wdiff draft-ietf-dtn-bpsec-03.txt draft-ietf-dtn-bpsec-04.txt

Delay-Tolerant Networking E. Birrane
Internet-Draft K. McKeever
Intended status: Standards Track JHU/APL
Expires: May 3, September 13, 2017 March 12, 2017 October 30, 2016

Bundle Protocol Security Specification
draft-ietf-dtn-bpsec-03
draft-ietf-dtn-bpsec-04

Abstract

This document defines a security protocol providing end to end data
integrity and confidentiality services for the Bundle Protocol.

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 May 3, September 13, 2017.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Supported Security Services . . . . . . . . . . . . . . . 3
1.3. Specification Scope . . . . . . . . . . . . . . . . . . . 4
1.4. Related Documents . . . . . . . . . . . . . . . . . . . . 5
1.5. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Key Properties . . . . . . . . . . . . . . . . . . . . . . . 7 6
2.1. Block-Level Granularity . . . . . . . . . . . . . . . . . 7 6
2.2. Multiple Security Sources . . . . . . . . . . . . . . . . 7
2.3. Mixed Security Policy . . . . . . . . . . . . . . . . . . 8 7
2.4. User-Selected Ciphersuites Cipher Suites . . . . . . . . . . . . . . . 8
2.5. Deterministic Processing . . . . . . . . . . . . . . . . 9 8
3. Security Blocks . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Block Definitions . . . . . . . . . . . . . . . . . . . . 9
3.1. Block
3.2. Uniqueness . . . . . . . . . . . . . . . . . . . . . . . 9
3.3. Target Multiplicity . . . . . . . . . . . . . . . . . . . 10
3.4. Target Identification . . . . . . . . . . . . . . . . . . 10
3.2.
3.5. Block Representation . . . . . . . . . . . . . . . . . . 10
3.3. 11
3.6. Abstract Security Block . . . . . . . . . . . . . . . . . 11
3.7. Block Integrity Block . . . . . . . . . . . . . . . . . . 13
3.4. 14
3.8. Block Confidentiality Block . . . . . . . . . . . . . . . 14
3.5. 15
3.9. Block Interactions . . . . . . . . . . . . . . . . . . . 16
3.6.
3.10. Parameters and Result Fields Types . . . . . . . . . . . . . . . 17
3.7.
3.11. BSP Block Example . . . . . . . . . . . . . . . . . . . . 18 20
4. Canonical Forms . . . . . . . . . . . . . . . . . . . . . . . 20 22
4.1. Technical Notes . . . . . . . . . . . . . . . . . . . . . 20 22
4.2. Primary Block Canonicalization . . . . . . . . . . . . . 21 23
4.3. Non-Primary-Block Canonicalization . . . . . . . . . . . 22 23
5. Security Processing . . . . . . . . . . . . . . . . . . . . . 22 24
5.1. Bundles Received from Other Nodes . . . . . . . . . . . . 23 24
5.1.1. Receiving BCB Blocks . . . . . . . . . . . . . . . . 23 24
5.1.2. Receiving BIB Blocks . . . . . . . . . . . . . . . . 23 25
5.2. Bundle Fragmentation and Reassembly . . . . . . . . . . . 24 26
6. Key Management . . . . . . . . . . . . . . . . . . . . . . . 25 26
7. Security Policy Considerations . . . . . . . . . . . . . . . . . . . . 25 26
8. Security Considerations . . . . . . . . . . . . . . . . . . . 26 27
8.1. Attacker Capabilities and Objectives . . . . . . . . . . 27 28
8.2. Attacker Behaviors and BPSec Mitigations . . . . . . . . 28 29
8.2.1. Eavesdropping Attacks . . . . . . . . . . . . . . . . 28 29
8.2.2. Modification Attacks . . . . . . . . . . . . . . . . 28 29
8.2.3. Topology Attacks . . . . . . . . . . . . . . . . . . 29 31
8.2.4. Message Injection . . . . . . . . . . . . . . . . . . 30 31
9. Ciphersuite Cipher Suite Authorship Considerations . . . . . . . . . . . . 30 32
10. Defining Other Security Blocks . . . . . . . . . . . . . . . 31 33
11. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 32 34
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 34
12.1. Bundle Block Types . . . . . . . . . . . . . . . . . . . 32
12.2. Cipher Suite Flags . . . . . . . . . . . . . . . . . . . 32
12.3. Parameters and Results . . . . . . . . . . . . . . . . . 33 34
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
13.1. Normative References . . . . . . . . . . . . . . . . . . 34
13.2. Informative References . . . . . . . . . . . . . . . . . 34 35
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35

1. Introduction

This document defines security features for the Bundle Protocol
[BPBIS] (BP)
[BPBIS]. This BP Security Specification (BPSec) is intended for use
in delay-tolerant networks, in order Delay Tolerant Networks (DTNs) to provide Delay-Tolerant Networking (DTN) end-to-end security
services.

1.1. Motivation

The Bundle Protocol is used specification [BPBIS] defines DTN as referring to
"a networking architecture providing communications in DTNs that overlay multiple networks,
some of which and/or through
highly stressed environments" where "BP may be challenged by limitations such viewed as intermittent
and possibly unpredictable loss sitting at
the application layer of some number of constituent networks, forming
a store-carry-forward overlay network". The term "stressed"
environment refers to multiple challenging conditions including
intermittent connectivity, long or large and/or variable
delay, delays, asymmetric
data rates, and high bit error rates. The purpose of
the Bundle Protocol

There 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 a reasonable expectation that BP may be deployed in environments where such a
way that a portion of the network might become compromised, posing
the usual security challenges related to confidentiality and
integrity. However, the stressed nature of the BP operating
environment imposes unique requirements such that the usual security
mechanisms to usual security challenges may not apply. For example,
the store-carry-forward nature of the network may require protecting
data at rest while also preventing unauthorized consumption of
critical resources such as storage space. The heterogeneous nature
of the networks comprising the BP overlay, and/or associated timing,
might prevent the establishment of an end-to-end session to provide a
context for a security service. The partitionability of a DTN might
prevent regular contact with a centralized security oracle (such as a
certificate authority).

An end-to-end security service is needed that operates in all of the
environments where the BP operates.

1.2. Supported Security Services

This specification supports

BPSec provides end-to-end integrity and confidentiality services associated with for
BP bundles.

Integrity services ensure data within a bundle are not changed. Data
changes may be caused by processing errors, environmental conditions,
or intentional manipulation. An integrity service is one that
provides sufficient confidence to a data receiver that data has not
changed since its value was last asserted.

Confidentiality services ensure that the values of some only authorized receivers can
view those data within a bundle can only identified as needing to be determined by authorized receivers of private
amongst the data.
When a bundle traverses data source and data receivers. A confidentiality
services is one that provides confidence to a DTN, many data receiver that
private data was not viewed by other nodes in as the network other than bundle traversed
the destination node MAY see the contents of a bundle. A
confidentiality service allows a destination node to generate data
values from otherwise encrypted contents of a bundle. DTN.

NOTE: Hop-by-hop authentication is NOT a supported security service
in this specification, for three reasons.

1. The term "hop-by-hop" is ambiguous in a BP overlay, as nodes that
are adjacent in the overlay may not be adjacent in physical
connectivity. This condition is difficult or impossible to
predict in the overlay and therefore makes the concept of hop-by-
hop authentication difficult or impossible to enforce at the
overlay.

