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A proxy signature scheme allows a proxy signer to sign messages on behalf of an original signer within a given context. It has lots of practical applications in distributed systems, grid computing, mobile agent applications, distributed shared object systems, global distribution networks, and mobile communications. Recently, Padhye et al. proposed a certificateless proxy signature scheme with message recovery and claimed the scheme is secure against both of the two types of adversaries. However, in this paper, we will show that Padhye et al.’s scheme is not secure against the Type I adversary. The analysis shows their scheme is not secure for practical applications.

We revisit the communication-efficient three-party password authenticated key exchange protocol recently proposed by Chang et al. We show it is insecure against partition attacks, whereby the adversary can guess the correct password off-line. Thereafter we propose an enhanced protocol that can resist the attack described and yet is quite efficient. Furthermore, we prove its security in a widely accepted model.

With the development of the wireless communication technology and the popularity of mobile devices, the mobile wireless network (MWN) has been widely used in our daily life. Through the access point (AP), users could access the Internet anytime and anywhere using their mobile devices. Therefore, MWNs can bring much convenience to us. Due to the limitation of APs coverage, the seamless handover frequently occurs in practical applications. How to guarantee the users privacy and security and identify the real identity when he/she brings harm to the system becomes very challenging. To achieve such goals, many anonymous handover authentication (AHA) protocols have been proposed in the last several years. However, most of them have high computation costs because mobile nodes need to carry out the bilinear pairing operations or the hash-to-point operations. Besides, most of them cannot satisfy some critical requirements, such as non-traceability and perfect forward secrecy. In this paper, we first outline the security requirements of AHA protocols, and then propose a new AHA protocol to eliminate weaknesses existing in previous AHA protocols. Based on the hardness of two famous mathematical problems, we demonstrate that the proposed AHA protocol is secure against different kinds of attacks and can meet a variety of security requirements. It can be seen from the details of implementations that the proposed AHA protocol also has much less computation cost than three latest AHA protocols.

In this paper, we propose 1-out-of-n oblivious transfer proto-col by using the group of matrices over group ring Zq[Sm]. The security of the proposal is on the basis of factorization problems of non-commutative algebraic structures. Meanwhile, some new intractable assumptions are de_ned based on the group factorization problem (GFP). Subsequently, we present a simpler 1-out-of-n oblivious transfer construction for un- derlying non-commutative group. Furthermore, to achieve the oblivious transfer for more challenged messages, an e_cient k-out-of-n oblivious transfer protocol with fewer public parameters is designed based on the newly de_ned hard assumptions.

To provide timely feedbacks to users, nearly every respectable Internet service now imposes a password strength meter (PSM) upon user registration or password change. It is a rare bit of good news in password research that well-designed PSMs do help improve the strength of user-chosen passwords. However, leading PSMs in the industrial world (e.g., Zxcvbn, KeePSM and NIST PSM) are mainly composed of simple heuristic rules and found to be highly inaccurate, while state-of-the-art PSMs from academia (e.g., probabilistic context-free grammar based ones and Markov-based ones) are still far from satisfactory, especially incompetent at gauging weak passwords. As preventing weak passwords is the primary goal of any PSM, this means that existing PSMs largely fail to serve their purpose. To fill this gap, in this paper we propose a novel PSM that is grounded on real user behavior. Our user survey reveals that when choosing passwords for a new web service, most users (77.38%) simply retrieve one of their existing passwords from memory and then reuse (or slightly modify) it. This is in vast contrast to the seemingly intuitive yet unrealistic assumption (often implicitly) made in most of the existing PSMs that, when user registers, a whole new password is constructed by mixing segments of letter, digit and/or symbol or by combining n-grams. To model users' realistic behaviors, we use passwords leaked from a less sensitiveservice as our base dictionary and another list of relatively strong passwords leaked from a sensitive service as our training dictionary, and determine how mangling rules are employed by users to construct passwords for new services. This process automatically creates a fuzzy probabilistic context-free grammar (PCFG) and gives rise to our fuzzy-PCFG-based meter, fuzzyPSM. It can react dynamically to changes in how users choose passwords and is evaluated by comparisons with five representative PSMs. Extensive experiments on 11 real-world password lists show that fuzzyPSM, in general, outperforms all its counterparts, especially accurate in telling apart weak passwords and suitable for services where online guessing attacks prevail.

