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<?rfc toc="yes"?> <!-- generate a table of contents -->
<?rfc symrefs="yes"?> <!-- use anchors instead of numbers for references -->
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<?rfc compact="yes" ?> <!-- conserve vertical whitespace -->
<?rfc subcompact="no" ?> <!-- but keep a blank line between list items -->

<rfc category="exp" ipr="trust200902" docName='draft-irtf-dtnrg-sbsp-01'>
<front>
<title>
	Streamlined Bundle Security Protocol Specification
</title>	

<author initials='E.J.'
        surname='Birrane'
        fullname='Edward J. Birrane, III'>
	<organization abbrev='JHU/APL'>
		The Johns Hopkins University Applied Physics Laboratory
	</organization>	

	<address>
		<postal>
			<street>11100 Johns Hopkins Rd.</street>
			<city>Laurel</city>
			<region>MD</region>
			<code>20723</code>
			<country>US</country>
		</postal>	

		<phone>+1 443 778 7423</phone>
		<email>Edward.Birrane@jhuapl.edu</email>
	</address>
</author>

<date month='May' year='2014'/>

<!-- Meta-data -->
<area>General</area>
<workgroup>Delay-Tolerant Networking Research Group</workgroup>
<keyword>security</keyword>
<keyword>bundle</keyword>
<keyword>integrity</keyword>
<keyword>authentication</keyword>
<keyword>confidentiality</keyword>

<abstract>
<t>
	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.
</t>  
</abstract>

</front>


<middle>
  
	<section anchor='intro' title='Introduction'>
		<t> 
			This document defines security features for the Bundle Protocol <xref target="RFC5050"/> 
			intended for use in delay-tolerant networks, in order to provide Delay-Tolerant 
			Networking (DTN) security services.
		</t>
		<t>
			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.  
		</t>
		<t>
			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.
		</t>
		<t>
			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.
		</t>
		<t>
			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.
		</t>

		<section anchor="reldoc" title="Related Documents">
			<t>
				This document is best read and understood within the context of the following 
				other DTN documents:		
			</t>	
			<t>
				"Delay-Tolerant Networking Architecture" <xref target='RFC4838'/> defines the architecture 
				for delay-tolerant networks, but does not discuss security at any length.		
			</t>
			<t>
				The DTN Bundle Protocol <xref target='RFC5050'/> defines the format and processing of the blocks 
				used to implement the Bundle Protocol, excluding the security-specific blocks defined here.
			</t>
			<t>
				The Bundle Security Protocol <xref target='RFC6257'/> introduces the concepts 
				of security blocks for authentication, confidentiality, and integrity.	The SBSP is based off of
				this document.
			</t>
		</section>

		<section anchor="term" title="Terminology">
			<t>
				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 <xref target='RFC2119'/>.
			</t>	

			<t>
				We introduce the following terminology for purposes of clarity.		
			
				<list style="symbols">
					<t>Source - the bundle node from which a bundle originates. </t>		
					<t>Destination - the bundle node to which a bundle is ultimately destined. </t>
					<t>Forwarder - the bundle node that forwarded the bundle on its most recent hop. </t>
					<t>Intermediate Receiver, Waypoint, or "Next Hop" - the neighboring bundle node to which a forwarder forwards a bundle.</t>
					<t>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.</t>
				</list>
			</t>
			
			<t>
				<xref target="bundle_example"/> below is adapted from <xref target='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.
   			</t>
   			
  			<figure anchor="bundle_example" title="Bundle Nodes Sit at the Application Layer of the Internet Model">
  			 	<artwork><![CDATA[
+---------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  --->|
|                     |                    |                      |
   				 	
  			 	]]></artwork>  				
   			</figure>   						
			
			<t>
				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 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.
			</t>
			
			<t>
				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).
			</t>
			
			<t>
				We introduce the following security-specific DTN terminology.
			