2. Networks in which BPSec may be deployed may have a mixture of
security-aware and not-security-aware nodes. Hop-by-hop
authentication cannot be deployed in a network if adjacent nodes
in the network have different security capabilities.

3. Hop-by-hop authentication can be viewed as a special case of data
integrity. As such, it is possible to develop policy that
provides a version of authentication can be achieved
by using the integrity mechanisms defined in this specification.

1.3. Specification Scope

This document describes defines the Bundle Protocol Security Specification
(BPSec), which provides security services for blocks within a bundle. provided by the BPSec.
This includes the data specification for individual representing these services
as BP extension
blocks blocks, and the processing instructions rules for those blocks. adding, removing, and
processing these blocks at various points in the bundle's traversal
of the DTN.

BPSec applies, by definition, applies only to those nodes that implement it, known as
"security-aware" nodes. There MAY might be other nodes in the DTN that
do not implement BPSec. All While all nodes in a BP overlay can interoperate with the
exception that exchange
bundles, BPSec security operations can only happen at BPSec
security-aware security-
aware nodes.

This specification does not address individual cipher suite
implementations. Different networking conditions and operational
considerations require varying strengths of security mechanism such
that mandating a cipher suite in this specification may result in too
much security for some networks and too little security in others.
The definition and enumeration of cipher suites
should is assumed to be
undertaken in other, separate specification documents.

This specification does not address the implementation of security
policy and does not provide a security policy for the BPSec.
Security Similar
to cipher suites, security policies are typically based on the nature and
capabilities of individual networks and network operational concepts. However,
this
This specification does recommend provide policy considerations when building a
security policy.

This specification does not address how to combine the BPSec security
blocks with other protocols, other BP extension blocks, or other best
practices to achieve security in any particular network
implementation.

1.4. 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 DTNs and identifies certain security at any length. assumptions
made by existing Internet protocols that are not valid in a DTN.

The DTN Bundle Protocol [BPBIS] defines the format and processing of the blocks used to implement
bundles that both carry the Bundle Protocol, excluding data and the
security-specific blocks defined here. security services operating
on those data. This document also defines the extension block format
used to capture BPSec security blocks.

The Bundle Security Protocol [RFC6257] and Streamlind Streamlined Bundle
Security Protocol [SBSP] introduce documents introduced the concepts of BP
security blocks for security services. services in a DTN. The BPSec is based off a
continuation and refinement of these documents.

1.5. 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].

This section defines those terms whose definition is important terminology either unique to the BPSec or
otherwise necessary for understanding of the concepts within defined in this
specification.

o Source Forwarder - the bundle any node from which that transmits a bundle originates.

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

o Forwarder - DTN. The Node
ID of the bundle node Bundle Protocol Agent (BPA) that forwarded sent the bundle on its
most recent hop.

o Intermediate Receiver, Waypoint, or "Next Hop" - the neighboring
bundle any node to which that
receives a forwarder forwards bundle from a bundle. Forwarder that is not the Destination.
The Node ID of the BPA at any such node.

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

The BPAs in the DTN.

o Security Block - a BPSec extension block in a bundle.

o Security Operation - the application of these terms applied a security service to a sample network topology
is shown
security target, notated as OP(security service, security target).
For example, OP(confidentiality, payload). Every security
operation in Figure 1. This figure shows four bundle nodes (BN1, BN2,
BN3, BN4) residing above some transport layer(s). Three distinct
transport and network protocols (T1/N1, T2/N2, and T3/N3) are also
shown.

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

Figure 1: Bundle Nodes Sitting Above the Transport Layer.

Consider the case where BN1 originates a bundle MUST be unique, meaning that it forwards a security
service can only be applied to
BN2. BN2 forwards a security target once in a bundle.
A security operation is implemented by a security block.

o Security Service - the bundle to BN3, security features supported by this
specification: integrity and BN3 forwards the confidentiality.

o Security Source - a bundle node that adds a security block to
BN4. BN1 is the source of a
bundle.

o Security Target - the block within a bundle and BN4 is that receives a
security-service as part of a security-operation.

o Source - the destination node which originates a bundle. The Node ID of the
BPA originating the bundle. BN1

2. Key Properties

The application of security services in a DTN is a complex endeavor
that must consider physical properties of the first forwarder, network, policies at
each node, 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) various application security requirements. This
section identifies and BN4 is the destination of the
bundle (as well as being defines the final intermediate receiver).

The following security-specific terminology is also defined to
clarify security operations in this specifiation.

o Security Service - key properties guiding design
decisions for the security features supported services provided by this
specification: integrity and confidentiality.

o specification.

2.1. Block-Level Granularity

Security Source - services within this specification MUST allow different
blocks within a bundle node that adds a to have different security block services applied to a
bundle.

o Security Target - the
them. As such, each security block within a bundle that receives a
security-service as part of MUST be
associated with a security-operation.

o Security Block - specific security operation.

Blocks within a BPSec extension bundle represent different types of information. The
primary block in contains identification and routing information. The
payload block carries application data. Extension blocks carry a bundle.

o Security Operation -
variety of data that may augment or annotate the application 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 service across an entire bundle fails to recognize that blocks in
a bundle may represent different types of information with different
security target, notated as OP(security service, security target). needs.

For example, 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 is implemented by a security block.

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
contents and an extension block containing summary information
related to the payload might be integrity signed but
otherwise unencrypted to
provide certain nodes waypoints access to payload-
related payload-related data without providing
access to the payload.

Each security block in a bundle will be associated with a specific
security operation.

2.2. Multiple Security Sources

A bundle MAY have multiple security blocks and these blocks MAY have
different 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,

When a node other than the bundle originator may add waypoint adds a security service to the bundle and, as such, bundle, the source for waypoint
is 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 for that service. The security block(s) which
represent that service at in the bundle destination.

Referring may need to Figure 1, if the bundle that originates at BN1 is given
security blocks by BN1, then BN1 is the record this security
source for those
blocks as well as being the source of the bundle. If the bundle that
originates at BN1 is then given destination might need this information for
processing. For example, a destination node might interpret policy
as it related to security block by BN2, then BN2 is blocks as a function of the security source
for that block even though BN1 remains the bundle
source. block.

2.3. Mixed Security Policy

Different

The security policy enforced by nodes in a the DTN may have different security related
capabilities. MAY differ.

Some nodes waypoints may not be security aware and will not
understand any be able to
process 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 Therefore, 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 will be treated
appropriately by non-security-aware nodes.

Extension blocks providing integrity services within a bundle MUST
support options to allow waypoint nodes to evaluate these signatures
if such nodes waypoints
Some waypoints will have the proper configuraton to do so.

2.4. User-Selected Ciphersuites

The security policies that require evaluating
security services defined in this specification rely on a variety even if they are not the bundle destination or the
final intended destination of cipher suites providing the service. For example, a waypoint
may choose to verify an integrity signatures, ciphertext, service even though the waypoint is
not the bundle destination and the integrity service will be needed
by other node along the bundle's path.

Some waypoints will determine, through policy, that they are the
intended recipient of the security service and terminate the security
service in the bundle. For example, a gateway node may determine
that, even though it is not the destination of the bundle, it should
verify and remove a particular integrity service or attempt to
decrypt a confidentiality service, before forwarding the bundle along
its path.

