Internet Engineering Task Force S. Yang
Internet-Draft X. Huang
Intended status: Informational CUHK(SZ)
Expires: April 23, 2019 R.W. Yeung
CUHK
J. Zao
NCTU
October 20, 2018
BATS Code Scheme for Multi-hop File Delivery
draft-yang-nwcrg-bats-code-00
Abstract
This document describe a BATS code scheme for communication through a
multi-hop network. BATS code is a class of efficient linear network
coding scheme with a matrix generalization of fountain codes as the
outer code, and batch-based linear network coding as the inner code.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 23, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Yang, et al. Expires April 23, 2019 [Page 1]
Internet-Draft BATS Code October 2018
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 3
2.2. File Partitioning and Padding . . . . . . . . . . . . . . 4
2.3. File Delivery Procedures . . . . . . . . . . . . . . . . 4
2.3.1. Source Node Procedures . . . . . . . . . . . . . . . 4
2.3.2. Intermediate Node Procedures . . . . . . . . . . . . 5
2.3.3. Destination Node Procedures . . . . . . . . . . . . . 6
2.4. Recommandation for the Parameters . . . . . . . . . . . . 6
2.5. Example FDP Packets . . . . . . . . . . . . . . . . . . . 7
3. BATS Code Specification . . . . . . . . . . . . . . . . . . . 7
3.1. Background . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Outer Code Encoder . . . . . . . . . . . . . . . . . . . 7
3.3. Inner Code Encoder (Recoder) Recommandations . . . . . . 7
3.4. Decoder Recommandations . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5.1. Provision of Confidentiality Protection . . . . . . . . . 8
5.2. Countermeasures against Pollution Attacks . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Additional Stuff . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
This document specifies a BATS code [BATS] scheme for file delivery
applications in multi-hop networks. The BATS code described here
includes an outer code and an inner code. The outer code is a matrix
generalization of the fountain codes (see also the RapterQ code
described in RFC 6330 [RFC6330]), which inherits the advantages of
reliability and efficiency and possesses the extra desirable property
of being network coding compatible. The inner code is formed by
linear network coding for combating packet loss, improving the
multicast efficiency, etc. A detailed design and analysis of BATS
codes are provided in BATSMonograph [BATSMonograph].
Yang, et al. Expires April 23, 2019 [Page 2]
Internet-Draft BATS Code October 2018
1.1. Requirements Language
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].
2. Procedures
2.1. Introduction
A BATS code scheme includes an outer code encoder (also called
encoder), an inner code encoder (also called recoder) and a decoder.
The BATS code scheme described in this document can be used by a File
Delivery Protocol (FDP) with the following procedures.
Encoding at a source node which has the file for transmission:
* The FDP provides the file to be delivered and the related
information to the BATS encoder.
* The BATS encoder generates a sequence of batches, each
consisting of a set of coded packets and the information
pertaining to the batch.
* The FDP forms and transmits the FDP packets using the batches
and the corresponding batch information.
Recoding at an intermediate node that does not need the file:
* The FDP extracts the batches and the corresponding batch
information from its received FDP packets.
* A BAST recoder generates recoded packets of a batch.
* The FDP forms and transmits FDP packets using the recoded
packets and the corresponding batch information.
Decoding at a destination node that needs the file:
* The FDP extracts the batches and the corresponding batch
information from its received FDP packets.
* A BATS decoder tries to recover the transmitted file using the
received batches.
* The FDP sends the decoded file to the application that needs
the file.
Yang, et al. Expires April 23, 2019 [Page 3]
Internet-Draft BATS Code October 2018
2.2. File Partitioning and Padding
Suppose that the FDP has a file of F octets for transmission. The
construction of source packets from the file depends on two
parameters K and T:
o K: the number of source packets.
o T: the size of a source packet, in octets.
If F is smaller than T*K, the file needs to be padded to have T*K
octets, so that file can be partitioned into K source packets, each
of which has T octets.
2.3. File Delivery Procedures
2.3.1. Source Node Procedures
A source node has the file for transmission. The FDP will first pad
and partition the file into K source packets, each containing T
octets. The FDP provides the BATS encoder with the following
information:
o Batch size (M): the number of coded packets in a batch.
o Recoding field size (q): the number of elements in the finite
field for recoding.
o The degree distribution (DD), optional.
o A sequence of batch IDs (ID[i],i=0,1,...).
o Number of source packets (K).
o Packet size (T): the number of octets in a source packet.
o The source packets (b[i],i=0,1,...,K-1).
Using this information, the (outer code) encoder generates a batch
for each batch ID. For each batch ID, the encoder returns the FDP
o a sparse degree (d), and
o M coded packets (X'[i],i=0,1,...,M-1), each containing T' octets.
Here T' = T + M*ceil(log2(q))/8.