In traditional authentication schemes for access control in mobile pay-TV systems, one-to-one delivery is used, i.e., one authentication message per request is delivered from a head-end system (HES) to a subscriber. The performance of one-to-one delivery for authentication is not satisfactory as it requires frequent operations which results in high bandwidth consumption. To address this issue, one-to-many authentication for access control in mobile pay-TV systems was developed. It requires only one broadcasted authentication message from a HES to subscribers if there are many requests for the same service in a short period of time. However, later it was revealed that the one-to-many authentication scheme was vulnerable to an impersonation attack, i.e., an attacker without any secret key could not only impersonate the mobile set (MS) to the HES but also impersonate the HES to the MS. Then, a new scheme has been recently introduced for secure operations of one-to-many authentication. However, as shown in this paper, the recent work for one-to-many authentication is still vulnerable to the impersonation attack. To mitigate this attack, in this paper, a new scheme for one-to-many authentication using bilinear pairing is proposed that eliminates security weaknesses in the previous work. Results obtained depict that the new improved scheme in this paper provides better performance in terms of computation and communication overheads.

Since public clouds are untrusted by many consumers, it is important to check whether their remote data keeps intact. Sometimes, it is necessary for many clients to cooperate to store their data in the public clouds. For example, a file needs many clients' approval before it is stored in the public clouds. Specially, different files need different client subsets' approval. After that, these stored remote data will be proved possession by the verifier. In some cases, the verifier has no ability to perform remote data possession proof, for example, the verifier is in the battlefield because of the war. It will delegate this task to its proxy. In this paper, we propose the concept of proxy provable data possession PPDP which supports a general access structure. We propose the corresponding system model, security model and a concrete PPDP protocol from n-multilinear map. Our concrete PPDP protocol is provably secure and efficient by security analysis and performance analysis. Since our proposed PPDP protocol supports the general access structure, only the clients of an authorized subset can cooperate to store the massive data to PCS Public Cloud Servers, and it is impossible for those of an unauthorized subset to store the data to PCS.

Recently, Chen et al. proposed a certificateless aggregate signature scheme with efficient verification. They claimed that their scheme could resist attacks of Type I adversary and Type II adversary. Unfortunately, we present a universal attack to demonstrate that their scheme cannot provide unforgeability. The adversary in the proposed attack can forge a legal signature on any message without any users' secret information. Copyright © 2016 John Wiley & Sons, Ltd.

Since certificateless public key cryptography (CLPKC) has received widespread attention due to its efficiency in avoiding key escrow problems in identity-based public key cryptography (ID-PKC), the certificateless authenticated key agreement (CLAKA) protocol, an important part of CLPKC, has been studied a great deal. Most CLAKA protocols are built from pairings which need costly operations. To improve the performance, several pairing-free CLAKA protocols have been proposed. In this paper, we propose a new pairing-free CLAKA protocol. Compared with the related protocols, our protocol has better performance. Also, our protocol is provably secure in a very strong security model—the extended Canetti–Krawczyk (eCK) model.

With the continue evaluation of mobile devices in terms of the capabilities and services, security concerns increase dramatically. To provide secured communication in mobile client-server environment, many user authentication protocols from pairings have been proposed. In 2009, Goriparthi et al. proposed a new user authentication scheme for mobile client-server environment. In 2010, Wu et al. demonstrated that Goriparthi et al.'s protocol fails to provide mutual authentication and key agreement between the client and the server. To improve security, Wu et al. proposed an improved protocol and demonstrated that their protocol is provably secure in random oracle model. Based on Wu et al.'s work, Yoon et al. proposed another scheme to improve performance. However, their scheme just reduces one hash function operation at the both of client side and the server side. In this paper, we present a new user authentication and key agreement protocol using bilinear pairings for mobile client-server environment. Performance analysis shows that our protocol has better performance than Wu et al.'s protocol and Yoon et al.'s protocol. Then our protocol is more suited for mobile client-server environment. Security analysis is also given to demonstrate that our proposed protocol is provably secure against previous attacks.

