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Versions: 00 01

Delay-Tolerant Networking Research Group                      E. Birrane
Internet-Draft                                                   JHU/APL
Intended status: Experimental                               May 27, 2014
Expires: November 28, 2014


           Streamlined Bundle Security Protocol Specification
                        draft-irtf-dtnrg-sbsp-01

Abstract

   This document defines a streamlined bundle security protocol, which
   provides data authentication, integrity, and confidentiality services
   for the Bundle Protocol.  Capabilities are provided to protect the
   bundle payload, and additional data that may be included within the
   bundle, along a single path through a network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 28, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 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.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Related Documents . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Security Block Definitions  . . . . . . . . . . . . . . . . .   6
     2.1.  Block Identification  . . . . . . . . . . . . . . . . . .   7
     2.2.  Abstract Security Block . . . . . . . . . . . . . . . . .   9
     2.3.  Block Ordering  . . . . . . . . . . . . . . . . . . . . .  12
     2.4.  Bundle Authentication Block . . . . . . . . . . . . . . .  12
     2.5.  Block Integrity Block . . . . . . . . . . . . . . . . . .  14
     2.6.  Block Confidentiality Block . . . . . . . . . . . . . . .  15
     2.7.  Block Interactions  . . . . . . . . . . . . . . . . . . .  16
     2.8.  Parameters and Result Fields  . . . . . . . . . . . . . .  18
     2.9.  BSP Block Example . . . . . . . . . . . . . . . . . . . .  20
   3.  Security Processing . . . . . . . . . . . . . . . . . . . . .  21
     3.1.  Canonical Forms . . . . . . . . . . . . . . . . . . . . .  21
       3.1.1.  Bundle Canonicalization . . . . . . . . . . . . . . .  22
       3.1.2.  Block Canonicalization  . . . . . . . . . . . . . . .  22
       3.1.3.  Considerations  . . . . . . . . . . . . . . . . . . .  25
     3.2.  Endpoint ID Confidentiality . . . . . . . . . . . . . . .  26
     3.3.  Bundles Received from Other Nodes . . . . . . . . . . . .  26
       3.3.1.  Receiving BAB Blocks  . . . . . . . . . . . . . . . .  26
       3.3.2.  Receiving BCB Blocks  . . . . . . . . . . . . . . . .  27
       3.3.3.  Receiving BIB Blocks  . . . . . . . . . . . . . . . .  27
     3.4.  Bundle Fragmentation and Reassembly . . . . . . . . . . .  28
     3.5.  Reactive Fragmentation  . . . . . . . . . . . . . . . . .  29
   4.  Key Management  . . . . . . . . . . . . . . . . . . . . . . .  29
   5.  Policy Considerations . . . . . . . . . . . . . . . . . . . .  29
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  30
   7.  Conformance . . . . . . . . . . . . . . . . . . . . . . . . .  31
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  31
     8.1.  Bundle Block Types  . . . . . . . . . . . . . . . . . . .  31
     8.2.  Cipher Suite Flags  . . . . . . . . . . . . . . . . . . .  31
     8.3.  Parameters and Results  . . . . . . . . . . . . . . . . .  32
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  33
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  33
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  34
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

   This document defines security features for the Bundle Protocol
   [RFC5050] intended for use in delay-tolerant networks, in order to
   provide Delay-Tolerant Networking (DTN) security services.





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   The Bundle Protocol is used in DTNs that overlay multiple networks,
   some of which may be challenged by limitations such as intermittent
   and possibly unpredictable loss of connectivity, long or variable
   delay, asymmetric data rates, and high error rates.  The purpose of
   the Bundle Protocol is to support interoperability across such
   stressed networks.

   The stressed environment of the underlying networks over which the
   Bundle Protocol operates makes it important for the DTN to be
   protected from unauthorized use, and this stressed environment poses
   unique challenges for the mechanisms needed to secure the Bundle
   Protocol.  Furthermore, DTNs may be deployed in environments where a
   portion of the network might become compromised, posing the usual
   security challenges related to confidentiality, integrity, and
   availability.

   This document describes the Streamlined Bundle Security Protocol
   (SBSP), which provides security services for blocks within a bundle
   from the bundle source to the bundle destination.  Specifically, the
   SBSP provides authentication, integrity, and confidentiality for
   bundles along a path through a DTN.

   SBSP applies, by definition, only to those nodes that implement it,
   known as "security-aware" nodes.  There MAY be other nodes in the DTN
   that do not implement SBSP.  All nodes can interoperate with the
   exception that SBSP security operations can only happen at SBSP
   security-aware nodes.

1.1.  Related Documents

   This document is best read and understood within the context of the
   following other DTN documents:

   "Delay-Tolerant Networking Architecture" [RFC4838] defines the
   architecture for delay-tolerant networks, but does not discuss
   security at any length.

   The DTN Bundle Protocol [RFC5050] defines the format and processing
   of the blocks used to implement the Bundle Protocol, excluding the
   security-specific blocks defined here.

   The Bundle Security Protocol [RFC6257] introduces the concepts of
   security blocks for authentication, confidentiality, and integrity.
   The SBSP is based off of this document.







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1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   We introduce the following terminology for purposes of clarity.

   o  Source - the bundle node from which a bundle originates.

   o  Destination - the bundle node to which a bundle is ultimately
      destined.

   o  Forwarder - the bundle node that forwarded the bundle on its most
      recent hop.

   o  Intermediate Receiver, Waypoint, or "Next Hop" - the neighboring
      bundle node to which a forwarder forwards a bundle.

   o  Path - the ordered sequence of nodes through which a bundle passes
      on its way from source to destination.  The path is not
      necessarily known by the bundle, or any bundle-aware nodes.

   Figure 1 below is adapted from [RFC5050] and shows four bundle nodes
   (denoted BN1, BN2, BN3, and BN4) that reside above some transport
   layer(s).  Three distinct transport and network protocols (denoted
   T1/N1, T2/N2, and T3/N3) are also shown.

   +---------v-|   +->>>>>>>>>>v-+     +->>>>>>>>>>v-+   +-^---------+
   | BN1     v |   | ^   BN2   v |     | ^   BN3   v |   | ^  BN4    |
   +---------v-+   +-^---------v-+     +-^---------v-+   +-^---------+
   | T1      v |   + ^  T1/T2  v |     + ^  T2/T3  v |   | ^  T3     |
   +---------v-+   +-^---------v-+     +-^---------v +   +-^---------+
   | N1      v |   | ^  N1/N2  v |     | ^  N2/N3  v |   | ^  N3     |
   +---------v-+   +-^---------v +     +-^---------v-+   +-^---------+
   |         >>>>>>>>^         >>>>>>>>>>^         >>>>>>>>^         |
   +-----------+   +------------+      +-------------+   +-----------+
   |                     |                    |                      |
   |<--  An Internet --->|                    |<--- An Internet  --->|
   |                     |                    |                      |


    Figure 1: Bundle Nodes Sit at the Application Layer of the Internet
                                   Model

   BN1 originates a bundle that it forwards to BN2.  BN2 forwards the
   bundle to BN3, and BN3 forwards the bundle to BN4.  BN1 is the source



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   of the bundle and BN4 is the destination of the bundle.  BN1 is the
   first forwarder, and BN2 is the first intermediate receiver; BN2 then
   becomes the forwarder, and BN3 the intermediate receiver; BN3 then
   becomes the last forwarder, and BN4 the last intermediate receiver,
   as well as the destination.

