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Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-26) exists of draft-ietf-p2psip-base-22 == Outdated reference: A later version (-09) exists of draft-ietf-p2psip-concepts-04 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 P2PSIP Working Group A. Knauf 3 Internet-Draft T C. Schmidt, Ed. 4 Intended status: Standards Track HAW Hamburg 5 Expires: April 12, 2013 G. Hege 6 daviko GmbH 7 M. Waehlisch 8 link-lab & FU Berlin 9 October 9, 2012 11 A Usage for Shared Resources in RELOAD (ShaRe) 12 draft-ietf-p2psip-share-00 14 Abstract 16 This document defines a RELOAD Usage for managing shared write access 17 to RELOAD Resources. Shared Resources in RELOAD (ShaRe) form a basic 18 primitive for enabling various coordination and notification schemes 19 among distributed peers. Access in ShaRe is controlled by a 20 hierarchical trust delegation scheme maintained within an access 21 list. A new USER-CHAIN-ACL access policy allows authorized peers to 22 write a Shared Resource without owning its corresponding certificate. 23 This specification also adds mechanisms to store Resources with a 24 variable name which is useful whenever peer-independent rendezvous 25 processes are required. 27 Status of this Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on April 12, 2013. 44 Copyright Notice 46 Copyright (c) 2012 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 3. Shared Resources in RELOAD . . . . . . . . . . . . . . . . . . 5 64 3.1. Mechanisms for Isolating Stored Data . . . . . . . . . . . 6 65 4. Access Control List Definition . . . . . . . . . . . . . . . . 7 66 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 7 67 4.2. Data Structure . . . . . . . . . . . . . . . . . . . . . . 8 68 5. Extension for Variable Resource Names . . . . . . . . . . . . 10 69 5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 10 70 5.2. Data Structure . . . . . . . . . . . . . . . . . . . . . . 10 71 5.3. Overlay Configuration Document Extension . . . . . . . . . 11 72 6. Access Control to Shared Resources . . . . . . . . . . . . . . 13 73 6.1. Granting Write Access . . . . . . . . . . . . . . . . . . 13 74 6.2. Revoking Write Access . . . . . . . . . . . . . . . . . . 14 75 6.3. Validating Write Access through an ACL . . . . . . . . . . 14 76 6.4. Operations of Storing Peers . . . . . . . . . . . . . . . 15 77 6.5. Operations of Accessing Peers . . . . . . . . . . . . . . 15 78 6.6. USER-CHAIN-ACL Access Policy . . . . . . . . . . . . . . . 15 79 7. ACL Kind Definition . . . . . . . . . . . . . . . . . . . . . 17 80 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 81 8.1. Resource Exhaustion . . . . . . . . . . . . . . . . . . . 18 82 8.2. Malicious or Misbehaving Storing Peer . . . . . . . . . . 18 83 8.3. Privacy Issues . . . . . . . . . . . . . . . . . . . . . . 18 84 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 85 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 86 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 87 11.1. Normative References . . . . . . . . . . . . . . . . . . . 21 88 11.2. Informative References . . . . . . . . . . . . . . . . . . 21 89 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 22 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 92 1. Introduction 94 This document defines a RELOAD Usage for managing shared write access 95 to RELOAD Resources and a mechanism to store Resources with a 96 variable name. The Usage for Shared Resources in RELOAD (ShaRe) 97 enables overlay users to share their exclusive write access to 98 specific Resource/Kind pairs with others. Shared Resources form a 99 basic primitive for enabling various coordination and notification 100 schemes among distributed peers. Write permission is controlled by 101 an Access Control List (ACL) Kind that maintains a chain of 102 Authorized Peers for a particular Shared Resource. A newly defined 103 USER-CHAIN-ACL access control policy enables shared write access in 104 RELOAD. 