Most of the previously proposed identity-based multiproxy multisignature (IBMPMS) schemes used pairings in their construction. But pairing is regarded as an expensive cryptographic primitive in terms of complexity. The relative computation cost of a pairing is approximately more than ten times of the scalar multiplication over elliptic curve group. So, to reduce running time, we first define a model of a secure MPMS scheme, then propose an IBMPMS scheme without using pairings. We also prove the security of our scheme against chosen message attack in random oracle model. Our scheme’s construction avoids bilinear pairing operations but still provides signature in the ID-based setting and reduces running time heavily. Therefore, proposed scheme is more applicable than previous schemes in terms of computational efficiency for practical applications.

With the popularity of Internet and wireless networks, more and more network architectures are used in multi-server environment, in which users remotely access servers through open networks. For the reliability of accessing these remote services, user must pass a verification procedure to obtain the authorization for legal resource acquisition and data exchange. Recently, several dynamic identity-based authentication protocols for multi-server environment have been proposed, but all of these protocols have been cryptanalyzed by other scholars. In this paper, we propose a new dynamic identity-based authentication protocol for multi-server environment using elliptic curve cryptography. The analysis shows that our protocol could overcome security weaknesses in the previously published protocols. Hence, our protocol is more suitable for practical applications. Copyright © 2012 John Wiley & Sons, Ltd.

Recently, Wang and Ma (Wireless Pers Commun, 2012. doi: 10.1007/s11277-011-0456-7 ) proposed a smart card based authentication scheme for multi-server environment. They also demonstrated that their scheme could overcome various attacks. In this paper, the security of Wang et al.'s scheme is evaluated. Our analysis shows their scheme is vulnerable to the server spoofing attack, the impersonation attack, the privileged insider attack and the off-line password guessing attack.

The session initiation protocol (SIP) is one of the most important protocols supporting multimedia services. With the wide spread of the internet, the security of SIP is becoming more and more important. In 2009, Tsai proposed an efficient authentication scheme as an enhancement to SIP. However, Arshad et al. demonstrated that Tsai's scheme was vulnerable to the off-line password-guessing attack and the stolen-verifier attack. They also pointed out that Tsai's scheme did not provide known-key secrecy and perfect forward secrecy. To overcome the weaknesses, Arshad et al. also proposed an improved authentication scheme based on the elliptic curve discrete logarithm problem for SIP and claimed that their scheme can withstand various attacks. In this paper, we do a cryptanalysis of the scheme by Arshad et al., and we show that their scheme is vulnerable to the off-line password-guessing attack. We also propose an improved authentication scheme based on the elliptic curve cryptography for SIP which is immune to the presented attacks. Copyright © 2012 John Wiley & Sons, Ltd.

Very recently, Lee et al. (C. Lee, C. Chen, C. Wu, S. Huang, An extended chaotic maps-based key agreement protocol with user anonymity, Nonlinear Dynamics, doi: 10.1007/s11071-011-0247-4 ) proposed a chaotic maps-based key agreement protocol with user anonymity and claimed their protocol could resist various attacks. In this paper, we will point out that Lee et al.’s protocol suffers from three weaknesses: (1) inability of resisting the privileged insider attack; (2) inability of resisting the denial-of-service attack; and (3) inability of providing anonymity. To overcome the weaknesses, we also proposed an improved protocol. The analysis shows our protocol is more suitable for practical applications.