   If node BN2 originates a bundle (for example, a bundle status report
   or a custodial signal), which is then forwarded on to BN3, and then
   to BN4, then BN2 is the source of the bundle (as well as being the
   first forwarder of the bundle) and BN4 is the destination of the
   bundle (as well as being the final intermediate receiver).

   We introduce the following security-specific DTN terminology.

   o  Security-Service - the security features supported by this
      specification: authentication, integrity, and confidentiality.

   o  Security-Source - a bundle node that adds a security block to a
      bundle.

   o  Security-Destination - a bundle node that evaluates a security
      block from a bundle.  When a security-service is applied hop-by-
      hop, the security-destination is the next intermediate receiver.
      Otherwise, the security-destination is the same as the bundle
      destination.

   o  Security-Target - the portion of a bundle (e.g., the primary
      block, payload block, extension block, or entire bundle) that
      receives a security-service as part of a security-operation.

   o  Security Block - a single instance of a SBSP extension block in a
      bundle.

   o  Security-Operation - the application of a security-service to a
      specific security-target, notated as OP(security-service,
      security-target).  For example, OP(authentication, bundle) or
      OP(confidentiality, payload).  Every security-operation in a
      bundle MUST be unique, meaning that a security-service can only be
      applied to a security-target once in a bundle.  A security-
      operation MAY be implemented by one or more security blocks.

   Referring to Figure 1 again:

   If the bundle that originates at BN1 is given security blocks by BN1,
   then BN1 is the security-source for those blocks as well as being the
   source of the bundle.  If the bundle that originates at BN1 is then
   given a security block by BN2, then BN2 is the security-source for
   that block even though BN1 remains the bundle source.



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   A bundle MAY have multiple security blocks and these blocks MAY have
   different security-sources.  Each security block in a bundle will be
   associated with a specific security-operation.  All security blocks
   comprising a security-operation MUST have the same security-source
   and security-destination.

   The destination of all security blocks in a bundle MUST be the bundle
   destination, with the exception of authentication security blocks,
   whose destination is the next hop along the bundle path.  In a DTN,
   there is typically no guarantee that a bundle will visit a particular
   intermediate receiver during its journey, or that a particular series
   of intermediate receivers will be visited in a particular order.
   Security-destinations different from bundle destinations would place
   a tight (and possibly intractable) coupling between security and
   routing services in an overlay network.

   As required in [RFC5050], forwarding nodes MUST transmit blocks in a
   bundle in the same order in which they were received.  This
   requirement applies to all DTN nodes, not just ones that implement
   security processing.  Blocks in a bundle MAY be added or deleted
   according to the applicable specification, but those blocks that are
   both received and transmitted MUST be transmitted in the same order
   that they were received.

   If a node is not security-aware, then it forwards the security blocks
   in the bundle unchanged unless the bundle's block processing flags
   specify otherwise.  If a network has some nodes that are not
   security-aware, then the block processing flags SHOULD be set such
   that security blocks are not discarded at those nodes solely because
   they cannot be processed there.  Except for this, the non-security-
   aware nodes are transparent relay points and are invisible as far as
   security processing is concerned.

2.  Security Block Definitions

   There are three types of security blocks that MAY be included in a
   bundle.  These are the Bundle Authentication Block (BAB), the Block
   Integrity Block (BIB), and the Block Confidentiality Block (BCB).

      The BAB is used to ensure the authenticity and integrity of the
      bundle along a single hop from forwarder to intermediate receiver.
      As such, BABs operate between topologically adjacent nodes.
      Security-aware nodes MAY choose to require BABs from a given
      neighbor in the network in order to receive and process a received
      bundle.

      The BIB is used to ensure the authenticity and integrity of its
      security-target from the BIB security-source, which creates the



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      BIB, to the bundle destination, which verifies the BIB
      authenticator.  The authentication information in the BIB MAY
      (when possible) be verified by any node in between the BIB
      security-source and the bundle destination.

      The BCB indicates that the security-target has been encrypted, in
      whole or in part, at the BCB security-source in order to protect
      its content while in transit to the bundle destination.

   Certain cipher suites may allow or require multiple instances of a
   block to appear in the bundle.  For example, an authentication cipher
   suite may require two security blocks, one before the payload block
   and one after.  Despite the presence of two security blocks, they
   both comprise the same security-operation - OP(authentication,bundle)
   in this example.

   A security-operation MUST NOT be applied more than once in a bundle.
   For example, the two security-operations: OP(integrity, payload) and
   OP(integrity, payload) are considered redundant and MUST NOT appear
   together in a bundle.  However, the two security operations
   OP(integrity, payload) and OP(integrity, extension_block_1) MAY both
   be present in the bundle.  Also, the two security operations
   OP(integrity, extension_block_1) and OP(integrity, extension_block_2)
   are unique and may both appear in the same bundle.

   Many of the fields in these block definitions use the Self-Delimiting
   Numeric Value (SDNV) type whose format and encoding is as defined in
   [RFC5050].

2.1.  Block Identification

   This specification requires that every target block of a security
   operation be uniquely identifiable.  In cases where there can only be
   a single instance of a block in the bundle (as is the case with the
   primary block and the payload block) then the unique identifier is
   simply the block type.  These blocks are described as "singleton
   blocks".  It is possible that a bundle may contain multiple instances
   of a block type.  In such a case, each instance of the block type
   must be uniquely identifiable and the block type itself is not
   sufficient for this identification.  These blocks are described as
   "non-singleton blocks".

   The definition of the extension block header from [RFC5050] does not
   provide additional identifying information for a block beyond the
   block type.  The addition of an occurrence number to the block is
   necessary to identify the block instance in the bundle.  This section
   describes the use of an Artificial EID (AEID) reference in a block
   header to add unique identification for non-singleton blocks.



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   Figure 7 of [RFC5050] illustrates that an EID reference in a block
   header is the 2-tuple of the reference scheme and the reference
   scheme specific part (SSP), each of which are encoded as SDNVs.  The
   AEID MUST encode the occurrence number in the reference scheme SDNV
   and MUST set the reference SSP to 0.  A reference SSP value of 0 is
   an invalid offset for an SSP in the bundle dictionary and, therefore,
   the use of 0 in this field identifies the reference as an AEID.

   The occurrence number MAY be any positive value that is not already
   present as an occurrence number for the same block type in the
   bundle.  These numbers are independent of relative block position
   within the bundle, and whether blocks of the same type have been
   added or removed from the bundle.  Once an AEID has been added to a
   block instance, it MUST NOT be changed until all security operations
   that target the block instance have been removed from the bundle.

   If a node wishes to apply a security operation to a target block it
   MUST determine whether the target block is a singleton block or a
   non-singleton block.  If the target block is non-singleton, then the
   node MUST find the AEID for the target.  If an AEID is not present in
   the target block header then the node MAY choose to either cancel the
   security operation or add an AEID to the block, in accordance with
   security policy.