106 The Usage for Shared Resources in RELOAD is designed for jointly 107 coordinated group applications among distributed peers (e.g., third 108 party registration, or distributed conferencing, 109 see[I-D.knauf-p2psip-disco]). Of particular interest are rendezvous 110 processes, where a single identifier is linked to multiple, dynamic 111 instances of a distributed cooperative service. Shared write access 112 is based on a trust delegation mechanism. It transfers the 113 authorization to write a specific Kind data by storing logical Access 114 Control Lists. An ACL contains the ID of the Kind to be shared and 115 contains trust delegations from one authorized to another (previously 116 unauthorized) user. 118 Shared write access augments the RELOAD security model, which is 119 based on the restriction that peers are only allowed to write 120 resources at a small set of well defined locations (Resource-IDs) in 121 the overlay. Using the standard access control rules in RELOAD, 122 these locations are bound to the username or Node-ID in the peer's 123 certificate. This document extends the base policies to enable a 124 controlled write access for multiple users to a common Resource Id. 126 Additionally, this specification defines an optional mechanism to 127 store Resources with a variable Resource Name. It enables the 128 storage of Resources whose name complies to a specific pattern. 129 Definition of the pattern is arbitrary, but must contain the username 130 of the Resource creator. 132 2. Terminology 134 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 135 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 136 document are to be interpreted as described in [RFC2119]. 138 This document uses the terminology and definitions from the RELOAD 139 base [I-D.ietf-p2psip-base]and the peer-to-peer SIP concepts draft 140 [I-D.ietf-p2psip-concepts]. Additionally, the following terms are 141 used: 143 Shared Resource: The term Shared Resource in this document defines a 144 RELOAD Resource with its associated Kinds, that can be written or 145 overwritten by multiple RELOAD users following the specifications 146 in this document. 148 Access Control List: The term Access Control List in this document 149 defines a logical list of RELOAD users allowed to write a specific 150 RELOAD Resource/Kind pair by following the specifications in this 151 document. The list items are stored as Access Control List Kinds 152 that map trust delegations from user A to user B, where A is 153 allowed to write a Shared Resource and the Access Control List, 154 while B is a user that obtains write access to specified Kinds 155 from A. 157 Resource Owner: The term Resource Owner in this document defines a 158 RELOAD peer that initially stored a Resource to be shared. The 159 Resource Owner possesses the RELOAD certificate that grants write 160 access to a specific Resource/Kind pair using the RELOAD 161 certificate-based access control policies. 163 Authorized Peer: The term Authorized Peer in this document defines a 164 RELOAD peer that was granted write access to a Shared Resource by 165 permission of the Resource Owner or another Authorized Peer. 167 3. Shared Resources in RELOAD 169 A RELOAD user that owns a certificate for writing at a specific 170 overlay location can maintain one or more RELOAD Kinds that are 171 designated for a non-exclusive write access shared with other RELOAD 172 users. The mechanism to share those Resource/Kind pairs with a group 173 of users consists of two basic steps. 175 1. Storage of the Resource/Kind pairs to be shared. 177 2. Storage of an Access Control List (ACL) associated with those 178 Kinds. 180 ACLs are created by the Resource Owner and contain ACL items, each 181 delegating the permission of writing the shared Kind to a specific 182 user called Authorized Peer. For each shared Kind data, its Resource 183 owner stores a root item that initiates an Access Control List. 184 Trust delegation to the Authorized Peer can include the right to 185 further delegate the write permission, enabling a tree of trust 186 delegations with the Resource Owner as trust anchor at its root. 188 The Resource/Kind pair to be shared can be any RELOAD Kind that 189 complies to the following specifications: 191 Isolated Data Storage: To prevent concurrent writing from race 192 conditions, each data item stored within a Shared Resource SHALL 193 be exclusively maintained by the RELOAD user who created it. 194 Hence, Usages that allow the storage of Shared Resources are 195 REQUIRED to use either the array or dictionary data model and 196 apply additional mechanisms for isolating data as described in 197 Section 3.1. 199 Access Control Policy: To ensure write access to Shared Resource by 200 Authorized Peers, each Usage MUST use the USER-CHAIN-ACL access 201 policy as described in Section 6.6. 