Due to the development of the network and the growth big data, data owner prefer to remotely outsource their data to cloud, which can avoid the local data management and decrease the local hardware cost. But some sensitive data, such as personal healthcare information and personal property information, must be encrypted firstly and then outsourced to the cloud. This can protect sensitive information. But the outsource encrypted data to cloud can increase the difficulty of the data retrieval, because data owner or unauthorized users can't search correctly the data they need, and also it is impractical to download all of the data to local side from the cloud, which will result in huge communication an computation overhead. Hence, some cloud data retrieval schemes has been proposed to solve this problem, these schemes not only can search the data they need correctly, but also can prevent sensitive data leaked out. In this paper, we survey the privacy preserving cloud data retrieval schemes and give a comparison of them with respect to the key principles of search and privacy assured.

Certificateless public key cryptography (CLPKC), which can simplify the complex certificate management in the traditional public key cryptography and resolve the key escrow problem in identity-based cryptography, has been widely studied. As an important part of CLPKC, certificateless two-party authenticated key agreement (CTAKA) protocols have also received considerable attention. Recently, many CTAKA protocols using bilinear pairings have been proposed. But the relative computation cost of the pairing is approximately twenty times higher than that of the scalar multiplication over elliptic curve group. To improve the performance, several CTAKA protocols without pairings have been proposed. In this paper, we will show a latest CTAKA protocol is not secure against a type 1 adversary. To improve the security and performance, we also propose a new CTAKA protocol without pairing. At last, we show the proposed protocol is secure under the random oracle model.

Certificateless public key cryptography simplifies the complex certificate management in the traditional public key cryptography and resolves the key escrow problem in identitybased cryptography. The certificateless signature scheme is studied widely as an important primitive. Following the pioneering work done by Al-Riyami et al., many certificateless signature schemes using bilinear pairings have been proposed ever since. However, the relative computation cost of the pairing is approximately 20 times higher than that of the scalar multiplication over the elliptic curve group. To improve the performance we propose a certificateless signature scheme without bilinear pairings. With the running time being reduced greatly, our scheme is more practical than the previous related schemes for practical application. Copyright © 2011 John Wiley & Sons, Ltd. (The key findings presented in the paper is described as follows. (1) We proposed an efficient certificateless signature scheme without pairings. (2) We also show the proposed scheme is secure in the random oracle. (3) The experimental results show the proposed scheme has better performance than the related schemes.)

The blind signature schemes are useful in some applications where the anonymity is a big issue. Examples include the online voting systems and the electronic cash systems. Since the first identity-based blind signature scheme was proposed by Zhang et al., many identity-based blind signature schemes using bilinear pairings have been proposed. But the relative computation cost of the pairing is approximately 20 times higher than that of the scalar multiplication over elliptic curve group. In order to save the running time and the size of the signature, we propose an identity based blind signature scheme without bilinear pairings. With both the running time and the size of the signature being saved greatly, our scheme is more practical than the related schemes in application.

Many certificateless two-party authenticated key agreement schemes using bilinear pairings have been proposed. But the relative computation cost of the pairing is approximately twenty times higher than that of the scalar multiplication over elliptic curve group In order to improve the performance we propose a certificateless two-party authenticated key agreement scheme without bilinear pairings in this paper. A security proof under random oracle model is also provided. Copyright © 2011 John Wiley & Sons, Ltd.

Bumby proved that the only positive solutions to the quartic Diophantine equation 3x 4 − 2y 2 = 1 are (x, y) = (1, 1), (3, 11). In this paper, we extend this result and prove that if the class number of the field $${{\rm Q}(\sqrt{1-3a^{2}})}$$ is not divisible by 2, the equation 3a 2 x 4 − By 2 = 1 has at most two solutions. However, both solutions occur in only one case, a = 1, b = 2, as solved by Bumby. The proof utilizes the law of quadratic reciprocity that seems very rare in solving Diophantine equations, and the solution will be also obtained effectively through the proof when it exists.

Since the concept of ubiquitous computing is firstly proposed by Mark Weiser, its connotation has been extending and expanding by many scholars. In pervasive computing application environment, many kinds of small devices containing smart cart are used to communicate with others. In 2013, Yang et al. proposed an enhanced authentication scheme using smart card for digital rights management. They demonstrated that their scheme is secure enough. However, Mishra et al. pointed out that Yang et al.’s scheme suffers from the password guessing attack and the denial of service attack. Moreover, they also demonstrated that Yang et al.’s scheme is not efficient enough when the user inputs an incorrect password. In this paper, we analyze Yang et al.’s scheme again, and find that their scheme is vulnerable to the session key attack. And, there are some mistakes in their scheme. To surmount the weakness of Yang et al.’s scheme, we propose a more efficient and provable secure digital rights management authentication scheme using smart card based on elliptic curve cryptography.

