Message authentication code (MAC) is one of the most fundamental cryptographic primitives, and aggregate message authentication code (AMAC) is an authentication technique that can compress multiple MAC tags into a short tag for messages from multiple senders. Although AMAC cannot specify an invalid message, AMAC with detecting functionality (AMAD) enables us to compress multiple MAC tags and to identify an invalid message. In this paper, we propose construction of AMAD from biorthogonal codes, and show that our AMAD achieves a better compression rate than other constructions of AMAD.

A novel technique for cryptanalysis of the stream cipher Grain-v1 is given. In a particular setting, the algorithms proposed in this study provide recovery of an internal state of Grain-v1 with the expected time complexity of only 254 table look-up operations employing a memory of dimension ∼270, assuming availability of 234 keystream sequences each of length 238 generated for different initial values, and the pre-processing time complexity of ∼288. These figures appear as significantly better in comparison with the previously reported ones. The proposed approach for cryptanalysis primarily depends on the order of normality of the employed Boolean function in Grain-v1. Accordingly, in addition to the security evaluation insights of Grain-v1, the results of this study are also an evidence of the cryptographic significance of the normality criteria of Boolean functions.

We introduce in this paper the concept of a correctable error set and a fixed initialization decoding, by noticing that the sum-product decoder with a given iteration number only depends on the initialized probability of error, for a BSC. Although this value has been conventionally selected as the BSC crossover probability, we show that other selections can provide better performance or faster convergence. We also prove that for any fixed initialization (i.e., any given correctable error set), the word-error-rate can be represented as a polynomial of the BSC crossover probability. This suggests that the word-error-rate can be analytically derived from the knowledge of the correctable error set.

In this paper, we consider quantum error correction over depolarizing channels with nonbinary low-density parity-check codes defined over Galois field of size 2p. The proposed quantum error correcting codes are based on the binary quasi-cyclic Calderbank, Shor, and Steane (CSS) codes. The resulting quantum codes outperform the best known quantum codes and surpass the performance limit of the bounded distance decoder. By increasing the size of the underlying Galois field, i.e., 2p, the error floors are considerably improved.

For designing low-density parity-check (LDPC) codes for quantum error-correction, we desire to satisfy the conflicting requirements below simultaneously. 1) The row weights of parity-check “should be large”: The minimum distances are bounded above by the minimum row weights of parity-check matrices of constituent classical codes. Small minimum distance tends to result in poor decoding performance at the error-floor region. 2) The row weights of parity-check matrices “should not be large”: The performance of the sum-product decoding algorithm at the water-fall region is degraded as the row weight increases. Recently, Kudekar et al. showed spatially-coupled (SC) LDPC codes exhibit capacity-achieving performance for classical channels. SC LDPC codes have both large row weight and capacity-achieving error-floor and water-fall performance. In this paper, we propose a new class of quantum LDPC codes based on spatially coupled quasi-cyclic LDPC codes. The performance outperforms that of quantum “non-coupled” quasi-cyclic LDPC codes.

In this paper, we propose a construction method for two-level quantum error-correcting codes via non-binary LDPC codes over an extended field of order 2p, p an integer p >; 1. The proposed quantum error-correcting codes are based on binary quasi-cyclic LDPC codes which have almost achieved a “Bounded Distance Decoding (BDD)” limit but have not surpassed the limit yet. Quantum codes constructed from the proposed method surpass the BDD limit. Furthermore the codes outperform the efficiently-decodable state-of-the-art quantum codes.

Recently, Radio Frequency IDentification (RFID) systems are intensively studied and widely used in every-day applications, such as, retailing, supply chain management, and medical equipment management. Tags in RFID systems are highly efficient to be managed and tracked, but at the same time suffering from impersonation and privacy problems. Consequently, RFID systems are required to provide both efficient management, as well as authentication and privacy protection. In this paper, on the basis of fast and light-weight Niederreiter public-key cryptosystem, we propose an efficient RFID authentication protocol which satisfies the above requirements, and enjoys the following merits: 1) unlike most of the previous works that employ symmetric key cryptographic techniques, our proposal has a fast computation to find authenticated ID and needs no exhaustive search in database, which reduces the searching time significantly; 2) the memory size to store the key in RFID tags can be greatly reduced by our novel methods.

Explosive progress in networking and outsourcing storage increases the use of information retrieval technologies, in massive datasets. Nowadays, there are varieties of storage-providers through the internet, such as e-mail accounts and public database, which are convenient to store and exchange electronic files and medias. Typically, the storage-provider offers users the capability to collect, retrieve and search, however, privacy issues are rarely considered at the same time. For example, it is unknown how to prevent some curious storage- provider from learning the private information of the user, such as, searching criterion and access pattern, as well as contents. In CRYPTO'07, Boneh et al. put forward a privacy-preserving solution to this problem, with the help of public key cryptography. In their work, the authors made use of PIR (Private Information Retrieval) and several combinatoric techniques, which are theoretically interesting and likely to be the best approach in the literature. In this paper, however, we show that their proposal seems unlikely to be implementable with the latest technology, due to a large amount of computation cost involved. Then, we provide an improved method to turn the keyword search more practical, which cannot only avoid the expensive computation cost caused by operations of public key encryption, but enable the privacy-preserving information retrieval, as well.

In this paper, we introduce the concept of correctable error set for the BSC, which allows to generalize sum-product decoding for this channel. As a result, better error performance or faster convergence can be achieved. Furthermore, the correctable error set allows to evaluate the error performance of generalized sum-product decoding with a given iteration number for the BSC.

A Boolean function is k-normal if it is constant on a k-dimensional flat of its domain. This paper demonstrates that k-normality of a Boolean function can be exploited to mount a dedicated algebraic attack on a stream cipher of the nonlinear filter generator type, which employs a k-normal Boolean function as its filter function. The cryptanalysis is based on the possibility for pre-computing a table of the state-key stream pairs via solving certain system of algebraic equations as a consequence of the employed k-normal Boolean function. This pre-computed table is the main origin for mounting the cryptanalysis and it is independent of a the sample for cryptanalysis and the secret key employed for generating the sample.

An authentication protocol is proposed which originates from the elements of the authentication protocols belonging to the HB-family and the protocols based on employment of pseudorandom number generators. Desired features of the proposed protocol have been achieved via combining the pseudorandomnes generated by a compact keystream generator, randomness and dedicated homophonic and error-correction coding. It is shown that implementation complexity of the protocol is low. Security of the proposed protocol is considered from an information-theoretic and a computational-complexity points of view assuming the passive attacking The performed security evaluation yields an indication for a conjecture on the security within certain active attacking scenarios as well.

Following some of the recently reported results, an approach for design of stream ciphers has been considered which is based on joint employment of pseudorandomness, randomness and dedicated wire-tap channel and error correction coding. The wire-tap channel coding controlled by the randomness, provides that an attacker faces not only the traditional problems of cryptanalysis but also the problem of decoding without the secret key which appears as complex as the exhaustive search over the possible secret keys. Security evaluation has been performed based on the algebraic representation of the proposed stream cipher. The given security evaluation has addressed hardness of the algebraic recovering of the secret key in the CPA scenario. It is shown that the secret key recovery is as hard as the LPNϵproblem where ϵ = (1-(1-2p)(m-ℓ)/2)/2 and m, ℓ and p are the stream cipher parameters.

