DTN Research Group S. Symington
Internet-Draft The MITRE Corporation
Expires: August 27, 2008 S. Farrell
Trinity College Dublin
H. Weiss
P. Lovell
SPARTA, Inc.
February 24, 2008
Bundle Security Protocol Specification
draft-irtf-dtnrg-bundle-security-05
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Abstract
This document defines the bundle security protocol, which provides
data integrity and confidentiality services. We also describe
various bundle security considerations including policy options.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Related Documents . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Security Blocks . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Abstract Security Block . . . . . . . . . . . . . . . . . 8
2.2. Bundle Authentication Block . . . . . . . . . . . . . . . 11
2.3. Payload Integrity Block . . . . . . . . . . . . . . . . . 13
2.4. Payload Confidentiality Block . . . . . . . . . . . . . . 14
2.5. Parameters and Result Fields . . . . . . . . . . . . . . . 17
2.6. Key Transport . . . . . . . . . . . . . . . . . . . . . . 18
2.7. PIB and PCB combinations . . . . . . . . . . . . . . . . . 19
3. Security Processing . . . . . . . . . . . . . . . . . . . . . 21
3.1. Nodes as policy enforcement points . . . . . . . . . . . . 21
3.2. Processing order of security blocks . . . . . . . . . . . 21
3.3. Security Zones . . . . . . . . . . . . . . . . . . . . . . 24
3.4. Canonicalisation of bundles . . . . . . . . . . . . . . . 25
3.5. Endpoint ID confidentiality . . . . . . . . . . . . . . . 31
3.6. Bundles received from other nodes . . . . . . . . . . . . 31
3.7. The At-Most-Once-Delivery Option . . . . . . . . . . . . . 33
3.8. Bundle Fragmentation and Reassembly . . . . . . . . . . . 33
3.9. Reactive fragmentation . . . . . . . . . . . . . . . . . . 34
4. Mandatory Ciphersuites . . . . . . . . . . . . . . . . . . . . 36
4.1. BAB-HMAC . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.2. PIB-RSA-SHA256 . . . . . . . . . . . . . . . . . . . . . . 37
4.3. PCB-RSA-AES128-PAYLOAD-PIB-PCB . . . . . . . . . . . . . . 38
5. Key Management . . . . . . . . . . . . . . . . . . . . . . . . 43
6. Default Security Policy . . . . . . . . . . . . . . . . . . . 44
7. Security Considerations . . . . . . . . . . . . . . . . . . . 46
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
9.1. Normative References . . . . . . . . . . . . . . . . . . . 48
9.2. Informative References . . . . . . . . . . . . . . . . . . 48
Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . .
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 52
Intellectual Property and Copyright Statements . . . . . . . . . . 53
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1. Introduction
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [1].
This document defines security features for the bundle protocol [2]
intended for use in delay tolerant networks, in order to provide the
DTN security services as described in the DTN Security Overview and
Motivations document [9].
The bundle protocol is used in DTNs which 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 bundle protocol is layered on top of
underlay-network-specific convergence layers, on top of network-
specific lower layers, to enable an application in one network to
communicate with an application in another network, both of which are
spanned by the DTN.
Security will be important for the bundle protocol. The stressed
environment of the underlying networks over which the bundle protocol
will operate makes it important that the DTN be protected from
unauthorized use, and this stressed environment poses unique
challenges on the mechanisms needed to secure the bundle protocol.
Furthermore, DTNs may very likely be deployed in environments where a
portion of the network might become compromised, posing the usual
security challenges related to confidentiality, integrity and
availability.
1.1. Related Documents
This document is best read and understood within the context of the
following other DTN documents:
The Delay-Tolerant Network Architecture [10] defines the
architecture for delay-tolerant networks, but does not discuss
security at any length.
The DTN Bundle Protocol [2] defines the format and processing of
the blocks used to implement the bundle protocol, excluding the
security-specific blocks defined here.
The Delay-Tolerant Networking Security Overview [9] provides an
informative overview and high-level description of DTN security.
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1.2. Terminology
We introduce the following terminology for purposes of clarity:
source - the bundle node from which a bundle originates
destination - the bundle node to which a bundle is ultimately
destined
forwarder - the bundle node that forwarded the bundle on its most
recent hop
intermediate receiver or "next hop" - the neighboring bundle node
to which a forwarder forwards a bundle.
In the figure below, which is adapted from figure 1 in the Bundle
Protocol Specification, four bundle nodes (denoted BN1, BN2, BN3, and
BN4) reside above some transport layer(s). Three distinct transport
and network protocols (denoted T1/N1, T2/N2, and T3/N3) are also
shown.
+---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+
| BN1 v | | ^ BN2 v | | ^ BN3 v | | ^ BN4 |
+---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+
| T1 v | + ^ T1/T2 v | + ^ T2/T3 v | | ^ T3 |
+---------v-+ +-^---------v-+ +-^---------v + +-^---------+
| N1 v | | ^ N1/N2 v | | ^ N2/N3 v | | ^ N3 |
+---------v-+ +-^---------v + +-^---------v-+ +-^---------+
| >>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^ |
+-----------+ +------------+ +-------------+ +-----------+
| | | |
|<-- An Internet --->| |<--- An Internet --->|
| | | |
BN = "Bundle Node" (as defined in the Bundle Protocol Specification
Bundle Nodes Sit at the Application layer of the Internet Model.
Figure 1
Bundle node 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
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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:
security-source - a bundle node that adds a security block to a
bundle
security-destination - a bundle node that processes a security
block of a bundle
security zone - that part of the network path from the security-
source to the security-destination
Referring to Figure 1 again:
If the bundle that originates at BN1 as source is given a security
block by BN1, then BN1 is the security-source of this bundle with
respect to that security block, as well as being the source of the
bundle.
If the bundle that originates at BN1 as source is given a security
block by BN2, then BN2 is the security-source of this bundle with
respect to that security block, even though BN1 is the source.
If the bundle that originates at BN1 as source is given a security
block by BN1 that is intended to be processed by BN3, then BN1 is the
security-source and BN3 is the security destination with respect to
this security block. The security zone for this block is BN1 to BN3.
A bundle may have multiple security blocks. The security-source of a
bundle with respect to a given security block in the bundle may be
the same as or different from the security-source of the bundle with
respect to a different security block in the bundle. Similarly, the
security-destination of a bundle with respect to each of that
bundle's security blocks may be the same or different. Therefore the
security zones for various blocks may be and often will be different.
If the bundle that originates at BN1 as source is given a security
block by BN1 that is intended to be processed by BN3, and BN2 adds a
security block with security-destination BN4, the security zones for
the two blocks overlap but not completely. This problem is discussed
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further in Section 3.3.
Forwarding nodes MUST transmit blocks in the same order as they were
received. This requirement applies to all dtn nodes, not just ones
which implement security processing. Blocks in a bundle may be added
or deleted according to the applicable specification, but those
blocks which are both received and transmitted MUST be transmitted in
the same order that they were received.
The block sequence also indicates the order in which certain
significant actions have affected the bundle, and therefore the
sequence in which actions must occur in order to produce the bundle
at its destination.
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2. Security Blocks
There are three types of security block that MAY be included in a
bundle. These are the Bundle Authentication Block (BAB), the Payload
Integrity Block (PIB), and the Payload Confidentiality Block (PCB).
The BAB is used to assure the authenticity and integrity of the
bundle along a single hop from forwarder to intermediate receiver.
The PIB is used to assure the authenticity and integrity of the
bundle from the PIB security-source, which creates the PIB, to the
PIB security-destination, which verifies the PIB authenticator.
The authentication information in the PIB may (if the ciphersuite
allows) be verified by any node inbetween the PIB security-source
and the PIB security-destination that has access to the
cryptographic keys and revocation status information required to
do so.
Since a BAB protects a bundle on a "hop-by-hop" basis and a PIB
protects on a (sort of) "end-to-end" basis, whenever both are
present the BAB MUST form the "outer" layer of protection - that
is, the BAB MUST always be calculated and added to the bundle
after the PIB has been calculated and added to the bundle.
The PCB indicates that some parts of the bundle have been
encrypted at the PCB security-source in order to protect the
bundle content while in transit to the PCB security-destination.
Each of the security blocks uses the Canonical Bundle Block Format as
defined in the Bundle Protocol Specification. That is, each security
block is comprised of the following elements:
- Block type code
- Block processing control flags
- Block EID reference list (optional)
- Block data length
- Block-type-specific data fields
Since the three security blocks have most fields in common, we can
shorten the description of the Block-type-specific data fields of
each security block if we first define an abstract security block
(ASB) and then specify each of the real blocks in terms of the fields
which are present/absent in an ASB. Note that no bundle ever
contains an ASB, which is simply a specification artifact.