   If a node chooses to add an AEID to a target block header it MUST
   perform the following activities.

   o  The "Block contains an EID reference field" flag MUST be set for
      the target block, if it is not already set.

   o  The EID reference count for the block MUST be updated to reflect
      the addition of the AEID.

   o  The scheme offset of the AEID MUST be a value greater than 0.  The
      scheme offset MUST NOT be the same as any other AEID of any other
      block in the bundle sharing the same block type.

   o  The SSP offset of the AEID MUST be the value 0.  There MUST NOT be
      any other EID in the block header that has a value of 0 for the
      SSP offset.

   If there is no AEID present in a block, and if a node is unable to
   add an AEID by following the above process, then the block MUST NOT
   have an SBSP security operation applied to it.

   It is RECOMMENDED that every block in a bundle other than the primary
   and payload blocks be treated as a non-singleton block.  However, the




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   identification of singleton blocks SHOULD be in accordance with the
   security policy of a node.

2.2.  Abstract Security Block

   Each security block uses the Canonical Bundle Block Format as defined
   in [RFC5050].  That is, each security block is comprised of the
   following elements:

   o  Block Type Code

   o  Block Processing Control Flags

   o  Block EID Reference List (OPTIONAL)

   o  Block Data Length

   o  Block Type Specific Data Fields

   Since the three security block types have most fields in common, we
   can shorten the description of the block type specific data fields if
   we first define an abstract security block (ASB) and then specify
   each of the real blocks in terms of the fields that are present/
   absent in an ASB.  Note that no bundle ever contains an actual ASB,
   which is simply a specification artifact.

   The structure of an Abstract Security Block is given in Figure 2.
   Although the diagram hints at a fixed-format layout, this is purely
   for the purpose of exposition.  Except for the "type" field, all
   fields are variable in length.

   +-----------------------------+----------------------------------+
   |    Block Type Code (BYTE)   | Processing Control Flags (SDNV)  |
   +-----------------------------+----------------------------------+
   |        EID Reference Count and List (Compound List)            |
   +-----------------------------+----------------------------------+
   |    Block Length (SDNV)      |    Security Target (Compound)    |
   +-----------------------------+----------------------------------+
   |    Cipher suite ID (SDNV)   |     Cipher suite Flags (SDNV)    |
   +-----------------------------+----------------------------------+
   |    Params Length (SDNV)     |      Params Data (Compound)      |
   +-----------------------------+----------------------------------+
   |    Result Length (SDNV)     |      Result Data (Compound)      |
   +-----------------------------+----------------------------------+

                Figure 2: Abstract Security Block Structure

   An ASB consists of the following fields, some of which are optional.



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   o  Block-Type Code (Byte) - as described in [RFC5050].  The block-
      type codes for security blocks are:

      *  BundleAuthenticationBlock - BAB: 0x02

      *  BlockIntegrityBlock - BIB: 0x03

      *  BlockConfidentialityBlock - BCB: 0x04

   o  Block Processing Control Flags (SDNV) - as described in [RFC5050].
      There are no general constraints on the use of the block
      processing control flags, and some specific requirements are
      discussed later.

   o  (OPTIONAL) EID Reference Count and List - as described in
      [RFC5050].  Presence of the EID reference field is indicated by
      the setting of the "Block contains an EID reference field"
      (EID_REF) bit of the block processing control flags.  If no EID
      fields are present, then the composite field itself MUST be
      omitted entirely and the EID_REF bit MUST be unset.  A count field
      of zero is not permitted.  The possible EIDs are:

         (OPTIONAL) Security-source - specifies the security-source for
         the block.  If this is omitted, then the source of the bundle
         is assumed to be the security-source unless otherwise indicated
         by policy or associated cipher suite definition.  When present,
         the security-source MUST be the first EID in the list.

         (OPTIONAL) AEID - specifies an identifier that can be used to
         uniquely identify an instance of a non-singleton block.  This
         field MUST be present for non-singleton blocks.  This field
         MUST NOT be present for singleton blocks, such as the primary
         block and the payload block.  The construction of the AEID is
         discussed in Section 2.1.

   o  Block Length (SDNV) - as described in [RFC5050].

   o  Block type specific data fields as follows:

      *  Security-Target (Compound) - Uniquely identifies the target of
         the associated security-operation.

         As discussed in Section 2.1 a singleton block is identified by
         its block type and a non-singleton block is identified by the
         combination of its block type and an occurrence number.  The
         security-target is a compound field that contains the block
         type (as a byte) and occurrence number (as an SDNV).




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         The occurrence number of a singleton block MUST be set to 0.
         The occurrence number of a non-singleton block MUST be set to
         the scheme offset of the AEID associated with the block being
         targeted by the security operation.

      *  Cipher suite ID (SDNV)

      *  Cipher suite flags (SDNV)

      *  (OPTIONAL) Cipher Suite Parameters - compound field of the next
         two items.

         +  Cipher suite parameters length (SDNV) - specifies the length
            of the next field, which is the cipher suite-parameters data
            field.

         +  Cipher suite parameters data - parameters to be used with
            the cipher suite in use, e.g., a key identifier or
            initialization vector (IV).  See Section 2.8 for a list of
            potential parameters and their encoding rules.  The
            particular set of parameters that is included in this field
            is defined as part of a cipher suite specification.

      *  (OPTIONAL) Security Result - compound field of the next two
         items.

         +  Security result length (SDNV) - contains the length of the
            next field, which is the security-result data field.

         +  Security result data - contains the results of the
            appropriate cipher suite specific calculation (e.g., a
            signature, Message Authentication Code (MAC), or cipher-text
            block key).

   The structure of the cipher suite flags field is shown in Figure 3.
   In each case, the presence of an optional field is indicated by
   setting the value of the corresponding flag to one.  A value of zero
   indicates the corresponding optional field is missing.  Presently,
   there are three flags defined for the field; for convenience, these
   are shown as they would be extracted from a single-byte SDNV.  Future
   additions may cause the field to grow to the left so, as with the
   flags fields defined in [RFC5050], the description below numbers the
   bit positions from the right rather than the standard RFC definition,
   which numbers bits from the left.

      bits 6-3 are reserved for future use.





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      src - bit 2 indicates whether the EID-reference field of the ASB
      contains the optional reference to the security-source.

      parm - bit 1 indicates whether or not the cipher suite parameters
      length and cipher suite parameters data fields are present.

      res - bit 0 indicates whether or not the ASB contains the
      security-result length and security-result data fields.

     Bit   Bit   Bit   Bit   Bit   Bit   Bit
      6     5     4     3     2     1     0
   +-----+-----+-----+-----+-----+-----+-----+
   |    reserved           | src |parm | res |
   +-----+-----+-----+-----+-----+-----+-----+

                       Figure 3: Cipher Suite Flags

2.3.  Block Ordering

   A security-operation may be implemented in a bundle using either one
   or two security blocks.  For example, the operation
   OP(authentication, bundle) MAY be accomplished by a single BAB block
   in the bundle, or it MAY be accomplished by two BAB blocks in the
   bundle.  To avoid confusion, we use the following terminology to
   identify the block or blocks comprising a security-operation.

   The terms "First" and "Last" are used ONLY when describing multiple
   security blocks comprising a single security-operation.  A "First"
   block refers to the security block that is closest to the primary
   block in the canonical form of the bundle.  A "Last" block refers to
   the security block that is furthest from the primary block in the
   canonical form of the bundle.