With the rapid progress of wireless mobile communications, the authenticated key agreement (AKA) protocol has attracted an increasing amount of attention. However, due to the limitations of bandwidth and storage of the mobile devices, most of the existing AKA protocols are not suitable for wireless mobile communications. Recently, Lo and others presented an efficient AKA protocol based on elliptic curve cryptography and included their protocol in 3GPP2 specifications. However, in this letter, we point out that Lo and others' protocol is vulnerable to an offline password guessing attack. To resist the attack, we also propose an efficient countermeasure.

Summary The e-commerce has got great development in the past decades and brings great convenience to people. Users can obtain all kinds of services through e-commerce platform with mobile device from anywhere and at anytime. To make it work well, e-commerce platform must be secure and provide privacy preserving. To achieve this goal, Islam et al. proposed a dynamic identity-based remote user mutual authentication scheme with smart card using Elliptic Curve Cryptography(ECC). Islam et al claimed that the security of their scheme was good enough to resist various attacks. However, we demonstrate that their scheme is vulnerable to insider attack and suffers from off-line password guessing attack if smart card is compromised. To overcome the deficiencies, we present an improved scheme over Islam's scheme. The security proof and analysis shows that our scheme can also provide user anonymity and mutual authentication, and the security is enough to against relay attack, impersonation attack, and other common secure attackers. The performance analysis shows that the proposed scheme is more efficient than Islam et al's scheme.

Summary Key agreement protocol is an important cryptographic primitive, which allows 2 parties to establish a secure session in an open network environment. A various of key agreement protocols were proposed. Nowadays, there still exists some other security flaws waiting to be solved. Owing to reduce the computational and communication costs and improve the security, chaotic map has been studied in-depth and treated as a good solution. Recently, Liu et al proposed a chaos-based 2-party key agreement protocol and demonstrated that it can defend denial-of-service attack and replay attack. We found, however, it cannot resist off-line password-guessing attack, and it also has some other security flaws. In this paper, we propose an improved chaos-based 2-party key agreement protocol. The results prove that the protocol can solve the threats of off-line password-guessing attack and other security flaws in the security proof section. What is more, performance analysis shows that the computational cost of the improved protocol is lower than Liu et al protocol.

The elliptic curve cryptosystem (ECC) achieves the security level equivalent to that of digital signature algorithm (DSA), but has a lower computational cost and a smaller key size than the DSA. Till now so many proxy multi-signature schemes based on ECC without pairings have been proposed. To the best of our knowledge, none of them are provable secure. Having motivated, we first define a formal security model and then propose a provable secure proxy multi-signature scheme based on ECC without pairings. Our proposed scheme can play a crucial role in application to distributed systems, grid computing, mobile agent environment etc. DOI: http://dx.doi.org/10.5755/j01.itc.43.2.5377

The radio frequency identification (RFID) technology has been widely adopted and being deployed as a dominant identification technology in a health care domain such as medical information authentication, patient tracking, blood transfusion medicine, etc. With more and more stringent security and privacy requirements to RFID based authentication schemes, elliptic curve cryptography (ECC) based RFID authentication schemes have been proposed to meet the requirements. However, many recently published ECC based RFID authentication schemes have serious security weaknesses. In this paper, we propose a new ECC based RFID authentication integrated with an ID verifier transfer protocol that overcomes the weaknesses of the existing schemes. A comprehensive security analysis has been conducted to show strong security properties that are provided from the proposed authentication scheme. Moreover, the performance of the proposed authentication scheme is analyzed in terms of computational cost, communicational cost, and storage requirement.