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2.1. Abstract Security Block
An ASB consists of the following mandatory and optional fields:
- Block-type code (one byte) - as in all bundle protocol blocks
except the primary bundle block. The block types codes for the
security blocks are:
BundleAuthentication Block - BAB: 0x02
PayloadIntegrity Block - PIB: 0x03
PayloadConfidentiality Block - PCB: 0x04
- Block processing control flags (SDNV) - defined as in all bundle
protocol blocks except the primary bundle block (as described in
the Bundle Protocol [2]). SDNV encoding is described in the
bundle protocol. There are no general constraints on the use of
the block processing flags, and some specific requirements are
discussed later.[Comment.1][Comment.2]
- EID references - composite field defined in [2] containing
references to one or two EIDs. 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 one or more references is present, flags in the
ciphersuite ID field, described below, specify which.
If no EID fields are present then the composite field itself is
omitted entirely, rather than containing a count field of zero,
since such a representation is not permitted. The EID_REF bit is
not set.
The possible EIDs are:-
- (optional) Security-source - specifies the security source
for the service. If this is omitted, then the source of the
bundle is assumed to be the security-source.
- (optional) Security-destination - specifies the security
destination for the service. If this is omitted, then the
destination of the bundle is assumed to be the security-
destination.
If two EIDs are present, security-source is first and security-
destination comes second.
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- Block data length (SDNV) - as in all bundle protocol blocks
except the primary bundle block. SDNV encoding is described in
the bundle protocol.
- Block-type-specific data fields as follows:
- Ciphersuite ID (SDNV)
- Ciphersuite flags (SDNV)
- (optional) Correlator - when more than one related block is
inserted then this field MUST have the same value in each
related block instance. This is encoded as an SDNV. See note
in Section 3.8 with regard to correlator values in bundle
fragments.
- (optional) Ciphersuite parameters - compound field of next
two items
- Ciphersuite parameters length - specifies the length of
the following Ciphersuite parameters data field and is
encoded as an SDNV.
- Ciphersuite parameters data - parameters to be used with
the ciphersuite in use, e.g. a key identifier or
initialization vector (IV). See Section 2.5 for a list of
potential parameters and their encoding rules. The
particular set of parameters that are included in this field
are defined as part of the ciphersuite specification.
- (optional) Security result - compound field of next two items
- Security result length - contains the length of the next
field and is encoded as an SDNV.
- Security result data - contains the results of the
appropriate ciphersuite-specific calculation (e.g. a
signature, MAC or ciphertext block key).
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+----------------+----------------+----------------+----------------+
| type | flags (SDNV) | EID ref list(comp) |
+----------------+----------------+----------------+----------------+
| length (SDNV) | ciphersuite (SDNV) |
+----------------+----------------+----------------+----------------+
| ciphersuite flags (SDNV) | correlator (SDNV) |
+----------------+----------------+----------------+----------------+
|params len(SDNV)| ciphersuite params data |
+----------------+----------------+----------------+----------------+
|res-len (SDNV) | security result data |
+----------------+----------------+----------------+----------------+
The structure of an abstract security block
Figure 2
Some ciphersuites are specified in Section 4, which also specifies
the rules which MUST be satisfied by ciphersuite specifications.
Additional ciphersuites MAY be defined in separate specifications.
Ciphersuite IDs not specified are reserved. Implementations of the
bundle security protocol decide which ciphersuites to support,
subject to the requirements of section Section 4. It is RECOMMENDED
that implementations that allow additional ciphersuites permit
ciphersuite ID values at least up to and including 127, and they MAY
decline to allow larger ID values.
The structure of the ciphersuite 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 five flags defined for the field and 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 [2], the description below numbers the bit
positions from the right rather than the standard RFC definition
which numbers bits from the left.
src - bit 4 indicates whether the EID-reference field of the ASB
contains the optional reference to the security-source.
dest - bit 3 indicates whether the EID-reference field of the ASB
contains the optional reference to the security-destination.
parm - bit 2 indicates whether the ciphersuite-parameters-length
and ciphersuite parameters data fields are present or not.
corr - bit 1 indicates whether or not the ASB contains an optional
correlator.
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res - bit 0 indicates whether or not the ASB contains the security
result length and security result data fields.
bits 5-6 are reserved for future use.
Ciphersuite flags
Bit Bit Bit Bit Bit Bit Bit
6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+
| reserved |src |dest |parm |corr |res |
+-----+-----+-----+-----+-----+-----+-----+
Figure 3
A little bit more terminology: if the block is a PIB then when we
refer to the "PIB-source", we mean the security source for the PIB as
represented by the EID reference in the EID-references field.
Similarly we may refer to the PCB-dest, meaning the security-
destination of the PCB, again as represented by an EID reference.
For example, referring to Figure 1 again, if the bundle that
originates at BN1 as source is given a Confidentiality Block (PCB) by
BN1 that is protected using a key held by BN3 and it is given a
Payload Integrity Block (PIB) by BN1, then BN1 is both the PCB-source
and the PIB-source of the bundle, and BN3 is the PCB-dest of the
bundle.
The correlator field is used to associate several related instances
of a security block. This can be used to place a BAB that contains
the ciphersuite information at the "front" of a (probably large)
bundle, and another correlated BAB that contains the security result
at the "end" of the bundle. This allows even very memory-constrained
nodes to be able to process the bundle and verify the BAB. There are
similar use cases for multiple related instances of PIB and PCB as
will be seen below.
The ciphersuite specification MUST make it clear whether or not
multiple block instances are allowed, and if so, under what
conditions. Some ciphersuites can of course leave flexibility to the
implementation, whereas others might mandate a fixed number of
instances.
2.2. Bundle Authentication Block
In this section we describe typical BAB field values for two
scenarios - where a single instance of the BAB contains all the
information and where two related instances are used, one "up front"
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which contains the ciphersuite and another following the payload
which contains the security result (e.g. a MAC).
For the case where a single BAB is used:
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.
The ciphersuite ID MUST be documented as a hop-by-hop
authentication-ciphersuite which requires one instance of the BAB.
The correlator field MUST NOT be present.
The ciphersuite parameters field MAY be present, if so specified
in the ciphersuite specification.
An EID reference to the security-source SHOULD be present and, if
so, it MUST identify the forwarder of the bundle. (If the
forwarding node is identified in another block of the bundle that
the next hop supports, e.g., the Previous Hop Insertion Block, the
forwarding node need not be identified in the BAB. Similarly, if
the forwarding node is known through other implementation-specific
means, such as from the convergence layer, an EID reference need
not be included.)
An EID reference to the security-destination SHOULD NOT be present
unless the ciphersuite requires this information (since the first
node receiving the bundle ought be the one to validate the BAB).
The security result MUST be present as it is effectively the
"output" from the ciphersuite calculation (e.g. the MAC or
signature) applied to the (relevant parts of) the bundle (as
specified in the ciphersuite definition).
For the case using two related BAB instances, the first instance is
as defined above, except the ciphersuite ID MUST be documented as a
hop-by-hop authentication ciphersuite that requires two instances of
the BAB. In addition, the correlator MUST be present and the
security result length and security result fields MUST be absent.
The second instance of the BAB MUST have the same correlator value
present and MUST contain security result length and security result
data fields. The other optional fields MUST NOT be present.
Typically, this second instance of a BAB will be the last block of
the bundle.
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2.3. Payload Integrity Block
A PIB 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.
The ciphersuite ID MUST be documented as an end-to-end
authentication-ciphersuite or as an end-to-end error-detection-
ciphersuite.
The correlator MUST be present if the ciphersuite requires more
than one related instance of a PIB be present in the bundle. The
correlator MUST NOT be present if the ciphersuite only requires
one instance of the PIB in the bundle.
The ciphersuite parameters field MAY be present.
An EID reference to the security-source MAY be present.
An EID reference to the security-destination MAY be present.
The security result is effectively the "output" from the
ciphersuite calculation (e.g. the MAC or signature) applied to the
(relevant parts of) the bundle. As in the case of the BAB, this
field MUST be present if the correlator is absent. If more than
one related instance of the PIB is required then this is handled
in the same way as described for the BAB above.
The ciphersuite may process less than the entire original bundle
payload, either because the current payload is a fragment of the
original bundle or just becuase it is defined to process some
subset. For whatever reason, if the ciphersuite processes less
than the complete, original bundle payload MUST specify, as part
of the ciphersuite parameters, which bytes of the bundle payload
are protected.
For some ciphersuites, (e.g. those using asymmetric keying to produce
signatures or those using symmetric keying with a group key), the
security information can be checked at any hop on the way to the
destination that has access to the required keying information. This
possibility is further discussed in Section 3.6 below.
Most asymmetric PIB-ciphersuites will use the PIB-source to indicate
the signer and will not require the PIB-dest field because the key
needed to verify the PIB authenticator will be a public key
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associated with the PIB-source.