   If a single security block implements the security-operation, then it
   is referred to as a "Lone" block.  For example, when a bundle
   authentication cipher suite requires a single BAB block we refer to
   it as a Lone BAB.  When a bundle authentication cipher suite requires
   two BAB blocks we refer to them as the First BAB and the Last BAB.

   This specification and individual cipher suites impose restrictions
   on what optional fields must and must not appear in First blocks,
   Last blocks, and Lone blocks.

2.4.  Bundle Authentication Block

   This section describes typical field values for the BAB, which is
   solely used to implement OP(authentication, bundle).




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      The block-type code field value MUST be 0x02.

      The block processing control flags value can be set to whatever
      values are required by local policy.  Cipher suite designers
      should carefully consider the effect of setting flags that either
      discard the block or delete the bundle in the event that this
      block cannot be processed.

      The security-target MUST be the entire bundle, which MUST be
      represented by a <block type><occurrence number> of <0x00><0x00>.

      The cipher suite ID MUST be documented as a hop-by-hop
      authentication cipher suite.  When a Lone BAB is used, the cipher
      suite MUST be documented as requiring one instance of the BAB.
      When a First BAB and Last BAB are used, the cipher suite MUST be
      documented as requiring two instances of the BAB.

      The cipher suite parameters field MAY be present, if so specified
      in the cipher suite specification.

      An EID-reference to the security-source MAY be present in either a
      First BAB or a Lone BAB.  An EID-reference to the security-source
      MUST NOT be present in a Last BAB.

      The security-result captures the result of applying the cipher
      suite calculation (e.g., the MAC or signature) to the relevant
      parts of the bundle, as specified in the cipher suite definition.
      This field MUST be present in either a Lone BAB or a Last BAB.
      This field MUST NOT be present in a First BAB.

   Notes:

   o  When multiple BAB blocks are used, the mandatory fields of the
      Last BAB must match those of the First BAB.

   o  The First BAB or Lone BAB, when present, SHOULD immediately follow
      the primary block.

   o  A Last BAB, when present, SHOULD be the last block in the bundle.

   o  Since OP(authentication, bundle) is allowed only once in a bundle,
      it is RECOMMENDED that users wishing to support multiple
      authentication signatures define a multi-target cipher suite,
      capturing multiple security results in cipher suite parameters.







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2.5.  Block Integrity Block

   A BIB is an ASB with the following additional restrictions:

      The block-type code value MUST be 0x03.

      The block processing control flags value can be set to whatever
      values are required by local policy.  Cipher suite designers
      should carefully consider the effect of setting flags that either
      discard the block or delete the bundle in the event that this
      block cannot be processed.

      The security-target MUST uniquely identify a block within the
      bundle.  The reserved block type 0x01 specifies the singleton
      payload block.  The reserved type 0x00 specifies the singleton
      primary block.  The security-target for a BIB MUST NOT reference a
      security block defined in this specification (BAB, BIB, or BCB).

      The cipher suite ID MUST be documented as an end-to-end
      authentication-cipher suite or as an end-to-end error-detection-
      cipher suite.

      The cipher suite parameters field MAY be present in either a Lone
      BIB or a First BIB.  This field MUST NOT be present in a Last BIB.

      An EID-reference to the security-source MAY be present in either a
      Lone BIB or a First BIB.  This field MUST NOT be present in a Last
      BIB.

      The security-result captures the result of applying the cipher
      suite calculation (e.g., the MAC or signature) to the relevant
      parts of the security-target, as specified in the cipher suite
      definition.  This field MUST be present in either a Lone BIB or a
      Last BIB.  This field MUST NOT be present in a First BIB.

      The cipher suite MAY process less than the entire security-target.
      If the cipher suite processes less than the complete, original
      security-target, the cipher suite parameters MUST specify which
      bytes of the security-target are protected.

   Notes:

   o  Since OP(integrity, target) is allowed only once in a bundle per
      target, it is RECOMMENDED that users wishing to support multiple
      integrity signatures for the same target define a multi-signature
      cipher suite, capturing multiple security results in cipher suite
      parameters.




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   o  For some cipher suites, (e.g., those using asymmetric keying to
      produce signatures or those using symmetric keying with a group
      key), the security information MAY be checked at any hop on the
      way to the destination that has access to the required keying
      information, in accordance with Section 2.7.

   o  The use of a generally available key is RECOMMENDED if custodial
      transfer is employed and all nodes SHOULD verify the bundle before
      accepting custody.

2.6.  Block Confidentiality Block

   A BCB is an ASB with the following additional restrictions:

      The block-type code value MUST be 0x04.

      The block processing control flags value can be set to whatever
      values are required by local policy, except that a Lone BCB or
      First BCB MUST have the "replicate in every fragment" flag set.
      This indicates to a receiving node that the payload portion in
      each fragment represents cipher-text.  This flag SHOULD NOT be set
      otherwise.  Cipher suite designers should carefully consider the
      effect of setting flags that either discard the block or delete
      the bundle in the event that this block cannot be processed.

      The security-target MUST uniquely identify a block within the
      bundle.  The security-target for a BCB MAY reference the payload
      block, a non-security extension block, or a BIB block.  The
      reserved type 0x01 specifies the singleton payload block.

      The cipher suite ID MUST be documented as a confidentiality cipher
      suite.

      Key-information, if available, MUST appear only in a Lone BCB or a
      First BCB.

      Any additional bytes generated as a result of encryption and/or
      authentication processing of the security-target SHOULD be placed
      in an "integrity check value" field (see Section 2.8) in the
      security-result of the Lone BCB or Last BCB.

      The cipher suite parameters field MAY be present in either a Lone
      BCB or a First BCB.  This field MUST NOT be present in a Last BCB.

      An EID-reference to the security-source MAY be present in either a
      Lone BCB or a First BCB.  This field MUST NOT be present in a Last
      BCB.  The security-source can also be specified as part of key-
      information described in Section 2.8.



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      The security-result MAY be present in either a Lone BCB or a Last
      BCB.  This field MUST NOT be present in a First BCB.  This
      compound field normally contains fields such as an encrypted
      bundle encryption key and/or authentication tag.

   The BCB is the only security block that modifies the contents of its
   security-target.  When a BCB is applied, the security-target body
   data are encrypted "in-place".  Following encryption, the security-
   target body data contains cipher-text, not plain-text.  Other
   security-target block fields (such as type, processing control flags,
   and length) remain unmodified.

   Fragmentation, reassembly, and custody transfer are adversely
   affected by a change in size of the payload due to ambiguity about
   what byte range of the block is actually in any particular fragment.
   Therefore, when the security-target of a BCB is the bundle payload,
   the BCB MUST NOT alter the size of the payload block body data.
   Cipher suites SHOULD place any block expansion, such as
   authentication tags (integrity check values) and any padding
   generated by a block-mode cipher, into an integrity check value item
   in the security-result field (see Section 2.8) of the BCB.  This "in-
   place" encryption allows fragmentation, reassembly, and custody
   transfer to operate without knowledge of whether or not encryption
   has occurred.