Authenticated Key Exchange (AKE) protocol is one of the ways for establishing secure channels between two parties where they authenticate each other and share a common session key. In particular, some AKE protocols using passwords and high-entropy secrets (i.e., two-factor AKE) are preferable since they provide stronger authentication than one-factor authentication. However, existing two-factor AKE protocols never equip ability to distinguish on-line dictionary attacks from other events, such as client's password mis-typing and communication errors. This problem submerges a critical symptom of high-entropy-secret-leakage (since without it adversaries cannot perform the on-line dictionary attacks) or it forces the users inconvenience by letting them change their passwords frequently to reset the entropy of it that might be guessed partially by the on-line dictionary attacks. In this paper, we propose two general methods to distinguish online dictionary attacks (performed by an attacker) from other harmless events in the two-factor AKE protocols.

It is anticipated that quantum key distribution enable us to share a secret key while guaranteeing unconditionally security. In this paper, we discuss the quantum key distribution using the Mean King Problem which was proposed by J. Bub in 2001. While this two-way quantum protocol is essentially different from the other one-way protocols like the BB84, it has been shown that Eve cannot gain any information without being detected even in this protocol. Assuming two attack scenarios in this protocol, we derive two trade-off inequalities showing that the larger Eve's information gain is, the higher the detectability becomes. These quantitative inequalities enables the legitimate users to estimate Eve's information gain.

OAEP is one of the few standardized and widely deployed public-key encryption schemes. It was designed by Bellare and Rogaway as a scheme based on a trapdoor permutation such as RSA. RSA-OAEP is standardized in RSA's PKCS #1 v2.1 and is part of several standards. OAEP was shown to be IND-CCA secure assuming the underlying trapdoor permutation is partial one-way, and RSA-OAEP was proven to be IND-CCA under the standard RSA assumption, both in the random oracle model. However, the latter reduction is not tight, meaning that the guaranteed level of security is not very high for a practical parameter choice. We observe that the situation is even worse because both analyses were done in the single-query setting, i.e., where an adversary gets a single challenge ciphertext. This does not take into account the fact that in reality an adversary can observe multiple ciphertexts of related messages. The results about the multiquery setting imply that the guaranteed concrete security can degrade by a factor of$q$, which is the number of challenge ciphertexts an adversary can get. We propose a very simple modification of the OAEP encryption, which asks that the trapdoor permutation instance is only applied to a part of the OAEP transform. We show that IND-CCA security of this scheme is tightly related to the hardness of one-wayness of the trapdoor permutation in the random oracle model. This implies tight security for RSA-OAEP under the RSA assumption. We also show that security does not degrade as the number of ciphertexts an adversary can see increases. Moreover, OAEP can be used to encrypt long messages without using hybrid encryption. We believe that this modification is easy to implement, and the benefits it provides deserves the attention of standard bodies.

Denial of Service (DoS) attacks are serious threats for network societies. For dealing with DoS attacks, Jakobsson and Juels first proposed the notion of useful client puzzles (UCPs) which simultaneously decrease servers' burden and increase clients'. In ACM CCS'04, Diament, Lee, Keromytis, and Yung introduced the decryption-based UCPs. In this paper, we give a general framework for constructing such UCPs which is based on identity-based cryptography along with well-analyzed symmetric key authenticated encryption techniques (without random oracles). By using this framework, we can flexibly construct various UCPs according to different types of system requirements. We also give some instantiations: the first is a UCP based on the Boneh-Boyen Identity based encryption scheme, with provable security in the standard model. Another one is a UCP based on the Boneh-Gentry-Hamburg identity-based encryption scheme, which doesn't require pairings.

Most of digital signatures require the secret key when signing a message, however, there does exists a kind of signature scheme which is able to sign by appending new message only, so-called append-only signature (AOS). Motivated by its numerous useful applications in network security such as secure routing, etc., in this paper, we propose new efficient AOS scheme with shorter public key (parameters) using ID- based cryptographic techniques. To our surprise, it is the first time to achieve a practical, adaptively secure AOS via ID-based encryption approach. The proposed signature enjoys the merit of security against adaptive attack, while the previously presented AOS is only secure in a weak sense of selective unforgeability. Finally, we also present a new restricted AOS (RAOS) signature, which may be of independent interest in practice.

In the emergency broadcast system (or emergency alert system) which aims to broadcast a warning information immediately in time of emergency such as a natural or civil disaster, computational power-restricted devices such as, pocket terminals and sensors need to instantly and securely verify correctness and integrity of the received message packets. Though a lot of broadcast authentication systems were proposed, most of them require relatively high computation cost. In this paper, we propose a new lightweight broadcast authentication protocol McSBA based on McEliece signature. It can be quickly verified with a tiny computation cost, applicable on power-restricted devices. We first estimate the time performance and compare McSBA with widely used RSA signature and well- known TESLA broadcast authentication protocol, to show that the verification of McSBA has a low cost and is faster than the others. Especially, it is shown by our estimation that McSBA can verify quickly less than Is in emergency situations, however RSA signature with the same security takes more than 4s. Then we make use of a simulation of verification of RSA signature and McSBA, on the same platform, to attest that verification of McSBA is about ten times faster than RSA signature, which also supports our estimation result. Consequently, we expect that our technique is useful in the emergency broadcast system.

This paper presents a novel security architecture for in-vehicle communication. The ratio of electronics to vehicle equipment is steadily increasing. And novel vehicles will also have connectibility to public networks to provide many kinds of services. Therefore, they are expected to suffer from a wide variety of threats and the electronic control units (ECUs) embedded in them may execute execute malicious programs because of tampering. The remote attestation scheme with the trusted platform module (TPM) has been attracting a great deal of attention to cope with such issues. However, it is not feasible for vehicle systems because the conventional attestation process cannot adapt to in-vehicle communication and TPM cannot adapt to time-constrained vehicle systems. We propose an attestation based security architecture that is suitable for novel vehicles.

In this paper, several investigations have been performed for solving the open problem that if small quaternion orthogonal design can be used to build larger one. The so called coordinate interleaved orthogonal designs (CIODs) are generalized into quaternion in the paper, and consequently it introduces a new construction technique for 4 n times 4 m rectangular matrices whose elements are quaternion variables based on any existing n times m quaternion orthogonal design for space-time block codes (STBCs). Analysis shows that maximum likelihood (ML) decoding can be applied for this design with reduced complexity , and the design reaches full diversity. As examples, 8 times 8 quaternion designs are constructed.

The 26 papers and six items of correspondence in this special issue focus on information theoretic security. The papers and items of correspondence are summarized here.

We prove that the commitment capacity of the power-constrained Gaussian channel, i.e., the optimal rate at which this channel can be used for implementing commitment schemes, is infinite.

We give a tracing algorithm for 2-secure probabilis- tic fingerprinting codes with the property that it never accuses innocent users when there are up to 2 attackers. Moreover, by using our code and tracing algorithm, innocent users are also unlikely to be accused even if either the number of attackers or attackers' abilities exceed our assumption. Our code is the first example of collusion-secure fingerprinting codes with both of these two properties. Furthermore, our code has shorter length among the preceding 2-secure codes, and possesses further properties desirable in a practical use.

In this paper, the gains achievable by proper decimation (or puncturing) of the received sample for fast correlation attack are investigated. In particular, the instances in which such an approach is interesting are clearly identified.

In this paper, a construction of a pair of quasi-cyclic LDPC codes to construct a quantum error-correcting code is proposed. Our construction method is based on algebraic combinatorics and have lots of variations for length, code rate.