Some waypoints may understand security blocks but refuse to process
them unless they are the bundle destination.

2.4. User-Selected Cipher Suites

The security services defined in this specification rely on a variety
of cipher suites providing integrity signatures, cipher-text, and
other information necessary to populate security blocks. Users may
wish to MAY
select different cipher suites to implement different security services. For
example, some users may wish to use might prefer a SHA-256 based hash for integrity
whereas other users may require prefer a SHA-384 hash instead. The security
services defined in this specification MUST provide a mechanism for
identifying what cipher suite has been used to populate a security
block.

2.5. Deterministic Processing

In all cases, the processing order of security services within

Whenever a
bundle node determines that it must avoid ambiguity when evaluating process more than one
security block in a received bundle (either because the policy at a
waypoint states that it should process security blocks or because the
node is the bundle
destination. destination) the order in which security blocks
are processed MUST be deterministic. All nodes MUST impose this same
deterministic processing order for all security blocks. This
specification MUST provide provides determinism in the application and evaluation
of security services, even when doing so results in a loss of
flexibility.

3. Security Blocks
3.1. Block Definitions

There are

This specification defines two types of security blocks that may be included in a
bundle. These are block: the Block
Integrity Block (BIB) and the Block Confidentiality Block (BCB).

The BIB is used to ensure the integrity of its security target(s).
The integrity information in the BIB MAY (when possible) be verified by any node
in between the BIB security source and the bundle destination.
Security-aware waypoints may add or remove BIBs MAY be added to, and removed from, from bundles as a matter of in
accordance with their security policy.

The BCB indicates that the security target(s) has been encrypted,
in whole or in part, at the BCB security source in order to
protect its content while in transit. The BCB may be decrypted by
appropriate
security-aware nodes in the network, up to and including the
bundle destination, as a matter of security policy.

3.2. Uniqueness

Security operations in a bundle MUST be unique - the same security operation
service MUST NOT be applied to a security target more than once in a
bundle.
For example, the two Since a security operation is represented as a security
block, this limits what security blocks may be added to a bundle: if
adding a security block to a bundle would cause some other security
block to no longer represent a unique security operation then the new
block MUST NOT be added.

If multiple security blocks representing the same security operations: operation
were allowed in a bundle at the same time, there would exist
ambiguity regarding block processing order and the property of
deterministic processing blocks would be lost.

Using the notation OP(service,target), several examples illustrate
this uniqueness requirement.

o Signing the payload twice: The two operations OP(integrity,
payload) and OP(integrity, payload) are considered redundant and MUST NOT appear
together cannot both
be present in a bundle. However, the same bundle at the same time.

o Signing different blocks: The two security operations OP(integrity,
payload) and OP(integrity, extension_block_1) MAY are not redundant
and both may be present in the bundle. Also, same bundle at the same time.
Similarly, the two security operations OP(integrity, extension_block_1) and OP(integrity, extension_block_2)
OP(integrity,extension_block_2) are unique also not redundant and may
both appear be present in the same bundle.

If bundle at the same security service is to time.

o Different Services on same block: The two operations
OP(integrity,payload) and OP(confidentiality, payload) are not
inherently redundant and may both be applied present in the bundle at the
same time, pursuant to other processing rules in this
specification.

3.3. Target Multiplicity

Under special circumstances, a single security block can represent
multiple security
targets, and cipher suite parameters for each operations as a way of reducing the overall number
of security service are
identical, then blocks present in a bundle. In these circumstances,
reducing the number of security blocks in the bundle reduces the
amount of redundant information in the bundle.

A set of security operations can may be represented as by a single security
block with multiple security targets. In such a
case, all if and only if the following conditions are true.

o The security operations represented in apply the same security service. For
example, they are all integrity operations or all confidentiality
operations.

o The cipher suite parameters and key information for the security
operations are identical.

o The security source for the security operations is the same.
Meaning the set of operations are being added/removed by the same
node.

o No security operations have the same security target, as that
would violate the need for security operations to be unique.

o None of the security operations conflict with security operations
already present in the bundle.

When representing multiple security operations in a single security
block, the information that is common across all operations is
represented once in the security block, and the information which is
different (e.g., the security targets) are represented individually.
When the security block is processed all security operations
represented by the security block MUST be applied/evaluated together.

3.1. Block Identification

This specification requires at that every
time.

3.4. Target Identification

A security target is a block of in the bundle to which a security
operation
service applies. This target MUST be uniquely identifiable. and unambiguously
identifiable when processing a security block. The definition of the
extension block header from [BPBIS] provides such a mechanism in the "Block Number" field, which provides a unique identifier field
for a block within
a bundle. Within exactly this specification, purpose. Therefore, a security target will be
identified by its unique Block Number.

A security block MAY apply to multiple security targets if and only
if all cipher suite parameters, security source, and key information
are common for the security operation. In such in a case, the security
block MUST contain security results for each covered security target.
The use be represented as the Block Number of multiple the target block.

3.5. Block Representation

Each security targets block uses the Canonical Bundle Block Format as defined
in a security block provides an
efficiency mechanism so that identical ciphersuite information does
not need to be repeated across multiple security blocks.

3.2. Block Representation

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

o Block Type Code

o Block Number

o Block Processing Control Flags

o CRC Type and CRC Field (if present)

o Block Data Length

o Block Type Specific Data Fields

Security-specific information for a security block is captured in the
"Block Type Specific Data Fields".

3.6. Abstract Security Block

The structure of the security-specific portions of a security block
is identical for both the BIB and BCB Block Type Specific Data fields are
identifcal and illustrated in Figure 2. In Types. Therefore, this figure, field names
prefaced with
section defines an '*' are optional Abstract Security Block (ASB) data structure and their inclusion in
discusses the block definition, processing, and other constraints for using
this structure. An ASB is
indicated by never directly instantiated within a
bundle, it is only a mechanism for discussing the Cipher Suite Flags field.

Figure 2: common aspects of
BIB and BCB Block Structure

Where the block fields are identified as follows.

o # Security Targets - security blocks.

The number fields of security targets for this
security block. This value MUST the ASB SHALL be at least 1.

o as follows, listed in the order in
which they MUST appear.

Security Targets - Targets:
This array contains field identifiers the unique identifier block or blocks that are the target
of the blocks targetted security operation(s) represented by this security operation.
block. Each security target MUST represent a block present in is identified as the Block Number
of the bundle. A security target MUST NOT block. This field SHALL be repeated in this array.

o represented by a CBOR
array of data items. Each target within this CBOR array SHALL
be represented by a CBOR unsigned integer. This array MUST
have at least 1 item.

Cipher suite ID - Identifies Suite Id:
This field identifies the cipher suite used to implement the
security service represented by this block and applied to each
security target.

o This field SHALL be represented by a CBOR
unsigned integer.

Cipher suite flags - Identifies Suite Flags:
This field identifiers which optional security block fields are present in the
security block. The structure of the Cipher
Suite Flags This field is shown in Figure 3. The presence of an
optional SHALL be represented as a CBOR
unsigned integer containing a bit field is indicated by setting the value of 5 bits indicating
the
corresponding flag to one. A value presence or absence of zero indicates the
corresponding optional field is not present. The BPSEC Cipher
Suite Flags are defined other security block fields, as
follows.

Bit 1 (the most-significant bit, 0x10): reserved.