   Notes:

   o  The cipher suite MAY process less than the entire original
      security-target body data.  If the cipher suite processes less
      than the complete, original security-target body data, the BCB for
      that security-target MUST specify, as part of the cipher suite
      parameters, which bytes of the body data are protected.

   o  The BCB's "discard" flag may be set independently from its
      security-target's "discard" flag.  Whether or not the BCB's
      "discard" flag is set is an implementation/policy decision for the
      encrypting node.  (The "discard" flag is more properly called the
      "Discard if block cannot be processed" flag.)

   o  A BCB MAY include information as part of additional authenticated
      data to address parts of the target block, such as EID references,
      that are not converted to cipher-text.

2.7.  Block Interactions

   The three security-block types defined in this specification are
   designed to be as independent as possible.  However, there are some




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   cases where security blocks may share a security-target creating
   processing dependencies.

   If confidentiality is being applied to a target that already has
   integrity applied to it, then an undesirable condition occurs where a
   security-aware intermediate node would be unable to check the
   integrity result of a block because the block contents have been
   encrypted after the integrity signature was generated.  To address
   this concern, the following processing rules MUST be followed.

   o  If confidentiality is to be applied to a target, it MUST also be
      applied to every integrity operation already defined for that
      target.  This means that if a BCB is added to encrypt a block,
      another BCB MUST also be added to encrypt a BIB also targeting
      that block.

   o  An integrity operation MUST NOT be applied to a security-target if
      a BCB in the bundle shares the same security-target.  This
      prevents ambiguity in the order of evaluation when receiving a BIB
      and a BCB for a given security-target.

   o  An integrity value MUST NOT be evaluated if the BIB providing the
      integrity value is the security target of an existing BCB block in
      the bundle.  In such a case, the BIB data contains cipher-text as
      it has been encrypted.

   o  An integrity value MUST NOT be evaluated if the security-target of
      the BIB is also the security-target of a BCB in the bundle.  In
      such a case, the security-target data contains cipher-text as it
      has been encrypted.

   o  As mentioned in Section 2.6, a BIB MUST NOT have a BCB as its
      security target.  BCBs may embed integrity results as part of
      cipher suite parameters.

   These restrictions on block interactions impose a necessary ordering
   when applying security operations within a bundle.  Specifically, for
   a given security-target, BIBs MUST be added before BCBs, and BABs
   MUST be added after all other security blocks.  This ordering MUST be
   preserved in cases where the current BPA is adding all of the
   security blocks for the bundle or whether the BPA is a waypoint
   adding new security blocks to a bundle that already contains security
   blocks.








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2.8.  Parameters and Result Fields

   Various cipher suites include several items in the cipher suite
   parameters and/or security-result fields.  Which items MAY appear is
   defined by the particular cipher suite description.  A cipher suite
   MAY support several instances of the same type within a single block.

   Each item is represented as a type-length-value.  Type is a single
   byte indicating the item.  Length is the count of data bytes to
   follow, and is an SDNV-encoded integer.  Value is the data content of
   the item.

   Item types, name, and descriptions are defined as follows.






































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                Cipher suite parameters and result fields.

   +-------+----------------+------------------------------------------+
   |  Type |      Name      | Description                              |
   +-------+----------------+------------------------------------------+
   |   0   |    Reserved    |                                          |
   +-------+----------------+------------------------------------------+
   |   1   | Initialization | A random value, typically eight to       |
   |       |  Vector (IV)   | sixteen bytes.                           |
   +-------+----------------+------------------------------------------+
   |   2   |    Reserved    |                                          |
   +-------+----------------+------------------------------------------+
   |   3   |      Key       | Material encoded or protected by the key |
   |       |  Information   | management system and used to transport  |
   |       |                | an ephemeral key protected by a long-    |
   |       |                | term key.                                |
   +-------+----------------+------------------------------------------+
   |   4   | Content Range  | Pair of SDNV values (offset,length)      |
   |       |                | specifying the range of payload bytes to |
   |       |                | which an operation applies. The offset   |
   |       |                | MUST be the offset within the original   |
   |       |                | bundle, even if the current bundle is a  |
   |       |                | fragment.                                |
   +-------+----------------+------------------------------------------+
   |   5   |   Integrity    | Result of BAB or BIB digest or other     |
   |       |   Signatures   | signing operation.                       |
   +-------+----------------+------------------------------------------+
   |   6   |   Unassigned   |                                          |
   +-------+----------------+------------------------------------------+
   |   7   |      Salt      | An IV-like value used by certain         |
   |       |                | confidentiality suites.                  |
   +-------+----------------+------------------------------------------+
   |   8   | BCB Integrity  | Output from certain confidentiality      |
   |       |  Check Value   | cipher suite operations to be used at    |
   |       |    (ICV) /     | the destination to verify that the       |
   |       | Authentication | protected data has not been modified.    |
   |       |      Tag       | This value MAY contain padding if        |
   |       |                | required by the cipher suite.            |
   +-------+----------------+------------------------------------------+
   | 9-255 |    Reserved    |                                          |
   +-------+----------------+------------------------------------------+

                                  Table 1








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2.9.  BSP Block Example

   An example of SBSP blocks applied to a bundle is illustrated in
   Figure 4.  In this figure the first column represents blocks within a
   bundle and the second column represents a unique identifier for each
   block, suitable for use as the security-target of a SBSP security-
   block.  Since the mechanism and format of a security-target is not
   specified in this document, the terminology B1...Bn is used to
   identify blocks in the bundle for the purposes of illustration.


            Block in Bundle            ID
   +=================================+====+
   |         Primary Block           | B1 |
   +---------------------------------+----+
   |          First BAB              | B2 |
   |   OP(authentication, Bundle)    |    |
   +---------------------------------+----+
   |          Lone BIB               | B3 |
   |  OP(integrity, target=B1)       |    |
   +---------------------------------+----+
   |          Lone BCB               | B4 |
   |  OP(confidentiality, target=B5) |    |
   +---------------------------------+----+
   |      Extension Block            | B5 |
   +---------------------------------+----+
   |          Lone BIB               | B6 |
   |  OP(integrity, target=B7)       |    |
   +---------------------------------+----+
   |      Extension Block            | B7 |
   +---------------------------------+----+
   |          Lone BCB               | B8 |
   |  OP(confidentiality, target=B9) |    |
   +---------------------------------+----+
   |   Lone BIB  (encrypted by B8)   | B9 |
   |  OP(integrity, target=B11)      |    |
   +---------------------------------+----+
   |          Lone BCB               |B10 |
   | OP(confidentiality, target=B11) |    |
   +---------------------------------+----+
   |         Payload Block           |B11 |
   +---------------------------------+----+
   |          Last BAB               |B12 |
   |   OP(authentication, Bundle)    |    |
   +---------------------------------+----+

                    Figure 4: Sample Use of BSP Blocks




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   In this example a bundle has four non-security-related blocks: the
   primary block (B1), two extension blocks (B5,B7), and a payload block
   (B11).  The following security applications are applied to this
   bundle.

   o  Authentication over the bundle.  This is accomplished by two BAB
      blocks: B2 and B12.

   o  An integrity signature applied to the canonicalized primary block.
      This is accomplished by a single BIB, B3.

   o  Confidentiality for the first extension block.  This is
      accomplished by a single BCB block, B4.

   o  Integrity for the second extension block.  This is accomplished by
      a single BIB block, B6.

   o  An integrity signature on the payload.  This is accomplished by a
      single BIB block, B9.

   o  Confidentiality for the payload block and it's integrity
      signature.  This is accomplished by two Lone BCB blocks: B8
      encrypting B9, and B10 encrypting B11.

