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Internet Research Task Force (IRTF)                          S. BurleighRequest for Comments: 6260                    Jet Propulsion Laboratory,Category: Experimental                California Institute of TechnologyISSN: 2070-1721                                               May 2011Compressed Bundle Header Encoding (CBHE)Abstract   This document describes a convention by which Delay-Tolerant   Networking (DTN) Bundle Protocol (BP) "convergence-layer" adapters   may represent endpoint identifiers in a compressed form within the   primary blocks of bundles, provided those endpoint identifiers   conform to the structure prescribed by this convention.   Compressed Bundle Header Encoding (CBHE) compression is a   convergence-layer adaptation.  It is opaque to bundle processing.   Therefore, it has no impact on the interoperability of different   Bundle Protocol implementations, but instead affects only the   interoperability of different convergence-layer adaptation   implementations.   This document is a product of the Delay-Tolerant Networking Research   Group and has been reviewed by that group.  No objections to its   publication as an RFC were raised.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for examination, experimental implementation, and   evaluation.   This document defines an Experimental Protocol for the Internet   community.  This document is a product of the Internet Research Task   Force (IRTF).  The IRTF publishes the results of Internet-related   research and development activities.  These results might not be   suitable for deployment.  This RFC represents the consensus of the   Delay-Tolerant Networking Research Group of the Internet Research   Task Force (IRTF).  Documents approved for publication by the IRSG   are not a candidate for any level of Internet Standard; seeSection 2   of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6260.Burleigh                      Experimental                      [Page 1]

RFC 6260                          CBHE                          May 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.Table of Contents1. Introduction ....................................................21.1. Requirements Language ......................................32. Compression Convention ..........................................32.1. Constraints ................................................32.2. Method .....................................................63. Specification ...................................................73.1. Transmission ...............................................73.2. Reception ..................................................74. IANA Considerations .............................................85. Security Considerations ........................................106. References .....................................................116.1. Normative References ......................................116.2. Informative References ....................................11Appendix A. Acknowledgments .......................................121.  Introduction   This document describes a convention by which Delay-Tolerant   Networking (DTN) Bundle Protocol (BP) [RFC5050] "convergence-layer"   adapters may represent endpoint identifiers (EIDs) in a compressed   form within the primary blocks of bundles, provided those endpoint   identifiers conform to the structure prescribed by this convention.   Each DTN bundle's primary block contains the following four BP   endpoint identifiers, of which any two, any three, or even all four   may be lexically identical: the endpoint identifiers of the bundle's   source, destination, report-to endpoint, and current custodian.  Each   EID is a Uniform Record Identifier (URI) as defined by [RFC3986].   More specifically, each BP EID is a URI consisting of a "scheme name"   followed by ":", followed by a sequence of characters --   historically, termed the "scheme-specific part" (SSP) in DTN   specifications -- conforming to URI syntax as defined byRFC 3986.Burleigh                      Experimental                      [Page 2]

RFC 6260                          CBHE                          May 2011   A degree of block compression is provided by the design of the   primary block: the scheme names and scheme-specific parts of the four   endpoints' IDs -- up to eight NULL-terminated strings -- are   concatenated at the end of the block in a variable-length character   array called a "dictionary", enabling each EID to be represented by a   pair of integers indicating the offsets (within the dictionary) of   the EID's scheme name and scheme-specific part.  Duplicate strings   may be omitted from the dictionary, so the actual number of   concatenated NULL-terminated strings in the dictionary may be less   than eight, and two or more of the scheme name or scheme-specific   part offsets in the block may have the same value.  Moreover, the   eight offsets in the primary block are encoded as Self-Delimiting   Numeric Values (SDNVs), which shrink to fit the encoded values; when   the total length of the dictionary is less than 127 bytes, all eight   offsets can be encoded into just eight bytes.   However, these strategems do not prevent the scheme names and   especially the scheme-specific parts themselves from being lengthy   strings of ASCII text.  It is therefore still possible for the length   of a bundle's primary header to be a very large fraction of the total   length of the bundle when the bundle's payload is relatively small,   as is anticipated for a number of DTN applications such as space   flight operations (and as is in any case true of bundles carrying BP   administrative records).   The Compressed Bundle Header Encoding (CBHE) convention was developed   to improve DTN transmission efficiency for such applications by   further reducing the number of bytes used by convergence-layer   adapters to represent EIDs in the primary blocks of bundles.1.1.  Requirements Language   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [RFC2119].2.  Compression Convention2.1.  Constraints   The only valid scheme name for BP EIDs identified to date is "dtn".   Although no specification of valid SSP syntax for URIs composed   within the "dtn" scheme has yet been formally defined, the syntax on   which rough agreement has been reached in practice is unsuitable for   CBHE's compression procedures.  For the purposes of CBHE, then, this   document defines an additional URI scheme named "ipn".  As noted inSection 4, IANA has registered this new URI scheme.Burleigh                      Experimental                      [Page 3]

