Internet DRAFT - draft-birrane-dtn-sbsp
draft-birrane-dtn-sbsp
Delay-Tolerant Networking E. Birrane
Internet-Draft JHU/APL
Intended status: Experimental J. Mayer
Expires: April 18, 2016 INSYEN AG
D. Iannicca
NASA GRC
October 16, 2015
Streamlined Bundle Security Protocol Specification
draft-birrane-dtn-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 blocks
in a bundle along a single path through a network.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 18, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Related Documents . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Key Properties . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Block-Level Granularity . . . . . . . . . . . . . . . . . 6
2.2. Multiple Security Sources . . . . . . . . . . . . . . . . 7
2.3. Single Security Destinations . . . . . . . . . . . . . . 7
2.4. Mixed Security Policy . . . . . . . . . . . . . . . . . . 8
2.5. User-Selected Ciphersuites . . . . . . . . . . . . . . . 8
2.6. Deterministic Processing . . . . . . . . . . . . . . . . 8
3. Security Block Definitions . . . . . . . . . . . . . . . . . 9
3.1. Block Identification . . . . . . . . . . . . . . . . . . 10
3.2. Abstract Security Block . . . . . . . . . . . . . . . . . 11
3.3. Block Ordering . . . . . . . . . . . . . . . . . . . . . 14
3.4. Bundle Authentication Block . . . . . . . . . . . . . . . 15
3.5. Block Integrity Block . . . . . . . . . . . . . . . . . . 16
3.6. Block Confidentiality Block . . . . . . . . . . . . . . . 17
3.7. Cryptographic Message Syntax Block . . . . . . . . . . . 19
3.8. Block Interactions . . . . . . . . . . . . . . . . . . . 20
3.9. Parameters and Result Fields . . . . . . . . . . . . . . 22
3.10. BSP Block Example . . . . . . . . . . . . . . . . . . . . 24
4. Security Processing . . . . . . . . . . . . . . . . . . . . . 27
4.1. Canonical Forms . . . . . . . . . . . . . . . . . . . . . 27
4.1.1. Bundle Canonicalization . . . . . . . . . . . . . . . 27
4.1.2. Block Canonicalization . . . . . . . . . . . . . . . 28
4.1.3. Considerations . . . . . . . . . . . . . . . . . . . 31
4.2. Endpoint ID Confidentiality . . . . . . . . . . . . . . . 32
4.3. Bundles Received from Other Nodes . . . . . . . . . . . . 32
4.3.1. Receiving BAB Blocks . . . . . . . . . . . . . . . . 32
4.3.2. Receiving BCB Blocks . . . . . . . . . . . . . . . . 33
4.3.3. Receiving BIB Blocks . . . . . . . . . . . . . . . . 33
4.4. Receiving CMSB Blocks . . . . . . . . . . . . . . . . . . 34
4.5. Bundle Fragmentation and Reassembly . . . . . . . . . . . 34
4.6. Reactive Fragmentation . . . . . . . . . . . . . . . . . 35
5. Key Management . . . . . . . . . . . . . . . . . . . . . . . 35
6. Policy Considerations . . . . . . . . . . . . . . . . . . . . 35
7. Security Considerations . . . . . . . . . . . . . . . . . . . 36
8. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 37
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
9.1. Bundle Block Types . . . . . . . . . . . . . . . . . . . 37
9.2. Cipher Suite Flags . . . . . . . . . . . . . . . . . . . 37
9.3. Parameters and Results . . . . . . . . . . . . . . . . . 38
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 39
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10.1. Normative References . . . . . . . . . . . . . . . . . . 39
10.2. Informative References . . . . . . . . . . . . . . . . . 39
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40
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.
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.
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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.
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.
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+---------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
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.
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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.
2. Key Properties
The application of security services in a DTN is a complex endeavor
that must consider physical properties of the network, policies at
each node, and various application security requirements. Rather
than enumerate all potential security implementations in all
potential DTN topologies, this specification defines a set of key
properties of a security system. The security primitives outlined in
this document MUST enable the realization of these properties in a
DTN deploying the Bundle Protocol.
2.1. Block-Level Granularity
Blocks within a bundle represent different types of information. The
primary block contains identification and routing information. The
payload block carries application data. Extension blocks carry a
variety of data that may augment or annotate the payload, or
otherwise provide information necessary for the proper processing of
a bundle along a path. Therefore, applying a single level and type
of security across an entire bundle fails to recognize that blocks in
a bundle may represent different types of information with different
security needs.
Security services within this specification MUST provide block level
granularity where applicable such that different blocks within a
bundle may have different security services applied to them.
For example, within a bundle, a payload might be encrypted to protect
its contents, whereas an extension block containing summary
information related to the payload might be integrity signed but
otherwise unencrypted to provide certain nodes access to payload-
related data without providing access to the payload.
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2.2. Multiple Security Sources
The Bundle Protocol allows extension blocks to be added to a bundle
at any time during its existence in the DTN. When a waypoint node
adds a new extension block to a bundle, that extension block may have
security services applied to it by that waypoint. Similarly, a
waypoint node may add a security service to an existing extension
block, consistent with its security policy. For example, a node
representing a boundary between a trusted part of the network and an
untrusted part of the network may wish to apply payload encryption
for bundles leaving the trusted portion of the network.