3.  Security Processing

   This section describes the security aspects of bundle processing.

3.1.  Canonical Forms

   In order to verify a signature of a bundle, the exact same bits, in
   the exact same order, MUST be input to the calculation upon
   verification as were input upon initial computation of the original
   signature value.  Consequently, a node MUST NOT change the encoding
   of any URI [RFC3986] in the dictionary field, e.g., changing the DNS
   part of some HTTP URL from lower case to upper case.  Because bundles
   MAY be modified while in transit (either correctly or due to
   implementation errors), canonical forms of security-targets MUST be
   defined.

   Many fields in various blocks are stored as variable-length SDNVs.
   These are canonicalized into an "unpacked form" as eight-byte fixed-
   width fields in network byte order.  The size of eight bytes is
   chosen because implementations MAY handle larger SDNV values as
   invalid, as noted in [RFC5050].






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3.1.1.  Bundle Canonicalization

   Bundle canonicalization permits no changes at all to the bundle
   between the security-source and the destination, with the exception
   of one of the Block Processing Control Flags, as described below.  It
   is intended for use in BAB cipher suites.  This algorithm
   conceptually catenates all blocks in the order presented, but omits
   all security-result data fields in security blocks having the bundle
   as their security-target.  For example, when a BAB cipher suite
   specifies this algorithm, we omit the BAB security-result from the
   catenation.  The inclusion of security-result length fields is as
   determined by the specified cipher suite.  A security-result length
   field MAY be present even when the corresponding security-result data
   fields are omitted.

   Notes:

   o  In the Block Processing Control Flags field the unpacked SDNV is
      ANDed with mask 0xFFFF FFFF FFFF FFDF to zero the flag at bit 5
      ("Block was forwarded without being processed").  If this flag is
      not zeroed out, then a bundle passing through a non-security aware
      node will set this flag which will change the message digest and
      the BAB block will fail to verify.

   o  In the above, we specify that security-result data is omitted.
      This means that no bytes of the security-result data are input.
      If the security-result length is included in the catenation, we
      assume that the security-result length will be known to the module
      that implements the cipher suite before the security-result is
      calculated, and require that this value be in the security-result
      length field even though the security-result data itself will be
      omitted.

   o  The 'res' bit of the cipher suite ID, which indicates whether or
      not the security-result length and security-result data field are
      present, is part of the canonical form.

   o  The value of the block data length field, which indicates the
      length of the block, is also part of the canonical form.  Its
      value indicates the length of the entire block when the block
      includes the security-result data field.

3.1.2.  Block Canonicalization

   This algorithm protects those parts of a block that SHOULD NOT be
   changed in transit.





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   There are three types of blocks that may undergo block
   canonicalization: the primary block, the payload block, or an
   extension block.

3.1.2.1.  Primary Block Canonicalization

   The canonical form of the primary block is shown in Figure 5.
   Essentially, it de-references the dictionary block, adjusts lengths
   where necessary, and ignores flags that may change in transit.

   +----------------+----------------+----------------+----------------+
   |    Version     |      Processing flags (incl. COS and  SRR)       |
   +----------------+----------------+---------------------------------+
   |                Canonical primary block length                     |
   +----------------+----------------+---------------------------------+
   |                Destination endpoint ID length                     |
   +----------------+----------------+---------------------------------+
   |                      Destination endpoint ID                      |
   +----------------+----------------+---------------------------------+
   |                    Source endpoint ID length                      |
   +----------------+----------------+----------------+----------------+
   |                        Source endpoint ID                         |
   +----------------+----------------+---------------------------------+
   |                  Report-to endpoint ID length                     |
   +----------------+----------------+----------------+----------------+
   |                      Report-to endpoint ID                        |
   +----------------+----------------+----------------+----------------+
   +                    Creation Timestamp (2 x SDNV)                  +
   +---------------------------------+---------------------------------+
   |                             Lifetime                              |
   +----------------+----------------+----------------+----------------+

         Figure 5: The Canonical Form of the Primary Bundle Block

   The fields shown in Figure 5 are as follows:

   o  The version value is the single-byte value in the primary block.

   o  The processing flags value in the primary block is an SDNV, and
      includes the class-of-service (COS) and status report request
      (SRR) fields.  For purposes of canonicalization, the unpacked SDNV
      is ANDed with mask 0x0000 0000 0007 C1BE to set to zero all
      reserved bits and the "bundle is a fragment" bit.

   o  The canonical primary block length value is a four-byte value
      containing the length (in bytes) of this structure, in network
      byte order.




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   o  The destination endpoint ID length and value are the length (as a
      four-byte value in network byte order) and value of the
      destination endpoint ID from the primary bundle block.  The URI is
      simply copied from the relevant part(s) of the dictionary block
      and is not itself canonicalized.  Although the dictionary entries
      contain "null-terminators", the null-terminators are not included
      in the length or the canonicalization.

   o  The source endpoint ID length and value are handled similarly to
      the destination.

   o  The report-to endpoint ID length and value are handled similarly
      to the destination.

   o  The unpacked SDNVs for the creation timestamp and lifetime are
      copied from the primary block.

   o  Fragment offset and total application data unit length are
      ignored, as is the case for the "bundle is a fragment" bit
      mentioned above.  If the payload data to be canonicalized is less
      than the complete, original bundle payload, the offset and length
      are specified in the cipher suite parameters.

3.1.2.2.  Payload Block Canonicalization

   When canonicalizing the payload block, the block processing control
   flags value used for canonicalization is the unpacked SDNV value with
   reserved and mutable bits masked to zero.  The unpacked value is
   ANDed with mask 0x0000 0000 0000 0077 to zero reserved bits and the
   "last block" bit.  The "last block" bit is ignored because BABs and
   other security blocks MAY be added for some parts of the journey but
   not others, so the setting of this bit might change from hop to hop.

   Payload blocks are canonicalized as-is, with the exception that, in
   some instances, only a portion of the payload data is to be
   protected.  In such a case, only those bytes are included in the
   canonical form, and additional cipher suite parameters are required
   to specify which part of the payload is protected, as discussed
   further below.

3.1.2.3.  Extension Block Canonicalization

   When canonicalizing an extension block, the block processing control
   flags value used for canonicalization is the unpacked SDNV value with
   reserved and mutable bits masked to zero.  The unpacked value is
   ANDed with mask 0x0000 0000 0000 0057 to zero reserved bits, the
   "last block" flag and the "Block was forwarded without being
   processed" bit.  The "last block" flag is ignored because BABs and



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   other security blocks MAY be added for some parts of the journey but
   not others, so the setting of this bit might change from hop to hop.

   The "Block was forwarded without being processed" flag is ignored
   because the bundle may pass through nodes that do not understand that
   extension block and this flag would be set.

   Endpoint ID references in blocks are canonicalized using the de-
   referenced text form in place of the reference pair.  The reference
   count is not included, nor is the length of the endpoint ID text.
   The EID reference is, therefore, canonicalized as <scheme>:<SSP>,
   which includes the ":" character.

   Since neither the length of the canonicalized EID text nor a null-
   terminator is used in EID canonicalization, a separator token MUST be
   used to determine when one EID ends and another begins.  When
   multiple EIDs are canonicalized together, the character "," SHALL be
   placed between adjacent instances of EID text.