RFC 6260                          CBHE                          May 2011   Compressed Bundle Header Encoding (CBHE) is possible only when all   endpoint IDs in the primary block of a given bundle are "CBHE   conformant".  The following two forms of endpoint ID are CBHE   conformant: (a) the null endpoint ID "dtn:none" and (b) any endpoint   ID formed within the "ipn" scheme.   The SSP of every URI formed within the "ipn" scheme must comprise:   1.  A sequence of ASCII numeric digits representing an integer in the       range 1 to (2^64 - 1), termed the "node number" of the URI.   2.  An ASCII period ('.') character.   3.  A sequence of ASCII numeric digits representing an integer in the       range 0 to (2^64 - 1), termed the "service number" of the URI.   The node number notionally identifies a BP node.  However, since CBHE   is not used universally in Delay-Tolerant Networking, it must not be   assumed that all BP nodes are identified by node numbers.   Negative integers and integers larger than (2^64 - 1) cannot be used   as node numbers because they cannot be encoded into the SDNVs that   are used for representation of scheme name and SSP offsets in the   primary blocks of bundles and therefore could not be compressed as   described later in this specification.  Node number zero is reserved   for representation of the null endpoint ID in the compressed form   described later; decompressing a compressed null EID must always   yield the standard null endpoint ID URI "dtn:none".   The service number notionally functions as a de-multiplexing token.   When the bundle payload is a protocol data unit of some protocol that   has its own de-multiplexing identifiers, the service number may   function in a manner similar to that of the protocol number in an IP   packet, characterizing the encapsulated protocol; alternatively, the   service number may function in a manner similar to that of the port   number in a UDP datagram.  Service numbers enable inbound bundles'   application data units to be de-multiplexed to instances of   application functionality that are designed to process them, so that   effective communication relationships can be developed between bundle   producers and consumers.   A service number must not be negative or exceed (2^64 - 1) for the   same reason that a node number must not do so.   For example, "ipn:9.37" would be a CBHE-conformant endpoint ID.Burleigh                      Experimental                      [Page 4]

RFC 6260                          CBHE                          May 2011   Conversion of a CBHE-conformant EID to and from a tuple of two   integers is therefore straightforward: all characters in the EID   other than the node number and service number are constant (as   defined by the "ipn" scheme definition), and the node number and   service number are taken as the two integers of the tuple.  This ease   of conversion enables an array of pairs of integers to serve the same   function as a dictionary of ASCII string EIDs.   Note, however, that CBHE decompression cannot faithfully recreate the   dictionary of a compressed primary block from an array of integer   pairs unless the order of the scheme names and scheme-specific part   strings in the dictionary of the original, uncompressed block is   known.  (The Bundle Protocol Specification does not require that the   strings in the dictionary appear in any particular order and does not   require that redundant strings be omitted from the dictionary.)   Therefore, a further precondition to CBHE compression is that the   strings in the dictionary of the bundle to be compressed must be   exactly as follows, in this order and without addition:   1.  The scheme name of the destination endpoint ID.   2.  The scheme-specific part of the destination endpoint ID.   3.  The scheme name of the source endpoint ID, if and only if       different from any prior string in the dictionary.   4.  The scheme-specific part of the source endpoint ID, if and only       if different from any prior string in the dictionary.   5.  The scheme name of the report-to endpoint ID, if and only if       different from any prior string in the dictionary.   6.  The scheme-specific part of the report-to endpoint ID, if and       only if different from any prior string in the dictionary.   7.  The scheme name of the current custodian endpoint ID, if and only       if different from any prior string in the dictionary.   8.  The scheme-specific part of the current custodian endpoint ID, if       and only if different from any prior string in the dictionary.   Note: this constraint implies that a bundle that includes any   extension blocks containing EID-references to endpoint IDs other than   the block's destination, source, report-to, and current custodian   cannot be CBHE compressed since such compression would result in a   dictionary that would deviate from this structure.Burleigh                      Experimental                      [Page 5]