Bit 2 (0x08): reserved.

Bit 3 (0x04): reserved.

Bit 4 (0x02): Security Source Present Flag.

Bit Bit Bit Bit
7 6 5 4 3 2 1 0
+-----------------------------------+-----+-----+
| reserved | src |parm |
+-----------------------------------+-----+-----+
MSB LSB

Figure 3: (the least-significant bit, 0x01): Cipher Suite Flags

Where:

* bits 7-2 are reserved for future use.

* src - bit
Parameters Present Flag.

In this field, a value of 1 indicates whether that the Security Source is present associated
security block field MUST be included in the security block.

* parm - bit A
value of 0 indicates whether or not that the Cipher Suite
Parameters associated security block field is present
MUST NOT be in the security block.

o (OPTIONAL)

Security Source (URI) - (Optional Field):
This field identifies the node Endpoint that inserted the security service
block in the bundle. If the security source field is not
present then the source MAY be inferred from other information,
such as the bundle source, source or the previous hop, or some other node as defined by
security policy.

o (OPTIONAL) This field SHALL be represented by a CBOR
array in accordance with [BPBIS] rules for representing
Endpoint Identifiers (EIDs).

Cipher Suite Parameters (Byte Array) - Compound (Optional Field):
This field of the
following two items.

* Length (Unsigned Integer) - specifies the length of the next
field, which captures the parameters data.

* Data (Byte Array) - A byte array encoding one or more cipher suite parameters, with each parameters that
should be provided to security-aware nodes when processing the
security service described by this security block. This field
SHALL be represented by a CBOR array. Each entry in this array
is a single cipher suite parameter. A single cipher suite
parameter SHALL also be represented as a Type-
Length-Value (TLV) triplet, defined CBOR array comprising
a 2-tuple of the type and value of the parameter, as follows.

+ Type (Byte) - The

* Parameter Type. This field identifiers which cipher suite
parameter type.

+ Length (Unsigned Integer) - The length of is being specified. This field SHALL be
represented as a CBOR unsigned integer. Potential parameter
types are described in Section 3.10. Other specifications
MAY define additional parameter types for use in this field.

* Parameter Value. This field captures the value associated
with this parameter.

+ Value (Byte Array) - The This field SHALL be represented by the
applicable CBOR representation of the parameter value.

See type. These
specifications are given in Section 3.6 3.10 for a list of parameter types
defined in this specification. Other specifications that
define other parameter types MUST include the appropriate
CBOR encoding of the parameter value.

Therefore, this field SHALL be
supported by BPSEC implementations. BPSEC cipher suite
specifications MAY define their own parameters represented as a CBOR array of
CBOR arrays.

Security Results:
This field captures the results of applying a security service
to the security targets in this security block. This field
SHALL be represented as a CBOR array. Each entry in this byte array.

o Security Result (Byte Array) - A security result is the output array
represents a "target list" of
an appropriate cipher suite specific calculation (e.g., security results for a
signature, Message Authentication Code (MAC), or cipher-text block
key). specific
security target. There MUST exist be one security result "target list" for each security
entry in the Security Targets field and target lists in the security block. A security result is a multi-field
component, described
Security Results field MUST be in the same order as follows.

* Total Length (Unsigned Integer) - specifies the length,
Security Targets field (e.g., the first "target list" MUST hold
results for the first entry in
bytes, of the remaining security result information.

* Results (Byte Array) - This field captures each Security Targets field, and
so on).

A "target list" is also represented as a CBOR array of the
individual security
results, catenated together, one results for each security target
covered by the that target. An individual
security block. Each result is captured by also represented as a CBOR array comprising
the
four-tuple of (Target, Type, Len, Value). The meaning 2-tuple of each
is given below.

+ Target (Optional) (Unsigned Integer) - If the security block
has multiple security targets, the target result type and result value, defined as
follows.

* Result Type. This field is captures the Block
Number type of the security target to which this
result. Some security result field
applies. If types capture the security block only has primary
output of a single cipher suite. Other security
target, this results contain
additional annotative information from the cipher suite
processing. This field is omitted.

+ Type (Unsigned Integer) - The type of security SHALL be represented as a CBOR
unsigned integer. Potential result types are described in
Section 3.10. Other specifications MAY define additional
result types for use in this field.

+ Length (Unsigned Integer) - The length

* Result Value. This field captures the value associated with
this result for this target. This field SHALL be
represented by the applicable CBOR representation of the
result field.

+ Value (Byte Array) - The results type. These specifications are given in Section 3.10
for result types defined in this specification. Other
specifications that define other result types MUST include
the appropriate CBOR encoding of the cipher suite
specific calculation.

3.3. result value.

3.7. Block Integrity Block

A BIB is an ASB a bundle extension block with the following characteristics: characteristics.

o The Block Type Code value MUST be 0x02. is as specified in Section 12.1.

o The Block Processing Control flags value can be set to whatever
values are required by local policy. Cipher suite designers
should carefully consider Type Specific Data Fields follow the effect structure of setting flags that either
discard the block or delete the bundle in the event that this
block cannot be processed.
ASB.

o A security target for a BIB listed in the Security Targets field MUST NOT
reference a security block defined in this specification (e.g., a
BIB or a BCB).

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

o An EID-reference to the security source MAY be present. If this
field is not present, then the security source of the block SHOULD
be inferred according to security policy and MAY default to the
bundle source. The security source may also be specified as part
of key information described in Section 3.6.

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. 3.10.

o 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 It is RECOMMENDED that cipher suite designers 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.

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.

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 3.5. 3.9.

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.

3.4.

3.8. Block Confidentiality Block

A BCB is an ASB a bundle extension block with the following characteristics: characteristics.

The Block Type Code value MUST be 0x03. is as specified in Section 12.1.

The Block Processing Control flags value can be set to whatever
values are required by local policy, except that this block MUST
have the "replicate in every fragment" flag set if the target of
the BCB is the Payload Block. Having that BCB in each fragment
indicates to a receiving node that the payload portion of each
fragment represents cipher-text. Cipher suite designers should
carefully consider

The Block Type Specific Data Fields follow the effect structure of setting flags that either discard the block or delete the bundle in the event that this block cannot
be processed.
ASB.

A security target for a BCB listed in the Security Targets field MAY
reference the payload block, a non-security extension block, or a
BIB block. A security target
in a BCB MUST NOT be include another BCB. BCB as a security
target. A BCB MUST NOT target the primary block.

The cipher suite ID Cipher Suite Id MUST be documented as a confidentiality cipher
suite.

Any additional bytes generated as a result of encryption and/or
authentication processing of from applying the cipher suite to a
security target SHOULD (such as additional authenticated text) MAY be
placed in an "integrity check value" field (see Section 3.6) or other
such appropriate area in the security result of the BCB.

An EID-reference to the security source MAY be (e.g., an Integrity Check
Value) in accordance with cipher suite and security policy.

An EID-reference to the security source MAY be present. If this
field is not present, then the security source of the block SHOULD
be inferred according to security policy and MAY default to the
bundle source. The security source may also be specified as part
of key information described in Section 3.6.

The security result MUST be present in the BCB. This compound
field normally contains fields such as an encrypted bundle
encryption key and/or authentication tag. 3.10.