				<list style="symbols">
					<t>Security-Service - the security features supported by 
					this specification: authentication,	integrity, and 
					confidentiality.
					</t>
							
					<t>Security-Source - a bundle node that adds a security 
					block to a bundle. 
					</t>
					
					<t>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.
					</t>
					
					<t>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. 
					</t>
					 
					<t>Security Block - a single instance of a SBSP extension 
					block in a bundle. 
					</t>
					
					<t>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.
					</t>
					
				</list>
			</t>
			
			<t>
				Referring to <xref target="bundle_example"/> again:
			</t>

			<t>
				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.
			</t>

			<t>
				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.
			</t>
			
			<t>
				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. 
			</t>
	
			<t>
				As required in <xref target="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.
			</t>
			
			<t>
				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.
			</t>
		</section>
	</section>	

	<section anchor="blockdef" title="Security Block Definitions">
		
		<t>
			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).
			<list>
				<t> 
					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.
				</t>
				<t>
					The BIB is used to ensure the authenticity and integrity of 
					its security-target from the BIB security-source, which creates 
					the 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.		
				</t>
				<t>
					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.			
				</t>
			</list>
		</t>	

		<t>
			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.
		</t>

		<t>
			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.   	
		</t>

		<t> 
			Many of the fields in these block definitions use the Self-Delimiting Numeric Value 
			(SDNV) type whose format and encoding is as defined in <xref target='RFC5050'/>.
		</t>
		
		<section anchor="OP_ID" title="Block Identification">
			<t>
				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".
			</t>
			
			<t>
				The definition of the extension block header from <xref target='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.
			</t>
			
			<t>
				Figure 7 of <xref target='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.
			</t>
			
			<t>			
				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.
			</t>
			
			<t>
				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. 
			</t>
			
			<t>
				If a node chooses to add an AEID to a target block header it MUST perform the following activities.
				
				<list style="symbols">
					<t>
						The "Block contains an EID reference field" flag MUST be set for the target block, if 
						it is not already set.
					</t>
					<t>
						The EID reference count for the block MUST be updated to reflect the addition of the AEID. 
					</t>
					<t>
						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.
					</t>
					<t>
						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.
					</t>
				</list>
			</t>
			
			<t>
				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. 
			</t>
			
			<t>
				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 identification of singleton blocks SHOULD be in accordance with
				the security policy of a node.
			</t>
			
		</section>
		
		<section anchor="ASB" title="Abstract Security Block">
			
			<t>
				Each security block uses the Canonical Bundle 
				Block Format as defined in <xref target="RFC5050"/>.  
				That is, each security block is comprised of the following elements:
		
				<list style='symbols'>
					<t>Block Type Code</t>
					<t>Block Processing Control Flags</t>
					<t>Block EID Reference List (OPTIONAL)</t>
					<t>Block Data Length</t>
					<t>Block Type Specific Data Fields</t>
				</list>
		
			</t>
			<t>
				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.
			</t>
			
			<t>
				The structure of an Abstract Security Block is given in <xref target="asb"/>. 
				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.	 
			</t>
			
<figure anchor="asb" title="Abstract Security Block Structure">
  			 	<artwork><![CDATA[
+-----------------------------+----------------------------------+
|    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)      |
+-----------------------------+----------------------------------+
  			 	]]></artwork>  				
   			</figure>


			<t>
			An ASB consists of the following fields, some of which are 
			optional.
			
				<list style="symbols">
					<t>
					Block-Type Code (Byte) - as described in <xref target="RFC5050"/>.  The block-type 
					codes for security blocks are:
						<list>
							<t>BundleAuthenticationBlock - BAB: 0x02</t>					
							<t>BlockIntegrityBlock - BIB: 0x03</t>
							<t>BlockConfidentialityBlock - BCB: 0x04</t>
						</list>			
					</t>

					<t> 			
					Block Processing Control Flags (SDNV) - as described in 
					<xref target="RFC5050"/>. There are no general constraints on 
					the use of the block processing control flags, and some 
					specific requirements are discussed later.
					</t>	

					<t>
					(OPTIONAL) EID Reference Count and List - as described in 
					<xref target="RFC5050"/>. Presence of the EID reference field 
						is indicated by the setting of the &quot;Block contains an 
						EID reference field&quot; (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:
						<list style="symbol">
							<t>
								(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.						
							</t>
							<t>
								(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 <xref target="OP_ID"/>.					
							</t>					
					
						</list>										
					</t>
					
					<t>
					Block Length (SDNV) - as described in <xref target="RFC5050"/>. 	
					</t>
					