   The block-length is canonicalized as its unpacked SDNV value.  If the
   data to be canonicalized is less than the complete, original block
   data, this field contains the size of the data being canonicalized
   (the "effective block") rather than the actual size of the block.

3.1.3.  Considerations

   o  The canonical forms for the bundle and various extension blocks is
      not transmitted.  It is simply an artifact used as input to
      digesting.

   o  We omit the reserved flags because we cannot determine if they
      will change in transit.  The masks specified above will have to be
      revised if additional flags are defined and they need to be
      protected.

   o  Our URI encoding does not preserve the null-termination convention
      from the dictionary field, nor do we canonicalize the scheme and
      scheme-specific part (SSP) separately.  Instead, the byte array <
      scheme name > : < scheme-specific part (SSP)> is used in the
      canonicalization.

   o  The URI encoding will cause errors if any node rewrites the
      dictionary content (e.g., changing the DNS part of an HTTP URL
      from lower case to upper case).  This could happen transparently
      when a bundle is synched to disk using one set of software and
      then read from disk and forwarded by a second set of software.
      Because there are no general rules for canonicalizing URIs (or




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      IRIs), this problem may be an unavoidable source of integrity
      failures.

   o  All SDNV fields here are canonicalized as eight-byte unpacked
      values in network byte order.  Length fields are canonicalized as
      four-byte values in network byte order.  Encoding does not need
      optimization since the values are never sent over the network.

   o  These canonicalization algorithms assume that endpoint IDs
      themselves are immutable and they are unsuitable for use in
      environments where that assumption might be violated.

   o  Cipher suites MAY define their own canonicalization algorithms and
      require the use of those algorithms over the ones provided in this
      specification.

3.2.  Endpoint ID Confidentiality

   Every bundle has a primary block that contains the source and
   destination endpoint IDs, and possibly other EIDs (in the dictionary
   field) that cannot be encrypted.  If endpoint ID confidentiality is
   required, then bundle-in-bundle encapsulation can solve this problem
   in some instances.

   Similarly, confidentiality requirements MAY also apply to other parts
   of the primary block (e.g., the current-custodian), and that is
   supported in the same manner.

3.3.  Bundles Received from Other Nodes

   Security blocks MUST be processed in a specific order when received
   by a security-aware node.  The processing order is as follows.

   o  All BAB blocks in the bundle MUST be evaluated prior to evaluating
      any other block in the bundle.

   o  All BCB blocks in the bundle MUST be evaluated prior to evaluating
      any BIBs in the bundle.  When BIBs and BCBs share a security-
      target, BCBs MUST be evaluated first and BIBs second.

3.3.1.  Receiving BAB Blocks

   Nodes implementing this specification SHALL consult their security
   policy to determine whether or not a received bundle is required by
   policy to include a BAB.

   If the bundle is not required to have a BAB then BAB processing on
   the received bundle is complete, and the bundle is ready to be



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   further processed for BIB/BCB handling or delivery or forwarding.
   Security policy may provide a means to override this default behavior
   and require processing of a BAB if it exists.

   If the bundle is required to have a BAB but does not, then the bundle
   MUST be discarded and processed no further.  If the bundle is
   required to have a BAB but the key information for the security-
   source cannot be determined or the security-result value check fails,
   then the bundle has failed to authenticate, and the bundle MUST be
   discarded and processed no further.

   If the bundle is required to have a BAB, and a BAB exists, and the
   BAB information is verified, then the BAB processing on the received
   bundle is complete, and the bundle is ready to be further processed
   for BIB/BCB handling or delivery or forwarding.

   A BAB received in a bundle MUST be stripped before the bundle is
   forwarded.  A new BAB MAY be added as required by policy.  This MAY
   require correcting the "last block" field of the to-be-forwarded
   bundle.

3.3.2.  Receiving BCB Blocks

   If the bundle has a BCB and the receiving node is the destination for
   the bundle, the node MUST decrypt the relevant parts of the security-
   target in accordance with the cipher suite specification.

   If the relevant parts of an encrypted payload cannot be decrypted
   (i.e., the decryption key cannot be deduced or decryption fails),
   then the bundle MUST be discarded and processed no further; in this
   case, a bundle deletion status report (see [RFC5050]) indicating the
   decryption failure MAY be generated.  If any other encrypted
   security-target cannot be decrypted then the associated security-
   target and all security blocks associated with that target MUST be
   discarded and processed no further.

   When a BCB is decrypted, the recovered plain-text MUST replace the
   cipher-text in the security-target body data

3.3.3.  Receiving BIB Blocks

   A BIB MUST NOT be processed if the security-target of the BIB is also
   the security-target of a BCB in the bundle.  Given the order of
   operations mandated by this specification, when both a BIB and a BCB
   share a security-target, it means that the security-target MUST have
   been encrypted after it was integrity signed and, therefore, the BIB
   cannot be verified until the security-target has been decrypted by
   processing the BCB.



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   If the security policy of a security-aware node specifies that a
   bundle SHOULD apply integrity to a specific security-target and no
   such BIB is present in the bundle, then the node MUST process this
   security-target in accordance with the security policy.  This MAY
   involve removing the security-target from the bundle.  If the removed
   security-target is the payload or primary block, the bundle MAY be
   discarded.  This action may occur at any node that has the ability to
   verify an integrity signature, not just the bundle destination.

   If the bundle has a BIB and the receiving node is the destination for
   the bundle, the node MUST verify the security-target in accordance
   with the cipher suite specification.  If a BIB check fails, the
   security-target has failed to authenticate and the security-target
   SHALL be processed according to the security policy.  A bundle status
   report indicating the failure MAY be generated.  Otherwise, if the
   BIB verifies, the security-target is ready to be processed for
   delivery.

   If the bundle has a BIB and the receiving node is not the bundle
   destination, the receiving node MAY attempt to verify the value in
   the security-result field.  If the check fails, the node SHALL
   process the security-target in accordance to local security policy.
   It is RECOMMENDED that if a payload integrity check fails at a
   waypoint that it is processed in the same way as if the check fails
   at the destination.

3.4.  Bundle Fragmentation and Reassembly

   If it is necessary for a node to fragment a bundle and security
   services have been applied to that bundle, the fragmentation rules
   described in [RFC5050] MUST be followed.  As defined there and
   repeated here for completeness, only the payload may be fragmented;
   security blocks, like all extension blocks, can never be fragmented.
   In addition, the following security-specific processing is REQUIRED:

   o  Due to the complexity of bundle fragmentation, including the
      possibility of fragmenting bundle fragments, integrity and
      confidentiality operations are not to be applied to a bundle
      fragment.  Specifically, a BCB or BIB MUST NOT be added to a
      bundle fragment, even if the security-target of the security block
      is not the payload.  When integrity and confidentiality must be
      applied to a fragment, we RECOMMEND that encapsulation be used
      instead.

   o  The authentication security policy requirements for a bundle MUST
      be applied individually to all the bundles resulting from a
      fragmentation event.




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   o  A BAB cipher suite MAY specify that it only applies to non-
      fragmented bundles and not to bundle fragments.

   o  The decision to fragment a bundle MUST be made prior to adding
      authentication to the bundle.  The bundle MUST first be fragmented
      and authentication applied to each individual fragment.

   o  If a bundle with a BAB is fragmented by a non-security-aware node,
      then the entire bundle must be re-assembled before being processed
      to allow for the proper verification of the BAB.

