Internet DRAFT - draft-li-dtn-hybrid-integrity
draft-li-dtn-hybrid-integrity
Delay-Tolerant Networking Taixin Li
Internet Draft Guanwen Li
Intended status: Informational Huachun Zhou
Expires: September 30, 2018 Beijing Jiaotong University
March 30, 2018
A Hybrid Integrity Assurance Strategy for Bundle Protocol
draft-li-dtn-hybrid-integrity-05.txt
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Abstract
Delay/Disruption Tolerant Networking (DTN) is designed for a severe
environment where communication quality is not guaranteed. It works
as an overlay network associated with Bundle Protocol (BP) and some
convergence layer protocols like Licklider Transmission Protocol
(LTP). However, there is no mechanism in both BP and LTP Protocol to
ensure integrity of a packet with the granularity of bit. Since the
integrity is crucial for packet transmission and necessary metadata
consumes extra costs, there should be a strategy to decide which
packets and how the packets are required to conduct integrity
assurance based on network resources and user requirements. Hence, in
this document, a hybrid integrity assurance strategy is proposed to
ensure the different levels of integrity of bundles based on the
status of network resources and the need of users.
Table of Contents
1. Introduction ................................................ 3
2. Conventions used in this document ............................ 3
3. Checksum Block Format ........................................ 4
4. Processing Rules of Integrity Detection ...................... 5
4.1. Processing Rules in Source Nodes ........................ 6
4.2. Processing Rules in Intermediate Nodes .................. 8
4.3. Processing Rules in Destination Nodes ................... 9
5. Error correcting code-based detecting mechanism ............. 10
6. Security Considerations ..................................... 11
7. IANA Considerations ........................................ 11
8. Conclusions ................................................ 11
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9. References ................................................. 12
9.1. Normative Reference ................................... 12
9.2. Informative Reference ................................. 12
10. Acknowledgments ........................................... 13
1. Introduction
Delay/Disruption Tolerant Networking (DTN) [RFC4838] is designed for
a severe environment where connectivity of network is intermittent
and communication quality is not guaranteed. It works as an overlay
network associated with Bundle Protocol (BP) [RFC5050] and
convergence layer protocols like Licklider Transmission Protocol (LTP)
[RFC5325] [RFC5326]. BP, which is an application layer protocol, is
based on a custody transfer mechanism and defines how to forward
bundles in DTN, while LTP ensures the reliability of bundle
transmission with the granularity of packet. However, there is no
mechanism in both BP and LTP Protocol to ensure integrity of a packet
with the granularity of bit. Integrity is crucial for packet
transmission since errors in the header leads to some unexpected
results while errors in the payload results in end-to-end
retransmission and waste of limited storing and link resources.
BPSEC [I-D.ietf-dtn-bpsec-06] defines a security protocol providing
end to end data integrity and confidentiality services for the Bundle
Protocol. However, necessary checksum metadata consumes costs, so
there should be a strategy to decide which packets and how the
packets are required to conduct integrity assurance based on the
network resources, such as buffer utilization rate, bandwidth, and
packet loss rate.
In this document, we define a new type of extension block to carry
the checksum field. Furthermore, we propose a hybrid integrity
assurance strategy to ensure the different levels of integrity of
bundles based on the status of network resources and the need of
users. The intermediate nodes make a hop-by-hop integrity detection
strategy according to network status while the end user makes an end-
to-end integrity detection strategy.
2. Conventions used in this document
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 RFC 2119 [RFC2119].
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3. Checksum Block Format
There are three parts in the bundle packet, primary block, payload
block, and extension block. Extension Block is designed to carry
additional information that DTN nodes can use to make processing
decisions that are related to bundles.
We define a new type of extension block and use it to carry the
checksum information in this document, and the basic format is based
on [RFC6258], which defines DTN metadata extension block.
The format of checksum block is as follows:
Checksum Block Format:
+------+-------+--------------------------------------------+
| Type | Flags | Length |Class of Detection|Type of Checksum|
| | (SDNV)| (SDNV) | (SDNV) | (SDNV) |
+------+----------------+------------------+----------------+
| Checksum |
| |
+-----------------------------------------------------------+
Figure 1 Checksum Block Format
o Block type code (1 byte) - defined in all bundle protocol blocks
except the primary bundle block (as described in the Bundle
Protocol). The block-type code for checksum is 0x20.
o Block processing control flags (SDNV) - defined in all bundle
protocol blocks except the primary bundle block. SDNV encoding is
described in the Bundle Protocol. The following block processing
control flag MUST be set "4 - Discard block if it can't be
processed", which means that if a bundle node receives a bundle
with a checksum block and it is not capable of supporting the
checksum block, it just discards this block without processing it.
o Block data length (SDNV) - defined in all bundle protocol blocks
except the primary bundle block. SDNV encoding is described in the
Bundle Protocol.