Recently Xie et al. [Q. Xie, N. Dong, X. Tan. D. Wong, G. Wang. Improvement of a three-party password-based key exchange protocol with formal verification. Information Technology and Control, 2013, Vol. 42, No. 3, 231-237] proposed an efficient three-party password-based key exchange protocol and used a formal verification tool to verify its security. In this paper, we demonstrate that their protocol is vulnerable to the off-line password guessing attack and the key compromise impersonation attack. The analysis shows that their protocol is not secure for practical applications. To overcome weaknesses in Xie et al.’s protocol, we also propose an improved 3PAKE protocol. Analysis shows that our protocol not only overcomes those weaknesses, but also has better performance. Therefore, our protocol is more suitable for practical applications. DOI: http://dx.doi.org/10.5755/j01.itc.43.1.5322

Conventional two-step ADC for CMOS image sensor requires full resolution noise performance in the first stage single slope ADC, leading to high power consumption and large chip area. This paper presents an 11-bit two-step single slope/successive approximation register (SAR) ADC scheme for CMOS image sensor applications. The first stage single slope ADC generates a 3-bit data and 1 redundant bit. The redundant bit is combined with the following 8-bit SAR ADC output code using a proposed error correction algorithm. Instead of requiring full resolution noise performance, the first stage single slope circuit of the proposed ADC can tolerate up to 3.125% quantization noise. With the proposed error correction mechanism, the power consumption and chip area of the single slope ADC are significantly reduced. The prototype ADC is fabricated using 0.18 μm CMOS technology. The chip area of the proposed ADC is 7 μm × 500 μm. The measurement results show that the energy efficiency figure-of-merit (FOM) of the proposed ADC core is only 125 pJ/sample under 1.4 V power supply and the chip area efficiency is 84 k μm2·cycles/sample.

With the development of wireless communication technology and sensor technology, the wireless sensor network (WSN) has been widely used in various applications, such as military surveillance, environment monitoring industry control, medical monitoring, and so on. In most of the cases, WSNs are deployed in unattended environment. So, these are more vulnerable to various attacks than traditional networks. To protect communications in WSNs, mutual authentication and key agreement schemes for WSNs have been studied widely. Recently, Xue et al. proposed a temporal-credential-based mutual authentication and key agreement scheme for WSNs and claimed their scheme could withstand various attacks. However, in this paper, we will point out that their scheme is vulnerable to the off-line password guessing attack, the user impersonation attack, the sensor node impersonation attack and the modification attack. To overcome weaknesses in Xue et al.'s scheme, we also propose a new temporal-credential-based mutual authentication and key agreement scheme for WSNs. Security analysis shows our scheme could overcome weaknesses in Xue et al.'s scheme. Performance analysis shows our scheme also has better performance. Therefore, our scheme is more suitable for providing secure communication in WSNs.

Recently, an improved remote user authentication scheme using smartcard was proposed. The authentication scheme by J. Chao claimed that it could provide user anonymity and withstand various attacks. In this paper, we analyze the security of Chao's scheme and point out that his scheme cannot provide user anonymity. Moreover, we demonstrate that his scheme cannot withstand the user masquerade attack and the server masquerade attack.

Recently, Chen et al. [B. Chen, W. Kuo, L. Wuu, A secure password-based remote user authentication scheme without smart cards, Information Technology and Control 41(1) (2012) 53-59] proposed a secure password-based remote user authentication scheme without smart cards and claimed that their scheme could withstand various attacks. Although Chen et al.’s scheme has many benefits; we find that it is vulnerable to the device stolen attack and the privileged insider attack. We also find that their scheme does not support perfect forward secrecy and no key control. Therefore, we propose an improved scheme to overcome weaknesses and maintain the benefits of the original scheme. DOI: http://dx.doi.org/10.5755/j01.itc.42.2.2554

