The threat of Distributed Denial of Service (DDoS) attack, that attempts to make a machine or network resource unavailable by multiple attacker is getting serious. Slow HTTP DoS attack is one of the DoS attack methods that targets HTTP servers. This method obstructs the service by saturating the processing requests with slow and many requests. It is known that Slow HTTP DoS attack by just one attacker can be prevented effectively by limiting the number of simultaneous requests for each IP address. On the other hand, it is also known that it is difficult to defend from Slow HTTP DoS attack performed by multiple attackers (i.e. Distributed Slow HTTP DoS attack). Therefore, the authors already proposed a defense method against Distributed Slow HTTP DoS attack. This method prevents to saturate the processing requests by disconnecting the clients holding the most connections that are established longer than a threshold t. However, the method to decide the thresholds used in our method appropriately is not known yet. We need its decision method to apply our defence method in real environments. In this paper, we discuss a method to decide the appropriate threshold t of our defence method.

Since mobile ad hoc networks do not have fixed or predefined infrastructures, nodes need to frequently flood control messages to discovery and maintain routes, which causes performance problems in traffic and energy consumption, contention, and collision. A general solution is to construct a virtual backbone as the basis of routing and broadcasting, and the Connected Dominating Set (CDS) has been widely used. This paper presents a distributed approach to constructing and maintaining a k-hop CDS. A unique characteristic that differentiates the proposed approach from existing ones is that, any value can be specified for k, and a larger k contributes to a smaller CDS. If k is large enough, the resulting CDS will contain only a single node. Simulation experiment results demonstrate the effectiveness of the proposed approach.

Internet threat monitoring systems are studied and developed to comprehend the malicious activities on the Internet. On the other hand, it is known that attackers devise a technique that locates the deployment of sensors that constitute the monitoring system. This technique is called as localization attacks to Internet threat monitors. If attackers can detect sensors, they can evade them when they initiate the malicious activities. The latest method can detect sensors with low probing traffic volume compared with the previous one because it adopts PN (Pseudo Noise) code-based scheme inspired from the spread spectrum technology. However, when other monitoring packets interfere as a strong noise, the detection accuracy of the method decreases. For this reason, we need to make elaborate preparations under the assumption that attackers improve the PN code-based method to boost resistance to a strong noise by exploiting multiple ports, rather than by a single port for detecting a sensor. Therefore, we devised the noise-tolerant PN code-based localization attack from a standpoint of attackers for the security research. Performance evaluation was conducted based on the real Internet monitoring dataset. In this paper, we show the detection accuracy and the stealthiness of our devised method compared with the existing one.

Since ad hoc networks do not have fixed or predefined infrastructures, nodes need to frequently flood control messages to discover and maintain routes, which causes performance problems in terms of unnecessary traffic and energy consumption, contention, and collision. A general solution is to construct a virtual backbone as the basis of routing and broadcasting, and the Connected Dominating Set (CDS) has been widely used. This paper gives a distributed approach to constructing k-Hop CDS with three unique characteristics: (1) the limitation on the range of k has been removed, (2) a token-based conflict avoidance mechanism has been introduced which can make the construction process faster and more effective, (3) a tree-type CDS can be constructed in bottom-up processing. Simulation experiments have been conducted to demonstrate the effectiveness of the proposed approach.

In recent years, one of the most widely used authentication methods is a password-based authentication method. In this method, users are required to create a secure (i.e.\ difficult to crack) and memorable (i.e.\ easy to remember) password when they create one. Taking account of these two important requirements, a mnemonic phrase-based password has been proposed. However, it is easy to crack a password if the users adopt famous phrases (e. g.\ music lyrics, movie quotes) to create a mnemonic phrase-based password. In this paper, we propose an associating image-based password creating method to create a password which is difficult to crack and easy to remember. Furthermore, we propose and develop a password creating support system for our method.

In recent years, one of the most widely used authentication methods is a password-based authentication method. When using the password-based authentication method, users are required to create a secure password according to various requirements such that the password is long enough, or it does not contain dictionary words nor user's personal information. As a result, it is difficult for users to create memorable passwords. To resolve the problem, we propose a new password based authentication scheme using multiple passphrases and its arrangement information. By experiment, we show our proposed scheme attains good usability and memorability. We also show it is invulnerable against shoulder surfing, dictionary attack and brute-force attack.