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o Class of detection (SDNV) - (CoD) indicates the bundle's class of
detection, which decides whether a bundle packet should conduct an
integrity assurance and which part should be detected. CoD is
decided by two factors, network resources status and user
requirements. For now, it contains three types: 00 = inadequate
resources, 01 = adequate resources, 10 = mandatory detection. Here,
00 and 01 are determined by the network status, and 10 is decided
by the user. The users have a higher priority, which means that if
CoD = 10, the bundle packets should be detected no matter what the
network status is.
o Type of Checksum (SDNV) - (ToC) indicates the type of checksum
data. For now, it contains four types: 00 = checksum of primary
block, 01 = checksum of payload block, 10 = checksum of primary
block and payload block, 11 = no checksum of either primary block
or payload block.
o Checksum data - contains the raw checksum data itself, which is
generated by some algorithms.
4. Processing Rules of Integrity Detection
As is discussed in [WOOD09] and [I-D.templin-dtnhiaps-00], integrity
detection is required on intermediate nodes in addition to
destination nodes. In order to make full use of the limited resources
in the severe environments, both the source nodes and the
intermediate nodes should monitor the usage rate of their resources
such as the storage and link. Then different integrity assurance
strategies will be made according to network resources status and
user requirements. The integrity detection is called if the network
resources are inadequate, the custody is needed, or it is demanded by
end users. Besides, intermediate nodes detect the header/primary
block or the payload block according to the Type of Checksum field
carried in the checksum block. If there are errors in the packet data,
forwarding process is stopped and retransmission is called. When the
destination nodes receive packets, they detect the checksum block and
if there are errors in the packet data, retransmission will be called.
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4.1. Processing Rules in Source Nodes
+--------------+
+-----+Create new CoD+-----+
| +-------+------+ |
| | |
+----v----+ +-----v----+ +----v----+
| CoD=00 | | CoD=10 | | CoD=01 |
+----+----+ +--+-------+ +----+----+
| | |
+----v----+ | +----v----+
+--+ Custody +--+ | +--+ Custody +--+
| +---------+ | | | +---------+ |
v v | v v
YES NO | YES NO
+ + | + +
| | | | |
+----v-----+ +------+--v+ +---v------+ +-----v----+
|SET ToC=00| |SET ToC=10| |SET ToC=01| |SET ToC=11|
+----+-----+ +------+---+ +---+------+ +-----+----+
| | | |
+------v----+ +--------v-----+ +--v--------+ |
|Compute | |Compute header| |Compute | |
|header | |and payload | |payload | |
|checksum | |checksum | |checksum | |
+------+----+ +--------+-----+ +--+--------+ |
| | | |
| +---------v----------v----------+ |
+-----> Queuing to be forwarded <----+
+-------------------------------+
Figure 2 Processing Rules in Source Nodes
The processing rules in source nodes are shown in Figure 2. The
source nodes collect the network link status, such as bandwidth and
packet loss rate, and create Class of Resource (CoD). The algorithm
of creating CoD is not discussed here.
If CoD=00 (inadequate resources), it means the network environment is
severe and error prone. The source nodes read Bundle Processing
Control Flags (defined in RFC5050). If custody is needed, Type of
Checksum (ToC) will be set 10 (checksum of primary block and payload
block), and the checksum of primary block and payload block will be
computed by a designated algorithm. The algorithm is not discussed
here. Then the Checksum data field will be filled. If custody is not
needed, ToC will be set 00 (checksum of primary block), and the
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checksum of primary block will be computed. Then the Checksum data
field will be filled.
If CoD=01 (adequate resources), it means the network resources are
relatively adequate. If custody is needed, ToC will be set 01
(checksum of payload block), and the checksum of payload block will
be computed. Then the Checksum data field will be filled. If custody
is not needed, ToC will be set 11 (no checksum of either primary
block or payload block), no checksum calculation actions will be
triggered. At last, the processed packets will queue and wait to be
forwarded.