203 Resource Name Extension: To enable Shared Resources to be stored 204 using a variable resource name, this document defines an optional 205 ResourceNameExtension structure. It contains the Resource Name of 206 the Kind data to be stored and allows any receiver of a shared 207 data to validate whether the Resource Name hashes to the 208 Resource-ID. The ResourceNameExtension is made optional by 209 configuration. The ResourceNameExtension field is only present in 210 the Kind data structure when configured in the corresponding kind- 211 block of the overlay configuration document (for more details see 212 Section 5.3). If the configuration allows variable resource 213 names, a Kind using the USER-CHAIN-ACL policy MUST use the 214 ResourceNameExtension as initial field within the Kind data 215 structure definition. Otherwise the Kind data structure does not 216 contain the ResourceNameExtension structure. 218 3.1. Mechanisms for Isolating Stored Data 220 This section defines mechanisms to avoid race conditions while 221 concurrently writing an array or dictionary of a Shared Resource. 223 If a dictionary is used in the Shared Resource, the dictionary key 224 MUST be the Node-ID of the certificate that will be used to sign the 225 stored data. Thus data access is bound to the unique ID-holder. 227 If the data model of the Shared Resource is an array, the following 228 algorithm will generate an array index that avoids collisions. 230 1. Obtain the Node-ID of the certificate that will be used to sign 231 the stored data 233 2. Take the least significant 24 bits of that Node-ID 235 3. Concatenate an 8 bit long short individual index value to those 236 24 bit of the Node-ID 238 The resulting 32 bits long integer MUST be used as the index for 239 storing an array entry in a Shared Resource. The 8 bit individual 240 index can be incremented individually for further array entries and 241 allows for 256 distinct entries per Peer. 243 The mechanism to create the array index is related to the pseudo- 244 random algorithm to generate an SSRC identifier in RTP, see Section 245 8.1 in [RFC3550] for calculating the probability of a collision. 247 4. Access Control List Definition 249 4.1. Overview 251 An Access Control List (ACL) is a (self-managed) shared resource that 252 contains a list of AccessControlListItem structures as defined in 253 Section 4.2. Each entry delegates write access for a specific Kind 254 data to a single RELOAD user. An ACL enables the RELOAD user who is 255 authorized to write a specific Resource-ID to delegate his exclusive 256 write access to a specific Kind to further users of a RELOAD 257 instance. Each Access Control List data structure therefore carries 258 the information about who obtains write access, the Kind-ID of the 259 Resource to be shared, and whether delegation includes write access 260 to the ACL itself. The latter condition grants the right to delegate 261 write access further for the Authorized Peer. Access Control Lists 262 are stored at the same overlay location as the Shared Resource and 263 use the RELOAD array data model. They are initially created by the 264 Resource Owner. 266 Figure 1 shows an example of an Access Control List. We omit the 267 res_name_ext field to simplify illustration. The array entry at 268 index 0x123abc001 displays the initial creation of an ACL for a 269 Shared Resource of Kind-ID 1234 at the same Resource-ID. It 270 represents the root item of the trust delegation tree for this shared 271 RELOAD Kind. The root entry MUST contain the username of the 272 Resource owner in the "to_user" field and can only be written by the 273 owner of the public key certificate associated with this Resource-ID. 274 The allow_delegation (ad) flag for a root ACL item is set to 1 by 275 default. The array index is generated by using the mechanism for 276 isolating stored data as described in Section 3.1. Hence, the most 277 significant 24 bits of the array index (0x123abc) are the least 278 significant 24 bits of the Node-ID of the Resource Owner. 280 The array item at index 0x123abc002 represents the first trust 281 delegation to an Authorized Peer that is thus permitted to write to 282 the Shared Resource of Kind-ID 1234. Additionally, the Authorized 283 peer Alice is also granted (limited) write access to the ACL as 284 indicated by the allow_delegation flag (ad) set to 1. This 285 configuration authorizes Alice to store further trust delegations to 286 the Shared Resource, i.e., add items to the ACL. On the contrary, 287 index 0x456def001 illustrates trust delegation for Kind-ID 1234, in 288 which the Authorized Peer Bob is not allowed to grant access to 289 further peers (ad = 0). Each Authorized Peer signs its ACL items 290 with its own private key, which makes the item ownership transparent. 