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Wei Songjie et al. proposed an identity-based signature scheme（named mIBS）, and used a security mediator（SEM） node to realize real-time revocation of entity identity in the mIBS scheme. The SEM held a part of the signature key, and generated a signature by working collaboratively with a signer. This paper analyzed the security of the mIBS scheme, found it had serious security flaws, and presented a specific attack instance. In the attack instance, a signer can stole the key held by the SEM through once normal signature interaction with a SEM, and then bypassed the SEM to implement a signature independently. This paper proposed an improved signature scheme（named mIBSG）. The mIBSG scheme remedied the security flaws of the original scheme by randomizing the private key held by the SEM. Further, this paper established a security model for mIBS scheme, named mEUF-CMIA, and defined a new type of adversary that simulated malicious but legitimate signers. The new adversary had the power to generate a forged signature independently through asking random oracles. Based on the new security model, this paper deduced the unforgeability of the mIBSG scheme as solving the CDH problem on a cyclic group. Comparative analysis showed that the mIBSG scheme achieved provable security with a small calculate efficiency loss. The mIBSG scheme can be used to build an IBC-based cross-domain authentication system. [ABSTRACT FROM AUTHOR]

Fuzzy identity based signature (FIBS) possesses error-tolerance property which allows a user with identity ID described as an attribute set ω = { ω i } i = 1 n to issue a signature that could be verifed with identity I D ′ described as an attribute set ω ′ = { ω i ′ } i = 1 n if and only if ω and ω ′ are within a certain distance. Most FIBS schemes'security proofs are given in the random oracle model (ROM). Although in random oracle model the cryptographic scheme is proved to be secure, in practical applications it may be insecure. In this paper, we construct a concrete FIBS scheme and its security proof is given in the standard model(SM). Finally, we compare the proposed scheme with several other signature schemes in terms of computation, communication and security model and show that the proposed scheme is more efficient and suitable for practical applications. [ABSTRACT FROM AUTHOR]

A triple receiver public key cryptosystem was proposed.In the cryptosystem,a sender encrypted a message and sent to three receivers,while the three receivers were able to decrypt the message with their own private keys.Based on bilinear map,two triple receiver public key encryption schemes with different security were constructed.If the gap bilinear Diffie-Hellman (GBDH) problem and the computational Diffie-Hellman (CDH) problem were proved formally to be intractable,then the two schemes proposed were semantically secure against chosen-plaintext attacks and against adaptive chosen ciphertext attacks respectively.The proposed scheme only added an exponential operation and a hash operation,and constructed three independent receivers which had a high efficiency.Analyses show that proposed scheme can improve the security of TLS protocol and apply to hierarchical public key cryptosystems.

A triple receiver public key cryptosystem was proposed. In the cryptosystem, a sender encrypted a message and sent to three receivers, while the three receivers were able to decrypt the message with their own private keys. Based on bilinear map, two triple receiver public key encryption schemes with different security were constructed. If the gap bilinear Diffie-Hellman (GBDH) problem and the computational Diffie-Hellman (CDH) problem were proved formally to be intractable, then the two schemes proposed were semantically secure against chosen-plaintext attacks and against adaptive chosen ciphertext attacks respectively. The proposed scheme only added an exponential operation and a hash operation, and constructed three independent receivers which had a high efficiency. Analyses show that proposed scheme can improve the security of TLS protocol and apply to hierarchical public key cryptosystems.