Yang, et al. Expires April 23, 2019 [Page 4]
Internet-Draft BATS Code October 2018
The FDP will use the batches to form FDP packets to be transmitted to
other network nodes towards the destination nodes. The FDP MUST
deliver with each coded packet its
o sparse degree,
o batch ID and certain extra information so that any receiver of the
coded packets of the batch can know whether the coded packets are
in the same batch or not, and whether two different batches are
generated from the same file or not.
The FDP MUST deliver the following information to each recoder:
o batch size M, and
o recoding field size q.
The FDP MUST deliver the following information to each decoder:
o batch size M,
o recoding field size q,
o the file size F, and
o the number of source packet K.
The packet length information is assumed to be known by all the
nodes.
2.3.2. Intermediate Node Procedures
An intermediate node does not need the file, but only helps to
deliver the file to the destination nodes. At an intermediate node,
the FDP only receives the FDP packets from the other network nodes,
and should be able to extract coded packets and the corresponding
batch information from these packets.
The FDP provides the recoder with the following information:
o the batch size M,
o the recoding field size q,
o a number of received coded packets of the same batch, each
containing T' octets, and
o a number M' of recoded packets to be generated.
Yang, et al. Expires April 23, 2019 [Page 5]
Internet-Draft BATS Code October 2018
The recoder uses the information provided by the FDP to generate M'
recoded packets, each containing T' octets. The FDP uses the M'
recoded packets to form the FDP packets for transmitting.
2.3.3. Destination Node Procedures
A destination node needs the file transmitted by the source node. At
the destination node, the FDP receives FDP packets from the other
network nodes, and should be able to extract coded packets and the
corresponding batch information from these packets.
The FDP provides the decoder with the following information:
o F: number of octets in the file,
o M: batch size,
o q: recoding field size,
o K: number of source packets
o A sequence of batches with their corresponding batch IDs and
degrees.
The decoder uses this information to decode the K source packets. If
successful, the decoder returns the recovered K source packets to the
FDP, which will use the source packets to form the source file.
2.4. Recommandation for the Parameters
The recommendation for the parameters M, K, T, and T' is shown as
follows:
o M is 8, 16 or 32.
o q is 2, 4, 8, 16, 32, 64, 128 or 256.
o T' is not larger than the maximum coded packet payload size.
o T = T' - M*ceil(log2(q))/8.
o K = ceil(F/T).
It is RECOMMENDED that K is at least 128. However, the encoder/
decoder SHALL support an arbitrary positive integer value of K.
Yang, et al. Expires April 23, 2019 [Page 6]
Internet-Draft BATS Code October 2018
2.5. Example FDP Packets
A FDP can form a FDP packet by appending a header and a footer to
each coded packets.
The header should include F, M, K, q, batch ID, and degree.
3. BATS Code Specification
3.1. Background
The T octets of a source packets are treated as a column vector of T
elements in GF[256]. Linear algebra and matrix operations over
finite fields are assumed in this section.
Assume that a pseudo-random number generator Rand() is given.
3.2. Outer Code Encoder
Let b[0], b[1], ...,b[K-1] be the K source packets. A batch with
batch ID bID is generated in the following steps.
First, a degree DEG=DEG(bID) is sampled using the give degree
distribution and Rand() with the default seed. After that,
initialize Rand() with bID as the seed.
Second, using Rand() sample DEG packets among all the source packets.
Suppose the indices of the packets sampled are i_1, i_2, ..., i_DEG.
Third, sample a DEGxM generator matrix G.
Fourth, form the batch X = (b[i_1], b[i_2], ..., b[i_DEG])*G, where
each column is a coded packet of the batch.
Last, append coefficient vectors to the packets of the batches. Let
X[i], i=0,1,...,M-1, be the (i+1)th column of X. The coefficient
vector of X[i] is the (i+1)th column of the MxM identity matrix with
entries in GF(q), which can be represented by M*log2(q)/8 octets.
The coded packet X'[i] is formed by appending the coefficient vector
before X[i].
3.3. Inner Code Encoder (Recoder) Recommandations
The inner code comprises (random) linear network coding applied on
the coded packets belonging to the same batch. At a particular
network node, recoded packets are generated by (random) linear
combinations of the received coded packets of a batch. The recoded
Yang, et al. Expires April 23, 2019 [Page 7]
Internet-Draft BATS Code October 2018
packets have the same batch ID, sparse degree and coded packet
length.
3.4. Decoder Recommandations
The belief propagation decoding algorithm suggested in the BATS code
paper [BATS] is recommanded.
4. IANA Considerations
This memo includes no request to IANA.
5. Security Considerations
Subsuming both Random Linear Network Codes (RLNC) and fountain codes,
BATS codes naturally inherit both their desirable capability of
offering confidentiality protection as well as their vulnerability
towards pollution attacks.