292 To manage Shared Resource access of multiple Kinds at a single 293 location, the Resource Owner can create new ACL entries that refer to 294 another Kind-ID as shown in array entry index 0x123abc003. Note that 295 overwriting existing items in an Access Control List that reference a 296 different Kind-ID revokes all trust delegations in the corresponding 297 subtree (see Section 6.2). Authorized Peers are only enabled to 298 overwrite existing ACL item they own. The Resource Owner is allowed 299 to overwrite any existing ACL item, but should be aware of its 300 consequences. 302 +------------------------------------------------------+ 303 | Access Control List | 304 +-----------+------------------------------+-----------+ 305 | #Index | Array Entries | signed by | 306 +-----------+------------------------------+-----------+ 307 | 123abc001 | to_user:Owner Kind:1234 ad:1 | Owner | 308 +-----------+------------------------------+-----------+ 309 | 123abc002 | to_user:Alice Kind:1234 ad:1 | Owner | 310 +-----------+------------------------------+-----------+ 311 | 123abc003 | to_user:Owner Kind:4321 ad:1 | Owner | 312 +-----------+------------------------------+-----------+ 313 | 123abc004 | to_user:Carol Kind:4321 ad:0 | Owner | 314 +-----------+------------------------------+-----------+ 315 | ... | ... | ... | 316 +-----------+------------------------------+-----------+ 317 | 456def001 | to_user:Bob Kind:1234 ad:0 | Alice | 318 +-----------+------------------------------+-----------+ 319 | ... | ... | ... | 320 +-----------+------------------------------+-----------+ 322 Figure 1: Simplified example of an Access Control including entries 323 for two different Kind-IDs and varying delegation (ad) configurations 325 Implementations of ShaRe should be aware that the trust delegation in 326 an Access Control List need not be loop free. Self-contained 327 circular trust delegation from A to B and B to A are syntactically 328 possible, even though not very meaningful. 330 4.2. Data Structure 332 The Kind data structure for the Access Control List is defined as 333 follows: 335 struct { 336 /* res_name_ext is optional, see documentation */ 337 ResourceNameExtension res_name_ext; 338 opaque to_user<0..2^16-1>; 339 KindId kind; 340 Boolean allow_delegation; 341 } AccessControlListItem; 342 The AccessControlListItem structure is composed of: 344 res_name_ext: This optional field contains the Resource Name of a 345 ResourceNameExtension (see Section 5.2) to be used by a Shared 346 Resource with variable resource name. This name serves the 347 storing peer for validating, whether a variable resources name 348 matches one of the predefined naming pattern from the 349 configuration document for this Kind. The presence of this field 350 is bound to a variable resource name element in the corresponding 351 kind-block of the configuration document whose "enable" attribute 352 is set to true (see Section 5.3). Otherwise, if the "enable" 353 attribute is false, the res_name_ext field SHALL NOT be present in 354 the Kind data structure. 356 to_user: This field contains the username of the RELOAD peer that 357 obtains write permission to the Shared Resource. 359 kind: This field contains the Kind-ID of the Shared Resource. 361 allow_delegation: If true, this Boolean flag indicates that the 362 Authorized Peer in the 'to_user' field is allowed to add 363 additional entries to the ACL for the specified Kind-ID. 365 5. Extension for Variable Resource Names 367 5.1. Overview 369 In certain use cases such as conferencing (c.f. 370 [I-D.knauf-p2psip-disco]) it is desirable to increase the flexibility 371 of a peer in using Resource Names beyond those defined by the 372 username or Node-ID fields in its certificate. For this purpose, 373 this document presents the concept for variable Resources Names that 374 enables providers of RELOAD instances to define relaxed naming 375 schemes for overlay Resources. 