Anonymity and specifically sender anonymity have become essential requirements for many privacy-related applications (e.g. net counselling and whistle blowing). On the other hand, anonymity may be abused for various malicious activities (e.g. redistribution of copy-righted contents and illegal drug trading). In this paper, we address both by proposing protocols for authenticated anonymous communications channels. In such channels, the client can authenticate the authentication server while the latter can only authenticate the fact that the client is one of the qualified members that are eligible to use the network (e.g. WLAN hot spots, WiMAX). Our protocols are based on an efficient anonymous password-based authenticated key exchange protocol and on an anonymous IP address assignment and have the following advantages: (1) they can restrict the usage of the established anonymous channels to certain fair purposes; (2) they do not involve rerouting of the packets through a chain of intermediate nodes; (3) they are available right after registration of a normal password to an authentication server as for a classical non-anonymous authentication (e.g. EAP-TTLS and PEAP) and do not require any special registration procedures that would reveal initially to the authentication server that the client belongs to a small list of users of anonymous services. Each protocol fits in a different authentication framework (IEEE802.1x and PANA) and is different with respect to providing controlled IP address assignment.

In this correspondence, iteration-1 of bit flipping decoding based on a set of nonorthogonal check sums is analyzed for both regular and irregular models. In particular, the tradeoff between the Hamming weight (and overlapping) of the check sums and the number of redundant check sums required to start converging under iterative decoding is investigated. The model is then applied to an iterative attack of McEliece public-key cryptosystem since a successful attack of this system can be achieved by algebraic bounded distance decoding of a random code. Based on this model, the attack can be decomposed into two phases: a preprocessing phase which, for one particular key kappa, consists of finding a sufficiently large set S of check sums up to a certain Hamming weight, and a bit flipping decoding phase which uses the set S for each message encrypted with the key kappa

In this paper, a general framework which enables to compare previously proposed block decoding approaches for the fast correlation attack is developed. All attacks are based on decoding using a set of parity check sums of an underlying linear code. The purpose of this paper is twofold:to provide a simple close form estimate about the number of check sums of a particular structure necessary for the corresponding attack to succeed;

A digital signature does not allow any alteration of the document to which it is attached. Appropriate alteration of some signed documents, however, should be allowed because there are security requirements other than the integrity of the document. In the disclosure of official information, for example, sensitive information such as personal information or national secrets is masked when an official document is sanitized so that its nonsensitive information can be disclosed when it is requested by a citizen. If this disclosure is done digitally by using the current digital signature schemes, the citizen cannot verify the disclosed information because it has been altered to prevent the leakage of sensitive information. The confidentiality of official information is thus incompatible with the integrity of that information, and this is called the digital document sanitizing problem. Conventional solutions such as content extraction signatures and digitally signed document sanitizing schemes with disclosure condition control can either let the sanitizer assign disclosure conditions or hide the number of sanitized portions. The digitally signed document sanitizing scheme we propose here is based on the aggregate signature derived from bilinear maps and can do both.

The concept of personal networks is very user- centric and representative for the next generation networks. However, the present security mechanism is not considering at all what happens whenever a mobile node (device) is compromised, lost or stolen. This kinds of leakage of stored secrets has been a great danger in the field of communication security since it sometimes leads to the complete breakdown of the intended security level. In order to solve the problem, we propose a 3-way leakage-resilient and forward-secure authenticated key exchange (3LRFS-AKE) protocol and its security architecture for personal networks. The 3LRFS-AKE protocol guarantees not only forward secrecy of the shared key between device and its server but also a new additional layer of security against leakage of stored secrets. The security architecture includes two different types of communications: PN wide communication and communication between P-PANs of two different users.

We consider bit commitment over additive white Gaussian noise channels. Our main result is that the maximum rate at which this class of channels can be used for implementing commitment protocols (the commitment capacity) is provably infinite, even under an average power constraint.

One of the most important primitives in two-party distrustful cryptography is oblivious transfer, a complete primitive for two-party computation. Recently introduced, the oblivious transfer capacity of a noisy channel measures an efficiency of information theoretical reductions from 1-out-of-k, l-string oblivious transfer to noisy channels. It is defined as the maximal achievable ratio l/n, where l is the length of the strings which are to be transferred and n is the number of times the noisy channel is invoked. This quantity is unknown in a general case. For discrete memoryless channels, it is known to be nonnegligible for honest-but-curious players, but the non-zero rates have not ever been proved achievable in the case of malicious players. Here, we show that in the particular case of the erasure channel, more precise answers can be obtained. We compute the OT capacity of the erasure channel for the case of honest-but-curious players and, for the fully malicious players, we give its lower bound.

Bit commitment is an important tool for constructing zero-knowledge proofs and multi-party computation. Unconditionally secure bit commitment can be based, in particular, on noisy channel or correlation where noise considered a valuable resource. Recently, Winter, Nascimento and Imai introduced the concept of commitment capacity, the maximal ratio between the length of a string which the sender commits to and the number of times the noisy channel/correlation is used. They also proved that for any discrete memoryless channel there exists a secure protocol achieving its commitment capacity however, no particular construction was given. Solving their open question, we provide an efficient protocol for achieving the commitment capacity of discrete memoryless systems (noisy channels and correlations).

A private-personal area network (P-PAN) is the very user-centric and basis component of personal networks. However, the current security mechanism is not robust against leakage of stored secrets that can happen when a mobile node (device) is compromised, lost or stolen. This results in unauthorized accesses to other devices and services. For that, this paper introduces a leakage-resilient and forward secure authenticated key exchange (LRFS-AKE) protocol and its usage in the relation to P-PANs. The LRFS-AKE protocol guarantees not only security against classical attacks but also a new additional layer of security against leakage of stored secrets

Network mobility introduces far more complexity than host mobility. To address the extensions needed for network mobility, the IETF NEMO working group has recently standardized the network mobility basic support protocol in RFC 3963. However, in this RFC, it is not mentioned how authentication authorization and accounting (AAA) issues are handled in NEMO environment. Also the use of IPsec to secure NEMO procedures does not provide robustness against leakage of stored secrets. To address this security issue and to achieve AAA with mobility, we propose new handover procedures to be performed by mobile routers and by visiting mobile nodes. These new handover procedures are based on leakage resilient-authenticated key establishment (LR-AKE) protocol.

In this paper, we survey the recent research results on privacy-preserving Identification suitable for limited-resource devices such as RFID, contactless smartcards, and introduce our recent results on a light-weight privacy-preserving identification scheme. The proposed scheme only requires (1) random bit generators, (2) simple bit-wise operations and (3) short storage for keys less than 1 Kbits. No cryptographic algorithms such as SHA-1 are required. On the other hand, security of the scheme is reducible to learning parity -with noise problem (LPN problem) which is further reducible to a problem in NP-complete.

Radio frequency identification systems (RFID systems) are becoming popular in various applications, such as supply chain management, animal husbandry and so on. They are useful to manage not only things but also living things. Privacy, however, must be taken in account when they are used around people since people with RFID tags can easily be tracked and traced. While several solutions have been proposed to solve this problem, they have drawbacks that the back-end servers (or the readers) must exhaustive-search all the registered IDs to identify the RFID tags and/or that database must synchronize with the tags. The former is not desirable when a huge number of RFID tags must be managed, and the latter is not desirable when restoring database from backup (since tags and the database are not synchronous after restoration). In this paper, we propose how to solve these problems without deteriorating the privacy protection ability.

