University Applied Physics Laboratory. 1454 Authors' Addresses 1456 Edward J. Birrane, III 1457 The Johns Hopkins University Applied Physics Laboratory 1458 11100 Johns Hopkins Rd. 1459 Laurel, MD 20723 1460 US 1462 Phone: +1 443 778 7423 1463 Email: Edward.Birrane@jhuapl.edu 1464 Kenneth McKeever 1465 The Johns Hopkins University Applied Physics Laboratory 1466 11100 Johns Hopkins Rd. 1467 Laurel, MD 20723 1468 US 1470 Phone: +1 443 778 2237 1471 Email: Ken.McKeever@jhuapl.edu