As vehicle speed is fast and on board units' (OBUs) computing power, storage space, bandwidth and other resources are very limited, the efficiency of message transmission in vehicular ad hoc network is of great concern. Certificate‐based aggregate signature scheme provides a way to combine numerous signatures into one short signature. The authors propose a certificate‐based aggregate signature scheme for vehicular ad hoc networks. In this study, the authors prove that the proposed scheme is secure against forgery attack in the random oracle model and under the computational Diffie–Hellman problem. It is efficient and suitable for vehicular ad hoc networks. [ABSTRACT FROM AUTHOR]

Boneh et al. introduced mediated RSA (mRSA) in 2001 in an attempt to achieve faster key revocation for medium-sized organizations via the involvement of a security mediator (SEM) as a semi-trusted third party to provide partial ciphertext decryption for the receiver. In this paper, a pairing-free security mediated encryption scheme based on an ElGamal variant is proposed. The scheme features a similar setting as in the mediated RSA but with a different underlying primitive. We show that the proposed security mediated encryption scheme is secure indistinguishably against chosen-ciphertext attack (IND-CCA) in the random oracle via the hardness assumption of the computational Diffie-Hellman (CDH) problem.

Searchable public key encryption enables a storage server to retrieve the publicly encrypted data without revealing the original data contents. It offers a perfect cryptographic solution to encrypted data retrieval in encrypted data storage systems. Certificateless cryptography (CLC) is a novel cryptographic primitive that has many merits. It overcomes the key escrow problem in identity-based cryptosystems and the cumbersome certificate problem in conventional public key cryptosystems. Motivated by the appealing features of CLC, three certificateless encryption with keyword search (CLEKS) schemes were presented in the literature. However, all of them were constructed with the costly bilinear pairing and thus are not suitable for the devices that have limited computing resources and battery power. So, it is interesting and worthwhile to design a CLEKS scheme without using bilinear pairing. In this study, we put forward a pairing-free CLEKS scheme that does not exploit bilinear pairing. We strictly prove that the scheme achieves keyword ciphertext indistinguishability against adaptive chosen-keyword attacks under the complexity assumption of the computational Diffie-Hellman problem in the random oracle model. Efficiency comparison and the simulation show that it enjoys better performance than the previous pairing-based CLEKS schemes. In addition, we briefly introduce three extensions of the proposed CLEKS scheme. [ABSTRACT FROM AUTHOR]

To solve the private key escrow problem of identity-based multi-receiver signcryption schemes,the security model for multi-receiver signcryption scheme was constructed,and then a certificateless multi-receiver signcryption scheme based on ECC was proposed.Furthermore,the security of the scheme in the random oracle was based on the computational Diffie-Hellman assumption and elliptic curve discrete logarithm assumption was proved.Meanwhile,the scheme was free from certificate management center and needed no bilinear paring operation in both signcryption and decryption phases.It can also protect both the sender and receivers’identity from leaking out.So the scheme can be applied conveniently to broadcast signcryption in network environment.

The security model of the certificateless aggregate signature scheme with universal designated verifier was studied,and then a certificateless aggregate signature scheme with universal designated verifier using bilinear pairings was proposed.In the random oracle mode,based on the hardness of the computational Diffie-Hellman problem,the new scheme was proved to be secure against three attacks of certificateless aggregate signature scheme with universal designated verifier.Meanwhile,the scheme satisfies properties of strong designated verify and non-transferability.Furthermore,the length of final aggregate signature is equivalent as the length of signal user’s signature,it is more efficient than others because the pairing computation is fixed among public verifies and designed verifies.

There are many variants of the computational Diffie-Hellman problem that are necessary to provide security of many cryptographic schemes. Two of them are the square Diffie-Hellman problem and the square root Diffie-Hellman problem. Recently, the first and third authors proved that these two problems are polynomial-time equivalent under a certain condition (Roh and Hahn in Des Codes Cryptogr 62(2):179-187, 2011). In this paper, we generalize this result. We introduce the l-th power Diffie-Hellman problem and the l-th root Diffie-Hellman problem and show that these two problems are polynomial-time equivalent for $$l = O (\log p)$$ under a condition similar to that of Roh and Hahn (2011), where p is the order of the underlying group. [ABSTRACT FROM AUTHOR]

The authentication of recommendation information transmitted through trust train is important for trust model in distributed environment. To solve this problem, the security model for the certificateless sequential multi-signature scheme was studied and then a certificateless sequential multi-signature scheme using elliptic curve cryptography and bi-linear pairings was proposed. It is proven in the random oracle that the security of the scheme is based on the fact that the computational Diffie-Hellman problem is hard. Meanwhile, the scheme needs no certificate management center and the length of signature is independent of the number of signers. It needs no bilinear pairing operation in the phase of partial signing, and just needs one each in verification phases of partial signing and integral signing. So it is computationally ef-ficient compared to the existing signature schemes and can be applied conveniently to trust transitivity in large scale dis-tributed environment.

