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We construct a short group signature which is proven secure without random oracles. By making certain reasonable assumptions and applying the technique of non-interactive proof system, we prove that our scheme is full anonymity and full traceability. Compared with other related works, such as BW06 [9], BW07 [10], ours is more practical due to the short size of both public key and group signature. [ABSTRACT FROM AUTHOR]

To construct a suitable and secure proxy re-signature scheme is not an easy job, up to now, there exist only three schemes, one is proposed by Blaze et al. [6] at EUROCRYPT 1998, and the others are proposed by Ateniese and Hohenberger [2] at ACM CCS 2005. However, none of these schemes is proved in the standard model (i.e., do not rely on the random oracle heuristic). In this paper, based on Waters' approach [20], we first propose a multi-use bidirectional proxy re-signature scheme, denoted as Smb, which is existentially unforgeable in the standard model. And then, we extend Smb to be a multi-use bidirectional ID-based proxy re-signature scheme, denoted by Sid − mb, which is also existentially unforgeable in the standard model. Both of these two proposed schemes are computationally efficient, and their security bases on the Computational Diffie-Hellman (CDH) assumption. [ABSTRACT FROM AUTHOR]

Transitive signature is an interesting primitive due to Micali and Rivest. During the past years, many constructions of transitive signatures have been proposed based on various assumptions. In this paper, we provide the first construction of transitive signature schemes by using braid groups. In the random oracle model, our proposals are proved to be transitively unforgeable against adaptively chosen message attack under the assumption of the intractability of one-more matching conjugate problem (OM-MCP) over braid groups. Moreover, the proposed schemes are invulnerable to currently known quantum attacks. [ABSTRACT FROM AUTHOR]

In this paper, we propose an efficient multi-receiver identity based signcryption scheme which only needs one pairing computation to signcrypt a message for n receivers and can provide confidentiality and authenticity simultaneously in the multi-receiver setting. We compare our scheme with several multi-receiver constructions from the security and efficiency points of view and argue that our provably secure scheme is more efficient than other known constructions. To address the security issues, we formulate security models and define strong security notions for multi-receiver identity based signcryption schemes. We also prove that our scheme satisfies these strong security requirements in the random oracle model. [ABSTRACT FROM AUTHOR]

Threshold proxy signature is a variant of the proxy signature scheme in which only some subgroup of proxy signers with efficient size can sign messages on behalf of the original signer. Some threshold proxy signature schemes have been proposed up to data. But nearly all of them are under the certificate-based (CA-based) public key systems. In this paper, we put forward an identity-based (ID-based) threshold proxy signature scheme with known signers from bilinear pairings for the first time. Most of our constructions would be simpler but still with high security due to the properties of bilinear map built from Weil pairing or Tate pairing. [ABSTRACT FROM AUTHOR]

Exposure of secret keys can be the most devastating attack on a signature scheme since such that security is entirely lost. In a certificated based environment, the certification revocation list (CRL) can be used to minimize the damage caused by key exposure. In an identity based environment however, key exposure may means that the corresponding entity of the exposed key cannot use his identity information as his public key any more, and is in fact removed from the identity based system. In last few years the notion of and implementations of key insulated cryptosystems have been suggested for protecting the security of cryptosystems. In this work, we apply the method of key insulation to identity based signature, and solve the key exposure problem existing in the identity based schemes. We start by developing the formal model for identity based key insulated signature. We then use the fact to construct a identity based key insulated signature scheme. Keywords: identity based cryptosystem, key insulated cryptosystem, bilinear Diffie-Hellman. [ABSTRACT FROM AUTHOR]

Password authentication has been accepted as an easy-to-use solution in network environment to protect unauthorized access to a remote server. Although many schemes have been proposed, none of them can achieve survivability in case of compromise of a server. Once a server’s secret key is leaked, the system is totally broken, and all the legally registered users have to be rejected for security reason, which is the most undesirable tragedy in business applications. In this paper, we propose a remote authentication scheme with forward security to reduce the potential damages caused by key exposure problem in authentication schemes. In our scheme, an intruder can not masquerade as an legal user registered at previous periods even if he has obtained server’s secret keys. [ABSTRACT FROM AUTHOR]

