Constructing formal rules to verify message communication in distributed systems

This study presents a method to construct formal rules used to run-time verify message passing between clients in distributed systems. Rules construction is achieved in four steps: (1) Visual specification of expected behavior of the sender, receiver, and network in sending and receiving a message, (2) Extraction of properties of sender, receiver, and network from the visual specification, (3) specification of constraints that should govern message passing in distributed systems, and (4) construction of verifier rules from the properties and the constraints. The rules are used to verify actual sender, receiver, and network behavior. Expected behavior of the client (process) is one that to be and the actual one is the behavior should be verified. The rules were applied to verify the behavior of client and servers that communicated with each other in order to compute Fibonacci numbers in parallel and some violations were discovered.     

用于流媒体的平滑传输控制协议

为减小传输流媒体业务时的速率抖动,提出一种平滑传输控制协议（Smooth Transmission Control Protocol）。该协议的速率控制主要在接收端实现：接收端不断检测丢包,如果发生丢包,就通过丢包率和当前的发送速率估算端到端的实际传输能力,依据纯属能力减小发送速率;如果没有发生丢包,则模拟TCP的和式增加策略以提高发送速率。使用丢失率降低发送速率,避免了TCP中积式减小的过激行为,减小了速率抖动,获得平滑的发送速率。仿真实验表明,STCP发送速率平滑,时延抖动小,具有TCP友好性,适用于流媒体的传输控制。     

针对持续Mix的统计暴露攻击研究

暴露攻击是一种典型的针对匿名通信的攻击方式。基于统计暴露攻击的基本原理,针对持续发送的Mix机制,提出了一种基于数据包数量的统计暴露攻击算法, 测试并分析了目标节点接收者个数、系统中总的发送者个数、接收者个数以及Mix延迟对该算法攻击能力的影响。在此基础上,指出匿名系统可以通过发送者掩护和背景干扰的填充包发送策略来防范这种攻击。     

Full and partial deniability for authentication schemes

Deniable authentication is a type of authentication protocol with the special property of deniability. However, there have been several different definitions of deniability in authentication protocols. In this paper, we clarify this issue by defining two types of deniable authentication: In the first type of deniable authentication, the receiver of the authenticated message cannot prove to a third party that the sender has authenticated any message to him. We call this type of deniability full deniability. In the second type of deniable authentication, whilst the receiver can prove to a third party that the sender has authenticated some message to him, but he cannot prove to a third party that the sender has authenticated any particular message to the receiver. We call this type of deniability partial deniability. Note that partial deniability is not implied by full deniability, and that it has applications different from those of full deniability. Consequently, we present two identity-based authentication schemes and prove that one is fully deniable while the other is partially deniable. These two schemes can be useful in different scenarios.     

基于JXTA的P2P即时通信系统设计

课题研究使用JXTA搭建P2P网络,完成即时通信系统。即时通信系统分为发送、中继转发和接收三部分。其中中继转发部分在启动时加入P2P网络,并且在P2P网络中发布提供即时通信服务的通告。发送部分加入P2P网络,通过查找P2P网络通告寻找提供服务的即时通信结点,选择结点形成P2P网络通道。发送端在这个通道基础上建立与接收端的SOCKET连接,将信息传递到接收端。     

Subliminal channels in the identity-based threshold ring signature

Subliminal signature schemes enable senders to hide subliminal messages in a digital signature such that no one besides the authorised subliminal message receiver (called designated receiver) can extract subliminal messages from that signature. This paper is the first to construct subliminal channels on the identity-based threshold ring signature scheme. Two types of subliminal channels are proposed. The first is the unknown-sender subliminal channel, wherein the sender is anonymously sending the subliminal message through an identity-based threshold ring signature. Although the designated receiver can extract the subliminal message and confirm that it is from the known ring of signers, he/she cannot identify the real sender. The other proposed subliminal channel is the known-sender subliminal channel in which the designated receiver can identify the actual sender. Furthermore, the proposed unknown-sender subliminal channel can be extended to permit the sender to send multiple subliminal messages to multiple designated receivers via a single threshold ring signature.     