The BCB modifies the contents of its security target. target(s). When a BCB
is applied, the security target body data are encrypted "in-place".
Following encryption, the security target body data Block Type Specific Data
Fields contains cipher-
text, cipher-text, not plain-text. Other security target block fields (such as
type, processing control flags, and length)
remain unmodified. unmodified, with the exception of the Block Data Length field,
which may be changed if the BCB is allowed to change the length of
the block (see below).

Fragmentation, reassembly, and custody transfer are adversely
affected by a change in size of the payload block 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 3.6) of the BCB. This "in-
place" "in-place" encryption allows fragmentation, reassembly,
and custody transfer to operate without knowledge of whether or not
encryption has occurred.

If a BCB cannot alter the size of the security target (e.g., the
security target is the payload block or block length modifications
are disallowed by policy) then differences in the size of the cipher-
text and plain-text MUST be handled in the following way. If the
cipher-text is shorter in length than the plain-text, padding must be
used in accordance with the cipher suite policy. If the cipher-text
is larger than the plain-text, overflow bytes MUST be placed in
overflow parameters in the Security Result field.

Notes:

o It is RECOMMENDED that cipher suite designers 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.

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 BCB block processing control flags 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 processing control flags of the
encrypting node. (The "discard" flag is more properly called the
"Discard if block cannot security target(s). The
setting of such flags SHOULD be processed" flag.) an implementation/policy decision
for the encrypting node.

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

3.5.

3.9. Block Interactions

The 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 waypoint 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 any integrity operation already defined for that
target. This means that if a BCB is added to encrypt a block,
another BCB MUST also be added to encrypt a BIB also targeting
that block.

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

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

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

o As mentioned in Section 3.3, 3.7, a BIB MUST NOT have a BCB as its
security target. BCBs may embed integrity results as part of
cipher suite parameters.
security results.

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. 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.

3.6.

3.10. Parameters and Result Fields

Various cipher suites include several items in the cipher Types

Cipher suite parameters and/or and security result fields. Which items MAY appear is
defined results may capture multiple
types of information in a security block. This section identifies a
set of parameters and results that are available in any BPSec
implementation for use by the particular any cipher suite description. suite. Individual cipher suites
MAY define additional parameters and results. A cipher suite MAY support several
include multiple instances of the same type within of parameter or result in
a single security block.

Each item is

Parameters and results are represented as a type-length-value. Type is using CBOR, and any
identification of a single
byte indicating the item. Length is new parameter or result type MUST include how the count
value of data bytes to
follow, and is an Unsigned Integer. Value is the data content of type will be represented using the
item.

Item types, name, and descriptions CBOR specification.
Types themselves are always represented as a CBOR unsigned integer.

Cipher suite parameter types, as defined by this specification, are
as follows.

Cipher suite parameters and result fields.

+-------+----------------+-----------------------------+------------+ Suite Parameter Types.

Table 1

Security result parameter types, as defined by this specification,
are as follows.

Security Result Types.

Table 1

3.7. 2

3.11. BSP Block Example

An example of BPSec blocks applied to a bundle is illustrated in
Figure 4. 1. 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 BPSec security
block. Since Block Number for the mechanism and format of a security target is not
specified in this document,
block, using the terminology B1...Bn is used to
identify blocks in the bundle for the purposes purpose of illustration.

Block in Bundle ID
+===================================+====+
| Primary Block | B1 |
+-----------------------------------+----+
| BIB | B2 |
| OP(integrity, target=B1) | |
+-----------------------------------+----+
| BCB | B3 |
| OP(confidentiality, target=B4) | |
+-----------------------------------+----+
| Extension Block | B4 |
+-----------------------------------+----+
| BIB | B5 |
| OP(integrity, target=B6) | |
+-----------------------------------+----+
| Extension Block | B6 |
+-----------------------------------+----+
| BCB | B7 |
| OP(confidentiality,target=B8,B9) OP(confidentiality,targets=B8,B9) | |
+-----------------------------------+----+
| BIB (encrypted by B7) | B8 |
| OP(integrity, target=B9) | |
+-----------------------------------+----|
| Payload Block | B9 |
+-----------------------------------+----+

Figure 4: 1: Sample Use of BSP BPSec Blocks

In this example a bundle has four non-security-related blocks: the
primary block (B1), three two extension blocks (B4,B6), and a payload block
(B9). The following security applications are applied to this
bundle.

o An integrity signature applied to the canonicalized primary block.
This is accomplished by a single BIB (B2).

o Confidentiality for the first extension block (B4). This is
accomplished by a BCB block (B3).

o Integrity for the second extension block (B6). This is
accomplished by a BIB block (B5). NOTE: If the extension block B6
contains a representation of the serialized bundle (such as a hash
over all blocks in the bundle at the time of its last
transmission) then the BIB block is also providing an
authentication service from the prior BPSEC-BPA to this BPSEC-BPA. service.

o An integrity signature on the payload (B10). This is accomplished
by a BIB block (B8).

o Confidentiality for the payload block and it's integrity
signature. This is accomplished by a BCB block, B7, encrypting B8
and B9.

4. Canonical Forms

By definition, an integrity In this case, the security source, key parameters, and
service determines whether any aspect of are identical, so a single security block MAY be used for
this purpose, rather than requiring two BCBs one to encrypt B8 and
one to encrypt B9.

4. Canonical Forms

By definition, an integrity service determines whether any aspect of
a block was changed from the moment the security service was applied
at the security source until the point of current evaluation. To
successfully verify the integrity of a block, the data passed to the
verifying cipher suite MUST be the same bits, in the same order, as
those passed to the signature-generating cipher suite at the security
source.

However, [BPBIS] does not specify a single on-the-wire encoding of
bundles. In cases where a security source generates a different
encoding than that used at a receiving node, care MUST be taken to
ensure that the inputs to cipher suites at the receiving node is a
bitwise match to inputs provided at the security source.

This section provides guidance on how to create a canonical form for
each type of block in a bundle. This form MUST be used when
generating inputs to cipher suites for use by BPSec blocks.

This specification does not define any security operation over the
entire bundle and, therefore, provides no canonical form for a
serialized bundle.

4.1. Technical Notes

The following technical considerations hold for all canonicalizations
in this section.

o Any numeric fields defined as variable-length MUST be expanded to
their "unpacked" form. For example, largest unpacked form before being used by a cipher suite.
If a field does not specify a maximum size, a 32-bit maximum size of 32
bits for integer value MUST and 64 bits for floating point values SHALL be unpacked to a four-byte representation.

o Each block encoding MUST follow the CBOR encodings provided in
[BPBISCBOR].
assumed.

o Canonical forms are not transmitted, they are used to generate
input to a cipher suite for secuity security processing at a security-aware security-
aware node.

o Reserved flags MUST NOT be included in any canonicalization as it
is not known if those flags will chaneg change in transit.

o These canonicalization algorithms assume that endpoint Endpoint IDs
themselves are immutable do not
change from the time at which a security source adds a security
block to a bundle and they are unsuitable for use in
environments where the time at which a node processes that assumption might be violated.
security block.

o Cipher suites MAY define their own canonicalization algorithms and
require the use of those algorithms over the ones provided in this
specification. In the event of conflicting canonicalization
algorithms, cipher suite algorithms take precedence over this
specification.