377 Each RELOAD node uses a certificate to identify itself using its user 378 name (or Node-ID) while storing data under a specific Resource-ID. 379 The specifications in this document scheme adhere to this paradigm, 380 but enable a RELOAD peer to store values of Resource Names that are 381 derived from the username in its certificate. This is done by using 382 a Resource Name with a variable substring that still matches the 383 username in the certificate using a pattern defined in the overlay 384 configuration document. Thus despite being variable, an allowable 385 Resource Name remains tied to the Owner's certificate. A sample 386 pattern might be formed as follows. 388 Example Pattern: 389 .*-conf-$USER@$DOMAIN 391 When defining the pattern, care must be taken to avoid conflicts 392 arising from two usernames of witch one is a substring of the other. 393 In such cases, the holder of the shorter name could threaten to block 394 the resources of the longer-named peer by choosing the variable part 395 of a Resource Name to contain the entire longer username. This 396 problem can easily be mitigated by delimiting the variable part of 397 the pattern from the username part by some fixed string, that by 398 convention is not part of a username (e.g., the "-conf-" in the above 399 Example). 401 5.2. Data Structure 403 This section defines the optional ResourceNameExtension structure for 404 every Kind that uses the USER-CHAIN-ACL access control policy. 406 enum { pattern (1), 407 (255)} ResourceNameType; 409 struct { 410 ResourceNameType type; 411 uint16 length; 412 select(type) { 413 case pattern: 414 opaque resource_name<0..2^16-1>; 416 /* Types can be extended */ 417 } 418 } ResourceNameExtension 420 The content of the ResourceNameExtension consist of 422 length: This field contains the length of the remaining data 423 structure. It is only used to allow for further extensions to 424 this data structure. 426 The content of the rest of the data structure depends of the 427 ResourceNameType. Currently, the only defined type is "pattern". 429 If the type is "pattern", then the following data structure contains 430 an opaque <0..2^16-1> field containing the Resource Name of the Kind 431 being stored. The type "pattern" further indicates that the Resource 432 Name MUST match to one of the variable resource name pattern defined 433 for this Kind in the configuration document. 435 The ResourceNameType enum and the ResourceNameExtension structure can 436 be extended by further Usages to define other naming schemes. 438 5.3. Overlay Configuration Document Extension 440 This section extends the overlay configuration document by defining 441 new elements for patterns relating resource names to user names. 443 The element serves as a container for one 444 or multiple sub-elements. It is an additional parameter 445 within the kind block and has a boolean "enable" attribute that 446 indicates, if true, that the overlay provider allows variable 447 resource names for this Kind. The default value of the "enable" 448 attribute is "false". In the absence of a 449 element for a Kind using the USER-CHAIN-ACL access policy (see 450 Section 6.6), implementors SHOULD assume this default value. 452 A element MUST be present if the "enabled" attribute of its 453 parent element is set to true. Each element defines a 454 pattern for constructing extended resource names for a single Kind. 455 It is of type xsd:string and interpreted as a regular expression. In 456 this regular expression, $USER and $DOMAIN are used as variables for 457 the corresponding parts of the string in the certificate username 458 field (with $USER preceding and $DOMAIN succeeding the '@'). Both 459 variables MUST be present in any given pattern definition. If no 460 pattern is defined for a Kind or the "enabled" attribute is false, 461 allowable Resource Names are restricted to the username of the signer 462 for Shared Resource. 464 The Relax NG Grammar for the Variable Resource Names Extension reads: 466 468 namespace share = "urn:ietf:params:xml:ns:p2p:config-base:share" 470 472 kind-parameter &= element share:variable-resource-names { 474 attribute enable { xsd:boolean } 476 478 element pattern { xsd:string }* 479 }? 481 6. Access Control to Shared Resources 483 6.1. Granting Write Access 485 Write access to a Kind that is intended to be shared with other 486 RELOAD users can solely be issued by the Resource Owner. A Resource 487 Owner can share RELOAD Kinds by using the following procedure. 