2.4. Payload Confidentiality Block
A typical confidentiality ciphersuite will encrypt the payload using
a randomly generated bundle encrypting key (BEK) and will use a PCB
security result to carry the BEK encrypted with some long term key
encryption key (KEK) or well-known public key. If neither the
destination nor security-destination resolves the key to use for
decryption, the ciphersuite parameters field can be used to indicate
the decryption key with which the BEK can be recovered. Subsequent
PCB security results will contain blocks encrypted using the BEK if
non-payload blocks are to be encrypted.
It is STRONGLY RECOMMENDED that a data integrity mechanism be used in
conjunction with confidentiality, and that encryption-only
ciphersuites NOT be used. The "authentication tag" or "integrity
check value" is stored into security-result rather than being
appended to the payload as is common in some protocols since, as
described below, it is important that there be no change in the size
of the payload.
The payload is encrypted "in-place", that is, following encryption,
the payload block payload field contains ciphertext, not plaintext.
The payload block processing flags are unmodified.[Comment.3]
The "in-place" encryption of payload bytes is to allow bundle payload
fragmentation and re-assembly, and custody transfer, to operate
without knowledge of whether or not encryption has occurred and, if
so, how many times.
Fragmentation and reassembly and custody transfer are adversely
affected by a change in size of the payload due to ambiguity about
what byte range of the original payload is actually in any particular
fragment. Ciphersuites SHOULD place any payload expansion, such as
authentication tags (integrity check values) and any padding
generated by a block-mode cipher, into an "integrity check value"
item in the security-result field (see Section 2.5) of the
confidentiality block.
Payload super-encryption is allowed. The second application of
confidentiality does not generally protect the parameters of the
first which represent a vulnerability in some circumstances.
Ciphersuites SHOULD define super-encryption such that it protects the
parameters of earlier encryption.
Confidentiality can be applied to blocks other than the payload and
in some cases this is recommended. The ciphersuite may apply
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different rules to confidentiality for non-payload blocks.
For example, multiple related PCB instances are required if both the
payload and the PS blocks in the bundle are to be encrypted. These
multiple PCB instances require correlators to associate them with
each other.
Confidentiality is normally applied to the payload, and possibly to
additional blocks. It is RECOMMENDED to apply a Payload
Confidentiality ciphersuite to non-payload blocks only if these
should be super-encrypted with the payload. If super-encryption if
the block is not desired then protection of the block should be done
by means other than a Payload Confidentiality ciphersuite.
There are situations where more than one PCB instance is required but
the instances are not "related" in the sense which requires
correlators. One example is where a payload is encrypted for more
than one security-destination so as to be robust in the face of
routing uncertainties. These multiple PCB instances, are not
"related" and should not contain correlators. [Comment.4]
A PCB 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 PCB containing
an encrypted key or a key reference MUST have the "replicate in
every fragment" flag set. This flag SHOULD NOT be set otherwise.
The ciphersuite ID MUST be documented as a confidentiality-
ciphersuite.
The correlator MUST be present if there is more than one related
PCB instance. The correlator MUST NOT be present if there are no
related PCB instances.
If a correlator is present, the encrypted key or key identifier
MUST be placed in the first PCB of the correlated set.
Any additional bytes generated as a result of encryption and/or
authentication processing of the payload SHOULD be placed in an
"integrity check value" field (see Section 2.5) in the security-
result of the first PCB.
The ciphersuite parameters field MAY be present.
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An EID reference to the security-source MAY be present.
An EID reference to the security-destination MAY be present.
The security result MAY be present and normally contains fields
such as an encrypted bundle encryption key, authentication tag or
the encrypted versions of bundle blocks other than the payload
block.
As was the case for the BAB and PIB, if the ciphersuite requires more
than one instance of the PCB, then the first occurrence MUST contain
any optional fields (e.g. security destination etc.) that apply to
all instances with this correlator. These MUST be contained in the
first instance and MUST NOT be repeated in other correlated blocks.
Fields that are specific to a particular instance of the PCB MAY
appear in that PCB. For example, security result fields MAY (and
probably will) be included in multiple related PCB instances, with
each result being specific to that particular block. Similarly,
several PCBs might each contain a ciphersuite parameters field with
an IV specific to that PCB instance.
Put another way: when confidentiality will generate multiple blocks,
it MUST first create a PCB with the required ciphersuite ID,
parameters etc. as specified above. Typically, this PCB will appear
"early" in the bundle. If this "first" PCB doesn't contain all of
the ciphertext, then it may be followed by other, correlated PCBs
which MUST NOT repeat the ciphersuite parameters, security-source, or
security-destination fields from the first PCB.
A PCB ciphersuite may, or may not, specify which blocks are to be
encrypted. If the ciphersuite doesn't specify this, then the node is
free to encrypt whichever blocks it wishes. If a PCB ciphersuite
does specify which blocks are to be encrypted, then doing otherwise
is an error.
The ciphersuite may process less than the entire original bundle
payload, either because the current payload is a fragment of the
original bundle or just becuase it is defined to process some subset.
For whatever reason, if the ciphersuite processes less than the
complete, original bundle payload MUST specify, as part of the
ciphersuite parameters, which bytes of the bundle payload are
protected.
After decryption the recovered plaintext should then replace the PCB
in the bundle for further processing (e.g. PIB verification). This
recovered plaintext MUST contain all the appropriate block type,
processing flags and length information. In other words delete the
PCB in question and place the recovered plaintext, which consists of
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some complete non-payload block, in the bundle at the location from
which the PCB was deleted.
A ciphersuite MUST NOT mix payload data and a non-payload block in a
single PCB.
Even if a to-be-encrypted block has the "discard" flag set, whether
or not the PCB'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.)
2.5. Parameters and Result Fields
Various ciphersuites include several items in the security-parameters
and/or security-result fields. Which fields may appear is defined by
the particular ciphersuite description.
Each field is represented as type-length-value. Type is a single
byte indicating which item this is. 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 are
0: reserved
1: initialization vector (IV)
2: reserved
3: key information
4: fragment range (offset and length as a pair of SDNVs)
5: integrity signature
6: reserved
7: C block salt
8: C block integrity check value (ICV)
9: reserved
10: encapsulated block
11: reserved
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12 - 191: reserved
192 - 250: private use
251 - 255: reserved
The folowing descriptions apply to usage of these items for all
ciphersuites. Additional characteristics are noted in the discussion
for specific suites.
- initialization vector(IV): random value, typically eight to
sixteen bytes
- key information: key material encoded or protected by the key
management system. This item is discussed further below
Section 2.6
- fragment range: pair of SDNV values (offset then length)
specifying the range of payload bytes to which a particular
operation applies. This is termed "fragment range" since that is
its typical use, even though sometimes it may describe a subset
range that is not a fragment
- integrity signature: result of BA or PS digest or signing
operation. This item is discussed further below Section 2.6
- C block salt: an IV-like value used by certain confidentiality
suites
- C block integrity check value(ICV): output from certain
confidentiality ciphersuite operations to be used at the
destination to verify that the protected data has not been
modified
- encapsulated block: result of confidentiality operation on
certain blocks, contains the ciphertext of the block and may also
contain an integrity check value appended to the ciphertext; may
also contain padding if required by the encryption mode; used for
non-payload blocks only
2.6. Key Transport
This specification endeavours to maintain separation between the
security protocol and key management. However these two interact in
the transfer of key information etc from security-source to security-
destination. In this discussion, "key information" includes keys,
key identifiers, integrity signatures and other similar information
protected by a key. It excludes payload, metadata and similar blocks
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even though these may be protected by a key.
The exact representation of "key information" and "integrity
signature" in their respective item types is currently a topic of
discussion. The general intent is that they should be ASN.1-encoded
as described in RFC 3369 [3] and related RFCs.
2.7. PIB and PCB combinations
Given the above definitions, nodes are free to combine applications
of PIB and PCB in any way they wish - the correlator value allows for
multiple applications of security services to be handled separately.
However, there are some clear security problems that could arise when
applying multiple services. For example, if we encrypted a payload
but left a PIB security result containing a signature in the clear,
payload guesses could be confirmed.
We cannot, in general, prevent all such problems since we cannot
assume that every ciphersuite definition takes account of every other
ciphersuite definition. However, we can limit the potential for such
problems by requiring that any ciphersuite which applies to one
instance of a PIB or PCB, must be applied to all instances with the
same correlator.
We now list the PIB and PCB combinations which we envisage as being
useful to support:
Encrypted tunnels - a single bundle may be encrypted many times
en-route to its destination. Clearly it must be decrypted an
equal number of times, but we can imagine each encryption as
representing the entry into yet another layer of tunnel. This is
supported by using multiple instances of PCB, but with the payload
encrypted multiple times, "in-place". Depending upon the
ciphersuite defintion, other blocks can and should be encrypted,
as discussed above and in Section 2.4 to ensure that parameters
are protected in the case of super-encryption.
Multiple parallel authenticators - a single security source might
wish to protect the integrity of a bundle in multiple ways. This
could be required if the bundle's path is unpredictable, and if
various nodes might be involved as security destinations.