Sequential pattern mining is a technique used to discoverfrequentsubsequencesaspatternsina sequencedatabase. Many excellent sequential pattern mining approaches such as GSP, SPADE, and PrefixSpan have been proposed. However, the existing approaches still encounter problems when the set of all different items in a sequence database is large. Scalability with respect to not only the varying size of a sequence database, but also the varying size of the set of all different items is crucial for many applications. In this paper we address the subject of mining frequent sequential patterns in the large sequence database with numerous kinds of items. An effective algorithm for the purpose, called SSPM (ScalableSequentialPattern Mining), is proposed. SSPM is characterized by its fast convergence, meaning that the search space will shrink quickly as mining operation proceeds. SSPM does not limit the number of different items in a sequence database, and thus it has better scalability, and can be applicable to a large scale of sequence databases. The experimental and analytical results demonstrated that SSPM is effective and is faster than conventional algorithms in the above stated cases.

A DoS (denial of service) attack is one of the most serious threats in the Internet. It is important to protect the resources and services from the DoS attack, but it is difficult to distinguish normal traffic and DoS attack traffic because the DoS attackers generally hide their true identities/origins. In this paper, we propose a technique to reduce the influence of the DoS attack without disturbing the demand of the regular users by allocating the information, when DoS attack occurs, to the filtering rules. This can be done by using DNS request replies.

Since digital contents are easy to copy or process, they tend to be unfairly used. A watermarking method is one of the effective countermeasures against such unfairness. In this paper, we propose watermarking schemes for Music XML, which represents a musical score by XML and able to display it and play back the corresponding music using a Web browser, and implement and evaluate the proposed schemes.

In this paper, we propose and develop a security scanner with high portability and usability. Recently, illegal access has been increasing explosively. Not only experts but also beginners need to cope up with vulnerability of a system promptly and properly. In such cases, a security scanner is an efficient tool to point out the vulnerability. However, for general users, most of the presently available security scanners are hard to install and operate because they have considerably poor usability. We have developed a security scanner with high usability, called USAGI. USAGI is a Web based security scanner, therefore it should not depend on operating systems, and should not need any installation. However, Web based scanners cannot inspect a host which cannot issue a scan request such as Internet appliance. Moreover, a Web based scanner is not effective for a host inside firewall, if one would like to check vulnerability against insider threat. To overcome these problems, we design a portable version of USAGI, while keeping high usability. We adopted Perl and Macromedia Flash for development of the security scanner to realize portability. Since all the scanning processes are performed only by a few mouse clicks, our security scanner can be implemented on a small handheld computer without keyboard. In functionality, we have realized high extensionality and reliability by using the external script of Nessus.

In this paper, we propose and develop a security scanner with high usability. Any user can operate the scanner easily. Recently, illegal access has been increasing tremendously. Not only the expert but also the beginners need to cope up with vulnerability of a system promptly and properly. In such cases, a security scanner is an efficient tool to point out the vulnerability. However, for general users, most of the presently available security scanners are hard to install and operate because they have considerably poor usability. Our design criteria of the security scanner are that it should be Web based, should not depend on operating systems, and should not need any installation. To attain these goals, we adopted Perl and Macromedia Flash for development of the security scanner. Moreover, since all the scanning processes are performed only by one mouse click, our security scanner improves usability enormously. Additionally, we have introduced an extension script file, which contains additional vulnerability information for beginner users, detailed description of vulnerability from OS or application vendor, translated description into users' local languages, and so on. In addition, we designed it based on the knowledge of human interface study such as displaying scanning progress bar. Usability of our security scanner was evaluated by comparing with the usability of the existing security scanners using several points of view. In functionality, we have realized very high extensionality and reliability by using the external script of Nessus.

This paper presents a new low-weight trellis-based soft-decision iterative decoding algorithm for binary linear block codes. The algorithm is devised based on a set of optimality conditions and the generation of a sequence of candidate codewords for an optimality test. The initial candidate codeword is generated by a simple decoding method. The subsequent candidate codewords, if needed, are generated by a chain of low-weight trellis searches, one at a time. Each search is conducted through a low-weight trellis diagram centered around the latest candidate codeword and results in an improvement over the previous candidate codewords that have been already tested. This improvement is then used as the next candidate codeword for a test of optimality. The decoding iteration stops whenever a candidate codeword is found to satisfy a sufficient condition on optimality or the latest low-weight trellis search results in a repetition of a previously generated candidate codeword. A divide-and-conquer technique is also presented for codes that are not spanned by their minimum-weight codewords. The proposed decoding algorithm has been applied to some well-known codes of lengths 48, 64, and 128. Simulation results show that the proposed algorithm achieves either practically optimal error performance for the example codes of length 48 and 64 or near optimal error performance for the (128, 29, 32) RM code with a significant reduction in computational decoding complexity.