Anonymous channels or similar techniques that achieve sender's anonymity play important roles in many applications, e.g. electronic voting. However, they will be meaningless if cryptographic primitives containing sender's identity are carelessly used during the transmission. In computationally secure settings, this problem may be easily overcome by using public key encryption and group signatures. However, in an unconditionally secure setting, in which no computational difficulty is assumed, this is not an easy case as such. As the increasing computational power approaches the point where security policy can no longer assume the difficulty of solving factoring or discrete logarithm problems, it must shift its focus to assuring the solvency of unconditionally secure schemes that provide long-term security. The main contribution of this paper is to study the security primitives for the above problem. In this paper, we first define the unconditionally secure asymmetric encryption scheme, which is an encryption scheme with unconditional security and where it is impossible for a receiver to deduce the identity of a sender from the encrypted message. We also investigate tight lower bounds on required memory sizes from an information theoretic viewpoint and show an optimal construction based on polynomials. It is remarkable to see that these bounds are considerably different from those in Shannon's model of the conventional unconditionally secure symmetric encryption. Other than the polynomial-based scheme, we also show a construction based on combinatorial theory, a non-malleable scheme and a multi-receiver scheme. Then, we define and formalize the group authentication code (GA-code), which is an unconditionally secure authentication code with anonymity like group signatures. In this scheme, any authenticated user will be able to generate and send an authenticated message while the receiver can verify the legitimacy of the message—that it has been sent from a legitimate user but at the same time retains his anonymity. However, by cooperating with the group authority, such as in the case of disputes, the receiver is able to obtain information of the user's identity. For GA-code, we show two concrete constructions.

Network mobility introduces far more complexity than host mobility. Therefore, host mobility protocols such as Mobile IPv6 (MIPv6) need to be extended to support this new type of mobility. To address the extensions needed for network mobility, the IETF NEMO working group has recently standardized the network mobility basic support protocol in RFC 3963. However, in this RFC, it is not mentioned how authentication authorization and accounting (AAA) issues are handled in NEMO environment. Also, the use of IPsec to secure NEMO procedures does not provide robustness against leakage of stored secrets. To address this security issue and to achieve AAA with mobility, we propose new handover procedures to be performed by mobile routers and by visiting mobile nodes. This new handover procedure is based on leakage resilient-authenticated key establishment (LR-AKE) protocol. Using analytical models, we evaluate the proposed handover procedure in terms of handover delay which affects the session continuity. Our performance evaluation is based on transmission, queueing and encryption delays over wireless links

The problem of minimizing the amount of secret information (secret bits) required for certain key management schemes related to data access control techniques is addressed. Particularly note that the importance of the secret storage minimization originates from the fact that this storage should be read-proof and tamper-proof one. This paper points out to a novel approach for minimization of the secret storage dimension and compare this approach with a straightforward one based on establishing a virtual secret storage employing data encryption. The novel approach yields: (i) provable security; (ii) it is not based on storing the encrypted data into a public storage, and (iii) it requires lower processing complexity. The proposed approach yields the secret storage minimization via exchange of a secret storage to a public one based on the efficient one-way mapping of the secret bits yielding significant additional flexibility and reduction of the secret storage overhead at the user's side as an appropriate trade-off with the required public storage and processing complexity. The overheads of the proposed technique are compared with the related previously reported ones, and advantages of the novel approach are pointed out.

In wireless networks, security is an essential feature that can be provided using a variety of protocols. On the other hand, the security protocols can affect applications to varying degrees depending on the network conditions. In this paper, we propose to evaluate the overhead introduced by the security mechanisms in WLAN such as authentication. To do so, we develop an analytical model based on random errors to evaluate the authentication delay for various error rates taking into account the reliability mechanisms involved. We also measure the authentication delay for WLAN 802.11b using CISCO access point and client cards. We generate the average, minimum and maximum delay for the different authentication configuration available in the CISCO security suite. The analytical and the experimental results are compliant. The major contributor of the authentication delay is the probing time needed to detect the surrounding access point.

In this paper, a general framework which enables to compare previously proposed approaches for the fast correlation attacks is developed. All attacks are based on decoding using a set of parity check sums of an underlying linear code. The purpose of this paper is two-fold: (a) to provide a simple close form estimate about the number of check sums of a particular structure necessary for the corresponding attack to succeed; (b) to illustrate how such estimates are useful in minimizing the computational complexity of each attack considered, and consequently, in establishing a unified framework for comparison

Copyright protection is a major issue in distributing digital content. On the other hand, improvements to usability are sought by content users. In this paper, we propose a secure traitor tracing scheme against key exposure (TTaKE) which contains the properties of both a traitor tracing scheme and a forward secure public key cryptosystem. Its structure fits current digital broadcasting systems and it may be useful in preventing traitors from making illegal decoders and in minimizing the damage from accidental key exposure. It can improve usability through these properties

Authenticated key exchange (AKE) protocols are designed to allow mutual authentication and generation of a cryptographically-secure session key. We revisit the conventional AKE protocols employed in IEEE 802.1x for wireless security considering the following situation: (1) a user has some insecure devices with built-in memory capacity; (2) the counterpart server is not perfectly secure; (3) neither PKI (public key infrastructure) nor TRM (tamper-resistant module) is available. In addition, the paper introduces a new kind of AKE protocol, which is secure against an active attacker in the above-mentioned situation, in order to enhance the overall security level and usability of passwords. For authenticity, the user's password is combined with an additional secret stored on insecure mobile devices. Nevertheless, the user remembers only one relatively short password while maintaining its connections with a variety of different servers.

The coupling of mobility and quality-of-service with security is a challenge that should be addressed in future wireless overlay systems. The mobility of a node can disrupt or even intermittently disconnect an ongoing real-time session because a secure handover must be performed to ensure continuous connectivity. The duration of the such interruptions is called disruption time or handover delay and can heavily affect the user satisfaction. The handover procedure needs to protect its integrity and confidentiality-otherwise, the packets may be rerouted to a malicious node and the legitimate handover may not be performed. The security procedure to ensure this should not lengthen significantly the handover delay to provide good quality real-time services. In this paper, we focus on the network-layer mobility, specifically, on Mobile Internet protocol version 6 (MIPv6) since it is the natural candidate for providing such mobility in future systems. To solve the problem of on-path attackers and prevent leakage of secrets, we propose a security architecture for MIPv6 based on leakage resilient-authenticated key establishment (LR-AKE) protocol and its cooperation with public key infrastructure. The proposed architecture prevents against on-path attackers which was not addressed in the specifications of MIPv6, and also provides robustness against leakage of secret values. Using analytical models, we evaluate MIPv6 handover delay for real-time services. We identify the crucial factors affecting the handover delay among transmission delays of MIPv6, security and LR-AKE messages, queueing delays and en/decryption delays.

This paper studies the optimisation of the channel with cryptographic primitives such as coin tossing and oblivious transfer by committing to a set of strings. The main contribution of this paper is that the commitment is possible from any nontrivial correlation at rates when the sender is Alice and Bob, those rates are optimal. Also the coin tossing capacity is infinite for every channel having a positive bit commitment rate.