RFC 6260                          CBHE                          May 20112.2.  Method   When the constraints enumerated above are met, the CBHE block   compression method can be applied by the convergence-layer adapter   (CLA) at the time the bundle is transmitted via a convergence-layer   protocol.  In a CBHE-compressed primary block, the eight SDNVs that   normally contain EIDs' scheme name and SSP offsets within the   dictionary are instead used to contain the eight integer values   listed below, in the order shown:   1.  The node number of the destination endpoint ID, or zero if the       destination endpoint is the null endpoint.   2.  The service number of the destination endpoint ID, or zero if the       destination endpoint is the null endpoint.   3.  The node number of the source endpoint ID, or zero if the source       endpoint is the null endpoint.   4.  The service number of the source endpoint ID, or zero if the       source endpoint is the null endpoint.   5.  The node number of the report-to endpoint ID, or zero if the       report-to endpoint is the null endpoint.   6.  The service number of the report-to endpoint ID, or zero if the       report-to endpoint is the null endpoint.   7.  The node number of the current custodian endpoint ID, or zero if       the current custodian endpoint is the null endpoint.   8.  The service number of the current custodian endpoint ID, or zero       if the current custodian endpoint is the null endpoint.   Further, the dictionary is omitted from the primary block and the   primary block's dictionary length is set to zero.   Upon reception, the receiving convergence-layer adaptation de-   compresses the block by simply reversing the process so that the   bundle presented to the bundle protocol agent has the standard form   (i.e., the dictionary is reconstituted).Burleigh                      Experimental                      [Page 6]

RFC 6260                          CBHE                          May 20113.  Specification   CBHE compression is a convergence-layer adaptation.  It is opaque to   bundle processing.  Therefore, it has no impact on the   interoperability of different Bundle Protocol implementations, but   instead affects only the interoperability of different convergence-   layer adaptation implementations.   Bundle Protocol convergence-layer adapters that conform to the CBHE   specification must implement the following procedures.3.1.  Transmission   When and only when required by the bundle protocol agent to transmit   a bundle whose primary block's endpoint IDs satisfy the constraints   identified inSection 2.1, the CLA MAY encode the primary block of   the bundle in accordance with the CBHE compression convention   described inSection 2.2 UNLESS the CLA to which the bundle is to be   transmitted is known not to be CBHE conformant.  Note that CBHE   compression may be applied only if the receiving CLA is known or   presumed to be CBHE conformant, i.e., able to decode the encoded   primary block.  Knowledge as to whether or not a receiving CLA is (or   might be) CBHE conformant may be asserted by node administration   and/or may be inferred from reception of a CBHE-compressed bundle as   noted inSection 3.2.3.2.  Reception   Upon receiving a bundle whose dictionary length is zero (and only in   this circumstance), a CBHE-conformant convergence-layer adapter:   1.  MAY infer that the CLA from which the bundle was received is CBHE       conformant.   2.  MUST decode the primary block of the bundle in accordance with       the CBHE compression convention described inSection 2.2 before       delivering it to the bundle protocol agent.   Note that when a CLA that is not CBHE conformant receives a bundle   whose dictionary length is zero, it has no choice but to pass it to   the bundle agent without modification.  In this case, the bundle   protocol agent will be unable to dispatch the received bundle,   because it will be unable to determine the destination endpoint; the   bundle will be judged to be malformed.  The behavior of the bundle   protocol agent in this circumstance is an implementation matter.Burleigh                      Experimental                      [Page 7]

RFC 6260                          CBHE                          May 20114.  IANA Considerations   IANA has registered a provisional registration (per [RFC4395]) for a   URI scheme for CBHE, with the string "ipn" as the scheme name, as   follows:   URI scheme name: "ipn"   Status: provisional   URI scheme syntax:   This specification uses the Augmented Backus-Naur Form (ABNF)   notation of [RFC5234], including the core ABNF syntax rule for DIGIT   defined by that specification.   ipn-uri = "ipn:" ipn-hier-part   ipn-hier-part = node-nbr nbr-delim service-nbr ; a path-rootless   node-nbr = 1*DIGIT   nbr-delim = "."   service-nbr = 1*DIGIT   None of the reserved characters defined in the generic URI syntax are   used as delimiters within URIs of the IPN scheme.   URI scheme semantics: URIs of the IPN scheme are used as endpoint   identifiers in the Delay-Tolerant Networking (DTN) Bundle Protocol   (BP) [RFC5050] as described inSection 2.1.   Encoding considerations: URIs of the IPN scheme are encoded   exclusively in US-ASCII characters.   Applications and/or protocols that use this URI scheme name: the   Delay-Tolerant Networking (DTN) Bundle Protocol (BP) [RFC5050].   Interoperability considerations: as noted above, URIs of the IPN   scheme are encoded exclusively in US-ASCII characters.   Security considerations:   o  Reliability and consistency: none of the BP endpoints identified      by the URIs of the IPN scheme are guaranteed to be reachable at      any time, and the identity of the processing entities operating on      those endpoints is never guaranteed by the Bundle Protocol itself.      Bundle authentication as defined by the Bundle Security Protocol      is required for this purpose.Burleigh                      Experimental                      [Page 8]