This paper presents a method for evaluating the bit-error probability of a concatenated coding system for BPSK transmission over the AWGN channel. In the concatenated system, a linear binary block code is used as the inner code and is decoded with the soft-decision maximum likelihood decoding, and a maximum distance separable code (or its interleaved code) is used as the outer code and is decoded with a bounded distance decoding. The method is illustrated through a specific example in which the inner code is a binary (64.40.8) Reed-Muller subcode and the outer code is the NASA standard (255, 223, 33) Reed-Solomon code over GF(2/sup 8/) interleaved to a depth of 5. This specific concatenated system is being considered for NASA's high-speed satellite communications. The bit-error performance is evaluated by a combination of simulation and analysis. The split weight enumerators for the maximum distance separable codes are derived and used for the analysis.

An upper bound on the effective error coefficient of a two-level code with two-stage decoding is presented. This bound provides a guideline for constructing two-level codes to achieve a good trade-off between the error performance and decoding complexity. Based on this bound, good two-level decompositions of some Reed-Muller codes for two-stage decoding are found. Simulation results on the error performances of some Reed-Muller codes of lengths up to 64 with two-stage soft-decision suboptimum decoding based on their two-level decompositions are given.>

To decode a long block code with a large minimum distance by maximum likelihood decoding is practically impossible because the decoding complexity is simply enormous. However, if a code can be decomposed into constituent codes with smaller dimensions and simpler structure, it is possible to devise a practical and yet efficient scheme to decode the code. This paper investigates a class of decomposable codes, their distance and structural properties. It is shown that this class includes several classes of well-known and efficient codes as subclasses. Several methods for constructing decomposable codes or decomposing codes are presented. A two-stage (soft-decision or hard-decision) decoding scheme for decomposable codes, their translates or unions of translates is devised, and its error performance is analyzed for an AWGN channel. The two-stage soft-decision decoding is suboptimum. Error performances of some specific decomposable codes based on the proposed two-stage soft-decision decoding are evaluated. It is shown that the proposed two-stage suboptimum decoding scheme provides an excellent trade-off between the error performance and decoding complexity for codes of moderate and long block length.>

It was shown earlier that for a punctured Reed-Muller (RM) code or a primitive BCH code, which contains a punctured RM code of the same minimum distance as a large subcode, the state complexity of the minimal trellis diagrams is much greater than that for an equivalent code obtained by a proper permutation of the bit positions. The problem of finding a permutation of the bit positions for a given code that minimizes the state complexity of its minimal trellis diagram is related to the generalized Hamming weight hierarchy of a code, and it is shown that, for RM codes, the standard binary order of bit positions is optimum at every bit position with respect to the state complexity of a minimal trellis diagram by using a theorem due to V.K. Wei (1991). The state complexity of the trellis diagram for the extended and permuted (64, 24) BCH code is discussed.>

An upper bound on the number of states of a minimal trellis diagram for a linear block code is derived. Using this derivation a cyclic (or shortened cyclic) code or its extended code is shown to be the worst in terms of trellis state complexity among the linear codes of the same length and dimension. The complexity of the minimal trellis diagrams for linear block codes of length 2/sup m/, including the Reed-Muller codes, is analyzed. The construction of minimal trellis diagrams for some extended and permuted primitive BCH codes is presented. It is shown that these codes have considerably simpler trellis structure than the original codes in cyclic form without bit-position permutation.>