4.2. Primary Block Canonicalization

The canonicalization of the primary block canonical form is the same as the CBOR encoding of
the block, specified in [BPBIS]
with certain modifications to account for allowed block
changes as the bundle traverses the DTN. The fields that compromise the primary block, and any special considerations for their
representation in a canonical form, are as follows.

o The Version field is included, without modification. following exceptions.

o The following Bundle Processing Control Flags field is used, with modification.
Certain bundle processing flags MAY change as a
bundle transits the DTN without indicating an integrity error. These flags, which
are identified below, error and,
therefore, MUST NOT be represented included in the canonicalized
form canonicalization of the bundle processing flags and, instead, be represented
by the bit 0.

* Reserved flags.
primary block.

* Bundle is a Fragment flag.

o The CRC Type, Destination EID, Source Node ID, Report-To EID,
Creation Timestamp, and Lifetime fields are included, without
modification.

o The fragment ID field MAY change if fragment. (Bit 15, 0x0001)

* Custody transfer requested for this bundle. (Bit 12, 0x0008)

* Reserved (Bits 0-2, 0xE000)

Regardless of the bundle is fragmented value of these flags in
transit and, as such, this field the primary block, they
MUST NOT be included in the
canonicalization. set to 0 when canonicalized for security processing.

o The CRC field MAY change at each hop - for example, if a bundle
becomes fragmented, each fragment will have a different CRC value
from the original signed primary block. As such, this field MUST
NOT be included in the canonicalization.

4.3. Non-Primary-Block Canonicalization

All non-primary blocks (NPBs) in [BPBIS] share the same block structure and should be are
canonicalized as specified in [BPBIS] with the same way.

Canonicalization for NPBs is dependent on whether following exceptions.

o If the security
operation service being performed is integrity or confidentiality. Integrity
operations consider every field in the block, whereas confidentiality
operations only consider the block-type-specific data. Since
confidentiality is applied to hide information (replacing plaintext
with ciphertext) it provides no benefit to include in the is a confidentiality calculation information that MUST remain readable,
such as block fields other than service, then
the block-type-specific data.

The fields that comprise a NPB, Block Type Code, Block Number, Block Processing Control Flags,
CRC Type and any special considerations for
their representation CRC Field (if present), and Block Data Length fields
MUST NOT be included in a canonical form, the canonicalization. Confidentiality
services are as follows.

o The used to convert the Block Type Code field is included, without modification, for
integrity operations and omitted for confidentiality operations.

o The Block Number field is included, without modification, for
integrity operations and omitted for confidentiality operations. Specific Data Fields
from plain-text to cipher-text.

o The Block Processing Control Flags field Type Specific Data Field is included, without
modification, for both integrity operations and omitted for confidentiality operations, services,
with the exception of reserved flags
which are treated as 0 in both cases.

o The CRC type and CRC fields are included, without modification,
for integrity operations and omitted for confidentiality
operations.

o The Block Type Specific Data field is included, without
modification, for both integrity and confidentiality operations,
with the exception that that in some cases only a portion of the
payload data is to be processed. 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 field is
included.

5. Security Processing

This section describes the security aspects of bundle processing.

5.1. 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 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.

5.1.1. Receiving BCB Blocks

If a received bundle contains a BCB, the receiving node MUST
determine whether it has the responsibility of decrypting the BCB
security target and removing the BCB prior to delivering data to an
application at the node or forwarding the bundle.

If the receiving node is the destination of the bundle, the node MUST
decrypt any BCBs remaining in the bundle. If the receiving node is
not the destination of the bundle, the node MAY decrypt the BCB if
directed to do so as a matter of security policy.

If the security policy of a security-aware node specifies that a
bundle should have applied confidentiality to a specific security
target and no such BCB 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 block, the bundle MAY be
discarded.

If the relevant parts of an encrypted payload block cannot be
decrypted (i.e., the decryption key cannot be deduced or decryption
fails), then the bundle MUST be discarded and processed no further.
If an encrypted security target other than the payload block cannot
be decrypted then the associated security target and all security
blocks associated with that target MUST be discarded and processed no
further. In both cases, requested status reports (see [BPBIS]) MAY
be generated to reflect bundle or block deletion.

When a BCB is decrypted, the recovered plain-text MUST replace the
cipher-text in the security target body data Block Type Specific Data Fields.
If the Block Data Length field was modified at the time of encryption
it MUST be updated to reflect the decrypted block length.

If a BCB contains multiple security targets, all security targets
MUST be processed if when the BCB is processed by the Node. The effect of
this is to processed. Errors and other
processing steps SHALL be the same made as if each security target had been
represented by an individual BCB with a single security target.

5.1.2. Receiving BIB Blocks

If a received bundle contains a BIB, the receiving node MUST
determine whether it has the final responsibility of verifying the
BIB security target and whether to remove the BIB removing it prior to delivering data to an
application at the node or forwarding the bundle. 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.

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

If the bundle has a BIB and the receiving node is the destination for does not have the bundle, final responsibility of
verifying the node MUST BIB it MAY still attempt to verify the security target in accordance
with BIB to prevent
the cipher suite specification. needless forwarding of corrupt data. If a BIB the check fails, the
node SHALL process 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 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. If the check passes, the node MUST
NOT remove the BIB prior to forwarding.

If a BIB contains multiple security targets, all security targets
MUST be processed if the BIB is processed by the Node. The effect of
this is to Errors and
other processing steps SHALL be the same made as if each security target had
been represented by an individual BIB with a single security target.

5.2. Bundle Fragmentation and Reassembly

If it is necessary for a node to fragment a bundle payload, and
security services have been applied to that bundle, the fragmentation
rules described in [BPBIS] MUST be followed. As defined there and repeated
summarized here for completeness, only the payload block may be
fragmented; security blocks, like all extension blocks, can never be
fragmented.

Due to the complexity of bundle payload block fragmentation, including the
possibility of fragmenting bundle payload block fragments, integrity and
confidentiality operations are not to be applied to a bundle
representing a fragment (i.e., fragment. Specifically, a BCB or BIB MUST NOT be
added to a bundle whose "bundle if the "Bundle is a Fragment" flag is set in the
Bundle Processing Control Flags field).
Specifically, a BCB or BIB MUST NOT be added to a bundle fragment,
even if field.

Security processing in the security target presence of the security payload block is not the payload.
When integrity and confidentiality must fragmentation
MAY be applied to a fragment, we
RECOMMEND that handled by other mechanisms outside of the BPSec protocol or
by applying BPSec blocks in coordination with an encapsulation be used instead.
mechanism.

6. Key Management

Key management

There exist a myriad of ways to establish, communicate, and otherwise
manage key information in delay-tolerant networks a DTN. Certain DTN deployments might
follow established protocols for key management whereas other DTN
deployments might require new and novel approaches. BPSec assumes
that key management is recognized handled as a
difficult topic separate part of network design
and is one that this specification does not attempt
to solve. neither defines nor requires a specific key
management strategy.

7. Security Policy Considerations

When implementing BPSec, 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. No single set of policy decisions is envisioned to
work for all secure DTN deployments.

o If a bundle is received that contains more than one security
operation, in violation of BPSec, 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.

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 a waypoint 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 BPSec 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.
blocks that absolutely need them. If a BPA were to apply security
operations such as integrity or confidentiality to every block in
the bundle, regardless of the block type, need, there could be downstream errors
processing blocks whose contents must be inspected or changed at
every hop in along the network path.

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 If this condition is likely to an encrypted security target. be
encountered, there are (at least) three possible policies that
could handle this situation.

