Low bandwidth consumption is an important issue in a busy commercial network whereas time may not be so crucial, for example, the end-of-day financial settlement for commercial transactions in a day. In this paper, we construct a secure and low bandwidth-consumption k-out-of-n oblivious transfer scheme based on bilinear pairings. We analyze the security and efficiency of our scheme and conclude that our scheme is more secure and efficient in communication bandwidth consumption than most of the other existing oblivious transfer schemes that we know.

Security and efficiency are two crucial issues in vehicular ad hoc networks. Many researches have devoted to these issues. However, we found that most of the proposed protocols in this area are insecure and can’t satisfy the anonymous property. Due to this observation, we propose a secure and anonymous method based on bilinear pairings to resolve the problems. After analysis, we conclude that our scheme is the most secure when compared with other protocols proposed so far.

In this paper, we use the ten security requirements proposed by Liao et al. for a smart card based authentication protocol to examine five recent work in this area. After analyses, we found that the protocols of Juang et al.’s, Hsiang et al.’s, Kim et al.’s, and Li et al.’s all suffer from the password guessing attack if the smart card is lost and the protocol of Xu et al.’s suffers from the insider attack.

In this paper, we analyze the protocols of Bindu et al., Goriparthi et al., Wang et al. and Hölbl et al.. After analyses, we found that Bindu et al.’s protocol suffers from the insider attack if the smart card is lost, both Goriparthi et al.’s and Wang et al.’s protocols can’t withstand the DoS attack on the password change phase which makes the password invalid after the protocol run, and Hölbl et al.’s protocol is vulnerable to the insider attack since a malevolent legal user can deduce KGC’s secret key xs.

Since Kerberos suffers from KDC (Key Distribution Center) compromise and impersonation attack, a multi-server password authentication protocol which highlights no verification table in the server end could therefore be an alternative. Typically, there are three roles in a multi-server password authentication protocol: clients, servers, and a register center which plays the role like KDC in Kerberos. In this paper, we exploit the theoretical basis for implementing a multi-server password authentication system under two constraints: no verification table and user privacy protection. We found that if a system succeeds in privacy protection, it should be implemented either by using a public key cryptosystem or by a register center having a table to record the information shared with corresponding users. Based on this finding, we propose a privacy-flexible system to let a user can employ a random-looking dynamic identity or employ a pseudonym with the register center online or offline to login a server respectively according to his privacy requirement. Compared with other related work, our scheme is not only efficient but also the most conformable to the requirements that previous work suggest.

Recently, Liaw et al. proposed a hash based electronic traveler’s check system. They claimed that their scheme is secure. However, after analyses, we found that their scheme is vulnerable to key compromise impersonation and parallel session attack. Further, we will improve their scheme to avoid such an attack.

Recently, Tsai and Liao et al. each proposed a multi-server authentication protocol. They claimed their protocols are secure and can withstand various attacks. But we found some security loopholes in each protocol. We will show the attacks on their schemes.

Recently, M. Hölbl et al. and I. E. Liao et al. each proposed an user authentication protocol. Both claimed that their schemes can withstand password guessing attack. However, T. Xiang et al. pointed out I. E. Liao et al.'s protocol suffers three kinds of attacks, including password guessing attacks. We present an improvement protocol to get rid of password guessing attacks. In this paper, we first point out the security loopholes of M. Hölbl et al.'s protocol and review T. Xiang et al.'s cryptanalysis on I. E. Liao et al.'s protocol. Then, we present the improvements on M. Hölbl et al.'s protocol and I. E. Liao et al.'s protocol, respectively.

In 2005, Hwang et al. [17] proposed a time-stamping protocol for digit watermarking. They claimed that their scheme is secure against attacks. However, in this article, we will show that their scheme is not secure enough for that when the owner of the image sends both the encrypted session key and image to the TSS, the attacker can intercept these transmitted data. Then, he can launch an off-line attack to analyze these intercepted data. We will describe the attacker’s action in this article. After that, we propose an improved scheme to prevent this off-line attack.