Ad-hoc networks are usually constructed with a lot of nodes managed by unknown users and have a vague reliability level. In order to establish a reliable connection with the target node, users somehow need to evaluate the nodes and connection paths as correctly as possible. One of the solutions to this problem is to employ the trust-metrics to the node-and-path evaluation of the ad-hoc network. The trust-metrics are mainly used to evaluate the reliability (validity) of the public-keys of unknown users, e.g. in PGP. We, however, point out that there are some drawbacks when applying the ever known metrics to the node-and-path evaluation of the ad-hoc networks. We show that they are either low privacy - high utility or high privacy - low utility. To overcome these disadvantages, we propose the realization of high privacy high utility trust metrics and its application for evaluating the node's performances in ad-hoc networks (electronic power consumption, transmission speed, etc).

In this paper, we focus on the suboptimality of iterative decoding on graphs with cycles, through examining the use of a reliability-based decoding algorithm for some concatenated codes with an interleaver, known as turbo-like codes. The a posteriori probabilities delivered by the iterative decoding are regarded as reliability information, and an efficient algorithm for the overall linear block code is applied at certain iterations. Simulation results show that the suboptimality of iterative decoding due to cycles can be at least partially compensated by this approach. Some insights about the potential additional coding gains achievable are investigated based on the characteristics of the constituent decoders. These characteristics are related to the nature of suboptimality in the overall iterative decoding. The effects of some code parameters and channel conditions on the behavior of iterative decoding are also studied for a better understanding of its suboptimality.

The effect of the phase noise on the performance of bandwidth-efficient coded modulation is studied. To this end, the average mutual information (AMI) for specific constellations such as 8-phase-shift keying and 16-quadrature amplitude modulation is calculated in the presence of carrier phase error caused by imperfect carrier tracking over an additive white Gaussian noise channel. The AMI not only quantifies the effect of the phase noise from an information-theoretic viewpoint, but also serves as an estimate for a permissible amount of the phase noise for a given signal-to-noise ratio. The bit-error rate (BER) performance of a near-optimal turbo trellis-coded modulation scheme is then investigated over such a channel. For this purpose, an optimal branch metric which best fits the channel characteristics is derived. Furthermore, simple branch metrics (referred to as suboptimal, simplified, and Gaussian metrics) are derived, which may offer the tradeoff between BER performance and computational complexity. Numerical analysis shows that a near-optimal coded-modulation scheme renders a transmission system more robust against phase noise than is the case with a conventional trellis-coded modulation scheme.

Broadcast Encryption allows a broadcaster to broadcast an encrypted message so that only a dynamically changing designated group of users can decrypt it. The stateless setting considers the case where the private key at each user is never updated. A central open problem in this area is to design a stateless scheme where both the size of transmission header which encapsulates the session key and the size of private key at each user are small and independent of the number of users (all/privileged/revoked users). We propose schemes that meet this requirement by providing a tradeoff between security against collusion and non-secret storage size. The proposed schemes are based upon new notions of one-way accumulators which are of independent interest.

McEliece public-key cryptosystem (PKC) is one of a few alternatives for the current PKCs that are mostly based on either the integer factoring problem (IFP) or the discrete logarithm problem (DLP) that would be solved in polynomial time after the emergence of quantum computers. The security of the McEliece PKC is based on the decoding problem and it is known that it satisfies, with an appropriate conversion, the strongest security notion, i.e., INDistinguishability of encryption against adaptively Chosen-Ciphertext Attacks (IND-CCA2), in the random oracle model under the assumption that the underlying primitive McEliece PKC satisfies a weak security notion of One-Wayness against Chosen-Plaintext Attacks (OW-CPA). OW-CPA is said to be satisfied if it is infeasible for chosen plaintext attacks to recover the whole plaintext of an arbitrarily given ciphertext. Currently, the primitive McEliece PKC satisfies OW-CPA if a parameter n/spl ges/2048 with optimum t and k is chosen since the binary work factor for (n,k,t)=(2048,1278,70) to break it with the best CPA is around 2/sup 106/, which is infeasible even if world-wide computational power is used. While the binary work factor for the next smaller parameter n=1024 is in a gray level of 2/sup 62/, it will be improved by applying Loidreau's modification that employs Frobenius automorphism in Goppa codes. In this paper, we carefully investigate the one-wayness of the Loidreau's modified McEliece PKC against ever known CPAs and new CPAs we propose, and then show that it certainly improves the one-wayness against ever known CPAs but it is vulnerable against our new CPAs. Thus, it is rather harmful to apply the new modification to the McEliece PKC.

In this paper, the use of a reliability-based decoding algorithm for some concatenated codes with an interleaver, known as turbo-like codes, is examined to address and overcome the suboptimality of iterative decoding. Simulation results show that the suboptimality of iterative decoding for moderate length codes can be at least partially compensated by this combined approach. Some insights about the potential additional coding gains achievable by the combined approach are investigated based on the characteristics of the constituent decoders, which highlights the nature of suboptimality in iterative decoding.

Summary form only given. We discuss information-theoretic methods to prove the security of cryptosystems. We study what is called, unconditionally secure (or information-theoretically secure) cryptographic schemes in search for a system that can provide long-term security and that does not impose limits on the adversary's computational power.

Efficient ID-based key sharing schemes are desired worldwide for secure communications on Internet and other networks. The Key Predistribution Systems (KPSs) are a large class of such key sharing schemes. The remarkable property of KPSs is that in order to share the key, a participant should only input its partner's identifier to its secret KPS algorithm. Although it has many advantages in terms of efficiency, on the other hand it is vulnerable to certain collusion attacks. While conventional KPSs establish communication links between any pair of entities in a communication system, in many practical communication systems, such as broadcasting, not all links are required. In this paper, we propose a new version of KPS which is called the Hierarchical KPS. In the Hierarchical KPS, simply by removing unnecessary communication links, we can significantly increase the collusion threshold. As an example, for a typical security parameter setting, the collusion threshold of the Hierarchical KPS is 16 times higher than that of the conventional KPS while using the same amount of memory at the KPS center. The memory required by the user is even reduced by a factor $1/16$ in comparison with the conventional linear scheme. Hence, Hierarchical KPS provides a more efficient method for secure communication.

We analyze the performance of the clipped orthogonal frequency division multiplexing (OFDM) system in terms of peak power reduction capability and degradation of channel capacity. The clipping is performed on the baseband OFDM signals with and without oversampling, followed by the ideal low-pass filter. First, the effect of the envelope clipping on the peak-to-average power ratio (PAPR) and the instantaneous power of the band-limited OFDM signal is studied. We then discuss the channel capacity of the oversampled and clipped OFDM signals over the additive white Gaussian noise and ideally interleaved Rayleigh fading channels. The capacity is calculated based on the assumption that the distortion terms caused by the clipping are Gaussian. It is shown that the SNR penalty due to the clipping can be considerably alleviated by using optimal coding and reducing the information data rate. The results are justified by the simulation results using near optimal turbo codes.

In this paper we present a new iterative decoding algorithm of the high-rate turbo codes which employ high-rate convolutional codes as component codes. This algorithm constructs a syndrome trellis using the parity check matrix of the code, and produces soft-output of each bit of a codeword. The algorithm is named "turbo syndrome decoding" (TSD). In the trellis diagram, only two paths merge into a node. It therefore leads to the significant reduction in both computational complexity of add-compare-select (ACS) operations and storage requirement for the soft-output to the subsequent decoder as compared with the classical decoding of the high-rate turbo codes. Nevertheless, the TSD algorithm has the same capability as the classical one in a sense that the most probable path is selected.