Summary As one of the enabling components of Internet of things (IoT), wireless sensor networks (WSNs) have found applications in a wide range of fields, in which outside users need to directly interact with sensors to obtain sensed data. However, WSNs are vulnerable to various attacks over wireless links, such as eavesdropping and tampering. How to ensure that sensitive or critical information is only available to legal users becomes a challenging issue. Two-factor authentication combining password and smart card perfectly matches this requirement because of its practicality. However, a dozen of two-factor authentication protocols have been suggested in recent years. Owing to the challenging mission of reconciling efficiency and security requirements, it is still challenging to propose a privacy-aware two-factor protocol that is capable of providing various security features while maintaining acceptable efficiency. In this paper, we put forward a privacy-aware two-factor authentication protocol based on elliptic curve cryptography for WSNs. Our new protocol accomplishes various security features necessary for real-life application environments while maintaining acceptable efficiency. We prove that the new protocol fulfills mutual authentication in the Burrows–Abadi–Needham logic. Additionally, by way of informal security analysis, we show that the new protocol can withstand a variety of attacks and provide desirable security features. Copyright © 2016 John Wiley & Sons, Ltd.

The three-party password-based authenticated key exchange (3PAKE) protocol allows two users to share a session key for future communication with the help of a trusted server in the public network. Recently, Zhao et al. [Zhao J., Gu D., Zhang L., Security analysis and enhancement for three-party password-based authenticated key exchange protocol, Security Communication Networks 2012; 5(3):273-278] proposed an efficient 3PAKE protocol using smart cards. They proved that their protocol can withstand various known attacks found in the previously published schemes. However, in this paper, we point out that their protocol is vulnerable to three kinds of attacks namely, off-line password-guessing attack, privileged insider attack and stolen smart card attack. Hence, Zhao et al.’s scheme is not recommended for practical applications.

Recently, Kwon et al. found that LKY scheme is vulnerable to off-line dictionary attack. They showed that LKY is not a complete PAKA scheme since it is possible for the involved two parties to not share a common session key as a result of executing LKY. In our paper, we will discuss the reasons for the above attack and propose two improved scheme to solve this problem.

Recently, Abdalla et al. proposed a new gateway-oriented password-based authenticated key exchange (GPAKE) protocol among a client, a gateway, and an authentication server, where each client shares a human-memorable password with a trusted server so that they can resort to the server for authentication when want to establish a shared session key with the gateway. In the letter, we show that a malicious client of GPAKE is still able to gain information of password by performing an undetectable on-line password guessing attack and can not provide the implicit key confirmation. At last, we present a countermeasure to against the attack., 6 pages

Seamless handover over multiple access points is highly desirable to mobile nodes, but ensuring security and efficiency of this process is challenging. Many such protocols have been proposed but most of them are either insecure or inefficient. Very recently, He et al. proposed an improved protocol to overcome the weakness of a novel handover authentication protocol, namely PairHand. Later, they pointed out that their protocol is vulnerable to a private key compromised problem under certain circumstances and proposed an improved protocol to overcome the weakness. In this paper, we examine the security of He et al.'s improved protocol and show it is vulnerable to a private key compromised problem. To improve security, we propose a new ID-based signature protocol and construct a new handover authentication protocol based on the proposed signature protocol.

Providing a security and efficiently key agreement for session initiation protocol SIP is so important to protect communication sessions on the internet. An authentication should be finished before a user utilises the SIP service provided by a server. However, there are some security problems with SIP authentication. Recently, Tu et al. improved Zhang et al.'s authenticated key agreement protocol. They also claimed that their protocol could be resistant to kinds of attacks. In our paper, we show that their protocol is susceptible to the server spoofing attack, user impersonation attack. We also proposed an enhanced protocol which can be more secure and flexible here.

An authentication scheme allows the user and the server to authenticate each other and establish a session key for future communication in an open network. Very recently, Wen et al. proposed a DoS-resistant ID-based password authentication scheme without using smart card. They claimed that their scheme could overcome various attacks. However, in this paper, we will point out that Wen et al.'s scheme is vulnerable to an impersonation attack and a privileged insider attack. To overcome weaknesses, we also propose an improved scheme. The analysis shows our scheme not only overcomes weaknesses in Wen et al.'s scheme but also has better performance. Then our scheme is more suitable for practical applications.