In 1997, Ruppe R. et al [17] first proposed a Near-Term Digital Radio (NTDR) network system which is a cluster-based ad hoc network intended to be used efficiently for military missions. In the same year, Zavgren J. [18] proposed a management protocol for the NTDR network system. But they both lack the security considerations. In 2003, Varadharajan et al [4] proposed a secure cluster-based ad hoc network protocol using public key infrastructure (PKI). However, in 2005, Chang et al pointed out that using PKI would be a heavy burden for the computation of each mobile node. Hence, they proposed a protocol [5] based on Diffie-Hellman method for securing network, in the same year, Liaw et al. proposed a secured key exchange protocol [20] for securing nodes communication in mobile ad hoc networks (MANETs). In 2006, also for security purpose, Chang and Lee [6] proposed the other scheme by using nodes’ identities. But after our analysis, we find that both of their protocols have some mistakes. Accordingly, we propose a new protocol based on ID-based bilinear pairing to get rid of nowadays unsolved security problem in NTDR network. After our analysis, we conclude that our scheme is not only secure but also very efficient.

In 2004, Ari Juels [1] proposed a Yoking-Proofs protocol for RFID systems. The aim is to permit tags to generate a proof which is verifiable off-line by a trusted entity even when the readers are potentially untrusted. However, we find that their protocol not only doesn’t possess the anonymity property but also suffers from both of the off-line and replay attacks. In 2006, Kirk H.M. Wong et al. [3] proposed an authentication scheme on RFID passive tags, attempting to as a standard for apparel products. Yet, to our view, their protocol suffers from the known-plaintext attack. In this paper, we first point out the weaknesses in the two above mentioned protocols. Then, we propose a novel efficient scheme which not only can achieve the mutual authentication between the server and tag but also possess the anonymity property needed in a RFID system.

Recently, Yoon et al. and Cao et al. propose two deniable authentication protocols respectively. They both claim that their protocols can achieve the deniable property. However, in this paper, we will point out that their protocols each suffers from some malicious attacks. After that, we propose a new identity-based deniable authentication protocol on pairings which can not only attain the desired deniable property but also can prevent attacks.

In 1997, Cranor and Cytron proposed an electronic voting protocol, Sensus protocol, intended to be applied in a real election. However, in 2005 Fabrizio et.al. pointed out there is a vulnerability exists in their protocol that the validator can impersonate anyone of those abstained voters to cast vote. They proposed a scheme, Seas protocol, to solve this weakness. But in this paper, we will show that Seas protocol is not only inefficient but also impractical. Moreover, we also propose a sound electronic voting protocol based on Sensus protocol from bilinear pairings, which can really satisfy the security requirements of an e-voting system.

In 2005, Manik et al. propose a novel remote user authentication scheme using bilinear pairings which allows a valid user to login to the remote system but prohibits too many users to login with the same login-ID. It also provides a flexible password change function. In this paper, we will show that this remote user authentication scheme is not secure, an adversary can always pass the authentication.

In 2003, Boyd and Mao proposed two deniable authenticated key establishment protocols using elliptic curve pairings for Internet protocols, one is based on Diffie-Hellman key exchange and the other is based on Public-Key Encryption approach. For the use of elliptic curve pairings, they declared that their schemes could be more efficient than the existing Internet Key Exchange (IKE), nowadays. However in this paper, we will show that both of Boyd-Mao??s protocols suffer from the key-Compromise Impersonation attack.

In this article we show that Shim??s new ID-based tripartite multiple-key agreement protocol still suffers from the impersonation attack, a malicious user can launch an impersonation attack on their protocol.

In 1999, Yang and shieh proposed two password authentication schemes using smart cards. But in 2003, Sun and Yeh indicated that their schemes are subject to the forgery attack. So in 2005, Yang and Wang proposed an improvement of Yang and Shieh??s schemes to resist against Sun and Yeh??s attack. However in this paper, we will point out that Yang and Wang??s schemes still suffer from the forgery attack. Because in their schemes, one can masquerade as a legal user and cheat the remote server successfully in the authentication phase.