Iterative decoding of multilevel coded modulation is discussed. Despite its asymptotic optimality with proper design, the error correcting capability of multilevel codes may not be fully exploited for finite block length with conventional multistage decoding. This fact stems from the suboptimality of multistage decoding giving rise to increased error multiplicity at lower index stages and the associated error propagation to higher stages. Such problems can be overcome in many situations by introducing iterative decoding which often significantly compensates the suboptimality of a staged decoder. The class of multilevel codes achieving practically important bit-error performance near the Shannon limit becomes far wider with iterative decoding.

The distribution of the peak-to-average power ratio (PAPR) in strictly band-limited orthogonal frequency-division multiplexing (OFDM) signals is studied. Assuming that the base-band OFDM signal is characterized as a band-limited complex Gaussian process, we first attempt to derive the exact distribution of the PAPR in the band-limited OFDM signals. Since this distribution cannot be expressed in a closed form, we further develop a simple closed-form approximation, based on the level-crossing rate analysis. Comparisons of the proposed distributions with those obtained by computer simulations show good agreement and convergence with an increase in the number of subcarriers.

Article Free Access Share on Reducing the round complexity of a sealed-bid auction protocol with an off-line TTP Authors: Yuji Watanabe Institute of Industrial Science, University of Tokyo, 7-22-1 Roppongi, Minatoku, Tokyo, 106-8558, Japan Institute of Industrial Science, University of Tokyo, 7-22-1 Roppongi, Minatoku, Tokyo, 106-8558, JapanView Profile , Hideki Imai Institute of Industrial Science, University of Tokyo, 7-22-1 Roppongi, Minatoku, Tokyo, 106-8558, Japan Institute of Industrial Science, University of Tokyo, 7-22-1 Roppongi, Minatoku, Tokyo, 106-8558, JapanView Profile Authors Info & Claims CCS '00: Proceedings of the 7th ACM conference on Computer and Communications SecurityNovember 2000 Pages 80–86https://doi.org/10.1145/352600.352612Online:01 November 2000Publication History 21citation458DownloadsMetricsTotal Citations21Total Downloads458Last 12 Months3Last 6 weeks0 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

This paper presents a new reduction method of both the computational complexity and storage requirements in the nonpunctured turbo decoding. The idea of the proposed algorithm is based on the computational complexity reduction, which is attendant upon the process of add-compare-select in each stage of iterative decoding. Therefore, the proposed method is completely different from all the other reduction algorithms presented before now. We compare the nonpunctured turbo code using the proposed reduction method with the punctured turbo code in terms of performance-complexity tradeoff. Simulation results show that the proposed approach provides an alternative encoding/decoding scheme of the classical punctured turbo coding for the application to high-data-rate wireless communications system.

The effect of digital envelope clipping on the peak power of the bandlimited OFDM signal is studied. The system consists of the concatenation of digital clipping of the OFDM signal with and without oversampling and bandpass filtering, followed by the ideal low-pass filter. It is shown that without oversampling, the clipped OFDM signal may suffer considerable peak power regrowth compared to those with oversampling. To justify this empirical result, the distribution of the instantaneous power in the digitally clipped OFDM signals without oversampling is theoretically analyzed by its lower bound.

The performance of the strictly band-limited OFDM systems with deliberate clipping is examined in terms of the peak-to-average power ratio (PAPR) and the resultant bit error performance. The clipping is performed on the OFDM signals sampled at the Nyquist rate, followed by the ideal low-pass filter, Since the low-pass filter considerably enlarges the PAPR, there is a severe limitation in PAPR reduction capability. Thus, in order to achieve further reduction of the PAPR, the application of the adaptive symbol selection scheme is also considered. It is shown that the significant PAPR reduction with moderate complexity can be achieved by the combination of the clipping and the adaptive symbol selection. The price to be paid for PAPR reduction by this scheme is its performance degradation. The paper theoretically analyzes the bit error rate performance of the OFDM system with the Nyquist-rate clipping combined with the adaptive symbol selection, and considers the use of the forward error correction for compensation of the degradation. It is shown that even though the clipping scheme causes severe loss in required signal-to-noise ratio, the use of a powerful channel coding scheme such as turbo codes significantly alleviates the bit error rate performance degradation.

In this paper, multilevel coded asymmetric modulation with multistage decoding and unequal error protection (UEP) is discussed. These results further emphasize the fact that unconventional signal set partitionings are more promising than traditional (Ungerboeck-type) partitionings, to achieve UEP capabilities with multilevel coding and multistage decoding. Three types of unconventional partitionings are analyzed for asymmetric 8-PSK and 16-QAM constellations over the additive white Gaussian noise channel to introduce design guidelines. Generalizations to other PSK and QAM type constellations follow the same lines. Upper bounds on the bit-error probability based on union bound arguments are first derived. In some cases, these bounds become loose due to the large overlappings of decision regions associated with asymmetric constellations and unconventional partitionings. To overcome this problem, simpler and tighter approximated bounds are derived. Based on these bounds, it is shown that additional refinements can be achieved in the construction of multilevel UEP codes, by introducing asymmetries in PSK and QAM signal constellations.

In this paper, theoretical upper bounds and computer simulation results on the error performance of multilevel block coded modulations for unequal error protection (UEP) and multistage decoding are presented. It is shown that nonstandard signal set partitionings and multistage decoding provide excellent UEP capabilities beyond those achievable with conventional coded modulation. The coding scheme is designed in such a way that the most important information bits have a lower error rate than other information bits. The large effective error coefficients, normally associated with standard mapping by set partitioning, are reduced by considering nonstandard partitionings of the underlying signal set. The bits-to-signal mappings induced by these partitionings allow the use of soft-decision decoding of binary block codes. Moreover, parallel operation of some of the staged decoders is possible, to achieve high data rate transmission, so that there is no error propagation between these decoders. Hybrid partitionings are also considered that trade off increased intraset distances in the last partition levels with larger effective error coefficients in the middle partition levels. The error performance of specific examples of multilevel codes over 8-PSK and 64-QAM signal sets are simulated and compared with theoretical upper bounds on the error performance.

Two simplified versions of the belief propagation algorithm for fast iterative decoding of low-density parity check codes on the additive white Gaussian noise channel are proposed. Both versions are implemented with real additions only, which greatly simplifies the decoding complexity of belief propagation in which products of probabilities have to be computed. Also, these two algorithms do not require any knowledge about the channel characteristics. Both algorithms yield a good performance-complexity trade-off and can be efficiently implemented in software as well as in hardware, with possibly quantized received values.

We discuss the construction method of orthogonal sequences for downlink OFDM-CDMA, in terms of the peak to average power ratio (PAPR) of the transmitted signals. The PAPR property is studied based on two orthogonal sets of sequences: Walsh-Hadamard and complementary sequences. It is shown that for relatively few active users, Walsh-Hadamard sequences tend to have very large PAPR, while the PAPR of complementary sequences remains stable near its theoretical value. A simple but effective peak reduction scheme is also proposed for OFDM-CDMA.

Authenticated session key establishment is a central issue in network security. This paper addresses the question of whether we can design a compact, efficient and authenticated key establishment protocol that has the following two properties: (1) each message exchanged between two participants can be transferred in a short packet such as an ATM cell whose payload has only 384 bits, and (2) messages that carry key materials are unforgeable and nonrepudiatable without the involvement of a trusted key distribution center. We discuss why the answer to this question is negative if one follows the currently standard approach to key establishment, namely employing secret/public key encryption and, possibly, digital signature. We then present a number of protocols that represent a positive answer to the question. Our protocols are all based on a cryptographic primitive called "signcryption" that fulfils both the functions of digital signature and public key encryption with a cost far smaller than that required by "digital signature followed by encryption".