Similarly, if the security source cannot determine in advance
which algorithms to use, then using all might be reasonable. This
would result in uses of PIB which presumably all protect the
payload, and which cannot in general protect one another. Note
that this logic can also apply to a BAB, if the unpredictable
routing happens in the convergence layer, so we also envisage
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support for multiple parallel uses of BAB.
Multiple sequential authenticators - if some security destination
requires assurance about the route that bundles have taken, then
it might insist that each forwarding node add its own PIB. More
likely, however would be that outbound "bastion" nodes would be
configured to sign bundles as a way of allowing the sending
"domain" to take accountability for the bundle. In this case, the
various PIBs will likely be layered, so that each protects the
earlier applications of PIB.
Authenticated and encrypted bundles - a single bundle may require
both authentication and confidentiality. Some specifications
first apply the authenticator and follow this by encrypting the
payload and authenticator. As noted previously in the case where
the authenticator is a signature, there are security reasons for
this ordering. (See the PCB-RSA-AES128-PAYLOAD-PIB-PCB
ciphersuite defined later in Section 4.3.) Others apply the
authenticator after encryption, that is, to the ciphertext. This
ordering is generally recommended and minimizes attacks which, in
some cases, can lead to recovery of the encryption key.
There are no doubt other valid ways to combine PIB and PCB instances,
but these are the "core" set supported in this specification. Having
said that, as will be seen, the mandatory ciphersuites defined here
are quite specific and restrictive in terms of limiting the
flexibility offered by the correlator mechanism. This is primarily
in order to keep this specification as simple as possible, while at
the same time supporting the above scenarios.
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3. Security Processing
This section describes the security aspects of bundle processing.
3.1. Nodes as policy enforcement points
All nodes are REQUIRED to have and enforce their own configurable
security policies, whether these policies be explicit or default, as
defined in Section 6.
All nodes serve as Policy Enforcement Points (PEP) insofar as they
enforce polices that may restrict the permissions of bundle nodes to
inject traffic into the network. Policies may apply to traffic
originating at the current node, traffic terminating at the current
node and traffic to be forwarded by the current node to other nodes.
If a particular transmission request, originating either locally or
remotely, satisfies the node's policy or policies and is therefore
accepted, then an outbound bundle can be created and dispatched. If
not, then in its role as a PEP, the node will not create or forward a
bundle. Error handling for such cases is currently considered out of
scope of this document.[Comment.5]
Policy enforcing code MAY override all other processing steps
described here and elsewhere in this document. For example, it is
valid to implement a node which always attempts to attach a PIB.
Similarly it is also valid to implement a node which always rejects
all requests which imply the use of a PIB.
Nodes MUST consult their security policy to determine the criteria
that a received bundle ought to meet before it will be forwarded.
These criteria MUST include a determination of whether or not the
received bundle must include a valid BAB, PIB or PCB. If the bundle
does not meet the node's policy criteria, then the bundle MUST be
discarded and processed no further; in this case, a bundle status
report indicating the failure MAY be generated.[Comment.6]
The node's policy MAY call for the node to add or subtract some
security blocks, for example, requiring the node attempt to encrypt
(parts of) the bundle for some security-destination, or requiring
that the node add a PIB. If the node's policy requires a BAB to be
added to the bundle, it MUST be added last so that the calculation of
its security result may take into consideration the values of all
other blocks in the bundle.
3.2. Processing order of security blocks
The processing order of security actions for a bundle is critically
important for the actions to complete successfully. In general, the
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actions performed at the originating node must be executed in the
reverse sequence at the destination. There are variations and
exceptions, and these are noted below.
The sequence is maintained in the ordering of security blocks in the
bundle. It is for this reason that blocks may not be rearranged at
forwarding nodes, whether they support the security protocols or not.
The only blocks that participate in this ordering are the primary and
payload blocks, and the security blocks themselves. All other
extension blocks are ignored for purposes of determining the
processing order.
The security blocks are added to and removed from a bundle in a last-
in-first-out (LIFO) manner, with the top of the stack immediately
after the primary block. A newly-created bundle has just the primary
and payload blocks, and the stack is empty. As security actions are
requested for the bundle, security blocks are pushed onto the stack
immediately after the primary block. The early actions have security
blocks close to the payload, later actions have blocks nearer to the
primary block. The actions deal with only those blocks in the bundle
at the time so, for example, the first to be added processes only the
payload and primary blocks, the next might process the first if it
chooses and the payload and primary, and so on. The last block to be
added can process all the blocks.
When the bundle is received, this process is reversed and security
processing begins at the top of the stack, immediately after the
primary block. The security actions are performed and the block is
popped from the stack. Processing continues with the next security
block until finally only the payload and primary blocks remain.
The simplicity of this description is undermined by various real-
world requirements. Nonetheless it serves as a helpful initial
framework for understanding the bundle security process.
The first issue is a very common one and easy to handle. The bundle
may be sent indirectly to its destination, requiring several
forwarding hops to finally arrive there. Security processing happens
at each node, assuming that the node supports bundle security. For
the following discussion, we assume that a bundle is created and that
confidentiality, then payload security and finally bundle
authentication are applied to it. The block sequence would therefore
be primary-BA-PS-C-payload. Traveling from source to destination
requires going through one intermediate node, so the trip consists of
two hops.
When the bundle is received at the intermediate node, the receive
processing validates the BA block and pops it from the stack.
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However the PS and C blocks have the final destination as their
security destination, so these can't be processed and removed. The
intermediate node then begins the send process with the four
remaining blocks in the bundle. The outbound processing adds any
security blocks required by local policy, and these are pushed on the
stack immediately after the primary block, ahead of the PS block. In
this example, the intermediate node adds a PS block as a signature
that the bundle has passed through the node.
The receive processing at the destination first handles the
intermediate node's PS block and pops it, next is the originator's PS
block, also popped, and finally the originator's confidentiality
block which allows the payload to be decrypted and the bundle handled
for delivery.
This simple scheme can easily be extended to very complex networks.
It cannot deal with security zones that overlap partially but not
completely and these are discussed further below Section 3.3.
Administrators SHOULD NOT configure security-sources and security-
destinations in a network such that overlapping security zones are
created.
The second issue relates to the reversibility of certain security
process actions. In general, the actions fall into two categories:
those which do not affect other parts of the bundle, and those which
are fully reversible. Creating a bundle signature, for example, does
not change the bundle content except for the result. The encryption
performed as part of the confidentiality processing does change the
bundle, but the reverse processing at the destination restores the
original content.
The third category is the one where the bundle content has changed
slightly and in a non-destructive way, but there is no mechanism to
reverse the change. The simplest example is the addition of an EID-
reference to a security block. The addition of the reference causes
the text to be added to the bundle's dictionary. The text may be
used also by other references so removal of the block and this
specific eid-reference does not cause removal of the text from the
dictionary. This shortcoming is of no impact to the "sequential" or
"wrapping" security schemes described above, but does cause failures
with "parallel" authentication mechanisms. Solutions for this
problem are implementation-specific and typically involve multi-pass
processing such that blocks are added at one stage and the security
results calculated at a later stage of the overall process.
Certain ciphersuites have sequence requirements for their correct
operation, most notably the BundleAuthentication ciphersuites.
Processing for BundleAuthentication is required to happen after all
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other sending operations, and prior to any receive operations at the
next hop node. It follows therefore that BA blocks must always be
pushed onto the stack after all others.
Although we describe the security block list as a stack, there are
some blocks which are placed after the payload and therefore are not
part of the stack. The BundleAuthentication ciphersuite #1 ("BA1")
requires a second, correlated block to contain the security-result
and this block is placed after the payload, usually as the last block
in the bundle. We can apply the stack rules even to these blocks by
specifying that they be added to the end of the bundle at the same
time that their "owner" or "parent" block is pushed on the stack. In
fact, they form a stack beginning at the payload but growing in the
other direction. Also, not all blocks in the main stack have a
corresponding entry in the trailing stack. The only blocks which
MUST follow the payload are those mandated by ciphersuites as
correlated blocks for holding a security-result. No other blocks are
required to follow the payload block and it is RECOMMENDED that they
NOT do so.
3.3. Security Zones
Each security block has a security zone, as described in the
discussion for Figure 1, and the zones for various blocks are often
different.
BA blocks are always for a single hop and these restricted zones
never cause conflict.
The zones for PS and C blocks are often from bundle source to bundle
destination, to provide end-to-end protection. A bundle-source-to-
bundle-destination zone likewise never causes a problem.
Another common scenario is for gateway-to-gateway protection of
traffic between two sub-networks.
Looking at Figure 1 and the simplified version shown in Figure 4, we
can regard BN2 and BN3 as gateways connecting the two subnetworks
labeled "An Internet". As long as they provide security for the BN2-
BN3 zone, all is well. Problems begin, for example, when BN2 adds
blocks with BN4 as the security-destination, and originating node BN1
has created blocks with BN3 as security-destination. We now have two
zones and neither is a subset of the other.