					<t>
						Block type specific data fields as follows:
						<list style="symbols">											
							<t>
								Security-Target (Compound) - Uniquely identifies the target of
							    the associated security-operation. 
								<vspace/><vspace/>
								As discussed in <xref target="OP_ID"/> 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).
								<vspace/><vspace/>
								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.
							</t>
							<t>Cipher suite ID (SDNV)</t>	
							<t>Cipher suite flags (SDNV)</t>					
							<t>
								(OPTIONAL) Cipher Suite Parameters - compound field of 
								the next two items.
								<list style="symbols">
									<t>
										Cipher suite parameters length (SDNV) - specifies the 
										length of the next field, which is the cipher suite-parameters 
										data field.
									</t>
									<t>
										Cipher suite parameters data - parameters to be 
										used with the cipher suite in use, e.g., a key 
										identifier or initialization vector (IV).  See 
										<xref target="parmresult" /> 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.								
									</t>							
								</list>
							</t>
							<t>
								(OPTIONAL) Security Result - compound field of the next 
								two items.
								<list style="symbols">
									<t>
										Security result length (SDNV) - contains the length of 
										the next field, which is the security-result data field.								
									</t>							
									<t>
										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).								
									</t>
								</list>						
							</t>
						</list>			
					</t>		
				</list>
			</t>
			
  			   						
			<t>
				The structure of the cipher suite flags field is shown 
				in <xref target="cs_flags"/>. 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 <xref target="RFC5050"/>, the description below numbers the bit positions 
				from the right rather than the standard RFC definition, which 
				numbers bits from the left.
			
				<list>
					<t> bits 6-3 are reserved for future use.</t>					
					<t> src - bit 2 indicates whether the EID-reference field of 
						the ASB contains the optional reference to the security-source.</t>
					<t> parm - bit 1 indicates whether or not the 
						cipher suite parameters length and cipher suite parameters 
						data fields are present.</t>
					<t> res - bit 0 indicates whether or not the ASB contains the 
						security-result length and security-result data fields.</t>
				</list>		
			</t>

			<figure anchor="cs_flags" title="Cipher Suite Flags">
  			 	<artwork><![CDATA[
  Bit   Bit   Bit   Bit   Bit   Bit   Bit
   6     5     4     3     2     1     0
+-----+-----+-----+-----+-----+-----+-----+
|    reserved           | src |parm | res |
+-----+-----+-----+-----+-----+-----+-----+
  			 	]]></artwork>  				
   			</figure>
		</section>

		<section anchor="enum" title="Block Ordering">
			<t>
				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. 
			</t>
			<t>
				 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.
			</t>
			<t>
				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. 
			</t>
			<t>	
				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.
			</t>
		</section>
		
		<section anchor="BAB" title="Bundle Authentication Block">
			<t>
				This section describes typical field values for the BAB, which
				is solely used to implement OP(authentication, bundle). 

				<list>
					<t> 
						The block-type code field value MUST be 0x02.
					</t>
					<t> 
						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.
					</t>
					<t>
						The security-target MUST be the entire bundle,
					    which MUST be represented by a &lt;block type&gt;&lt;occurrence number&gt; 
						of &lt;0x00&gt;&lt;0x00&gt;.  						
					</t>
					<t>
						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.
					</t>
					<t>
						The cipher suite parameters field MAY be present, if so 
						specified in the cipher suite specification. 
					</t>
					<t>
						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.  
					</t>
					<t>
						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.
					</t>
				</list>		
			</t>
			<t>
				Notes:
				<list style="symbols">
					<t> 
						When multiple BAB blocks are used, the mandatory fields of
						the Last BAB must match those of the First BAB.
					</t>
					<t>
						The First BAB or Lone BAB, when present, SHOULD immediately 
						follow the primary block.				
					</t> 
					<t>
						A Last BAB, when present, SHOULD be the last block in the bundle.				
					</t>
					<t>
						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.
					</t>

				</list>	 
			</t>
		</section>

		<section anchor="BIB" title="Block Integrity Block">
			<t>
				A BIB is an ASB with the following additional restrictions:
				<list>
					<t> 
						The block-type code value MUST be 0x03.
					</t>
					<t> 
						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.
					</t>
					<t>
						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).
					</t>
					<t>
						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.
					</t>
					<t>
						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.
					</t>
					<t>
						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.  
					</t>
					<t>
						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.
					</t>
					<t>
						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. 
					</t>
				</list>		
			</t>