H∞ output tracking control for uncertain networked control systems via a switched system approach

In this paper, the problem of H_∞ output tracking control for networked control systems with random time delays and system uncertainties is investigated. Effective sampling instant that is tightly related with transmission delay from sensor to actuator is proposed to ensure that the random variable time delay is always shorter than one effective sampling period. By using both active time‐varying sampling period strategy and hybrid node‐driven mechanism, the switching instant is coincided with the effective sampling instant. An augmented time‐varying networked tracking system model is provided by including the output tracking error as an additional state. However, random transmission delay causes indeterminate sampling period, which induces infinite subsystems. Gridding approach is introduced to transform the continuous time axis into discrete‐time sequences, which guarantees the finite number of switching rules. By employing multiple Lyapunov–Krasovskii functions, linear matrix inequality (LMI)‐based output tracking H_∞ performance analysis is presented, and robust switching H_∞ model reference tracking controller for networked control systems with communication constraints and system uncertainties is designed to guarantee asymptotic tracking of prescribed reference outputs while rejecting disturbances. Finally, simulation results illustrate the correctness and effectiveness of the proposed approaches. Copyright © 2015 John Wiley & Sons, Ltd.     

Sampled-data chain-observer design for a class of delayed nonlinear systems

The problem of observer design is addressed for a class of triangular nonlinear systems with not-necessarily small delay and sampled output measurements. One more difficulty is that the system state matrix is dependent on the un-delayed output signal which is not accessible to measurement, making existing observers inapplicable. A new chain observer, composed of m elementary observers in series, is designed to compensate for output sampling and arbitrary large delays. The larger the time-delay the larger the number m. Each elementary observer includes an output predictor that is conceived to compensate for the effects of output sampling and a fractional delay. The predictors are defined by first-order ordinary differential equations (ODEs) much simpler than those of existing predictors which involve both output and state predictors. Using a small gain type analysis, sufficient conditions for the observer to be exponentially convergent are established in terms of the minimal number m of elementary observers and the maximum sampling interval.     

Moving horizon control of nonlinear systems with input saturation,disturbances and plant uncertainty

We present a moving horizon feedback system, based on constrained optimal control algorithms, for nonlinear plants with input saturation, disturbances and plant uncertainty. The system is a non-conventional sampled-data system: its sampling periods vary from sampling instant to sampling instant, and the control during the sampling time is not constant, but determined by the solution of an open loop optimal control problem. We show that the proposed moving horizon control system is robustly stable and is capable of attenuating L∞ bounded disturbances.     

Measures on MV-algebras

 We study sequentially continuous measures on semisimple M V-algebras. Let A be a semisimple M V-algebra and let I be the interval [0,1] carrying the usual Łukasiewicz M V-algebra structure and the natural sequential convergence. Each separating set H of M V-algebra homomorphisms of A into I induces on A an initial sequential convergence. Semisimple M V-algebras carrying an initial sequential convergence induced by a separating set of M V-algebra homomorphisms into I are called I-sequential and, together with sequentially continuous M V-algebra homomorphisms, they form a category SM(I). We describe its epireflective subcategory ASM(I) consisting of absolutely sequentially closed objects and we prove that the epireflection sends A into its distinguished σ-completion σ _H (A). The epireflection is the maximal object in SM(I) which contains A as a dense subobject and over which all sequentially continuous measures can be continuously extended. We discuss some properties of σ _H (A) depending on the choice of H. We show that the coproducts in the category of D-posets [9] of suitable families of I-sequential M V-algebras yield a natural model of probability spaces having a quantum nature. The motivation comes from probability: H plays the role of elementary events, the embedding of A into σ _H (A) generalizes the embedding of a field of events A into the generated σ-field σ(A), and it can be viewed as a fuzzyfication of the corresponding results for Boolean algebras in [8, 11, 14]. Sequentially continuous homomorphisms are dual to generalized measurable maps between the underlying sets of suitable bold algebras [13] and, unlike in the Loomis–Sikorski Theorem, objects in ASM(I) correspond to the generated tribes (no quotient is needed, no information about the elementary events is lost). Finally, D-poset coproducts lift fuzzy events, random functions and probability measures to events, random functions and probability measures of a quantum nature. Supported by VEGA Grant 2/7193/01     