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+---------v-| +->>>>>>>>>>v-+ +->>>>>>>>>>v-+ +-^---------+
| BN1 v | | ^ BN2 v | | ^ BN3 v | | ^ BN4 |
+---------v-+ +-^---------v-+ +-^---------v-+ +-^---------+
>>>>>>>>^ >>>>>>>>>>^ >>>>>>>>^
<------------- BN1 to BN3 zone ------------>
<------------- BN2 to BN4 zone ------------>
Overlapping security zones
Figure 4
Consider the case where the security concern is for data integrity,
so the blocks are PayloadIntegrity. BN1 creates one ("PSa") along
with the new bundle, and BN2 pushes its own PS block "PSb" on the
stack, with security-destination BN4. When this bundle arrives at
BN3, the bundle blocks are
primary - PSb - PSa - payload
Block PSb is not destined for this node BN3 so must be forwarded.
This is the security-destination for block PSa so, after validation,
it should be removed from the bundle. But that will invalidate the
PSb signature when the block is checked at the final destination.
The PSb signature includes the primary block, PSb itself, PSa and the
payload block, so PSa MUST remain in the bundle. This is why
security blocks are treated as a stack and add/remove operations are
permitted only at the top-of-stack.
The situation would be worse if the security concern is
confidentiality, so C blocks are employed, such as the
confidentiality ciphersuite #3 ("C3") described in Section 4.3. In
this scenario, BN1 would encrypt the bundle with BN3 as security-
destination, BN2 would super-encrypt the payload and encapsulate the
C3 block for security-destination BN4. BN3 forwards all the blocks
without change. BN4 decrypts the payload from its super-encryption
and decapsulates the C3 block, only to find that it should have been
processed earlier. Assuming that BN4 has no access to BN3's key
store, BN4 has no way to decrypt the bundle and recover the original
content.
3.4. Canonicalisation of bundles
In order to verify a signature or MAC on 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 or MAC value. Consequently, a node MUST NOT change the
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encoding of any URI 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), a canonical form of any given bundle (that
contains a BAB or PIB) must be defined.
This section defines two bundle canonicalisation algorithms which can
be used by various ciphersuites.
3.4.1. Strict canonicalisation
The first algorithm that can be used permits no changes at all to the
bundle between the security-source and the security-destination. It
is mainly intended for use in BAB ciphersuites. This algorithm
conceptually catenates all blocks in the order presented, but omits
all security result data fields in blocks of this ciphersuite type.
That is, when a BA ciphersuite specifies this algorithm then we omit
all BAB security results for all BA ciphersuites, when a PIB
ciphersuite specifies this algorithm then we omit all PIB security
results for all PS ciphersuites. All security result length fields
are included, even though their corresponding security result data
fields are omitted.
Notes:
- In the above we specify that security result data is omitted.
This means that no bytes of the security result data are input.
We do not set the security result length to zero. Rather, we
assume that the security result length will be known to the module
that implements the ciphersuite 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.
- The 'res' bit of the ciphersuite ID, which indicates whether or
not the security result length and security result data field are
present, is part of the canonical form.
-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 bundle when the bundle
includes the security result data field.
-BABs are always added to bundles after PIBs, so when a PIB
ciphersuite specifies this strict canonicalisation algorithm and
the PIB is received with a bundle that also includes one or more
BABs, application of strict canonicalisation as part of the PIB
security result verification process requires that all BABs in the
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bundle be ignored entirely.
3.4.2. Mutable canonicalisation
This algorithm is intended to protect parts of the bundle which
should not be changed in-transit. Hence it omits the mutable parts
of the bundle.
The basic approach is to define a canonical form of the primary block
and catenate it with the security and payload blocks in the order
that they will be transmitted. This algorithm ignores all other
blocks because it cannot be determined whether or not they will
change as the bundle transits the network.
Many fields in various blocks are stored as variable-length SDNVs.
These are canonicalized in unpacked form, as eight-byte fixed-width
fields in network byte order. The size of eight bytes is chosen
because implementations may handle larger values as invalid, as noted
in [2].
The canonical form of the primary block is shown in Figure 5.
Essentially, it de-references the dictionary block, adjusts lengths
where necessary and ignores flags that may change in transit.
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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 |
+----------------+----------------+----------------+----------------+
The canonical form of the primary bundle block.
Figure 5
The fields shown in Figure 5 are:
Version is the single-byte value in the primary block.
Processing flags 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 SDNV is unpacked into a
fixed-width field and some bits are masked out. The unpacked
field is ANDed with mask 0x0000 0000 003E 031F to set to zero all
reserved bits and the "bundle is a fragment" bit.
Length - a four-byte value containing the length (in bytes) of
this structure, in network byte order.[Comment.7]
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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 canonicalised. Although the dictionary entries
contain null-terminators, the null-terminators are not included in
the length or the canonicalization.
Source endpoint ID length and value are handled similarly to the
destination.
Report-to endpoint ID length and value are handled similarly to
the destination.
Creation time (2 x SDNV) and Lifetime (SDNV) are simply copied
from the primary block, with the SDNV values being represented as
eight-byte unpacked values.
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 security-parameters.
For non-primary blocks being included in the canonicalization, the
block processing 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 and the "last block" flag. 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.
Endpoint ID references in security blocks are canonicalized using the
de-referenced text form in place of the reference pair. The
reference count is not included, nor is the length of the endpoint ID
text.
The block-length is canonicalized as an eight-byte unpacked value in
network byte order. If the payload data to be canonicalized is less
than the complete, original bundle payload, this field contain the
size of the data being canonicalized (the "effective block") rather
that the actual size of the block.
Payload blocks are generally cononicalized 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 ciphersuite parameters are required to
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specify which part of the payload is protected, as discussed further
below.
Security blocks are handled likewise, except that the ciphersuite
will likely specify that the "current" security block security result
field not be considered part of the canonical form. This differs
from the strict canonicalisation case since we might use the mutable
canonicalisation algorithm to handle sequential signatures such that
signatures cover earlier ones.
Notes:
- The canonical form of the bundle is not transmitted. It is
simply an artifact used as input to digesting.
- We omit the reserved flags because we cannot determine if they
will change in transit. The masks specified above may have to be
revised if additional flags are defined and they need to be
protected.
- Our URI encoding does not preserve the "null-termination"
convention from the dictionary field, nor do we separate the
scheme and ssp as is done there.
- 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 canonicalising URIs (or IRIs), this
problem may be an unavoidable source of integrity failures.
- 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.
If a bundle is fragmented before the PIB is applied then the PIB
applies to a fragment and not the entire bundle. However, the
protected fragment could be subsequently further fragmented, which
would leave the verifier unable to know which bytes were protected
by the PIB. Even in the absence of frgmentation the same
situation applies if the ciphersuite is defined to allow
protection of less than the entire, original bundle payload.
For this reason, PIB ciphersuites which support applying a PIB to
less than the complete, original bundle payload MUST specify, as
part of the ciphersuite parameters, which bytes of the bundle
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payload are protected. When verification occurs, only the
specified range of the payload bytes are input to PIB
verification. It is valid for a ciphersuite to be specified so as
to only apply to entire bundles and not to fragments. A
ciphersuite may be specified to apply to only a portion of the
payload, regardless of whether the payload is a fragment or the
complete original bundle payload.
The same fragmentation issue applies equally to PCB ciphersuites.
Ciphersuites which support applying confidentiality to fragments
MUST specify, as part of the ciphersuite parameters, which bytes
of the bundle payload are protected. When decrypting a fragment,
only the specified bytes are processed. It is also valid for a
confidentiality ciphersuite to be specified so as to only apply to
entire bundles and not to fragments.
3.5. Endpoint ID confidentiality
Every bundle MUST contain a primary block that cannot be encrypted
which also contains the source and destinations endpoint IDs, and
others. If endpoint ID confidentiality is required, then a fake
primary block with false values for these fields must be constructed
and with a new block type to contain the actual values. There is
presently no mechanism defined that supports such a "fake block" or
possibly "fake dictionary". Bundle-in-bundle encapsulation may solve
this problem in some instances.
Similarly, confidentiality requirements may also apply to other parts
of the primary block (e.g. the current-custodian) and that is
supported in the same manner.
3.6. Bundles received from other nodes
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 PCB/PIB handling or
delivery or forwarding.
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 all of its BABs identify a different node
other than the receiving node as the BAB security destination, then
the bundle MUST be discarded and processed no further.
If the bundle has one or more BABs that identify the receiving node
as the BAB security destination, or for which there is no security
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destination, then the value in the security result field(s) of the
BAB(s) MUST be verified according to the ciphersuite specification.
If for all such BABs in the bundle either the BAB security source
cannot be determined or the security result value check fails, the
bundle has failed to authenticate and the bundle MUST be discarded
and processed no further. Otherwise, if any of the BABs present
verify, the bundle is ready for further processing as determined by
extension blocks and/or policy.