			<t>
				Notes:
				<list style="symbols">
					<t>	
					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.
					</t>

					<t>
					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 <xref target="interact"/>.
					</t>

					<t>
					The use of a generally available key is RECOMMENDED if custodial 
					transfer is employed and all nodes SHOULD verify the bundle before 
					accepting custody.
					</t>
				</list>	 
			</t>
		</section>

		<section anchor="BCB" title="Block Confidentiality Block">
			
			<t>
				A BCB is an ASB with the following additional restrictions:	
				<list>
					<t> 
						The block-type code value MUST be 0x04.
					</t>
					<t>
						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.
					</t>
					<t>
						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. 
					</t>
					<t>
						The cipher suite ID MUST be documented as a 
						confidentiality cipher suite.
					</t>
					<t>  
						Key-information, if available, MUST appear only in a Lone BCB or a First BCB.  
					</t>
					<t>
						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 <xref target="parmresult" />) in the security-result of 
						the Lone BCB or Last BCB.
					</t>
					<t>
						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.
					</t>
					<t>
						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 <xref target="parmresult" />.
					</t>
					<t>
						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.
					</t>
				</list>
			</t>
			<t>
				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.		
			</t>
			<t>
				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 
				<xref target="parmresult" />) of the BCB. This "in-place" 
				encryption allows fragmentation, reassembly, and custody transfer 
				to operate without knowledge of whether or not encryption has occurred.	
			</t>
			<t>
				Notes:
				<list style="symbols">
					<t>
					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.
					</t>

					<t>
					The BCB&apos;s &quot;discard&quot; flag may be set independently from its 
					security-target&apos;s &quot;discard&quot; flag. Whether or not the BCB's &quot;discard&quot; 
					flag is set is an implementation/policy decision for the encrypting 
					node.  (The &quot;discard&quot; flag is more properly called the &quot;Discard if 
					block cannot be processed&quot; flag.)		
					</t>
					
					<t>
					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.
					</t>
					
				</list>	 
			</t>
						
		</section>
	
		<section anchor="interact" title="Block Interactions">
			<t>
			The three security-block types defined in this specification are designed to
			be as independent as possible. However, there are some cases where security blocks 
			may share a security-target creating processing dependencies. 
			</t>
			<t>
			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.			
			</t>
			<t>
			 	<list style="symbols">
				<t>
				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.
				</t>
				<t>
				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.
				</t>
				<t>
				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.			
				</t>
				<t>
				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.
				</t>
				<t>
				As mentioned in <xref target="BCB"/>, a BIB MUST NOT have a BCB as its security target. BCBs may embed integrity
				results as part of cipher suite parameters.
				</t>
				</list>	 
			</t>

			<t>
				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. 
			</t>
			
					</section>

		<section anchor="parmresult" title="Parameters and Result Fields">
			<t>
				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.		
			</t>
			<t>
				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.	
			</t>
			<t>
				Item types, name, and descriptions are defined as follows.
			</t>
			
				<texttable style="all" anchor="type_code_table">
				<preamble>
					Cipher suite parameters and result fields.	
				</preamble>
				<ttcol align='center'> Type </ttcol>
				<ttcol align='center'> Name </ttcol>
				<ttcol align='left'> Description </ttcol>
				
				<c>0</c>
				<c>Reserved</c>
				<c> </c>
				
				<c>1</c>
				<c>Initialization Vector (IV)</c>
				<c> A random value, typically eight to sixteen bytes.</c>

				<c>2</c>
				<c>Reserved</c>
				<c> </c>
				
				<c>3</c>
				<c>Key Information</c>
				<c>Material encoded or protected by the key management system and used to transport 
				   an ephemeral key protected by a long-term key.</c>

				<c>4</c>
				<c>Content Range</c>
				<c>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.</c>
	
	   			<c>5</c>
				<c>Integrity Signatures</c>
				<c>Result of BAB or BIB digest or other signing operation. </c>

			    <c>6</c>
				<c>Unassigned</c>
				<c> </c>

			    <c>7</c>
				<c>Salt</c>
				<c>An IV-like value used by certain confidentiality suites.</c>