489 o The Resource Owner stores an ACL root item at the Resource-ID of 490 the Shared Resource. The root item contains the resource name 491 extension field (see Section 5.2), the username of the Resource 492 Owner and Kind-ID of the Shared Resource. The allow_delegation 493 flag is set to 1. The index of array data structure MUST be 494 generated as described in Section 3.1 496 o Further ACL items for this Kind-ID stored by the Resource Owner 497 will delegate write access to Authorized Peers. These ACL items 498 contain the same resource name extension field, the username of 499 the Authorized Peer and the Kind-Id of the Shared Resource. 500 Optionally, the Resource Owner sets the "ad" to 1 (the default 501 equals 0) to enable the Authorized Peer to further delegate write 502 access. Each succeeding ACL item created by the Resource Owner 503 can be stored in the numerical order of the array index starting 504 with the index of the root item incremented by one. 506 An Authorized Peer with delegation allowance ("ad"=1) can extend the 507 access to an existing Shared Resource as follows. 509 o An Authorized Peer can store additional ACL items at the 510 Resource-ID of the Shared Resource. These ACL items contain the 511 resource name extension field, the username of the newly 512 Authorized Peer, and the Kind-Id of the Shared Resource. 513 Optionally, the "ad" flag is set to 1 for allowing the Authorized 514 Peer to further delegate write access. The array index MUST be 515 generated as described in Section 3.1. Each succeeding ACL item 516 can be stored in the numerical order of the array index. 518 A store request by an Authorized Peer that attempts to overwrite any 519 ACL item signed by another Peer is unauthorized and causes an 520 Error_Forbidden response from the Storing Peer. Such access 521 conflicts could be caused by an array index collision. However, the 522 probability of a collision of two or more identical array indices 523 will be negligibly low using the mechanism for isolating stored data 524 (see Section 3.1) 526 6.2. Revoking Write Access 528 Write permissions are revoked by storing a non-existent value 529 [I-D.ietf-p2psip-base] at the corresponding item of the Access 530 Control List. Revoking a permission automatically invalidates all 531 delegations performed by that user including all subsequent 532 delegations. This allows to invalidate entire subtrees of the 533 delegations tree with only a single operation. Overwriting the root 534 item with a non-existent value of an Access List invalidates the 535 entire delegations tree. 537 An existing ACL item MUST only be overwritten by the user who 538 initially stored the corresponding entry, or by the Resource Owner 539 that is allowed to overwrite all ACL items for revoking write access. 541 6.3. Validating Write Access through an ACL 543 Access Control Lists are used to transparently validate authorization 544 of peers for writing a data value at a Shared Resource. Thereby it 545 is assumed that the validating peer is in possession of the complete 546 and most recent ACL for a specific Resource/Kind pair. The 547 corresponding procedure consists of recursively traversing the trust 548 delegation tree and proceeds as follows. 550 1. Obtain the username of the certificate used for signing the data 551 stored at the Shared Resource. 553 2. Validate that an item of the corresponding ACL (i.e., for this 554 Resource/Kind pair) contains a "to_user" field whose value equals 555 the username obtained in step 1. If the Shared Resource under 556 examination is an Access Control List Kind, further validate if 557 the "ad" flag is set to 1. 559 3. Select the username of the certificate that was used to sign the 560 ACL item obtained in step 2. 562 4. Validate that an item of the corresponding ACL contains a 563 "to_user" field whose value equals the username obtained in step 564 3. Additionally validate that the "ad" flag is set to 1. 566 5. Repeat steps 3 and 4 until the "to_user" value is equal to the 567 username of the signer of the previously selected ACL item. This 568 final ACL item is expected to be the root item of this ACL which 569 SHALL be further validated by verifying that the root item was 570 signed by the owner of the ACL Resource. 572 The trust delegation chain is valid if and only if all verification 573 steps succeed. In this case, the creator of the data value of the 574 Shared Resource is an Authorized Peer. 576 Note that the ACL validation procedure can be omitted whenever the 577 creator of data at a Shared Resource is the Resource Owner itself. 578 The latter can be verified by its public key certificate as defined 579 in Section 6.6. 