BABs received in a bundle MUST be stripped before the bundle is
forwarded. New BABs MAY be added as required by policy. This may
require correcting the "last block" field of the to-be-forwarded
bundle.
Further processing of the bundle must take place in the order
indicated by the various blocks from the primary block to the payload
block, except as defined by an applicable specification.
If the bundle has a PCB and the receiving node is the PCB destination
for the bundle (either because the node is listed as the bundle's
PCB-dest or because the node is listed as the bundle's destination
and there is no PCB-dest), the node MUST decrypt the relevant parts
of the bundle in accordce with the ciphersuite specification. The
PCB SHALL be deleted. If the relevant parts of the bundle 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 the Bundle Protocol
[2]) indicating the decryption failure MAY be generated. If the PCB
security result included the ciphertext of a block other than the
payload block, the recovered plaintext block MUST be placed in the
bundle at the location from which the PCB was deleted.[Comment.8]
If the bundle has one or more PIBs for which the receiving node is
the bundle's PIB destination (either because the node is listed in
the bundle's PIB-dest or because the node is listed as the bundle's
destination and there is no PIB-dest), the node MUST verify the value
in the PIB security result field(s) in accordance with the
ciphersuite specification. If all the checks fail, the bundle has
failed to authenticate and the bundle SHALL be processed according to
the security policy. A bundle status report indicating the failure
MAY be generated. Otherwise, if the PIB verifies, the bundle is
ready to be processed for either delivery or forwarding. Before
forwarding the bundle, the node SHOULD remove the PIB from the
bundle, subject to the requirements of Section 3.2, unless it is
likely that some downstream node will also be able to verify the PIB.
If the bundle has a PIB and the receiving node is not the bundle's
PIB-dest the receiving node MAY attempt to verify the value in the
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security result field. If it is able to check and the check fails,
the node SHALL discard the bundle and it MAY send a bundle status
report indicating the failure.[Comment.9][Comment.10]
3.7. The At-Most-Once-Delivery Option
An application may request (in an implementation specific manner)
that a node be registered as a member of an endpoint and that
received bundles destined for that endpoint be delivered to that
application.
An option for use in such cases is known as "at-most-once-delivery".
If this option is chosen, the application indicates that it wants the
node to check for duplicate bundles, discard duplicates, and deliver
at most one copy of each received bundle to the application. If this
option is not chosen, the application indicates that it wants the
node to deliver all received bundle copies to the application. If
this option is chosen, the node SHALL deliver at most one copy of
each received bundle to the application. If the option is not
chosen, the node SHOULD, subject to policy, deliver all bundles.
To enforce this the node MUST look at the source/timestamp pair value
of each complete (reassembled, if necessary) bundle received and
determine if this pair, which uniquely identifies a bundle, has been
previously received. If it has, then the bundle is a duplicate. If
it has not, then the bundle is not a duplicate. The source/timestamp
pair SHALL be added to the list of pair values already received by
that node.
Each node implementation may decide how long to maintain a table of
pair value state.
Additional discussion relevant to at-most-delivery is in the DTN
Retransmission Block specification [11].
3.8. 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 [2] 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:
The security policy requirements for a bundle must be applied
individually to all the bundles resulting from a fragmentation event.
If the original bundle contained a PIB, then each of the PIB
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instances MUST be included in some fragment.
If the original bundle contained one or more PCBs, then any PCB
instances containing a BEK MUST have the "replicate in every
fragment" flag set, and thereby be replicated in every fragment.
This is to ensure that the canonical block-sequence can be recovered
during reassembly.
If the original bundle contained one or more correlated PCBs not
containing a BEK, then each of these MUST be included in some
fragment, but SHOULD NOT be sent more than once. They MUST be placed
in a fragment in accordance with the fragmentation rules described in
[2].
Note: various fragments may have additional security blocks added at
this or later stages and it is possible that correlators may collide.
In order to facilitate uniqueness, ciphersuites SHOULD include the
fragment-offset of the fragment as a high-order component of the
correlator.
3.9. 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 ciphersuite
used to calculate the BAB authentication information, if required.
(Some BAB ciphersuites, i.e., the mandatory BAB-HMAC ciphersuite
defined in Section 4.1, do not accommodate reactive fragmentation
because the security result in the BAB requires that the entire
bundle be signed. It is conceivable, however, that a BAB ciphersuite
could be defined such that multiple security results are calculated,
each on a different segment of a bundle, and that these security
results could be interspersed between bundle payload segments such
that reactive fragmentation could be accommodated.)
If the bundle is reactively fragmented by the intermediate receiver
and the BAB-ciphersuite is of an appropriate type (e.g. with multiple
security results embedded in the payload), the bundle MUST be
fragmented immediately after the last security result value in the
partial payload that is received. Any data received after the last
security result value MUST be dropped.
If a partial bundle is received at the intermediate receiver and is
reactively fragmented and forwarded, only the part of the bundle that
was not received MUST be retransmitted, though more of the bundle MAY
be retransmitted. Before retransmitting a portion of the bundle, it
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SHALL be changed into a fragment and, if the original bundle included
a BAB, the fragmented bundle MUST also, and its BAB SHALL be
recalculated.
This specification does not currently define any ciphersuite which
can handle this reactive fragmentation case.
An interesting possibility is a ciphersuite definition such that the
transmission of a follow-up fragment would be accompanied by the
signature for the payload up to the restart point.
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4. Mandatory Ciphersuites
This section defines the mandatory ciphersuites for this
specification. There is currently one mandatory ciphersuite for use
with each security block type (BAB, PIB and PCB). The BAB
ciphersuite is based on shared secrets using HMAC. The PIB
ciphersuite is based on digital signatures using RSA with SHA256.
The PCB ciphersuite is based on using RSA for key transport and AES
for bulk encryption.
4.1. BAB-HMAC
The BAB-HMAC ciphersuite has ciphersuite ID value 0x001.
Security parameters are optional with this scheme, but if used then
the only field that can be present is key information (see
Section 2.5). The exact type of key information to be used is an
implementation issue. In the absence of key information the receiver
is expected to be able to find the correct key based on the sending
identity. The sending identity may be known from the security-source
field or the content of a previous-hop block in the bundle. It may
also be determined using implementation-specific means such as the
convergence layer.
BAB-HMAC uses the strict canonicalisation algorithm in Section 3.4.1.
Strict canonicalization supports digesting of a fragment-bundle. It
does not permit the digesting of only a subset of the payload, but
only the complete contents of the payload of the current bundle,
which might be a fragment. The "fragment range" item for security-
parameters is not used to indicate a fragment, as this information is
digested within the primary block.
The variant of HMAC to be used is HMAC-SHA1 as defined in RFC 2104
[4].[Comment.11]
This ciphersuite requires the use of two related instances of the
BAB. It involves placing the first BAB instance (as defined in
Section 2.2) just after the primary block. The second (correlated)
instance of the BAB MUST be placed after all other blocks (except
possibly other BAB blocks) in the bundle.
This means that normally, the BAB will be the second and last blocks
of the bundle. If a forwarder wishes to apply more than one
correlated BAB pair, then this can be done. There is no requirement
that each application "wrap" the others, but the forwarder MUST
insert all the "up front" BABs, and their "at back" "partners"
(without any security result), before canonicalising.
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Inserting more than one correlated BAB pair would be useful if the
bundle could be routed to more than one potential "next-hop" or if
both an old or a new key were valid at sending time, with no
certainty about the situation that will obtain at reception time.
The security result is the output of the HMAC-SHA1 calculation with
input being the result of running the entire bundle through the
strict canonicalisation algorithm. Both required BAB instances MUST
be included in the bundle before canonicalisation.
4.2. PIB-RSA-SHA256
The PIB-RSA-SHA256 ciphersuite has ciphersuite ID value 0x002.
If the bundle being signed has been fragmented before signing, then
we have to specify which bytes were signed in case the signed bundle
is subsequently fragmented for a second time. If the bundle is a
fragment, then the ciphersuite parameters MUST include a fragment-
range field, as described in Section 2.5, specifying the offset and
length of the signed fragment. If the entire bundle is signed then
these numbers MUST be omitted.
The ciphersuite parameters field MAY also contain a key identifier.
The exact type of key identifier to be used is an implementation
issue. In the absence of a key identifier, the verifier of the PIB
is expected to be able to use the security source (if supplied) or
else the bundle source (if no security source is present) in order to
determine the correct public key to use for PIB verification.
PIB-RSA-SHA256 uses the mutable canonicalisation algorithm
Section 3.4.2, with the security-result data field for only the
"current" block being excluded from the canonical form. The
resulting canonical form of the bundle is the input to the signing
process. This ciphersuite requires the use of a single instance of
the PIB.
RSA is used with SHA256 as specified for the sha256WithRSAEncryption
PKCSv1.5 signature scheme in RFC 4055 [5]. The output of the signing
process is the security result item for the PIB.