If CoD=10 (mandatory detection), it means that end users at the
source node want their packets to be detected no matter what the
network status is. So ToC is set 10 (checksum of primary block and
payload block), and the checksum of primary block and payload block
will be computed. Then the checksum data field will be filled. At
last, the processed packets will queue and wait to be forwarded.
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4.2. Processing Rules in Intermediate Nodes
+---------------+
+------------------->Receive packets|
| +-------+-------+
| |
| +---------v---------+
| +------+Read Checksum Block+------+
| | +---+-----------+---+ |
| | | | |
| +--v---+ +---v--+ +--v---+ +---v--+
| |ToC=00| |ToC=10| |ToC=01| |ToC=11|
| +--+---+ +---+--+ +--+---+ +---+--+
| | | | |
| | +--------v----+ +----v--------+ |
| | |Check storage| |Check storage| |
| | +--------+----+ +----+--------+ |
| | | | |
| | +-----v--+ +--v-----+ |
| | +--+Free>50%| |Free>50%+--+ |
| | | +-----+--+ +--+-----+ | |
+ | v v v v |
YES | YES NO NO YES |
^ | + + + + |
| | | +-----+----+ +---+-----+ | |
| | | |Header and| |payload | | |
| | | |payload | |detection| | |
| | | |detection | | | | |
| | | +-----+----+ +---+-----+ | |
| +--------v-v-----+ | | | |
| |header detection| | | | |
| +----------+-----+ | | | |
| | | | | |
| +-v--------v-----------v-+ | |
+----------+ Retransmission +---+ | |
+------------------------+ v | |
NO | |
+ | |
+---------------v--v-v-------+
|repeat the steps in Figure 2|
+----------------------------+
Figure 3 Processing Rules in intermediate nodes
The processing rules in intermediate nodes are shown in Figure 3.
When intermediate nodes receive packets, they first read Checksum
Block.
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If ToC = 00 (checksum of primary block), the primary block (header)
will be checked. If ToC = 10(checksum of primary block and payload
block), storage space will be detected and if free storage is more
than 50%, the primary block will be checked. If free storage is less
than 50%, both the primary block and the payload block will be
checked. If ToC = 01 (checksum of payload block), storage space will
be detected and if free storage is less than 50%, the payload block
will be checked. If errors are detected, retransmission will be
called. If no errors are detected, or ToC = 11 (no checksum of either
primary block or payload block), or free storage is more than 50%
when ToC = 01, the following processing steps will be the same as the
source nodes in Figure 2. However, if the CoD of received packets is
10, there is no need to collect the network status and calculate new
CoD. In other words, the decision of mandatory detection at the
source node by the end users should not be modified by the
intermediate nodes.
4.3. Processing Rules in Destination Nodes
+---------------+
^--------------->Receive packets|
| +-------+-------+
| |
| +---------+---------+
| +------+Read Checksum Block+-+
| | +--+---------+------+ |
| | | | |
| +--v---+ +---v--+ +---v--+ +---v--+
| |ToC=00| |ToC=01| |ToC=10| |ToC=11|
| +----+-+ +---+--+ +--+---+ +---+--+
| | | | |
| +-v-------v--------v-+ |
| | Checksum detection | |
| +----------+---------+ |
| | |
| +-------v------+ |
+-+Yes<---+Retransmission| |
+-------+------+ |
| |
| +----------v------+
+>No+-->Cache in the node|
+-----------------+
Figure 4 Processing Rules in Destination Nodes
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The processing rules in destination nodes are shown in Figure 4. When
destination nodes receive packets, they will read the checksum block.
If ToC is 00 (checksum of primary block), or 01 (checksum of payload
block), or 10 (checksum of primary block and payload block), the
related blocks will be checked by a designated algorithm. If errors
are detected, retransmission will be called. If no errors are
detected, or ToC is 11, the received packets will be regarded as
acceptable and be cached and stored in local.