581 6.4. Operations of Storing Peers 583 Storing peers, i.e., peers at which Shared Resource and ACL are 584 physically stored, are responsible for controlling storage attempts 585 to a Shared Resource and its corresponding Access Control List. To 586 assert the USER-CHAIN-ACL access policy (see Section 6.4), a storing 587 peer MUST perform the access validation procedure described in 588 Section 6.3 on any incoming store request using the most recent 589 Access Control List for every Kind that uses the USER-CHAIN-ACL 590 policy. It SHALL further ensure that only the Resource Owner stores 591 new ACL root items for Shared Resources. 593 6.5. Operations of Accessing Peers 595 Accessing peers, i.e., peers that fetch a Shared Resource, MAY 596 validate that the originator of a Shared Resource was authorized to 597 store data at this Resource-ID by processing the corresponding ACL. 598 To enable an accessing peer to perform the access validation 599 procedure described in Section 6.3, it first needs to obtain the most 600 recent Access Control List in the following way. 602 1. Send a Stat request to the Resource-ID of the Shared Resource to 603 obtain all array indexes of stored ACL Kinds. 605 2. Fetch all indexes of existing ACL items at this Resource-ID by 606 using the array ranges retrieved in the Stat request answer. 608 Peers can cache previously fetched Access Control Lists up to the 609 maximum lifetime of an individual item. Since stored values could 610 have been modified or invalidated prior to their expiration, an 611 accessing peer SHOULD use a Stat request to check for updates prior 612 to using the data cache. 614 6.6. USER-CHAIN-ACL Access Policy 616 This document specifies an additional access control policy to the 617 RELOAD base draft [I-D.ietf-p2psip-base]. The USER-CHAIN-ACL policy 618 allows Authorized Peers to write a Shared Resource, even though they 619 do not own the corresponding certificate. Additionally, the USER- 620 CHAIN-ACL allows the storage of Kinds with a variable resource name 621 that are following one of the specified naming pattern. Hence, on an 622 inbound store request on a Kind that uses the USER-CHAIN-ACL access 623 policy, the following rules MUST be applied: 625 In the USER-CHAIN-ACL policy, a given value MUST be written or 626 overwritten, if either one of USER-MATCH or USER-NODE-MATCH 627 (mandatory if the data model is dictionary) access policies of the 628 base document [I-D.ietf-p2psip-base] applies. 630 Otherwise, the value MUST be written if the certificate of the signer 631 contains a username that matches to one of the variable resource name 632 pattern (c.f. Section 5) specified in the configuration document 633 and, additionally, the hashed Resource Name matches the Resource-ID. 634 The Resource Name of the Kind to be stored MUST be taken from the 635 mandatory ResourceNameExtension field in the corresponding Kind data 636 structure. 638 Otherwise, the value MUST be written if the ACL validation procedure 639 described in Section 6.3 has been successfully applied. 641 7. ACL Kind Definition 643 This section defines the ACCESS-CONTROL-LIST Kind previously 644 described in this document. 646 Name: ACCESS-CONTROL-LIST 648 Kind IDs: The Resource Name for ACCESS-CONTROL-LIST Kind-ID is the 649 Resource Name of the Kind that will be shared by using the ACCESS- 650 CONTROL-LIST Kind. 652 Data Model: The data model for the ACCESS-CONTROL-LIST Kind-ID is 653 array. The array indexes are formed by using the mechanism for 654 isolated stored data as described in Section 3.1 656 Access Control: USER-CHAIN-ACL (see Section 6.6) 658 8. Security Considerations 660 In this section we discuss security issues that are relevant to the 661 usage of shared resources in RELOAD. 663 8.1. Resource Exhaustion 665 Joining a RELOAD overlay inherently poses a certain resource load on 666 a peer, because it has to store and forward data for other peers. In 667 common RELOAD semantics, each Resource ID and thus position in the 668 overlay may only be written by a limited set of peers - often even 669 only a single peer, which limits this burden. In the case of Shared 670 Resources, a single resource may be written by multiple peers, who 671 may even write an arbitrary number of entries (e.g., delegations in 672 the ACL). This leads to an enhanced use of resources at individual 673 overlay nodes. The problem of resource exhaustion can easily be 674 mitigated for Usages based on the ShaRe-Usage by imposing 675 restrictions on size, i.e., element for a certain Kind in 676 the configuration document. 