Efficient Error Control Decoder Architectures for Noncoherent Random Linear Network Coding

Random linear network coding is an efficient technique for disseminating information in networks, but it is highly susceptible to errors. Kötter-Kschischang (KK) codes and Mahdavifar-Vardy (MV) codes are two important families of subspace codes that provide error control in noncoherent random linear network coding. List decoding has been used to decode MV codes beyond half distance. Existing hardware implementations of the rank metric decoder for KK codes suffer from limited throughput, long latency and high area complexity. The interpolation-based list decoding algorithm for MV codes still has high computational complexity, and its feasibility for hardware implementations has not been investigated. In this paper we propose efficient decoder architectures for both KK and MV codes and present their hardware implementations. Two serial architectures are proposed for KK and MV codes, respectively. An unfolded decoder architecture, which offers high throughput, is also proposed for KK codes. The synthesis results show that the proposed architectures for KK codes are much more efficient than rank metric decoder architectures, and demonstrate that the proposed decoder architecture for MV codes is affordable.     

基于神经网络的纠错输出编码方法研究

构造基于数据编码矩阵是目前利用纠错输出编码解决多类分类问题的研究重点.为此提出利用单层感知器作为学习框架,结合解码策略把输出编码矩阵各码元值映射为感知器网络中的权值,同时引入含权值取值约束的目标函数作为该网络代价函数,并对其进行学习,最终得到基于子类划分的数据编码矩阵.实验中利用人工数据集和UCI数据集并选择线性逻辑分类器作为基分类器分别进行测试,通过与几种经典编码方法比较,结果表明该编码方法能在编码长度较小情况下得到更好的分类效果.     

基于网络编码的多信源组播通信系统

本文首先介绍网络编码理论的基本概念,回顾了近年来网络编码的研究动态。接着在使用NetFPGA开发平台的基础上,提出网络编码组播通信系统及其整体设计方案。由于本系统的主要功能是由硬件实现,所以和传统组播通信网络相比,具有时延小,没有了调度和排队时间,使得网络中链路负载更均衡,体现出了网络编码的优势。     

Adaptive Defense Against Various Network Attacks

In defending against various network attacks, such as distributed denial-of-service (DDoS) attacks or worm attacks, a defense system needs to deal with various network conditions and dynamically changing attacks. Therefore, a good defense system needs to have a built-in “adaptive defense” functionality based on cost minimization—adaptively adjusting its configurations according to the network condition and attack severity in order to minimize the combined cost introduced by false positives (misidentify normal traffic as attack) and false negatives (misidentify attack traffic as normal) at any time. In this way, the adaptive defense system can generate fewer false alarms in normal situations or under light attacks with relaxed defense configurations, while protecting a network or a server more vigorously under severe attacks. In this paper, we present concrete adaptive defense system designs for defending against two major network attacks: SYN flood DDoS attack and Internet worm infection. The adaptive defense is a high-level system design that can be built on various underlying nonadaptive detection and filtering algorithms, which makes it applicable for a wide range of security defenses.     

Message Authentication Codes Against Related-Key Attacks Under LPN and LWE

Message authentication code (MAC)guarantees the authenticity of messages and is one of the most important primitives in cryptography.We study related-key attacks with which the adversary is able to choose function f and observe the behavior of the MAC under the modified authenticated key f(k),and consider unforgeability of MAC under (selectively) chosen message attack with f(k).We focus on MAC schemes from the Learning parity with noise (LPN) and the Learning with errors (LWE) problem by Kiltz et al.in EUROCRYPT 2011.We first prove that the MAC schemes from LPN/LWE can resist key-shift attacks and enlarge the key-shift function set to support a subclass of affine functions.     