5. Error correcting code-based detecting mechanism
In this section, we introduce a detecting mechanism that based on the
idea of error correcting code. This mechanism is designed to reduce
the checksum computing times.
hash +--+ hash +---+
x1+x2+x4+---->+h1| x1'+x2'+x4'+---->+h1'|
| | | |
hash | +------------> hash | |
x1+x3+x4+---->+h2|transmission x1'+x3'+x4'+---->+h2'|
| +------------> | |
hash | | hash | |
x2+x3+x4+---->+h3| x2'+x3'+x4'+---->+h3'|
+-++ +-+-+
| |
+---------------------------------+
compare
Figure 5 Error Correcting Code-based Detecting Mechanism
We introduce the mechanism taking hamming code as an example. As is
shown in Figure 5, we suppose that a file is transmitted in the form
of four packets, x1, x2, x3, and x4. The source node and the
destination node will compute the checksum for each of the four
packet in the traditional way. But in our design, the source node
conducts the hash operation for data (x1+x2+x4) and get h1. Then the
source node conducts the same operation for data (x1+x3+x4) and
(x2+x3+x4), and get h2 and h3. h1, h2 and h3 are carried along with
the packets. The destination node just need to conducts hash
operation three times, for (x1+x2+x4), (x1+x3+x4) and (x2+x3+x4), and
get h1', h2', and h3'. Then the destination node should compare h1,
h2 and h3 with h1', h2', and h3'. If h1, h2 and h3 are the same as
h1', h2', and h3', then, there are no wrong data in the four packets.
If one or several of h1, h2 and h3 is different from h1', h2', and
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h3', then the packet that carries wrong data can be located and
retransmission will be called to retransmit the wrong packet.
In this way, the checksum computing times can be reduced.
6. Security Considerations
The Multi-strategy Based Payload Integrity Assurance method provides
data integrity service for the Bundle Protocol, which is a necessary
aspect of security problems.
The proposed method can suit with the Payload Integrity Block (PIB)
and Bundle Authentication Block (BAB) in Bundle Security Protocol
[RFC6257].
7. IANA Considerations
This specification allocates a codepoint from the "Bundle Block
Types" registry defined in [RFC6255].
Additional Entry for the Bundle Block Type Codes Registry:
+-------+---------------+--------------+
| Value | Description | Reference |
+--------------------------------------+
| 20 |Checksum Block | This document|
+-----------------------+--------------+
Figure 6 Additional Entry for the Bundle Block Type Codes Registry
8. Conclusions
The hybrid integrity assurance strategy proposed in this document
describes how to ensure the different levels of integrity of bundles
based on different environments.
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9. References
9.1. Normative References
[RFC4838]Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R.,
Scott, K., Fall, K., and Weiss, H., "Delay-Tolerant
Networking Architecture", RFC 4838, April 2007.
[RFC5050] Scott, K., and Burleigh, S., "Bundle Protocol
Specification", RFC 5050, RFC5050, November 2007.
[RFC5325] Burleigh, S., Ramadas, M., and Farrell, S., "Licklider
Transmission Protocol - Motivation", RFC 5325, September
2008.
[RFC5326] Ramadas, M., Burleigh, S., and Farrell, S., "Licklider
Transmission Protocol - Specification", RFC 5326, September
2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6258] Symington, S., "Delay-Tolerant Networking Metadata
Extension Block", RFC 6258, May 2011.
[RFC6255] Blanchet, M., "Delay-Tolerant Networking (DTN) Bundle
Protocol IANA Registries", RFC 6255, May 2011.
[RFC6257] Symington, S., Farrell, S., Weiss, H., Lovell, P., "Bundle
Security Protocol Specification ", RFC 6257, May 2011.
9.2. Informative References
[WOOD09] Wood, L., Eddy, W., and Holliday, P., "A Bundle of Problems",
Proc. Aerospace conference 2009 pp. 1-17.
[I-D.templin-dtnhiaps-00] Templin, F., "Delay Tolerant Networking
Header Integrity Assurance-Problem Statement", draft-
templin-dtnhiaps-00 (Expires), March 2014.
[I-D.ietf-dtn-bpsec-06] Birrane, E., "Bundle Protocol Security
Specification", draft-ietf-dtn-bpsec-06, October 2017.
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10. Acknowledgments
The work in this document was supported by National High Technology
of China ("863 program") under Grant No.2015AA015702.
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Authors' Addresses
Taixin Li
Beijing Jiaotong University
Beijing, 100044, P.R. China
Email: 14111040@bjtu.edu.cn
Guanwen Li
Beijing Jiaotong University
Beijing 100044, P.R. China
Email: 14120079@bjtu.edu.cn
Huachun Zhou
Beijing Jiaotong University
Beijing 100044, P.R. China
Email: hchzhou@bjtu.edu.cn
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