678 8.2. Malicious or Misbehaving Storing Peer 680 The RELOAD overlay is designed to operate despite the presence of a 681 small set of misbehaving peers. This is not different for Shared 682 Resources since a small set of malicious peers does not disrupt the 683 functionality of the overlay in general, but may have implications 684 for the peers needing to store or access information at the specific 685 locations in the ID space controlled by a malicious peer. A storing 686 peer could withhold stored data which results in a denial of service 687 to the group using the specific resource. But it could not return 688 forged data, since the validity of any stored data can be 689 independently verified using the attached signatures. 691 8.3. Privacy Issues 693 All data stored in the Shared Resource is publicly readable, thus 694 applications requiring privacy need to encrypt the data. The ACL 695 needs to be stored unencrypted, thus the list members of a group 696 using a Shared Resource will always be publicly visible. 698 9. IANA Considerations 700 TODO: register Kind-ID code point at the IANA 702 10. Acknowledgments 704 This work was stimulated by fruitful discussions in the P2PSIP 705 working group and SAM research group. We would like to thank all 706 active members for constructive thoughts and feedback. In 707 particular, the authors would like to thank (in alphabetical order) 708 Lothar Grimm, Cullen Jennings, Peter Musgrave, Joerg Ott, Marc Petit- 709 Huguenin, Peter Pogrzeba, and Jan Seedorf. This work was partly 710 funded by the German Federal Ministry of Education and Research, 711 projects HAMcast and Mindstone. 713 11. References 715 11.1. Normative References 717 [I-D.ietf-p2psip-base] 718 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and 719 H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) 720 Base Protocol", draft-ietf-p2psip-base-22 (work in 721 progress), July 2012. 723 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 724 Requirement Levels", BCP 14, RFC 2119, March 1997. 726 11.2. Informative References 728 [I-D.ietf-p2psip-concepts] 729 Bryan, D., Willis, D., Shim, E., Matthews, P., and S. 730 Dawkins, "Concepts and Terminology for Peer to Peer SIP", 731 draft-ietf-p2psip-concepts-04 (work in progress), 732 October 2011. 734 [I-D.knauf-p2psip-disco] 735 Knauf, A., Hege, G., Schmidt, T., and M. Waehlisch, "A 736 RELOAD Usage for Distributed Conference Control (DisCo)", 737 draft-knauf-p2psip-disco-05 (work in progress), May 2012. 739 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 740 Jacobson, "RTP: A Transport Protocol for Real-Time 741 Applications", STD 64, RFC 3550, July 2003. 743 Appendix A. Change Log 745 The following changes have been made from version 746 draft-knauf-p2psip-share-02: 748 1. Editorial improvements 750 2. Updated References 752 The following changes have been made from version 753 draft-knauf-p2psip-share-01: 755 1. Simplified the ACL data structure in response to WG feedback 757 2. Added ResourceNameExtension data structure to simplify the use of 758 variable resource names 760 3. Restructured document 762 4. Many editorial improvements 764 The following changes have been made from version 765 draft-knauf-p2psip-share-00: 767 1. Integrated the USER-PATTERN-MATCH access policy into USER-CHAIN- 768 ACL 770 2. Access Control List Kind uses USER-CHAIN-ACL exclusively 772 3. Resources to be shared use USER-CHAIN-ACL exclusively 774 4. More precise specification of mandatory User_name and 775 Resource_name fields for Shared Resources 777 5. Added mechanism for isolating stored data to prevent race 778 conditions while concurrent storing 780 6. XML Extension for variable resource names uses its own namespace 782 7. Many editorial improvements 784 Authors' Addresses 786 Alexander Knauf 787 HAW Hamburg 788 Berliner Tor 7 789 Hamburg D-20099 790 Germany 792 Phone: +4940428758067 793 Email: alexanderknauf@gmail.com 794 URI: 796 Thomas C. Schmidt 797 HAW Hamburg 798 Berliner Tor 7 799 Hamburg D-20099 800 Germany 802 Email: schmidt@informatik.haw-hamburg.de 803 URI: http://inet.cpt.haw-hamburg.de/members/schmidt 805 Gabriel Hege 806 daviko GmbH 807 Am Borsigturm 50 808 Berlin D-13507 809 Germany 811 Phone: +493043004344 812 Email: hege@daviko.com 813 URI: 815 Matthias Waehlisch 816 link-lab & FU Berlin 817 Hoenower Str. 35 818 Berlin D-10318 819 Germany 821 Email: mw@link-lab.net 822 URI: http://www.inf.fu-berlin.de/~waehl