"Commensurate strength" cryptography is generally held to be a good
idea. A combination of RSA with SHA256 is reckoned to require a 3076
bit RSA key according to this logic. Few implementations will choose
this length by default (and probably some just won't support such
long keys). Since this is an experimental protocol, we expect that
1024 or 2048 bit RSA keys will be used in many cases, and that that
will be fine since we also expect that the hash function "issues"
will be resolved before any standard would be derived from this
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protocol.[Comment.12]
4.3. PCB-RSA-AES128-PAYLOAD-PIB-PCB
[Comment.13]
The PCB-RSA-AES128-PAYLOAD-PIB-PCB ciphersuite has ciphersuite ID
value 0x003.
This scheme encrypts PIBs, PCBs and the payload. The key size for
this ciphersuite is 128 bits.
Encryption is done using the AES algorithm in Galois/Counter Mode
(GCM) as described in RFC 5084 [12] [Note: parts of the following
description are borrowed from RFC 4106].
The choice of GCM avoids expansion of the payload, which causes
problems with fragmentation/reassembly and custody transfer. GCM
also includes authentication, essential in preventing attacks that
can alter the decrypted plaintext or even recover the encryption key.
GCM is a block cipher mode of operation providing both
confidentiality and data origin authentication. The GCM
authenticated encryption operation has four inputs: a secret key, an
initialization vector (IV), a plaintext, and an input for additional
authenticated data (AAD) which is not used here. It has two outputs,
a ciphertext whose length is identical to the plaintext, and an
authentication tag, also known as the Integrity Check Value (ICV).
For consistency with the description in [12], we refer to the GCM IV
as a nonce. The same key and nonce combination MUST NOT be used more
than once. The nonce has the following layout
+----------------+----------------+---------------------------------+
| salt |
+----------------+----------------+---------------------------------+
| |
| initialization vector |
| |
+----------------+----------------+---------------------------------+
Nonce format.
Figure 6
The salt field is a four-octet value, usually chosen at random. It
MUST be the same for all PCBs which have the same correlator value.
The salt need not be kept secret.
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The initialization vector (IV) is an eight-octet value, usually
chosen at random. It MUST be different for all PCBs which have the
same correlator value. The value need not be kept secret.
The key (bundle encryption key, BEK) is a sixteen-octet (128 bits)
value, usually chosen at random. The value MUST be kept secret, as
described below.
The integrity check value is a sixteen-octet value used to verify
that the protected data has not been altered. The value need not be
kept secret.
This ciphersuite requires the use of a single PCB instance to deal
with payload confidentiality. If the bundle already contains PIBs or
PCBs then the ciphersuite will create additional correlated blocks to
protect these PIBs and PCBs. These "additional" blocks replace the
original blocks on a one-for-one basis, so the number of blocks
remains unchanged. All these related blocks MUST have the same
correlator value. The term "first PCB" in this section refers to the
single PCB if there is only one or, if there are several, then to the
one containing the key or key-identifier. This MUST be the first of
the set.
First PCB - the first PCB may contain a correlator value, and may
specify security-source and/or security-destination in the eid-list.
If not specified, the bundle-source and bundle-destination
respectively are used for these values, as with other ciphersuites.
The block MUST contain security-parameters and security-result
fields. Each field may contain several items formatted as described
in Section 2.5.
Security-parameters
salt
IV (this instance applies only to payload)
fragment offset and length, if bundle is a fragment
Security-result
key information
ICV
Subsequent PCBs MUST contain a correlator value to link them to the
first PCB. Security-source and security-destination are implied from
the first PCB, however see the discussion below concerning eid-list
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entries. They MUST contain security-parameters and security-result
fields as follows:
Security-parameters
IV for this specific block
Security-result
encapsulated block
The security-parameters and security-result fields in the subsequent
PCBs MUST NOT contain any items other than these two. Items such as
key and salt are supplied in the first PCB and MUST NOT be repeated.
Protection of the key is performed as defined in the Key Management
Specification [tbd]. Key management for this ciphersuite MUST
support PKCSv1.5 rsaEncryption as specified in RFC 3370 [6] and MAY
support other schemes. The output from the key management protection
scheme ("key information") is placed in the security-result field of
the first PCB.
If the bundle being encrypted is a fragment-bundle we have to specify
which bytes are encrypted in case the bundle is subsequently
fragmented again. If the bundle is a fragment the ciphersuite
parameters MUST include a fragment-range field, as described in
Section 2.5, specifying the offset and length of the encrypted
fragment. Note that this is not the same pair of fields which appear
in the primary block as "offset and length". The "length" in this
case is the length of the fragment, not the original length. If the
bundle is not a fragment then this field MUST be omitted.
The confidentiality processing for payload and other blocks is
different, mainly because the payload might be fragmented later at
some other node.
For the payload, only the bytes of the bundle payload field are
affected, being replaced by ciphertext. The salt, IV and key values
specified in the first PCB are used to encrypt the payload, and the
resultant authentication tag (ICV) is placed in an ICV item in the
security-result field of that first PCB. The other bytes of the
payload block, such as type, flags and length, are not modified.
For each PIB or PCB to be protected, the entire original block is
encapsulated in a "replacing" PCB. This replacing PCB is placed in
the outgoing bundle in the same position as the original block, PIB
or PCB. As mentioned above, this is one-for-one replacement and
there is no consolidation of blocks or mixing of data in any way.
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The encryption process uses AES-GCM with the salt and key values from
the first PCB, and an IV unique to this PCB. The process creates
ciphertext for the entire original block, and an authentication tag
for validation at the security destination. For this encapsulation
process, unlike the processing of the bundle payload, the
authentication tag is appended to the ciphertext for the block and
the combination is stored into the "encapsulated block" item in
security-result.
The replacing block, of course, also has the same correlator value as
the first PCB with which it is associated. It also contains the
block-specific IV in security-parameters, and the combination of
original-block-ciphertext and authentication tag, stored as an
"encapsulated block" item in security-result.
Any existing eid-list in the to-be-encapsulated original block
remains exactly as-is, and become the eid-list for the replacing
block. The encapsulation process MUST NOT replace or remove the
existing eid-list entries. This is critically important for correct
updating of entries at the security-destination.
At the security-destination, either specific destination or the
bundle destination, the processes described above are reversed. The
payload is decrypted in-place using the salt, IV and key values in
the first PCB, including verification using the ICV. Each correlated
PCB is also processed at the same destination, using the salt and key
values from the first PCB and the block-specific IV item. The
"encapsulated block" item in security-result is decrypted, and
validated using the tag which was appended to the ciphertext of the
original block data. Assuming the validation succeeds, the resultant
plaintext, which is the entire content of the original block,
replaces the PCB at the same place in the bundle. The block type
reverts to that of the original block prior to encapsulation, and the
other block-specific data fields also return to their original
values. Implementors are cautioned that this "replacement" process
requires delicate stitchery, as the eid-list contents in the
decapsulated block are invalid. As noted above, the eid-list
references in the original block were preserved in the replacing PCB,
and will have been updated as necessary as the bundle has toured the
dtnet. The references from the PCB MUST replace the references
within the eid-list of the newly-decapsulated block. Caveat
implementor.
If the payload was fragmented after encryption then all those
fragments MUST be present and reassembled before decryption. This
process mighht be repeated several times at different destinations if
multiple fragmentation actions have occurred.
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The size of the GCM counter field limits the payload size to 2^39 -
256 bytes, about half a terabyte. A future revision of this
specification will address the issue of handling payloads in excess
of this size.
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5. Key Management
Since key management in delay tolerant networks is still a research
topic we cannot provide much in the way of useful key management
here. However, solely in order to support implementation and
testing, implementations SHOULD support:
- Long-term pre-shared-symmetric keys for the BAB-HMAC
ciphersuite.
- The use of well-known RSA public keys for PIB-RSA-SHA256 and
PCB-RSA-AES128-PAYLOAD-PIB-PCB ciphersuites.
Since endpoint IDs are URIs and URIs can be placed in X.509 [7]
public key certificates (in the subjectAltName extension)
implementations SHOULD support this way of distributing public keys.
Implementations SHOULD NOT be very strict in how they process X.509
though, for example, it would probably not be correct to insist on
Certificate Revocation List (CRL) checking in many DTN contexts.
Other than that, key management is for future study.
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6. Default Security Policy
Every node serves as a Policy Enforcement Point insofar as it
enforces some policy that controls the forwarding and delivery of
bundles via one or more convergence layer protocol implementation.
Consequently, every node SHALL have and operate according to its own
configurable security policy, whether the policy be explicit or
default. The policy SHALL specify:
Under what conditions received bundles SHALL be forwarded.
Under what conditions received bundles SHALL be required to
include valid BABs.
Under what conditions the authentication information provided in a
bundle's BAB SHALL be deemed adequate to authenticate the bundle.