In this study, the authors consider certificateless signature (CLS) schemes for strong non‐repudiation. They show that previous security models which ensure that any user can have a unique key pair cannot guarantee a CLS scheme to achieve strong non‐repudiation. The authors then fix the security model and propose a new CLS scheme which provides strong non‐repudiation under the new model, assuming the computational Diffie–Hellman problem is intractable. [ABSTRACT FROM AUTHOR]

In order to deal with key exposure problem, we introduce forward secure technique into certificateless proxy signature scheme, and propose the formal definition and security model of the forward secure certificateless proxy signature. Our security model takes into account the super adversary in certificateless signature. Furthermore, we present a construction of forward secure certificateless proxy signature scheme with bilinear maps. Based on the difficulty of computational Diffie-Hellman problem, we prove the scheme is secure against chosen message attack in the random oracle model. Finally, we analyze efficiency of the proposed scheme. [ABSTRACT FROM AUTHOR]

Many cryptographic schemes are based on computationally hard problems. The computational Diffie-Hellman problem is the most well-known hard problem and there are many variants of it. Two of them are the square Diffie-Hellman problem and the square root Diffie-Hellman problem. There have been no known reductions from one problem to the other in either direction. In this paper we show that these two problems are polynomial time equivalent under a certain condition. However, this condition is weak, and almost all of the parameters of cryptographic schemes satisfy this condition. Therefore, our reductions are valid for almost all cryptographic schemes. [ABSTRACT FROM AUTHOR]

In 2009, Lee et al. (Ann Telecommun 64:735-744, ) proposed a new authenticated group key agreement protocol for imbalanced wireless networks. Their protocol based on bilinear pairing was proven the security under computational Diffie-Hellman assumption. It remedies the security weakness of Tseng's nonauthenticated protocol that cannot ensure the validity of the transmitted messages. In this paper, the authors will show that Lee et al.'s authenticated protocol also is insecure. An adversary can impersonate any mobile users to cheat the powerful node. Furthermore, the authors propose an improvement of Lee et al.'s protocol and prove its security in the Manulis et al.'s model. The new protocol can provide mutual authentication and resist ephemeral key compromise attack via binding user's static private key and ephemeral key. [ABSTRACT FROM AUTHOR]

We propose a distributed key generation protocol for pairing-based cryptosystems which is adaptively secure in the erasure-free and secure channel model, and at the same time completely avoids the use of interactive zero-knowledge proofs. Utilizing it as the threshold key generation protocol, we present a secure (t,n) threshold signature scheme based on the Waters' signature scheme. We prove that our scheme is unforgeable and robust against any adaptive adversary who can choose players for corruption at any time during the run of the protocols and make adaptive chosen-message attacks. And the security proof of ours is in the standard model (without random oracles). In addition our scheme achieves optimal resilience, that is, the adversary can corrupt any t

Boneh et al. introduced mediated RSA (mRSA) in 2001 in an attempt to achieve faster key revocation for medium-sized organizations via the involvement of a security mediator (SEM) as a semi-trusted third party to provide partial ciphertext decryption for the receiver. In this paper, a pairing-free security mediated encryption scheme based on an ElGamal variant is proposed. The scheme features a similar setting as in the mediated RSA but with a different underlying primitive. We show that the proposed security mediated encryption scheme is secure indistinguishably against chosen-ciphertext attack (IND-CCA) in the random oracle via the hardness assumption of the computational Diffie-Hellman (CDH) problem. [ABSTRACT FROM AUTHOR]