Binary multilevel convolutional codes (CCs) with unequal error protection (UEP) capabilities are studied. These codes belong to the class of generalized concatenated (GC) codes. Binary CCs are used as outer codes. Binary linear block codes of short length, and selected subcodes in their two-way subcode partition chain, are used as inner codes. Multistage decodings are presented that use Viterbi decoders operating on trellises with similar structure to that of the constituent binary CCs. Simulation results of example binary two-level CC's are also reported.

This paper considers block-coded 8-phase-shift-keying (PSK) modulations for the unequal error protection (UEP) of information transmitted over Rayleigh-fading channels. Both conventional linear block codes and linear UEP (LUEP) codes are combined with a naturally labeled 8-PSK signal set, using the multilevel construction of Imai and Hirakawa (1977). Computer simulation results are presented showing that, over Rayleigh-fading channels, it is possible to improve the coding gain for the most significant bits with the use of binary LUEP codes as constituent codes, in comparison with using conventional binary linear codes alone.

An overview of the many practical applications of channel coding theory in the past 50 years is presented. The following application areas are included: deep space communication, satellite communication, data transmission, data storage, mobile communication, file transfer, and digital audio/video transmission. Examples, both historical and current, are given that typify the different approaches used in each application area. Although no attempt is made to be comprehensive in the coverage, the examples chosen clearly illustrate the richness, variety, and importance of error-control coding methods in modern digital applications.

For the class of rate k/(k+1) convolutional codes, Yamada et al. (1983) proposed an efficient maximum-likelihood decoding algorithm called the YHM algorithm. In order to reduce the complexity of the YHM algorithm, this paper presents two techniques for simplifying the trellis diagram used in the YHM algorithm. We further observe that the proposed techniques effectively reduce the complexity of the YHM algorithm for two classes /spl Xi/ and /spl Xi//sub f/ (which is a subclass of /spl Xi/) of rate k/(k+1) convolutional codes. The construction of codes in these classes is also discussed. It is shown that /spl Xi/ codes with d/sub free/=3,4 can be obtained by simple construction. A code search algorithm for /spl Xi/ codes with d/sub free//spl ges/5 is also introduced. Computer searches are performed to construct good /spl Xi/ and /spl Xi//sub f/ codes. For specified decoding complexities, a number of these new codes give better error performance than previously reported codes.

This brief contribution proposes a new class of systolic-arrays to perform Binary Reed-Solomon (RS) decoding procedures including erasure correction. Such RS decoder is suitable for VLSI implementation since the arrays consist of simple processing elements of the same type.>

Proposes and investigates a method for designing pseudonoise (PN) sequences having both good odd and even correlation properties, which are important for acquisition and demodulation in spread spectrum (SS) communications. Odd correlation properties of PN sequences should be designed as well as their even or periodic correlation properties so that the cochannel interference can be reduced as small as possible. Polyphase PN sequences with such good correlation properties can be derived from biphase PN sequences with a good aperiodic correlation property under a certain condition. Absolute values of odd and even correlation functions of these sequences are equal at each shift. The authors evaluated their peak correlations properties and bit error rate performance. Numerical evaluations show that the derived polyphase sequences have lower peaks of correlations and lower bit error rate than their original sequences. Furthermore, the authors defined the generalized odd correlation function for polyphase SS systems, and derived a way to improve the generalized odd correlation properties.>

The paper proposes and investigates a multiuser detection scheme baseEEon canceling cochannel interference (CCI) to improve spectral efficiency or to increase user capacity in an MFSK (multilevel frequency shift keying)/FH-SSMA (frequency hopping-spread spectrum multiple access) system. In the MFSK/FH-SSMA system, an address code is employed as a hopping sequence to hop the carrier frequency in MFSK. In the proposed scheme, it is assumed that the address codes of all users in MFSK/FH-SSMA are known. Then, candidates of the transmitted vector which are regenerated from the time-frequency matrices decoded by all the users' address codes are added with logical OR operation to produce candidates of the received matrix. The candidates of the received matrix are utilized in order to estimate a pattern of all users' data symbols which has the most number of coincident entries with the received matrix. Its BER (bit error rate) performance is evaluated by theoretical analysis and computer simulation in order to show the improvement of user capacity. Moreover, the authors investigate a hybrid scheme combining a multiuser detection scheme and the decoding scheme of an error-correcting code for the coded MFSK/FH-SSMA system.>

The authors propose and analyze a direct-sequence spread-spectrum multiaccess (DS/SSMA) receiver that employs a cascade of cochannel interference (CCl) cancellers for communication over multipath fading channels. The receiver first coherently demodulates and despreads the received signal to produce correlator outputs and initial data estimates. Based on these estimates, the cancellation scheme essentially creates replicas of the contributions of the CCl embedded in the correlator outputs and removes them for a second improved hard data decision. By repeating this operation over and over, a cascade of CCl cancellers is derived. Through theoretical analysis and simulation, the authors investigate the canceller's bit error rate (BER) performance in both the absence and presence of errors in the amplitude and phase estimates of each user's received signal. Numerical results show the considerably large improvement in performance that can be attained by the cancellation scheme, even under partially degraded estimates.>

Codes for correcting and detecting unidirectional byte errors are investigated. The relations between distances and the error-correcting and -detecting capabilities of such codes are derived. It is shown that a two-fold unidirectional b-bit-byte error-correcting (2-UbEC) code requires at least three check bytes and that a one-fold unidirectional b-bit-byte error-correcting/2-fold unidirectional b-bit-byte error-detecting (1-UbEC/2-UbED) code requires at least two check bytes. Construction methods for 2-UbEC codes with three check bytes and 1-UbEC/2-UbEd codes with two check bytes are proposed.>

Codes are considered for correction and detection of unidirectional byte errors. A code construction based on the generalized concatenated code construction is proposed. This construction gives a large number of efficient codes. For example, from this construction, a 72-input-bit encoder of the triple unidirectional 8-bit-byte error-correcting and fourfold unidirectional 8-bit-byte error-detecting code with a length of 112 bits and rate 9/14 is obtained, whereas the ordinary triple 8-bit-byte error-correcting and fourfold 8-bit-byte error-detecting code of the same length has only 56 information bits and is of rate 1/2. The proposed construction is generalized to one that gives efficient short-length codes.>

The paper first proposes a method to correctly update the weights of an adaptive array antenna using the inherent processing gain of a spread spectrum (SS) receiver, even for received signals with very low desired-to-undesired signal power ratio (DUR). Since the method reduces effect of the delay in the controlling loop, stable convergence can be guaranteed in a fading channel. Secondly the method is applied to a tapped delay line (TDL) adaptive array antenna in order to improve performance of rejecting co-channel interference in CDMA. The array is investigated corresponding to the DUR and bandwidth of SS signals.>

Codes correcting/detecting unidirectional byte errors are investigated. It is shown that such codes have the capability of correcting combinations of bidirectional and unidirectional byte errors and code constructions. These are derived from the combination of two codes. One is a code for encoding the Hamming weights of data bytes and is used to estimate error locations. The other is a byte-error-correcting code for error evaluation. Moreover, the authors describe a decoding procedure for the codes, correcting combinations of bidirectional and unidirectional byte errors. The constructions provide many efficient codes of short length. For example, when a byte consists of 32 bits, a systematic code can be constructed with 61 information bytes and 3 check bytes that has the capability of correcting a single bidirectional byte error for double unidirectional byte errors, whereas the best known double-byte-error-correcting code requires 4 check bytes.>

This paper proposes image compression using an advanced neural network in which a variable input-output function of a neural unit can be learnt as well as a weight coefficient of a neural connection corresponding to information source and application. Since the neural network has the improved learning capability for local nonlinearity of information source, its application to compression of nonlinear information such as image is investigated. A learning algorithm and adaptive controlling schemes of input-output functions are derived. Simulation results show that the neural network can achieve higher SNR and shorter learning time than a conventional network having only variable weights.