Coding for Errors and Erasures in Random Network Coding

The problem of error-control in random linear network coding is considered. A “noncoherent” or “channel oblivious” model is assumed where neither transmitter nor receiver is assumed to have knowledge of the channel transfer characteristic. Motivated by the property that linear network coding is vector-space preserving, information transmission is modeled as the injection into the network of a basis for a vector space $V$ and the collection by the receiver of a basis for a vector space $U$. A metric on the projective geometry associated with the packet space is introduced, and it is shown that a minimum-distance decoder for this metric achieves correct decoding if the dimension of the space $V cap U$ is sufficiently large. If the dimension of each codeword is restricted to a fixed integer, the code forms a subset of a finite-field Grassmannian, or, equivalently, a subset of the vertices of the corresponding Grassmann graph. Sphere-packing and sphere-covering bounds as well as a generalization of the Singleton bound are provided for such codes. Finally, a Reed–Solomon-like code construction, related to Gabidulin's construction of maximum rank-distance codes, is described and a Sudan-style “list-1” minimum-distance decoding algorithm is provided.      

Relations Between Random Coding Exponents and the Statistical Physics of Random Codes

The partition function pertaining to finite-temperature decoding of a (typical) randomly chosen code is known to have three types of behavior, corresponding to three phases in the plane of rate versus temperature: the ferromagnetic phase, corresponding to correct decoding, the paramagnetic phase, of complete disorder, which is dominated by exponentially many incorrect codewords, and the glassy phase (or the condensed phase), where the system is frozen at minimum energy and dominated by subexponentially many incorrect codewords. We show that the statistical physics associated with the two latter phases are intimately related to random coding exponents. In particular, the exponent associated with the probability of correct decoding at rates above capacity is directly related to the free energy in the glassy phase, and the exponent associated with probability of error (the error exponent) at rates below capacity, is strongly related to the free energy in the paramagnetic phase. In fact, we derive alternative expressions of these exponents in terms of the corresponding free energies, and make an attempt to obtain some insights from these expressions. Finally, as a side result, we also compare the phase diagram associated with a simple finite-temperature universal decoder, for discrete memoryless channels, to that of the finite-temperature decoder that is aware of the channel statistics.      

基于社会计算的IM恶意代码防御机制

即时通信(IM,Instant Messaging)网络已成为恶意代码传播的主要途径之一,本文提出了一种基于社会计算的IM恶意代码防御机制:利用用户与好友之间的社会信任关系,通过社会计算集成网络中多种反病毒软件的检测结果及用户的安全经验形成群体智慧,从而构成一个分布式协作防御机制.该机制利用即时通信网络平台,并依据好友间的交互行为计算动态信任,在IM客户端部署方案,用户之间实时相互协作抵御通过IM传播的恶意代码.实验结果表明,在大多数用户接受好友警告的情况下,即时通信网络中所有节点最终都被免疫,提高了整个社会网络防御IM恶意代码的能力.     

可伸缩视频编码标准中的差错控制

可伸缩视频编码标准（SVC）是由ISO/IEC的MPEG专家组和ITU-T的VCEG专家组联合组成的联合视频专家组制定的对H.264/AVC视频编码标准的可伸缩性扩展。SVC通过对时间分辨率、空间分辨率和质量等参数的可伸缩性来适应不同网络环境下用户对视频资料的分辨率、帧率、质量的不同需求,是目前解决这一问题的最好方法之一。由于信道传输中大量存在的衰减、误码和数据丢失,差错控制显得十分重要,因而两种有效的对抗措施——错误弹性编码和错误隐藏技术被引入到SVC中：一部分是直接从H.264中继承而来;还有一部分则是利用了可伸缩视频的自身特性而提出的。文中将对SVC中一些有代表性的错误弹性和错误隐藏技术进行介绍,并给出部分实验结果来展示这些技术带来的性能提升。     

宽带无线网络中的纠错编码

随着高速多媒体业务的迅速发展,如何提高第三代移动通信系统（3G）以及新一代移动通信系统（Beyond3G）的性能和容量愈发受到人们的重视。在业务无线接入时的服务质量（QoS）问题上,高效的纠错编码是必不可少且行之有效的解决方法之一。文中简要回顾了纠错码在前两代移动通信中的应用,并着重介绍了目前的研究热点——Turbo码和LDPC码的研究现状及发展前景。     

Linear Network Error Correction Codes in Packet Networks

In this paper, we study basic properties of linear network error correction codes, their construction and error correction capability for various kinds of errors. Our discussion is restricted to the single-source multicast case. We define the minimum distance of a network error correction code. This plays the same role as it does in classical coding theory. We construct codes that can correct errors up to the full error correction capability specified by Singleton bound for network error correction codes recently established by Cai and Yeung. We propose a decoding principle for network error correction codes, based on which we introduce two decoding algorithms and analyze their performance. We formulate the global kernel error correction problem and characterize the error correction capability of codes for this kind of error.     