Frequency Domain Frequency Shift for Optimal Filtering of Cyclostationary Signals

Parker, G., Frequency Domain Frequency Shift for Optimal Filtering of Cyclostationary Signals, Digital Signal Processing12 (2002) 561–589Optimum reconstruction of corrupted cyclostationary signals is achieved using the filter class known as the frequency shift filter. This filter requires the received signal to be shifted by the frequencies of cyclostationarity of the signal and with a frequency domain implementation it will often be best to effect the frequency shifts directly in the frequency domain. This paper introduces techniques for exactly achieving these shifts as well as providing more computationally efficient approximate solutions.     

Adaptive Data Hiding,Using Pixel-Value-Differencing and LSB Substitution

With the development of Internet communications, the security of message sending on the Internet has become very important. This article proposes a new adaptive data hiding method with a large data-embedding capacity for gray-scale images to raise the security of sending a message between sender and receiver in networks. At first, the image is divided into some blocks consisting of two consecutive pixels. If the values of both pixels are small, fewer secret bits will be embedded within the two pixels, otherwise, the difference value of two pixels is calculated, and according to the obtained difference value, the method will estimate the number of embedding bits into LSBs of two pixels. This number is adaptive and depends on the range to which the difference value belongs. A readjusting phase is presented to keep the difference of value pixels in the same range before and after embedding. Experimental results show that our method has increased the capacity of embedding bits in comparison with the several other methods.     

一种接收方驱动的无线TCP拥塞控制机制

为了提高有线/无线异构网络中TCP的传输性能,提出了一种新的接收方驱动的TCP拥塞控制机制TCP_LEB.该机制在接收方计算当前带宽和往返时间(RTT),并根据以往的带宽推导以后的可用带宽,然后反馈到发送方作为发送依据.同其他类似研究相比,该方法明显提高了无线网络中TCP的性能.仿真实验结果验证了算法的良好效果.     

Guaranteed H∞ robustness bounds for Wiener filtering and prediction

The paper deals with special classes of H_∞ estimation problems, where the signal to be estimated coincides with the uncorrupted measured output. Explicit bounds on the difference between nominal and actual H_∞ performance are obtained by means of elementary algebraic manipulations. These bounds are new in continuous‐time filtering and discrete‐time one‐step ahead prediction. As for discrete‐time filtering, the paper provides new proofs that are alternative to existing derivations based on the Krein spaces formalism. In particular, some remarkable H_∞ robustness properties of Kalman filters and predictors are highlighted. The usefulness of these results for improving the estimator design under a mixed H₂/H_∞ viewpoint is also discussed. The dualization of the analysis allows one to evaluate guaranteed H_∞ robustness bounds for state‐feedback regulators of systems affected by actuator disturbances. Copyright © 2001 John Wiley & Sons, Ltd.     