1. 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.

2. The encrypted block may be replicated as a new block and
integrity signed.

3. 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.

8. Security Considerations

Given the nature of delay-tolerant networking DTN applications, it is expected that bundles may
traverse a variety of environments and devices which each pose unique
security risks and requirements on the implementation of security
within BPSEC. BPSec. For these reasons, it is important to introduce key
threat models and describe the roles and responsibilities of the BPSEC
BPSec protocol in protecting the confidentiality and integrity of the
data against those threats
throughout the DTN. threats. This section provides additional
discussion on security threats that BPSEC BPSec will face and describe in additional
detail describes how BPSEC
BPSec security mechanisms operate to mitigate these threats.

It should be noted that BPSEC addresses only the security of data
traveling over the DTN, not the underlying DTN itself. Additionally,
BPSEC
BPSec addresses neither the fitness of externally-defined
cryptographic methods nor the security of their implementation. It
is the responsibility of the BPSEC BPSec implementer that appropriate
algorithms and methods are chosen. Furthermore, the BPSEC BPSec protocol
does not address threats which share computing resources with the DTN
and/or BPSEC BPSec software implementations. These threats may be
malicious software or compromised libraries which intend to intercept
data or recover cryptographic material. Here, it is the
responsibility of the BPSEC BPSec implementer to ensure that any
cryptographic material, including shared secret or private keys, is
protected against access within both memory and storage devices.

The threat model described here is assumed to have a set of
capabilities identical to those described by the Internet Threat
Model in [RFC3552], but the BPSEC BPSec threat model is scoped to
illustrate threats specific to BPSEC BPSec operating within DTN
environments and therefore focuses on man-in-the-middle (MITM)
attackers.

8.1. Attacker Capabilities and Objectives

BPSEC

BPSec was designed to protect against MITM threats which may have
access to a bundle during transit from its source, Alice, to its
destination, Bob. A MITM node, Mallory, is a non-cooperative node
operating on the DTN between Alice and Bob that has the ability to
receive bundles, examine bundles, modify bundles, forward bundles,
and generate bundles at will in order to compromise the
confidentiality or integrity of data within the DTN. For the
purposes of this section, any MITM node is assumed to effectively be
security-aware even if it does not implement the BPSec protocol.
There are three classes of MITM nodes which are differentiated based
on their access to cryptographic material:

o Unprivileged Node: Mallory has not been provisioned within the
secure environment and only has access to cryptographic material
which has been publicly-shared.

o Legitimate Node: Mallory is within the secure environment and
therefore has access to cryptographic material which has been
provisioned to Mallory (i.e., K_M) as well as material which has
been publicly-shared.

o Privileged Node: Mallory is a privileged node within the secure
environment and therefore has access to cryptographic material
which has been provisioned to Mallory, Alice and/or Bob (i.e.

K_M, K_A, and/or K_B) as well as material which has been publicly-
shared.

If Mallory is operating as a privileged node, this is tantamount to
compromise; BPSec does not provide mechanisms to detect or remove
Mallory from the DTN or BPSec secure environment. It is up to the
BPSec implementer or the underlying cryptographic mechanisms to
provide appropriate capabilities if they are needed. It should also
be noted that if the implementation of BPSec uses a single set of
shared cryptographic material for all nodes, a legitimate node is
equivalent to a privileged node because K_M == K_A == K_B.

A special case of the legitimate node is when Mallory is either Alice
or Bob (i.e., K_M == K_A or K_M == K_B). In this case, Mallory is
able to impersonate traffic as either Alice or Bob, which means that
traffic to and from that node can be decrypted and encrypted,
respectively. Additionally, messages may be signed as originating
from one of the endpoints.

8.2. Attacker Behaviors and BPSec Mitigations

8.2.1. Eavesdropping Attacks

Once Mallory has received a bundle, she is able to examine the
contents of that bundle and attempt to recover any protected data or
cryptographic keying material from the blocks contained within. The
protection mechanism that BPSec provides against this action is the
BCB, which encrypts the contents of its security target, providing
confidentiality of the data. Of course, it should be assumed that
Mallory is able to attempt offline recovery of encrypted data, so the
cryptographic mechanisms selected to protect the data should provide
a suitable level of protection.

When evaluating the risk of eavesdropping attacks, it is important to
consider the lifetime of bundles on a DTN. Depending on the network,
bundles may persist for days or even years. If a bundle does persist
on the network for years and the cipher suite used for a BCB provides
inadequate protection, Mallory may be able to recover the protected
data before that bundle reaches its intended destination.

8.2.2. Modification Attacks

As a node participating in the DTN between Alice and Bob, Mallory
will also be able to modify the received bundle, including non-BPSec
data such as the primary block, payload blocks, or block processing
control flags as defined in [BPBIS]. Mallory will be able to
undertake activities which include modification of data within the
blocks, replacement of blocks, addition of blocks, or removal of
blocks. Within BPSec, both the BIB and BCB provide integrity
protection mechanisms to detect or prevent data manipulation attempts
by Mallory.

The BIB provides that protection to another block which is its
security target. The cryptographic mechansims mechanisms used to generate the
BIB should be strong against collision attacks and Mallory should not
have access to the cryptographic material used by the originating
node to generate the BIB (e.g., K_A). If both of these conditions
are true, Mallory will be unable to modify the security target or the
BIB and lead Bob to validate the security target as originating from
Alice.

Since BPSec security operations are implemented by placing blocks in
a bundle, there is no in-band mechanism for detecting or correcting
certain cases where Mallory removes blocks from a bundle. If Mallory
removes a BCB block, but keeps the security target, the security
target remains encrypted and there is a possibility that there may no
longer be sufficient information to decrypt the block at its
destination. If Mallory removes both a BCB (or BIB) and its security
target there is no evidence left in the bundle of the security
operation. Similarly, if Mallory removes the BIB but not the
security target there is no evidence left in the bundle of the
security operation. In each of these cases, the implementation of
BPSec MUST be combined with policy configuration at endpoints in the
network which describe the expected and required security operations
that must be applied on transmission and are expected to be present
on receipt. This or other similar out-of-band information is
required to correct for removal of security information in the
bundle.

A limitation of the BIB may exist within the implementation of BIB
validation at the destination node. If Mallory is a legitimate node
within the DTN, the BIB generated by Alice with K_A can be replaced
with a new BIB generated with K_M and forwarded to Bob. If Bob is
only validating that the BIB was generated by a legitimate user, Bob
will acknowledge the message as originating from Mallory instead of
Alice. In order to provide verifiable integrity checks, both a BIB
and BCB should be used. Alice creates a BIB with the protected data
block as the security target and then creates a BCB with both the BIB
and protected data block as its security targets. In this
configuration, since Mallory is only a legitimate node and does not
have access to Alice's key K_A, Mallory is unable to decrypt the BCB
and replace the BIB.

8.2.3. Topology Attacks

If Mallory is in a MITM position within the DTN, she is able to
influence how any bundles that come to her may pass through the
network. Upon receiving and processing a bundle that must be routed
elsewhere in the network, Mallory has three options as to how to
proceed: not forward the bundle, forward the bundle as intended, or
forward the bundle to one or more specific nodes within the network.