5.1. Provision of Confidentiality Protection
Since the transported messages are linearly combined with random
coefficients at each recoding node, it is statistically impossible to
recover individual messages by capturing the coded messages at any
one or small number of nodes. As long as the coding matrices of the
transported messages cannot be fully recovered, any attempt of
decoding is equivalent to randomly guessing the transported messages.
Thus, with the use of BATS codes, information confidentiality
throughout the data transport process is assured.
The only thread towards confidentiality exists in the form of
eavesdropping onto the initial encoding process, which takes place at
the encoding nodes. In these nodes, the transported files are
presented in plain text and can be read along their transfer paths.
Hence, information isolation between the encoding process and all
other user processes running on the node must be assured.
In addition, the authenticity and trustworthiness of the encoding,
recoding and decoding program running on all the nodes must be
attested by a trusted authority. Such a measure is also necessary in
countering the pollution attacks.
5.2. Countermeasures against Pollution Attacks
Like all network codes, BATS codes are vulnerable under pollution
attacks. In these attacks, one or more compromised coding node(s)
can pollute the coded messages or inject forged messages into the
coding network. These attacks can prevent the receivers from
Yang, et al. Expires April 23, 2019 [Page 8]
Internet-Draft BATS Code October 2018
recovering the transported files correctly. Although error detection
mechanisms can be put in place to prevent the receivers from getting
the wrong messages, detection and discard of the polluted messages
still constitute a form of denial-of-service (DoS) attack.
The research community has long been investigating the use of various
signature schemes (including homomorphic signatures) to identify the
forged messages and stall the attacks (see Zhao07 [Zhao07], Yu08
[Yu08], Agrawal09 [Agrawal09]). Nevertheless, these counter measures
are regarded as being computationally to expensive to be employed in
broadband communications. A practical approach to protect against
pollution attacks consists of the following system-level
countermeasures:
1. Attestation and Validation of all encoding, recoding and decoding
nodes in the network. Remote attestation and repetitive
validation of a node based on valid public key certificates with
proper authorization MUST be a pre-requisite of admitting that
node into a network and permitting it to remain in that network.
2. Attestation of all encoding, recoding and decoding programs used
in the coding nodes. All programs used to perform the BATS
encoding, recoding and decoding processes MUST be remotely
attested before they are permitted to run on any of the coding
nodes. Reloading or alteration of programs MUST NOT be permitted
during an encoding session. Programs MUST be attested or
validated again when they are executed in new execution
environments instantiated even in the same nodes.
3. Original Authentication of all coded messages using network or
transport level secure protocols such as IP-sec or TLS/DTLS MUST
be used to provide Peer or Message Origin Authentication to every
coded message sent through the coding network.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
6.2. Informative References
Yang, et al. Expires April 23, 2019 [Page 9]
Internet-Draft BATS Code October 2018
[Agrawal09]
S. Agrawal and D. Boneh, "Homomorphic MACs: MAC-based
integrity for network coding", International Conference on
Applied Cryptography and Network Security , 2009.
[BATS] S. Yang and R.W. Yeung, "Batched Sparse Codes", IEEE
Transactions on Information Theory 60(9), 5322-5346, 2014.
[BATSMonograph]
S. Yang and R.W. Yeung, "BATS Codes: Theory and Practice",
Morgan & Claypool Publishers , 2017.
[RFC6330] Luby, M., Shokrollahi, A., Watson, M., Stockhammer, T.,
and L. Minder, "RaptorQ Forward Error Correction Scheme
for Object Delivery", RFC 6330, DOI 10.17487/RFC6330,
August 2011, <https://www.rfc-editor.org/info/rfc6330>.
[Yu08] Z. Yu, Y. Wei, B. Ramkumar, and Y. Guan, "An Efficient
Signature-Based Scheme for Securing Network Coding Against
Pollution Attacks", NFOCOM , 2008.
[Zhao07] F. Zhao, T. Kalker, M. Medard, and K.J. Han, "Signatures
for content distribution with network coding", ISIT ,
2007.
Appendix A. Additional Stuff
This becomes an Appendix.
Authors' Addresses
Shenghao Yang
CUHK(SZ)
Shenzhen, Guangdong
China
Phone: +86 755 8427 3827
Email: shyang@cuhk.edu.cn
Xuan Huang
CUHK(SZ)
Shenzhen, Guangdong
China
Phone: +86 755 8427 3814
Email: 115010159@link.cuhk.edu.cn
Yang, et al. Expires April 23, 2019 [Page 10]
Internet-Draft BATS Code October 2018
Raymond W. Yeung
CUHK
Hong Kong, Hong Kong SAR
China
Phone: +852 3943 8375
Email: whyeung@ie.cuhk.edu.hk
John Zao
NCTU
Hsinchu, Taiwan
China
Email: jkzao@ieee.org
Yang, et al. Expires April 23, 2019 [Page 11]