计算机串行无线通信的抗干扰研究

很多嵌入式设备中的无线串行通信采用ASK调制方式。串口通信具有突发通信的特点,当发射方没有数据发射的时候,高增益接收模块会接收到很多干扰信号,干扰的存在使通信口无法判断通信数据到来的时刻。对干扰的种类进行了分析,通过在不修改原有的串行通信的基础上,添加通信同步头来实现接收同步,针对通信同步头的接收,给出了接收状态机的描述。     

结合时间戳的指纹密钥数据加解密传输方案

目的 对于生物密钥而言，生物特征数据的安全与生物密钥的管理存储都很关键。为了构造能够应用在通信数据传输场景的生物密钥，同时保证生物特征本身的模糊性与密码学的精确性处于一种相对平衡状态，提出一种基于时间戳与指纹密钥的数据加解密传输方案。方法 利用发送方指纹特征点之间的相对信息，与保密随机矩阵生成发送方指纹密钥；借助通信双方的预先设定数与时间戳，生成接收方恢复指纹密钥时所需的辅助信息；利用发送方指纹密钥加密数据，实现密文数据的传输。结果 本文方法在仿真通信双方数据加解密的实现中，测试再生指纹密钥的识别率（GAR）与误识率（FAR）。通过实验数据分析，表明了本文提出的指纹密钥生成方法的可用性，以及指纹密钥作为数字身份所具备的可认证性，其中真实发送方的再生指纹密钥识别率可高达99.8%，并且本方案还可用于即时通信、对称加密等多种场景当中。结论 本文方法利用时间戳确定了通信事件的唯一性与不可否认性，同时实现了指纹密钥恢复时的"一次一密"。此外，方案通过保密随机矩阵实现了发送方指纹密钥的可撤销，极大程度保障了指纹数据的安全性。     

一种新型可靠网络隐蔽信道的研究

针对传统IP时间隐蔽信道传输速率低,在广域网中缺少一种稳定的时间同步机制,难以实现收发双方间可靠、稳定传输隐蔽信息的问题,提出了一种可靠网络隐蔽信道的模型。这种信道利用在固定时间窗口内发送的IP数据包数量作为载体传输隐蔽信息。通过引入一种新的信息编码机制,显著提高了网络隐蔽信道的传输带宽。进一步提出了一种比特块定界方法,解决了传统IP时间隐蔽信道的时间同步问题。实验结果表明,提出的可靠网络隐蔽信道的传输速率和稳定性均好于传统的IP时间隐蔽信道。     

Markovian bulk service queue with delayed vacations

An M/M(a, b)/1 queueing system with multiple vacations is studied, in which if the number of customers in the queue is a - 1 either at a service completion epoch or at a vacation completion point, the server will wait for an exponential time in the system which is called the changeover time. During this changeover time if there is an arrival the server will start service immediately, otherwise at the end of the changeover time the server will go for a vacation. The duration of vacation is also exponential. This paper is concerned with the determination of the stationary distribution of the number of customers in the queue and the waiting time distribution of an arriving customer. The expected queue length is also obtained. Sample numerical illustrations are given.     

基于多示例学习的不经意传输协议安全性分析

不经意传输协议在执行过程中要能够同时保证发送方的隐私和接收方的隐私。本文提出一种基于多示例学习的模型,对不经意传输协议的安全性进行了分析。研究发现,在以下前提下利用此模型可以使不经意传输协议的发送方经过几次通信后算得接收方所选择的数据：（1）接收方的询问请求具有连续性;（2）发送方对接收方的选择兴趣有一定的先验知识。从而表明在不经意传输协议的执行过程中接收方的隐私会受到侵犯,不经意传输协议对接收方不是绝对安全的。     

一种适用于流媒体传输的无线TCP友好速率控制机制

综合无线错误丢包以及拥塞丢包事件的统计特征,基于丢包区分,本文提出一种适用于流媒体传输的无线TCP友好速率控制(Wireless TCP-Friendly Rate Control,WTFRC)方程并建立实用的速率控制机制.该机制包括服务器或者代理发送端和用户接收端两部分,分别负责往返传输时间(Round-Trip Time,RTT)估计、发送速率估计调整和丢包区分、丢包率(Pack-et Loss Ratio,PLR)统计、接收速率估计.仿真结果验证了该机制能够获得较高的吞吐量和较平缓的发送速率,并具备较好的TCP友好特征.