In each case, a node other than the bundle originator may be adding a
security service to the bundle and, as such, the source for the
security service will be different than the source of the bundle
itself. Security services MUST track their orginating node so as to
properly apply policy and key selection associated with processing
the security service at the bundle destination.
Referring to Figure 1, 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.
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.
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.
2.3. Single Security Destinations
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.
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Security-destinations different from bundle destinations would place
a tight (and possibly intractable) coupling between security and
routing services in an overlay network.
2.4. Mixed Security Policy
Different nodes in a DTN may have different security-related
capabilities. Some nodes may not be security-aware and will not
understand any security-related extension blocks. Other nodes may
have security policies that require evaluation of security services
at places other than the bundle destination (such as verifying
integrity signatures at certain waypoint nodes). Other nodes may
ignore any security processing if they are not the destination of the
bundle. The security services described in this specification must
allow each of these scenarios.
Extension blocks representing security services MUST have their block
processing flags set such that the block (and bundle, where
applicable) will be treated appropriately by non-security-aware
nodes.
Extension blocks providing integrity and authentication services
within a bundle MUST support options to allow waypoint nodes to
evaluate these signatures if such nodes have the proper configuraton
to do so.
2.5. User-Selected Ciphersuites
The security services defined in this specification rely on a a
variety of ciphersuites providing integrity signatures, ciphertext,
and other information necessary to populate security blocks. Users
may wish to select differing ciphersuites to implement different
security services. For example, some users may wish to use a SHA-1
based hash for integrity whereas other users may require a SHA-2 hash
instead. The security services defined in this specification MUST
provide a mechanism for identifying what ciphersuite has been used to
populate a security block.
2.6. Deterministic Processing
In all cases, the processing order of security services within a
bundle must avoid ambiguity when evaluating security at the bundle
destination. This specification MUST provide determinism in the
application and evaluation of security services, even when doing so
results in a loss of flexibility.
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3. Security Block Definitions
There are four types of security blocks that MAY be included in a
bundle. These are the Bundle Authentication Block (BAB), the Block
Integrity Block (BIB), the Block Confidentiality Block (BCB), and the
Cryptographic Messaging Syntax Block (CMSB).
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
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.
The CMSB contains a Cryptographic Message Syntax (CMS) payload
used to describe a security service applied to another extension
block. NOTE: Applications may choose to simply place CMS text as
the payload to the bundle. In such cases, security is considered
to be implemented at the application layer and CMSBs are not
required in that case.
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.
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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].
3.1. 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.
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.
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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
identification of singleton blocks SHOULD be in accordance with the
security policy of a node.
3.2. 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 four 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.
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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.
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
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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 3.1.
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 3.1 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).
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.
* (OPTIONAL) Cipher suite ID (SDNV)
* (OPTIONAL) 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 3.9 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.
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+ 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.
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
3.3. 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.
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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.
3.4. Bundle Authentication Block
This section describes typical field values for the BAB, which is
solely used to implement OP(authentication, bundle).
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
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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.
3.5. 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.
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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.
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 3.8.
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.
3.6. 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-tex
t. 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
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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 3.9) 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 3.9.
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 3.9) 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:
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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.
3.7. Cryptographic Message Syntax Block
A CMSB is an ASB with the following additional restrictions:
The block-type code value MUST be 0x05.
The content of the block must contain valid CMS data, as defined
in RFC 5652, and encoded in X.690 BER or DER encoding.
The block processing control flags value can be set to whatever
values are required by local policy. 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 reserved block type 0x01 specifies the singleton
payload block.
The security operation(s) will be performed on the security-target
block's data and the resulting CMS content will be stored within
the CMSB block's security-result field. The security-target
block's data will then be removed.
A CMSB block MAY include multiple CMS security operations within a
single block to allow for multiple nested operations to be
performed on a bundle block. Multiple CMSB blocks MAY be included
in a bundle as long as the security-target for each is unique.
Key-information, if available, MUST appear within the CMS content
contained in the security-result field.
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A CMSB block is created with its corresponding security-target field
pointing to a unique bundle block. The CMS security operations are
performed upon the security-target's data field and the resulting
encoded CMS content is stored within the CMS security-result field of
the CMSB's payload. The security-target block's data MAY be left
intact, replaced with alternate data, or completely erased based on
the specification of the utilized CMS ciphersuite definition and
applicable policy.
Multiple CMS operations may be nested within a single CMSB block to
allow more than one security operation to be performed upon a
security-target.
CMS Operations can be considered to have SBSP parallels: CMSB
Enveloped-Data content type SHALL be considered as equivalent to a
SBSP BCB block, and a CMSB Signed-Data type SHALL be considered as
equivalent to a SBSP BIB block.
3.8. Block Interactions
The four 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.
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.