With the flourish of applications over the wired /wireless networks, how to keep user's privacy has drawn growing concerns in recent years. Although the issue of user anonymity has been addressed in digital signature field by introducing the concepts of ring and group signatures, they are not suitable to anonymously authenticate a user in wireless mobile applications, because these signature schemes need infrastructure support and heavy computational costs which is beyond the computational ability of a smart card embedded in a hand-held device. In this paper, we propose an anonymous authentication scheme which also supports Diffie-Hellman key exchange. Our scheme is very efficient since it mainly uses hash and XOR operations. Moreover, our scheme possesses many good virtues of existing authentication schemes. [ABSTRACT FROM AUTHOR]

Proxy signcryption, proposed by Gamage et al. [1], is a cryptographic primitive, which combines the functionality of a proxy signature scheme with that of an encryption. But to date, no formal definitions of security have been provided. In this paper, we first propose the syntax of warrant-based proxy signcryption scheme, then formalize notions of security for it. After that, we present a warrant-based proxy signcryption scheme based on integer factorization assumption. Keywords: proxy Signcryption, integer factorization, provable security. [ABSTRACT FROM AUTHOR]

Proxy signcryption is a cryptographic primitive which combines the functionalities of a proxy signature scheme and a signcryption scheme. In this paper, based on bilinear pairings, we would like to propose two efficient proxy singcryption schemes. One is certificate based and the other is identity based. Also we analyze the two proposed schemes from efficiency point of view. We show that the certificate based scheme achieves great efficiency in terms of communication cost and computation overhead. And the identity based scheme is much more efficient than the scheme proposed by Li and Chen. What's more, we also argument that the two proposed schemes are secure in the random oracle model without a secure channel. Keywords: proxy signature, signcryption, proxy signcryption, bilinear pairings. [ABSTRACT FROM AUTHOR]

Signcryption denotes a cryptographic method, which can process encryption and digital signature simultaneously. So, adopting such schemes, computational cost of encryption and signature compared to traditional signature-then-encryption can be reduced to a great extent. Based on the existing distributed signcryption schemes, Kwak and Moon proposed a new distributed signcryption scheme with sender ID confidentiality and extended it to a group signcryption. Their scheme is more efficient in both communication and computation aspects. Unfortunately we will demonstrate that their scheme is insecure by identifying some security flaws. Exploring these flaws, an attacker without any secret can mount universal forging attacks. That is, anyone (not necessary the group member) can forge valid group signatures on arbitrary messages of his/her choice. [ABSTRACT FROM AUTHOR]

In this paper, we first construct a security model for delegation-by-warrant ID-based proxy signcryption schemes and formalize notions of security for them. To the best of our knowledge, no related work has been done. Then we present such a scheme based on the bilinear pairings, and show that it is provably secure in the random oracle model. Specifically, we prove its semantic security under the DBDH assumption and its unforgeability under the BDH assumption. [ABSTRACT FROM AUTHOR]

In this paper, based on bilinear pairings, we would like to construct an identity based proxy signature scheme and an identity based proxy signcryption scheme without secure channel. We also analyze the two proposed schemes from efficiency point of view and show that they are more efficient than the existed ones. What's more, our proposed schemes satisfy all of the security requirements to proxy signature and proxy signcryption schemes assuming the CDH problem and BDH problem are hard to solve. [ABSTRACT FROM AUTHOR]

We analyze the relationship and subtle difference between the notion of certificateless public key cryptography (CL-PKC) and identity-based schemes without a trusted private key generator (PKG), then propose a certificateless threshold signature scheme based on bilinear pairings. The proposed scheme is robust and existentially unforgeable against adaptive chosen message attacks under CDH assumption in the random oracle model. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel cryptosystem based on reversible second-order cellular automata. The cryptosystem is featured by its large key space and high speed due to cellular automata's parallel information processing property. Moreover, the encryption and decryption devices share the identical module, which preserves the merit of local connection of cellular automata in both encryption and decryption devices. So the scheme could be implemented in hardware efficiently. We also apply such system in message and image encryption. [ABSTRACT FROM AUTHOR]