Attacks that involve re-routing the packets throughout the network
are essentially a special case of the modification attacks described
in this section where the attacker is modifying fields within the
primary block of the bundle. Given that BPSec cannot encrypt the
contents of the primary block, alternate methods must be used to
prevent this situation. These methods MAY include requiring BIBs for
primary blocks, using encapsulation, or otherwise strategically
manipulating primary block data. The specifics of any such
mitigation technique are specific to the implementation of the
deploying network and outside of the scope of this document.

Furthermore, routing rules and policies may be useful in enforcing
particular traffic flows to prevent topology attacks. While these
rules and policies may utilize some features provided by BPSec, their
definition is beyond the scope of this specification.

8.2.4. Message Injection

Mallory is also able to generate new bundles and transmit them into
the DTN at will. These bundles may either be copies or slight
modifications of previously-observed bundles (i.e., a replay attack)
or entirely new bundles generated based on the Bundle Protocol,
BPSec, or other bundle-related protocols. With these attacks
Mallory's objectives may vary, but may be targeting either the bundle
protocol or application-layer protocols conveyed by the bundle
protocol.

BPSec relies on cipher suite capabilities to prevent replay or forged
message attacks. A BCB used with appropriate cryptographic
mechanisms (e.g., a counter-based cipher mode) may provide replay
protection under certain circumstances. Alternatively, application
data itself may be augmented to include mechanisms to assert data
uniqueness and then protected with a BIB, a BCB, or both along with
other block data. In such a case, the receiving node would be able
to validate the uniqueness of the data.

9. Ciphersuite Cipher Suite Authorship Considerations

Cipher suite developers or implementers should consider the diverse
performance and conditions of networks on which the Bundle Protocol
(and therefore BPSec) will operate. Specifically, the delay and
capacity of delay-tolerant networks can vary substantially. Cipher
suite developers should consider these conditions to better describe
the conditions when those suites will operate or exhibit
vulnerability, and selection of these suites for implementation
should be made with consideration to the reality. There are key
differences that may limit the opportunity to leverage existing
cipher suites and technologies that have been developed for use in
traditional, more reliable networks:

o Data Lifetime: Depending on the application environment, bundles
may persist on the network for extended periods of time, perhaps
even years. Cryptographic algorithms should be selected to ensure
protection of data against attacks for a length of time reasonable
for the application.

o One-Way Traffic: Depending on the application environment, it is
possible that only a one-way connection may exist between two
endpoints, or if a two-way connection does exist, the round-trip
time may be extremely large. This may limit the utility of
session key generation mechanisms, such as Diffie-Hellman, as a
two-way handshake may not be feasible or reliable.

o Opportunistic Access: Depending on the application environment, a
given endpoint may not be guaranteed to be accessible within a
certain amount of time. This may make asymmetric cryptographic
architectures which rely on a key distribution center or other
trust center impractical under certain conditions.

When developing new cipher suites for use with BPSec, the following
information SHOULD be considered for inclusion in these
specifications.

o New Parameters. Cipher suites MAY define new parameter types that
may appear in security blocks and used to configure the cipher
suite.

o New Results. Cipher suites MAY define new security result types
that may appear in security blocks and capture the outputs of the
cipher suite.

o New Canonicalizations. Cipher suites MAY define new
canonicalization algorithms as necessary.

10. Defining Other Security Blocks

Other security blocks (OSBs) may be defined and used in addition to
the security blocks identified in this specification. Both the usage
of BIB, BCB, and any future OSBs MAY co-exist within a bundle and MAY
be considered in conformance with BPSec if each of the following
requirements are met by any future identified security blocks.

o Other security blocks (OSBs) MUST NOT reuse any enumerations
identified in this specification, to include the block type codes
for BIB and BCB.

o An OSB definition MUST state whether it can be the target of a BIB
or a BCB. The definition MUST also state whether the OSB can
target a BIB or a BCB.

o An OSB definition MUST provide a deterinistic deterministic processing order in
the event that a bundle is received containing BIBs, BCBs, and
OSBs. This processing order MUST NOT alter the BIB and BCB
processing orders identified in this specification.

o An OSB definition MUST provide a canonicalization algorithm if the
default non-primary-block canonicalization algorithm cannot be
used to generate a deterministic input for a cipher suite. This
requirement MAY be waived if the OSB is defined so as to never be
the security target of a BIB or a BCB.

o An OSB definition MAY NOT require any behavior of a BPSEC-BPA that
is in conflict with the behavior identified in this specification.
In particular, the security processing requirements imposed by
this specification MUST be consistent across all BPSEC-BPAs in a
network.

o The behavior of an OSB when dealing with fragmentation MUST be
specified and MUST NOT lead to ambiguous processing states. In
particular, an OSB definition should address how to receive and
process an OSB in a bundle fragment that may or may not also
contain its security target. An OSB definition should also
address whether an OSB may be added to a bundle marked as a
fragment.

Additionally, policy considerations for the management, monitoring,
and configuration associated with blocks SHOULD be included in any
OSB definition.

NOTE: The burden of showing compliance with processing rules is
placed upon the standards defining new security blocks and the
identification of such blocks shall not, alone, require maintenance
of this specification.

11. Conformance

All implementations are strongly RECOMMENDED to provide some method
of hop-by-hop verification by generating a hash to some canonical
form of the bundle and placing an integrity signature on that form
using a BIB.

12. IANA Considerations

This protocol has fields that have been registered by IANA.

12.1. 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 | Block Integrity Block | This document |
| 3 | Block Confidentiality Block | This document |
+-------+-----------------------------+---------------+

Table 2

12.2. 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
Cipher Suite Flag Registry:

Table 3

12.3. Parameters and Results

This protocol has fields for cipher suite parameters and results. configuration associated with blocks SHOULD be included in any
OSB definition.

NOTE: The field burden of showing compliance with processing rules is a type-length-value triple
placed upon the standards defining new security blocks and a registry is required
for the "type" sub-field. The values for "type" apply
identification of such blocks shall not, alone, require maintenance
of this specification.

11. Conformance

All implementations are strongly RECOMMENDED to both provide some method
of hop-by-hop verification by generating a hash to some canonical
form of the
cipher suite parameters bundle and the cipher suite results fields. Certain
values are defined. An placing an integrity signature on that form
using a BIB.

12. 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. Considerations

Registries of Cipher Suite Parameters IDs, Cipher Suite Flags, Cipher Suite
Parameter Types, and Results Type Security Result Types will be required.

12.1. Bundle Block Types

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

Additional Entries for the Bundle Block-Type Codes Registry:

+---------+-------------------------------------------+-------------+

Table 4 3

13. References

13.1. Normative References

[BPBIS] Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol",
draft-ietf-dtn-bpbis-04
draft-ietf-dtn-bpbis-06 (work in progress), July 2016.

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

[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<http://www.rfc-editor.org/info/rfc3552>.

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

13.2. Informative References

[BPBISCBOR]
Burleigh, S., "Bundle Protocol CBOR Representation
Specification", draft-burleigh-dtn-rs-cbor-01 (work in
progress), April 2016.

[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.

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

[SBSP] Birrane, E., "Streamlined Bundle Security Protocol",
draft-birrane-dtn-sbsp-01 (work in progress), October
2015.

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

Kenneth McKeever
The Johns Hopkins University Applied Physics Laboratory
11100 Johns Hopkins Rd.
Laurel, MD 20723
US

Phone: +1 443 778 2237
Email: Ken.McKeever@jhuapl.edu