增强型轻量级防窃听安全网络编码算法

研究了网络编码中的防窃听问题,在实际的网络编码环境中,敌人通常拥有完整的窃听能力。提出一种新颖的防全局窃听者的编码算法,利用r个映射值来随机化原始数据包,这表明每个数据包只需要一个被加密的符号,对于中间节点没有其他附加的要求。与其他的方法相比,本方法的效率更高,并且计算复杂度也适中。     

高速并行调制解调器中差错控制方法

本文简单介绍了适合高速并行调制解调器中差错控制的Reed-Solomon编码，提出了适合DSP软件实现的一整套的RS码的编码、译码实用方法，并对该编、译码法采用数字信号处理器TMS320C5410b进行仿真，对其性能与传统方法进行了对比。     

改进型自适应随机卷积网络编码算法

To address the issue of field size in ran-dom network coding, we propose an Improved A-daptive Random Convolutional Network Coding (IARCNC) algorithm to considerably reduce the a-mount of occupied memory. The operation of IARCNC is similar to that of Adaptive Random Convolutional Network Coding (ARCNC), with the coefficients of local encoding kernels chosen uni-formly at random over a small finite field. The difference is that the length of the local encoding kernels at the nodes used by IARCNC is constrained by the depth; meanwhile, increases until all the re-lated sink nodes can be decoded. This restriction can make the code length distribution more reasona-ble. Therefore, IARCNC retains the advantages of ARCNC, such as a small decoding delay and partial adaptation to an unknown topology without an early estimation of the field size. In addition, it has its own advantage, that is, a higher reduction in memo-ry use. The simulation and the example show the ef-fectiveness of the proposed algorithm.     

基于Hadamard矩阵的随机网络编码

在分析介绍随机网络编码理论应用于无线网络环境的优越性的同时,对Hadamard矩阵的性质展开研究,提出了基于Hadamard矩阵的随机网络编码方法,并且通过实例证明,基于Hadamard矩阵的编码系数矩阵不仅可以实现有效的网络编码信息传输,而且可以保证信息传输的安全性,同时降低了现有随机网络编码算法的复杂度。     

On Metrics for Error Correction in Network Coding

The problem of error correction in both coherent and noncoherent network coding is considered under an adversarial model. For coherent network coding, where knowledge of the network topology and network code is assumed at the source and destination nodes, the error correction capability of an (outer) code is succinctly described by the rank metric; as a consequence, it is shown that universal network error correcting codes achieving the Singleton bound can be easily constructed and efficiently decoded. For noncoherent network coding, where knowledge of the network topology and network code is not assumed, the error correction capability of a (subspace) code is given exactly by a new metric, called the injection metric, which is closely related to, but different than, the subspace metric of KÖtter and Kschischang. In particular, in the case of a non-constant-dimension code, the decoder associated with the injection metric is shown to correct more errors then a minimum-subspace-distance decoder. All of these results are based on a general approach to adversarial error correction, which could be useful for other adversarial channels beyond network coding.      

针对网络信息审计系统的DoS攻击检测

提出了一种针对网络信息审计系统的拒绝服务攻击(DoS)的检测算法。该算法通过分析系统告警的频率与分散度提取能够标示系统状态变化的两维特征向量，然后使用经过样本训练的K最近邻分类器检测DoS攻击。实验结果表明，该算法能够及时发现、防御DoS攻击，有效地阻止DoS攻击对网络信息审计系统的破坏。     

基于差错控制编码的水印检测

提出了一种基于差错控制编码(ECC)的水印检测方法,并且依据编码原理提出了进行水印检测的门限值的确定方法.基本思想是利用ECC对原始水印信息进行编码,水印检测时把提取出的待测编码水印与反馈水印进行比较,将其差值与设定的门限值进行比较,从而来判断水印存在与否.实验是基于DWT,采用的是ECC的Turbo码进行水印检测.仿真结果表明,该方法大大减少了水印图像在传输中的错误,水印的鲁棒性得到了极大的提高.