				<c>8</c>
				<c>BCB Integrity Check Value (ICV) / Authentication Tag</c>
				<c>Output from certain confidentiality cipher suite operations to be used at 
				   the destination to verify that the protected data has 
				   not been modified. This value MAY contain padding if 
				   required by the cipher suite.</c>

				<c>9-255</c>
				<c>Reserved</c>
				<c> </c>				   																   								
			</texttable>
				
		</section>
		
		<section anchor="bsp_example" title="BSP Block Example">
			
			<t>
				An example of SBSP blocks applied to a bundle is illustrated in <xref target="bsp_bundle_fig"/>. 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.
			</t>
			
			<figure anchor="bsp_bundle_fig" title="Sample Use of BSP Blocks">
  				<artwork><![CDATA[
  			 			
         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)    |    |
+---------------------------------+----+  			 			  			 	
  			 	]]></artwork>  				
   			</figure>

			<t>
				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.
			
				<list style="symbols">
					<t>
						Authentication over the bundle. This is accomplished by two BAB blocks: B2 and B12.				
					</t>
					<t> 
						An integrity signature applied to the canonicalized primary block. This is accomplished by a single BIB, B3.
					</t>
					<t>
						Confidentiality for the first extension block. This is accomplished by a single BCB block, B4.  
					</t>
					<t>
						Integrity for the second extension block. This is accomplished by a single BIB block, B6.
					</t>
					<t>
						An integrity signature on the payload. This is accomplished by a single BIB block, B9.  
					</t>
					<t>
						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.
					</t>
				</list>
			</t>
		 
		</section>

	</section>

	<section anchor="SecProc" title="Security Processing">
		<t>
			This section describes the security aspects of bundle processing.	
		</t>
		
		<section anchor="CanonBundle" title="Canonical Forms">
			<t>
				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.	
			</t>
			<t>
				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 <xref target="RFC5050"/>.
			</t>
						
			<section anchor="BundleCanon" title="Bundle Canonicalization">
				<t>
					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.			
				</t>
				<t>
					Notes:
					<list style="symbols">
						<t> 
							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 (&quot;Block was forwarded without being processed&quot;).  
							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.
						</t>
						<t>
							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.
						</t>
						<t>
							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.
						</t>
						<t>
							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.
						</t>
					</list>			
				</t>	
	
			</section>

			<section anchor="BlockCanon" title="Block Canonicalization">
				<t>
					This algorithm protects those parts of a block 
					that SHOULD NOT be changed in transit.  
				</t>
				<t>
					There are three types of blocks that may undergo block 
					canonicalization: the primary block, the payload block, 
					or an extension block.
				</t>
	
				<section anchor="PrimaryCanon" title="Primary Block Canonicalization">
					<t>
						The canonical form of the primary block is shown in 
						<xref target="pblock"/>. Essentially, it de-references the dictionary 
						block, adjusts lengths where necessary, and ignores 
						flags that may change in transit.			
					</t>			

					<figure anchor="pblock" title="The Canonical Form of the Primary Bundle Block">
  			 			<artwork><![CDATA[
+----------------+----------------+----------------+----------------+
|    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                              |
+----------------+----------------+----------------+----------------+
  			 			]]></artwork>  				
   					</figure>

					<t>
						The fields shown in <xref target="pblock"/> are as follows:
						<list style="symbols">
							<t> 
								The version value is the single-byte value in 
								the primary block.
							</t>
							<t>
								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.
							</t>
							<t>
								The canonical primary block length value is a 
								four-byte value containing the length (in bytes) 
								of this structure, in network byte order.
							</t>
							<t>
								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.
							</t>
							<t>
								The source endpoint ID length and value are handled 
								similarly to the destination.
							</t>
							<t>
								The report-to endpoint ID length and value are 
								handled similarly to the destination.
							</t>
							<t>
								The unpacked SDNVs for the creation timestamp and lifetime 
								are copied from the primary block.
							</t>
							<t>
								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.
							</t>
						</list>			
					</t>
				</section>	
				<section anchor="PayloadCanon" title="Payload Block Canonicalization">
	
					<t>
						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 
						&quot;last block&quot; bit. The &quot;last block&quot; 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. 
					</t>
	
					<t>
						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.				
					</t>				
				</section>
					