Authenticated key agreement protocols are essential for secure communications in open and distributed environments. In 2004, Ryu et al. proposed an efficient two-party identity-based authenticated key agreement protocol based on pairings. However, in this paper, we demonstrate that their protocol is vulnerable to a key-compromise impersonation attack. The attacking scenario is described in details. Furthermore,we point out that their protocol provides the property of deniability and at the same time it is the mechanism used to achieve deniability that allows the key-compromise impersonation attack. [ABSTRACT FROM AUTHOR]

Proxy signature is an active cryptographic research area, and a wide range of literature can be found nowadays suggesting improvement and generalization of existing protocols in various direction. However, most of previously proposed schemes in these literatures are based on discrete logarithm problems. To our best knowledge, there still doesn't exist an indeed proxy signature scheme based on factoring. The paper present a new proxy signature scheme based on factoring, along with a complete proof of security in the Random Oracle model. The proposed scheme does not need a secure channel to transmit proxy private key. [ABSTRACT FROM AUTHOR]

A novel ID-based proxy-protected signature scheme based on identity information is presented in this paper. We review the concept ID-Based signature introduced by Shamir, define the security notion of an ID-Based signature. We also improve the Shamir's ID-Based signature and prove its security under the proposed security notion. From the improved Shamir's ID-Based signature scheme we construct an ID-Based proxy signature scheme, the security is based on the underlying ID-based signature scheme. Our scheme is efficient and easy to implement. The scheme simplifies the public key as the user's id and can be easily applied to all the RSA-type cryptosystems. Keywords: proxy signature, identity-based signature, provably secure, RSA, random oracle model [ABSTRACT FROM AUTHOR]

Proxy cryptosystem was first proposed by Mambo and Okamoto, for the delegation of the power to decrypt ciphertexts. However, to our knowledge, there is no reasonable mode aimed at this cryptographic notion. In this paper, we first present a practical mode: proxy cryptosystem based on time segmentation. Under this mode, a secure model is proposed and a proxy cryptosystem is constructed. Our construction uses ideas from the HIBE scheme of Gentry and Silverberg, the FSPE scheme of Canetti et al. and the scheme of Fujisaki and Okamoto, and is proven to be secure based on the hardness of bilinear Diffie-Hellman assumption. At last, we give an identity based (ID-based) version of the proxy cryptosystem based on time segmentation. Keywords: Proxy cryptosystem, bilinear Diffie-Hellman, ID-based. [ABSTRACT FROM AUTHOR]

The property of forward-security can be used to reduce the potential damages caused by key exposure. However, none of the existing proxy signature schemes has taken forward-security into consideration. And most proxy signature schemes are based on discrete logarithm problem. In this paper, we first present a forward-secure proxy signature scheme based on factoring problem. Next, we present a forward-secure threshold proxy signature scheme. [ABSTRACT FROM AUTHOR]

So far, all of proposed threshold proxy signature schemes are based on public key systems with certificates and most of them use Shamir's threshold secret share scheme. Self-certified public key system has attracted more and more attention because of its advantages. Based on Hsu et al's self-certified public key system and Li et al's proxy signature scheme, one threshold proxy signature scheme is proposed. The new scheme can provide the properties of proxy protection, verifiability, strong identifiability, strong unforgeability, strong repudiability, distinguishability, known signers and prevention of misuse. In the proxy signature verification phase, the authentication of original and proxy signers' public keys and the verification of the threshold proxy signature are executed together. In addition, the computation overhead and communication cost of the scheme are less than previous works with Shamir's secret share protocol and the public key system based on certificates. [ABSTRACT FROM AUTHOR]