In the realization of code-division multiple access based on a spread-spectrum communication system, i.e. spread-spectrum multiple access (SSMA), reduction of cochannel interference is an important problem. An adaptive array antenna system is proposed that includes a cancellor of cochannel interference, which can improve performance by a combination of temporal and spatial filtering. While the adaptive array suppresses interference sources with arrival angles different from those of the desired user, the adaptive digital filter-canceller rejects those whose arrival angles are the same as those of the desired user. The proposed system can achieve stable acquisition and low error rate of demodulated data even in a heavy-interference channel where a conventional array antenna system cannot achieve satisfactory acquisition.>

The authors propose and investigate an adaptive canceller of intersymbol and cochannel interference due to channel distortion and cross-correlation among pseudonoise sequences assigned to individual users of a DS-SSMA (direct-sequence spread-spectrum multiple-access) system. In order to implement a local area network (LAN) by using a power line installed in a building wall as a transmission channel, the authors have investigated utilization of DS-SSMA which has advantages such as robustness against narrow-band interference and noise and realization of asynchronous code division multiple access. In a power line, however, restriction of transmission bandwidth for communications makes it difficult to suppress cochannel interference and the channel is also time-varying due to fluctuation of loads. Since the proposed canceller adaptively eliminates cochannel interference as well as intersymbol interference, it can facilitate synchronization and increase the number of the simultaneously accessing users on a power line with restricted processing gain. The error probability in the output of the canceller is theoretically calculated for the steady-state case by using a Markov model. Computer simulations illustrate stable convergence properties of the canceller.>

The authors give a tabulation of the numbers of codewords in new binary codes with the asymmetric/unidirectional error-correcting capabilities of 3, 4, 5, 6 for lengths 14, 15, . . . , 23. The new codes have greater sizes than the known codes for 14>

The authors propose an automatic equalizer, applicable to trellis-coded modulation, that includes a Viterbi decoder and a carrier-phase controller and achieves reliable high-speed voiceband data transmission at 14.4 kb/s and above. The equalizer can perform the operations of equalization, demodulation, and decoding. Since the system reduces misadjustment of tap values and estimated carrier-phase shift due to decision errors, stable convergence can be achieved. Also presented is a method to utilize the reliability of decoded data in order to minimize misadjustment of the adaptive digital filters and the phase controller owing to undetected errors and miscorrected data in decoding.>

In this paper, some efficient methods of solving equations over Galois field GF(2m) are proposed. Using these algorithms, decoders for triple-and quadruple-error-correcting Bose–Chaudhuri–Hocquenghem (BCH) codes are shown. More- over, we propose a new method of making high-speed decoders for double-error-correcting/triple-error-detecting BCH or Reed- Solomon (RS) codes by adding a simple error-identifying circuit to a decoder for double-error-correcting codes. By incorporating ROM's (read only memory) in a decoder, the complex logic circuits are eliminated and then we can easily construct a high- speed decoder. We evaluate the complexity of the decoders and show that each of them can be accommodated in a single chip LSI.

Effective utilization of an error-correcting code (ECC) is proposed in order to make a low-hit-rate adaptive differential PCM (ADPCM) system robust against bit errors in noisy channels, such as mobile radio. In 16 kb/s ADPCM systems, the inverse-quantizers with a small number (four) of levels lead to large offsets in stepsizes due to channel errors, and high-order all-pole predictors are very sensitive to them. For the purpose of solving these problems, we present a robust ADPCM system using an ECC, in which the reliability of words decoded by the ECC decoder is utilized to control the updating of the inverse-quantizer and also to stabilize the predictor in the receiver. Moreover, on condition that a sampling rate of the system is reduced from 8 to 6.4 kHz, the proposed system is compared with a forward adaptation system [8]. A computer simulation shows a maximum of 1.8 dB improvement over an usual system using the same ECC in segmental SNR forBER\geq10^{-2}.

A new proposed automatic equalizer including a decoder of error-correcting code (AEDEC) is obtained by the joint adaptive operation of an automatic equalizer and a decoder. This AEDEC can reduce misadjustment of tap values and error propagation owing to decision errors, and stabilize convergence even without a known training signal in noisy channels.

A class of binary error-correcting codes, called generalized tensor product codes, is presented with their decoding algorithm. These codes are constructed by combining a number of codes on various extension fields with shorter binary codes. A general algorithm is provided to do bounded distance decoding for these codes. Simply decodable codes such as Wolf's tensor product codes are shown to be special cases of this class of codes. Simply decodable and more efficient codes than Wolf's codes are also included as special cases.

A new multilevel coding method that uses several error-correcting codes is proposed. The transmission symbols are constructed by combining symbols of codewords of these codes. Usually, these codes are binary error-correcting codes and have different error-correcting capabilities. For various channels, efficient systems can be obtained by choosing these codes appropriately. Encoding and decoding procedures for this method are relatively simple compared with those of other multilevel coding methods. In addition, this method makes effective use of soft-decisions to improve the performance of decoding. The decoding error probability is analyzed for multiphase modulation, and numerical comparisons to other multilevel coding systems are made. When equally complex systems are compared, the new system is superior to other multilevel coding systems.

Many classes of comma-free codes have been proposed. Among them, path-invariant comma-free codes have the advantage of relative simplicity of encoding and decoding. In this correspondence, we present a construction method for these codes which is a unified generalization of the known construction methods. By this method some new classes of path-invariant comma-free codes are obtained.

To improve the reliability of two-dimensional information, codes that can correct two-dimensional bursts (or spots) may be useful. In this paper a class of two-dimensional burst-correcting codes, called two-dimensional Fire codes, is proposed. The definition of these codes is a natural extension of that of the conventional Fire codes. The two-dimensional Fire code is a two-dimensional cyclic code designed for single two-dimensional burst correction. Several important properties such as the burst-correcting capability and the positions of the check symbols are presented. Also, encoding and decoding methods are presented. It is shown that the encoding and decoding are easily implemented by using two-dimensional feedback shift registers.

In this paper, two-dimensional arrays of elements of an arbitrary finite field are examined, especially arrays having maximum-area matrices. We first define two-dimensional linear recurring arrays. In order to study the characteristics of two-dimensional linear recurring arrays, we also define two-dimensional linear cyclic codes. A systematic method of constructing two-dimensional linear recurring arrays having maximum-area matrices is given using the theory of two-dimensional cyclic codes. These arrays, here called\gamma \beta-arrays, may be said to be two-dimensional analogs ofM-sequences. A\gamma \beta-array of areaN_x \times N_yexists overGF(q)if and only ifN_x N_yis equal toq^N _ 1for some positive integerN. Many interesting characteristics of the\gamma \beta-array, such as the properties of its autocorrelation function and the properties of the characteristic arrays, are deduced and explained.