				<section anchor="ESBCanon" title="Extension Block Canonicalization">
					<t>
						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 
						&quot;last block&quot; flag and the &quot;Block was forwarded without 
						being processed&quot; bit. The &quot;last block&quot; flag 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. 
					</t>
					<t>
						The &quot;Block was forwarded without being processed&quot; 
						flag is ignored because the bundle may pass through 
						nodes that do not understand that extension block 
						and this flag would be set.
					</t>
					<t>
						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 &lt;scheme&gt;:&lt;SSP&gt;, which
					    includes the ":" character.
					</t>
					<t>
						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.
					</t>
					
					<t>
						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.				
					</t>				
				</section>
			</section>	

		<section anchor="notesCanon" title="Considerations"> 
			<t>
				<list style="symbols">
					<t>	
						The canonical forms for the bundle and various extension blocks is 
						not transmitted.  It is simply an artifact used as 
						input to digesting.
					</t>
					<t>
						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.
					</t>
					<t>
						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 &lt; scheme name &gt; : 
						&lt; scheme-specific part (SSP)&gt; is used in the 
						canonicalization.   
					</t>

					<t>
						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 IRIs), 
						this problem may be an unavoidable source of integrity 
						failures.
					</t>
					<t>
						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.
					</t>
					<t>
						These canonicalization algorithms assume that endpoint 
						IDs themselves are immutable and they are unsuitable for use in 
						environments where that assumption might be violated.
					</t>
					<t>
						Cipher suites MAY define their own canonicalization algorithms and
						require the use of those algorithms over the ones provided in this
						specification.
					</t>
					
				</list>			
			</t>

		</section>
	</section>
		
	<section anchor="EIDConf" title="Endpoint ID Confidentiality">
		<t>
		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.
		</t>
		<t>
		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.
		</t>
	</section>
				
		<section anchor="BundleRX" title="Bundles Received from Other Nodes">
			<t>
				Security blocks MUST be processed in a specific order when received by a security-aware node.
				The processing order is as follows.
				<list style="symbols">
					<t>
						All BAB blocks in the bundle MUST be evaluated prior to evaluating any other block in the bundle.
					</t>
					<t>
						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.
					</t>
				</list>	
			</t>
		

			<section title="Receiving BAB Blocks">
				<t>
					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.  
				</t>
			
				<t>
					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 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.
				</t>
				<t>
					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.
				</t>
				<t> 
					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.
				</t>
				<t>
					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.
				</t>
			</section>

			<section title="Receiving BCB Blocks">
				<t>
					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.  
				</t>
				<t>
					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 <xref target="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.
				</t>
				<t>
					When a BCB is decrypted, the recovered plain-text MUST replace 
					the cipher-text in the security-target body data
				</t>
			</section>
						
			<section title="Receiving BIB Blocks">	
				<t>
					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.
				</t>
				<t>
					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.   
				</t>
				<t>
					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.  
				</t>
				<t>
					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. 
				</t>
				
			</section>
			
		</section>
		
		<section anchor="FragRe" title="Bundle Fragmentation and Reassembly">
			<t> 
				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 <xref target="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:
			
				<list style="symbols">
					<t>						
						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.	
					</t>
					
					<t>
						The authentication security policy requirements for a bundle MUST be 
						applied individually to all the bundles resulting from 
						a fragmentation event.
					</t>

					<t>
						A BAB cipher suite MAY specify that it only applies to 
						non-fragmented bundles and not to bundle fragments.
					</t>
					<t> 
						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.
					</t>
					
					<t>
						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.
					</t>				
				</list>
			</t>
		</section>
		
		<section anchor="React" title="Reactive Fragmentation">
			<t>
				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. 		
			</t>	
			
			<t>
				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. 
			</t>
			<t>
				If reactive fragmentation is allowed, then all BAB blocks must be removed from created fragments.
			</t>
		</section>

	</section>

	<section anchor="KeyMgmt" title="Key Management">
		<t>
			Key management in delay-tolerant networks is recognized as a difficult 
			topic and is one that this specification does not attempt to solve.  	
		</t>
	</section>

	<section anchor="PolCons" title="Policy Considerations">
		<t>
			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.
		

		<list style="symbols">
			<t>
				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.
			</t>

			<t>
				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. 
			</t>
			
			<t>
				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.
			</t>
			
			<t>
				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.				
			</t>
			
		</list>
		
		</t>
	</section>
	
	<section anchor="SecCons" title="Security Considerations">
		<t>
			Certain applications of DTN need to both sign and encrypt a message, 
			and there are security issues to consider with this.
		