3.5.  Reactive Fragmentation

   When a partial bundle has been received, the receiving node SHALL
   consult its security policy to determine if it MAY fragment the
   bundle, converting the received portion into a bundle fragment for
   further forwarding.  Whether or not reactive fragmentation is
   permitted SHALL depend on the security policy and the cipher suite
   used to calculate the BAB authentication information, if required.

   Specifically, if the security policy does not require authentication,
   then reactive fragmentation MAY be permitted.  If the security policy
   does require authentication, then reactive fragmentation MUST NOT be
   permitted if the partial bundle is not sufficient to allow
   authentication.

   If reactive fragmentation is allowed, then all BAB blocks must be
   removed from created fragments.

4.  Key Management

   Key management in delay-tolerant networks is recognized as a
   difficult topic and is one that this specification does not attempt
   to solve.

5.  Policy Considerations

   When implementing the SBSP, several policy decisions must be
   considered.  This section describes key policies that affect the
   generation, forwarding, and receipt of bundles that are secured using
   this specification.

   o  If a bundle is received that contains more than one security-
      operation, in violation of the SBSP, then the BPA must determine
      how to handle this bundle.  The bundle may be discarded, the block
      affected by the security-operation may be discarded, or one
      security-operation may be favored over another.




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   o  BPAs in the network MUST understand what security-operations they
      should apply to bundles.  This decision may be based on the source
      of the bundle, the destination of the bundle, or some other
      information related to the bundle.

   o  If an intermediate receiver has been configured to add a security-
      operation to a bundle, and the received bundle already has the
      security-operation applied, then the receiver MUST understand what
      to do.  The receiver may discard the bundle, discard the security-
      target and associated SBSP blocks, replace the security-operation,
      or some other action.

   o  It is recommended that security operations only be applied to the
      payload block, the primary block, and any block-types specifically
      identified in the security policy.  If a BPA were to apply
      security operations such as integrity or confidentiality to every
      block in the bundle, regardless of the block type, there could be
      downstream errors processing blocks whose contents must be
      inspected at every hop in the network path.

6.  Security Considerations

   Certain applications of DTN need to both sign and encrypt a message,
   and there are security issues to consider with this.

   o  To provide an assurance that a security-target came from a
      specific source and has not been changed, then it should be signed
      with a BIB.

   o  To ensure that a security-target cannot be inspected during
      transit, it should be encrypted with a BCB.

   o  Adding a BIB to a security-target that has already been encrypted
      by a BCB is not allowed.  Therefore, we recommend three methods to
      add an integrity signature to an encrypted security-target.
      First, at the time of encryption, an integrity signature may be
      generated and added to the BCB for the security-target as
      additional information in the security-result field.  Second, the
      encrypted block may be replicated as a new block and integrity
      signed.  Third, an encapsulation scheme may be applied to
      encapsulate the security-target (or the entire bundle) such that
      the encapsulating structure is, itself, no longer the security-
      target of a BCB and may therefore be the security-target of a BIB.








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7.  Conformance

   All implementations are strongly RECOMMENDED to provide at least a
   BAB cipher suite.  A relay node, for example, might not deal with
   end-to-end confidentiality and data integrity, but it SHOULD exclude
   unauthorized traffic and perform hop-by-hop bundle verification.

8.  IANA Considerations

   This protocol has fields that have been registered by IANA.

8.1.  Bundle Block Types

   This specification allocates three block types from the existing
   "Bundle Block Types" registry defined in [RFC6255].

       Additional Entries for the Bundle Block-Type Codes Registry:

         +--------+-----------------------------+---------------+
         | Value  |         Description         |   Reference   |
         +--------+-----------------------------+---------------+
         |   2    | Bundle Authentication Block | This document |
         |   3    |    Block Integrity Block    | This document |
         |   4    | Block Confidentiality Block | This document |
         +--------+-----------------------------+---------------+

                                  Table 2

8.2.  Cipher Suite Flags

   This protocol has a cipher suite flags field and certain flags are
   defined.  An IANA registry has been set up as follows.

   The registration policy for this registry is: Specification Required

   The Value range is: Variable Length















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                        Cipher Suite Flag Registry:

   +--------------------------+-------------------------+--------------+
   |  Bit Position (right to  |       Description       |  Reference   |
   |          left)           |                         |              |
   +--------------------------+-------------------------+--------------+
   |            0             |  Block contains result  |     This     |
   |                          |                         |   document   |
   |            1             |      Block Contains     |     This     |
   |                          |        parameters       |   document   |
   |            2             |  Source EID ref present |     This     |
   |                          |                         |   document   |
   |            >3            |         Reserved        |     This     |
   |                          |                         |   document   |
   +--------------------------+-------------------------+--------------+

                                  Table 3

8.3.  Parameters and Results

   This protocol has fields for cipher suite parameters and results.
   The field is a type-length-value triple and a registry is required
   for the "type" sub-field.  The values for "type" apply to both the
   cipher suite parameters and the cipher suite results fields.  Certain
   values are defined.  An IANA registry has been set up as follows.

   The registration policy for this registry is: Specification Required

   The Value range is: 8-bit unsigned integer.






















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            Cipher Suite Parameters and Results Type Registry:

       +---------+---------------------------------+---------------+
       |  Value  |           Description           |   Reference   |
       +---------+---------------------------------+---------------+
       |    0    |             reserved            | This document |
       |    1    |    initialization vector (IV)   | This document |
       |    2    |             reserved            | This document |
       |    3    |         key-information         | This document |
       |    4    |  content-range (pair of SDNVs)  | This document |
       |    5    |       integrity signature       | This document |
       |    6    |            unassigned           | This document |
       |    7    |               salt              | This document |
       |    8    | BCB integrity check value (ICV) | This document |
       |  9-191  |             reserved            | This document |
       | 192-250 |           private use           | This document |
       | 251-255 |             reserved            | This document |
       +---------+---------------------------------+---------------+

                                  Table 4

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5050]  Scott, K. and S. Burleigh, "Bundle Protocol
              Specification", RFC 5050, November 2007.

   [RFC6255]  Blanchet, M., "Delay-Tolerant Networking Bundle Protocol
              IANA Registries", RFC 6255, May 2011.

9.2.  Informative References

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC4838]  Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst,
              R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant
              Networking Architecture", RFC 4838, April 2007.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.




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   [RFC6257]  Symington, S., Farrell, S., Weiss, H., and P. Lovell,
              "Bundle Security Protocol Specification", RFC 6257, May
              2011.

Appendix A.  Acknowledgements

   The following participants contributed technical material, use cases,
   and useful thoughts on the overall approach to this security
   specification: Scott Burleigh of the Jet Propulsion Laboratory, Amy
   Alford and Angela Hennessy of the Laboratory for Telecommunications
   Sciences, and Angela Dalton and Cherita Corbett of the Johns Hopkins
   University Applied Physics Laboratory.

Author's Address

   Edward J. Birrane, III
   The Johns Hopkins University Applied Physics Laboratory
   11100 Johns Hopkins Rd.
   Laurel, MD  20723
   US

   Phone: +1 443 778 7423
   Email: Edward.Birrane@jhuapl.edu




























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