RFC 6260                          CBHE                          May 2011   o  Malicious construction: malicious construction of a conformant      IPN-scheme URI is limited to the malicious selection of node      numbers and the malicious selection of service numbers.  That is,      a maliciously constructed IPN-scheme URI could be used to direct a      bundle to an endpoint that might be damaged by the arrival of that      bundle or, alternatively, to declare a false source for a bundle      and thereby cause incorrect processing at a node that receives the      bundle.  In both cases (and indeed in all bundle processing), the      node that receives a bundle should verify its authenticity and      validity before operating on it in any way.   o  Back-end transcoding: the limited expressiveness of URIs of the      IPN scheme effectively eliminates the possibility of threat due to      errors in back-end transcoding.   o  Rare IP address formats: not relevant, as IP addresses do not      appear anywhere in conformant IPN-scheme URIs.   o  Sensitive information: because IPN-scheme URIs are used only to      represent the identities of Bundle Protocol endpoints, the risk of      disclosure of sensitive information due to interception of these      URIs is minimal.  Examination of IPN-scheme URIs could be used to      support traffic analysis; where traffic analysis is a plausible      danger, bundles should be conveyed by secure convergence-layer      protocols that do not expose endpoint IDs.   o  Semantic attacks: the simplicity of IPN-scheme URI syntax      minimizes the possibility of misinterpretation of a URI by a human      user.   Contact:      Scott Burleigh      Jet Propulsion Laboratory,      California Institute of Technology      scott.c.burleigh@jpl.nasa.gov      +1 (800) 393-3353   Author/Change controller:      Scott Burleigh      Jet Propulsion Laboratory,      California Institute of Technology      scott.c.burleigh@jpl.nasa.gov      +1 (800) 393-3353   References: S. Burleigh, "Compressed Bundle Header Encoding (CBHE)",RFC 6260, May 2011.Burleigh                      Experimental                      [Page 9]

RFC 6260                          CBHE                          May 20115.  Security Considerations   The Bundle Security Protocol (BSP) may, under some conditions, insert   additional endpoint ID strings into the dictionary of a bundle and   reference those strings in BSP extension blocks.  Because a bundle   that includes any extension blocks containing EID-references to   endpoint IDs other than the block's destination, source, report-to,   and current custodian cannot be CBHE compressed, bundles cannot be   compressed under those conditions.   Specifically, the specification detailed above implies that a bundle   cannot be CBHE compressed when the security-source endpoint for the   Bundle Authentication Block (BAB) is noted in the dictionary   (typically, because there is no other way for the receiving bundle   protocol agent to determine the security-source endpoint); when the   security-destination endpoint for the BAB is noted in the dictionary   (in the rare case that the receiving endpoint is not the security-   destination endpoint); when the security-source endpoint for the   Payload Integrity Block (PIB), Payload Confidentiality Block (PCB),   or Extension Security Block (ESB) is not the source endpoint; or when   the security-destination endpoint for the PIB, PCB, or ESB is not the   destination endpoint.   Also, the CBHE-conformance inference mechanism identified inSection 3.2 introduces a possible denial-of-service attack.   Malicious code could issue a CHBE-compressed bundle whose source EID   falsely identifies the bundle origin as some node whose CLA is not   CBHE conformant; a CBHE-conformant CLA receiving this bundle might   incorrectly infer that the CLA at the purported source node was CBHE   conformant and might then begin CBHE compressing all bundles that it   sends to that node, thus preventing those bundles from being   dispatched by the node's bundle protocol agent.  Nodes can defend   against such an attack by requiring Bundle Authentication Blocks and   discarding any inference of CBHE conformance for the CLAs at nodes   from which inauthentic bundles are received.   These caveats aside, CBHE introduces no new security considerations   beyond those discussed in the DTN Bundle ProtocolRFC 5050 [RFC5050]   and Bundle Security ProtocolRFC 6257 [RFC6257] Specifications.Burleigh                      Experimental                     [Page 10]

RFC 6260                          CBHE                          May 20116.  References6.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform              Resource Identifier (URI): Generic Syntax", STD 66,RFC 3986, January 2005.   [RFC5050]  Scott, K. and S. Burleigh, "Bundle Protocol              Specification",RFC 5050, November 2007.   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF", STD 68,RFC 5234, January 2008.   [RFC6257]  Symington, S., Farrell, S., Weiss, H., and P. Lovell,              "Bundle Security Protocol Specification",RFC 6257,              May 2011.6.2.  Informative References   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and              Registration Procedures for New URI Schemes",BCP 35,RFC 4395, February 2006.Burleigh                      Experimental                     [Page 11]

RFC 6260                          CBHE                          May 2011Appendix A.  Acknowledgments   This research was carried out at the Jet Propulsion Laboratory,   California Institute of Technology, under a contract with the   National Aeronautics and Space Administration.  Government   sponsorship acknowledged.Author's Address   Scott Burleigh   Jet Propulsion Laboratory, California Institute of Technology   4800 Oak Grove Drive, m/s 301-490   Pasadena, CA  91109   USA   Phone: +1 818 393 3353   EMail: Scott.C.Burleigh@jpl.nasa.govBurleigh                      Experimental                     [Page 12]