		<list style="symbols">
			<t>
				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.
			</t>
			<t>
				To ensure that a security-target cannot be inspected during transit, it should be encrypted
				with a BCB.
			</t>
			<t>
				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.
			</t>
		</list>
		</t>
	</section>
	
	<section anchor="Conf" title="Conformance">
		<t>
			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.	
		</t>
	</section>
	
	<section anchor="IANA" title="IANA Considerations">
		<t>
			This protocol has fields that have been registered by IANA.
		</t>
	
		<section anchor="BlockType" title="Bundle Block Types">
			<t>
				This specification allocates three block types from the existing
   				"Bundle Block Types" registry defined in [RFC6255].
			</t>	
	
			<texttable anchor="iana_table">
				<preamble>
					Additional Entries for the Bundle Block-Type Codes Registry:	
				</preamble>
				<ttcol align='center'> Value </ttcol>
				<ttcol align='center'> Description </ttcol>
				<ttcol align='center'> Reference </ttcol>
				<c>2</c>
				<c>Bundle Authentication Block</c>
				<c>This document</c>
				
				<c>3</c>
				<c>Block Integrity Block</c>
				<c>This document</c>

				<c>4</c>
				<c>Block Confidentiality Block</c>
				<c>This document</c>
			</texttable>
		</section>		

		<section anchor="CipherFlag" title="Cipher Suite Flags">
			<t>
				This protocol has a cipher suite flags field and certain flags are
   				defined.  An IANA registry has been set up as follows.
			</t>
			<t>
   				The registration policy for this registry is: Specification Required
			</t>
			<t>
   				The Value range is: Variable Length
			</t>
	
			<texttable anchor="cflag_table">
				<preamble>
					Cipher Suite Flag Registry:	
				</preamble>
				<ttcol align='center'> Bit Position (right to left) </ttcol>
				<ttcol align='center'> Description </ttcol>
				<ttcol align='center'> Reference </ttcol>
				<c>0</c>
				<c>Block contains result</c>
				<c>This document</c>
				
				<c>1</c>
				<c>Block Contains parameters</c>
				<c>This document</c>

				<c>2</c>
				<c>Source EID ref present</c>
				<c>This document</c>
				
				<c>>3</c>
				<c>Reserved</c>
				<c>This document</c>

			</texttable>
		</section>	

		<section anchor="ParmAndResult" title="Parameters and Results">
			<t>
				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.
			</t>
			<t>
   				The registration policy for this registry is: Specification Required
			</t>
			<t>
   				The Value range is: 8-bit unsigned integer.
			</t>
	
			<texttable anchor="pr_table">
				<preamble>
					Cipher Suite Parameters and Results Type Registry:	
				</preamble>
				<ttcol align='center'> Value </ttcol>
				<ttcol align='center'> Description </ttcol>
				<ttcol align='center'> Reference </ttcol>
				<c>0</c> <c>reserved</c> <c>This document</c>
				<c>1</c> <c>initialization vector (IV)</c> <c>This document</c>
				<c>2</c> <c>reserved</c> <c>This document</c>
				<c>3</c> <c>key-information</c> <c>This document</c>
				<c>4</c> <c>content-range (pair of SDNVs)</c> <c>This document</c>
				<c>5</c> <c>integrity signature</c> <c>This document</c>
				<c>6</c> <c>unassigned</c> <c>This document</c>
				<c>7</c> <c>salt</c> <c>This document</c>
				<c>8</c> <c>BCB integrity check value (ICV)</c> <c>This document</c>
				<c>9-191</c> <c>reserved</c> <c>This document</c>
				<c>192-250</c> <c>private use</c> <c>This document</c>
				<c>251-255</c> <c>reserved</c> <c>This document</c>
			</texttable>
		</section>	
	</section>

</middle>


<back>
	<references title="Normative References">
		&RFC5050;
		&RFC2119;
		&RFC6255;
	</references>
	
	<references title="Informative References">
	&RFC4838;
	&RFC3986;
	&RFC6257;
	&RFC5751;
	</references>
	
	<section anchor="contr" title="Acknowledgements">
		<t>
			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.
		</t>
	</section>
</back>
</rfc>