Multistage decoding of multilevel block multilevel phase-shift keying (M-PSK) modulation codes for the additive white Gaussian noise (AWGN) channel is investigated. Several types of multistage decoding, including a suboptimum soft-decision decoding scheme, are devised and analyzed. Upper bounds on the probability of an incorrect decoding of a code are derived for the proposed multistage decoding schemes. Error probabilities of some specific multilevel block 8-PSK modulation codes are evaluated and simulated. The computation and simulation results for these codes show that with multistage decoding, significant coding gains can be achieved with large reduction in decoding complexity. In one example, it is shown that the difference in performance between the proposed suboptimum multistage soft-decision decoding and the single-stage optimum decoding is small, only a fraction of a dB loss in SNR at the block error probability of 10/sup -6/.>

Two important structural properties of block M(=2/sup '/)-ary PSK modulation codes, linear structure and phase symmetry, are investigated. An M-ary modulation code is first represented as a code with symbols from the integer group S/sub M-PSK/=(0,1,2,---,M-1) under modulo-M addition. Then the linear structure of block M-PSK modulation codes over S/sub M-PSK/ with respect to modulo-M vector addition is defined, and conditions are derived under which a block M-PSK modulation code is linear. Once the linear structure is developed, the phase symmetry of block M-PSK modulation codes is studied. In particular, a necessary and sufficient condition for a block M-PSK modulation code that is linear as a binary code to be invariant under 2/sup h/180 degrees /M phase rotation, for 1>

The multilevel technique for combining block coding and modulation is investigated. A general formulation is presented for multilevel modulation codes in terms of component codes with appropriate distance measures. A specific method for constructing multilevel block modulation codes with interdependency among component codes is proposed. Given a multilevel block modulation code C with no interdependency among the binary component codes, the proposed method gives a multilevel block modulation code C' that has the same rate as C, a minimum squared Euclidean distance not less than that of C, a trellis diagram with the same number of states as that of C, and a smaller number of nearest neighbor codewords than that of C. Finally, a technique is presented for analyzing the error performance of block modulation codes for an additive white Gaussian noise (AWGN) channel based on soft-decision maximum likelihood decoding. Error probabilities of some specific codes are evaluated by simulation and upper bounds based on their Euclidean weight distributions.>

A concatenated coded modulation scheme is presented for error control in data communications. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary phase-shift keying (PSK) modulation. Error performance of the scheme is analyzed for an additive white Gaussian noise (AWGN) channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner-code and a relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The scheme is particularly effective for high-speed satellite communications for large file transfer where high reliability is required. A simple method is also presented for constructing block codes for M-ary PSK modulation. Soome short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft-decision Viterbi decoding algorithm. Furthermore, some of these codes are phase invariant under multiples of 45 degrees rotation.>

A robust error control coding system is presented. This system is a cascaded FEC (forward error control) scheme supported by parity retransmissions for further error correction in the erroneous data words. The error performance and throughput efficiency of the system are analyzed. Two specific examples of the error control system are studied. The first example does not use an inner code, and the outer code, which is not interleaved, is a shortened code of the NASA standard RS code over GF(2/sup 8/). The second example, as proposed for NASA uses the same shortened RS code as the base outer code C/sub 2/, except that it is interleaved to a depth of 2. It is shown that both examples provide high reliability and throughput efficiency even for high channel bit-error rates in the range of 10/sup -2/.>

A coding scheme for error control in data communication systems is investigated. The scheme is obtained by cascading two error-correcting codes, called the inner and outer codes. Its error performance is analyzed for a binary symmetric channel with a bit-error rate epsilon>

Recently Kasami {\em et al.} presented a linear programming approach to the weight distribution of binary linear codes [2]. Their approach to compute upper and lower bounds on the weight distribution of binary primitive BCH codes of length2^{m} - 1withm \geq 8and designed distance2t + 1with4 \leq t \leq 5is improved. From these results, the relative deviation of the number of codewords of weightj\leq 2^{m-1}from the binomial distribution2^{-mt} \left( \stackrel{2^{m}-1}{j} \right)is shown to be less than 1 percent for the following cases: (1)t = 4, j \geq 2t + 1andm \geq 16; (2)t = 4, j \geq 2t + 3and10 \leq m \leq 15; (3)t=4, j \geq 2t+5and8 \leq m \leq 9; (4)t=5,j \geq 2t+ 1andm \geq 20; (5)t=5, j \geq 2t+ 3and12 \leq m \leq 19; (6)t=5, j \geq 2t+ 5and10 \leq m \leq 11; (7)t=5, j \geq 2t + 7andm=9; (8)t= 5, j \geq 2t+ 9andm = 8.