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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 3.6, a BIB MUST NOT have a BCB as its
security target. BCBs may embed integrity results as part of
cipher suite parameters.
o As mentioned in Section 4.4, CMS operations are considered to have
operational parallels. When a CMSB is used, these parallels MUST
be considered for block interactions (e.g., a Signed-Data
structure MUST NOT be evaluated if the security-target of the
operation is also the security-target of a BCB)
o If a single bundle is going to contain a CMSB as well as other
security blocks, the CMS operations MUST be performed and the CMSB
MUST be created before any other security operation is applied.
o On reception of a bundle containing a CMSB and other security
blocks, the CMSB must be decoded last.
Additionally, since the CMSB block may contain either integrity or
confidentiality information in its encapsulated CMS, there is no way
to evaluate conflicts when a BIB/BCB and a CMSB have the same
security target. To address this concern, the following processing
rules MUST be followed.
o If an extension block is the target of a BIB or a BCB, then the
extension block MUST NOT also be the target of a CMSB, and vice-
versa.
o If a bundle is the target of a BAB block, then the bundle MUST NOT
also be the target of a CMSB, and vice-versa.
o Generally, a CMSB MUST be processed before any BIB or BCB blocks
are processed.
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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3.9. 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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3.10. 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.
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Block in Bundle ID
+=========================================+====+
| Primary Block | B1 |
+-----------------------------------------+----+
| First BAB | B2 |
| OP(authentication, Bundle) | |
+-----------------------------------------+----+
| Lone CMSB | B3 |
| security-target=0x01 | |
| security-result= | |
| | |
| Signed-Data { | |
| Digest Algorithm(s), | |
| Enveloped-Data { | |
| Encrypted Data, | |
| Encrypted Encryption Key(s) | |
| }, | |
| Signature(s) and Certificate Chain(s) | |
| } | |
| | |
+-----------------------------------------+----+
| Payload Block | B4 |
| (Empty Data Field) | |
+-----------------------------------------+----+
| Last BAB | B5 |
| OP(authentication, Bundle) | |
+-----------------------------------------+----+
Figure 5: Sample Bundle With CMS Block
In this example a bundle has two non-security-related blocks: the
primary block (B1) and a payload block (B4). This method would allow
for the bundle to carry multiple CMS payloads by utilizing a multiple
CMSB ASBs. The following security applications are applied to this
bundle.
o Authentication over the bundle. This is accomplished by two BAB
blocks: B2 and B5.
o Encrypted and signed CMS content contained within the CMSB block.
The first CMS operation, encryption, is performed on the data
contained within the block the security-target points to, in this
case, the payload block. The resulting encrypted data is then
signed and the final CMS content is stored within the CMSB block's
security-result field. The payload block's data is subsequently
removed now that the original data has been encoded within the
CMSB block.
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4. Security Processing
This section describes the security aspects of bundle processing.
4.1. 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].
4.1.1. 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.
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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.
4.1.2. Block Canonicalization
This algorithm protects those parts of a block that SHOULD NOT be
changed in transit.
There are three types of blocks that may undergo block
canonicalization: the primary block, the payload block, or an
extension block.
4.1.2.1. Primary Block Canonicalization
The canonical form of the primary block is shown in Figure 6.
Essentially, it de-references the dictionary block, adjusts lengths
where necessary, and ignores flags that may change in transit.
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+----------------+----------------+----------------+----------------+
| 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 6: The Canonical Form of the Primary Bundle Block
The fields shown in Figure 6 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.
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.
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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.
4.1.2.2. 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.
4.1.2.3. 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
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.
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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.
4.1.3. 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
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.
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o Cipher suites MAY define their own canonicalization algorithms and
require the use of those algorithms over the ones provided in this
specification.
4.2. 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.
4.3. 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.
4.3.1. 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
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.
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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.
4.3.2. 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
4.3.3. 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.
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.
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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.
4.4. Receiving CMSB Blocks
A CMSB MUST NOT be processed if its security target is also the
security target of any BAB, BIB, or BCB in the bundle.
The security services provided by a CMSB will be considered
successful if all services in the CMSB are validated. If any one
service encapsulated in the CMSB fails to validate, then the CMSB
MUST be considered as having failed to validate and MUST be
dispositioned in accordance with security policy.
4.5. 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.
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o The authentication security policy requirements for a bundle MUST
be applied individually to all the bundles resulting from a
fragmentation event.
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.
4.6. 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.
5. 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.
6. 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
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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.
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.
7. 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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8. 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.
9. IANA Considerations
This protocol has fields that have been registered by IANA.
9.1. 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
9.2. 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
9.3. 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
10. References
10.1. 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.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<http://www.rfc-editor.org/info/rfc5652>.
[RFC6255] Blanchet, M., "Delay-Tolerant Networking Bundle Protocol
IANA Registries", RFC 6255, May 2011.
10.2. 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.
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[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[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.
Authors' Addresses
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
Jeremy Pierce-Mayer
INSYEN AG
Muenchner Str. 20
Oberpfaffenhofen, Bavaria DE
Germany
Phone: +49 08153 28 2774
Email: jeremy.mayer@insyen.com
Dennis C. Iannicca
NASA Glenn Research Center
21000 Brookpark Rd.
Brook Park, OH 44135
US
Phone: +1-216-433-6493
Email: dennis.c.iannicca@nasa.gov
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