Under what conditions received bundles SHALL be required to have
valid PIBs and/or PCBs.
Under what conditions the authentication information provided in a
bundle's PIB SHALL be deemed adequate to authenticate the bundle.
Under what conditions a BAB SHALL be added to a received bundle
before that bundle is forwarded.
Under what conditions a PIB SHALL be added to a received bundle
before that bundle is forwarded.
Under what conditions a PCB SHALL be added to a received bundle
before that bundle is forwarded.
The actions that SHALL be taken in the event that a received
bundle does not meet the receiving node's security policy
criteria.
This specification does not address how security policies get
distributed to nodes. It only REQUIRES that nodes have and enforce
security policies. [Comment.14]
If no security policy is specified at a given node, or if a security
policy is only partially specified, that node's default policy
regarding unspecified criteria SHALL consist of the following:
Bundles that are not well-formed do not meet the security policy
criteria.
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The mandatory ciphersuites MUST be used.
All bundles received MUST have a BAB which MUST be verified to
contain a valid security result. If the bundle does not have a
BAB, then the bundle MUST be discarded and processed no further; a
bundle status report indicating the authentication failure MAY be
generated.
No received bundles SHALL be required to have a PIB; if a received
bundle does have a PIB, however, the PIB can be ignored unless the
receiving node is the PIB-dest, in which case the PIB MUST be
verified.
No received bundles SHALL be required to have a PCB; if a received
bundle does have a PCB, however, the PCB can be ignored unless the
receiving node is the PCB-dest, in which case the PCB MUST be
processed. If processing of a PCB yields a PIB, that PIB SHALL be
processed by the node according to the node's security policy.
A PIB SHALL NOT be added to a bundle before sourcing or forwarding
it.
A PCB SHALL NOT be added to a bundle before sourcing or forwarding
it.
A BAB MUST always be added to a bundle before that bundle is
forwarded.
If a destination node receives a bundle that has a PIB-dest but
the value in that PIB-dest is not the EID of the destination node,
the bundle SHALL be delivered at that destination node.
If a received bundle does not satisfy the node's security policy
for any reason, then the bundle MUST be discarded and processed no
further; in this case, a bundle deletion status report (see the
Bundle Protocol [2]) indicating the failure MAY be generated.
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7. Security Considerations
[Comment.15]
If a BAB ciphersuite uses digital signatures but doesn't include the
security destination (which for a BAB is the next host), then this
allows the bundle to be sent to some node other than the intended
adjacent node. Because the BAB will still authenticate, the
receiving node may erroneously accept and forward the bundle. When
asymmetric BAB ciphersuites are used, the security destination field
SHOULD therefore be included in the BAB.
If a bundle's PIB-dest is not the same as its destination, then some
node other than the destination (the node identified as the PIB-dest)
is expected to validate the PIB security result while the bundle is
en route. However, if for some reason the PIB is not validated,
there is no way for the destination to become aware of this.
Typically, a PIB-dest will remove the PIB from the bundle after
verifying the PIB and before forwarding it. However, if there is a
possibility that the PIB will also be verified at a downstream node,
the PIB-dest will leave the PIB in the bundle. Therefore, if a
destination receives a bundle with a PIB that has a PIB-dest (which
isn't the destination), this may, but does not necessarily, indicate
a possible problem.
If a bundle is fragmented after being forwarded by its PIB-source but
before being received by its PIB-dest, the payload in the bundle MUST
be reassembled before validating the PIB security result in order for
the security result to validate correctly. Therefore, if the PIB-
dest is not capable of performing payload reassembly, its utility as
a PIB-dest will be limited to validating only those bundles that have
not been fragmented since being forwarded from the PIB-source.
Similarly, if a bundle is fragmented after being forwarded by its
PIB-source but before being received by its PIB-dest, all fragments
MUST be received at that PIB-dest in order for the bundle payload to
be able to be reassembled. If not all fragments are received at the
PIB-dest node, the bundle will not be able to be authenticated, and
will therefore never be forwarded by this PIB-dest node.
Specification of a security-destination other than the bundle
destination creates a routing requirement that the bundle somehow be
directed to the security-destination node on its way to the final
destination. This requirement is presently private to the
ciphersuite, since routing nodes are not required to implement
security processing.
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8. IANA Considerations
None at this time. If the bundle protocol becomes a standards track
protocol, then we may want to consider having IANA establish a
register of block types, and in particular for this specification a
separate register of ciphersuite specifications.
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9. References
9.1. Normative References
[1] Bradner, S. and J. Reynolds, "Key words for use in RFCs to
Indicate Requirement Levels", RFC 2119, October 1997.
[2] Scott, K. and S. Burleigh, "Bundle Protocol Specification",
RFC 5050, November 2007.
[3] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3369,
August 2002.
[4] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[5] Schaad, J., Kaliski, B., and R. Housley, "Additional Algorithms
and Identifiers for RSA Cryptography for use in the Internet
X.509 Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 4055, June 2005.
[6] Housley, R., "Cryptographic Message Syntax (CMS) Algorithms",
RFC 3370, August 2002.
[7] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 3280, April 2002.
[8] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode (GCM)
in IPsec Encapsulating Security Payload (ESP)", RFC 4106,
June 2005.
9.2. Informative References
[9] Farrell, S., Symington, S., Weiss, H., and P. Lovell, "Delay-
Tolerant Networking Security Overview",
draft-irtf-dtnrg-sec-overview-04.txt, work-in-progress,
February 2008.
[10] Cerf, V., Burleigh, S., Durst, R., Fall, K., Hooke, A., Scott,
K., Torgerson, L., and H. Weiss, "Delay-Tolerant Network
Architecture", RFC 4838, April 2007.
[11] Symington, S., "Delay-Tolerant Network Retransmission Block",
draft-irtf-dtnrg-bundle-retrans-00.txt, work-in-progress,
April 2007.
[12] Housley, R., "Using AES-CCM and AES-GCM Authenticated
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Encryption in the Cryptographic Message Syntax (CMS)",
RFC 5084, November 2007.
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Editorial Comments
[] Stephen: I guess there could be some weird corner case
where a PCB ciphersuite using counter-mode would allow
fragments to be individually decrypted, and in that
case, we might want to set replication for each
fragment. So we can't fully rule out setting that flag
for all PIB/PCB.
[] plovell: in fact, we do need it set for C blocks (first
only if a correlated set) in order to recover canonical
processing order after fragmentation/reassembly
[] Stephen: This to be revisited!
[] Note: there is no ciphersuite definition which supports
this "parallel" encryption scheme -- needs thought. All
definitions so far are for sequential encryptors, and
we don't have a way to indicate "parallel". Maybe it's
just that the PCB-dest is different? I hate to think
what the API would look like :)
[] Stephen: Do we need to specify error handling for the
case where a node drops a bundle for policy reasons?
Does/can it signal back to the source that its done so?
[] Howie: The security policy database will need to be
discussed somewhere. Does it belong in this document,
the bundle protocol spec., both, some other document?
[] Editors: Check that mask value at the very last moment
(incl. during auth-48) to be sure its (still) correct.
[] plovell: do we generate a report even if the failure
was a security failure? That's often regarded as poor
practice.
[] plovell: should this be "SHALL discard" or "SHALL
delete" ?
[] plovell: do we generate a report even if the failure
was a security failure? That's often regarded as poor
practice.
[] Editors: At the moment there appears to be no security
reason to move away from HMAC-SHA1 since the HMAC
construct is not as far as we know affected by
collisions in the underlying digest algorithm (which
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are nearly practically computable for SHA-1).
Nevertheless, since we use SHA-256 in the signature
ciphersuite (since collisions do matter there), it may
be desirable to move to HMAC-SHA-256 as specified in
RFC 4321. So if you're writing code based on this...be
warned!
[] Editors: There are currently unresolved "issues" with
digest algorithms which might cause a change here prior
to, but more likely, after, an RFC has issued. So
expect change!
[] Editors: This section has progressed to Woodman status.
[] Howie: Eventually we will need to state where the
security policy information/DB does get discussed/
specified.
[] Editors: Much more text is needed here no doubt.
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Authors' Addresses
Susan Flynn Symington
The MITRE Corporation
7515 Colshire Drive
McLean, VA 22102
US
Phone: +1 (703) 983-7209
Email: susan@mitre.org
URI: http://mitre.org/
Stephen Farrell
Trinity College Dublin
Distributed Systems Group
Department of Computer Science
Trinity College
Dublin 2
Ireland
Phone: +353-1-608-1539
Email: stephen.farrell@cs.tcd.ie
Howard Weiss
SPARTA, Inc.
7110 Samuel Morse Drive
Columbia, MD 21046
US
Phone: +1-443-430-8089
Email: hsw@sparta.com
Peter Lovell
SPARTA, Inc.
7110 Samuel Morse Drive
Columbia, MD 21046
US
Phone: +1-443-430-8052
Email: peter.lovell@sparta.com
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