Non-interactive Blind Signatures for Random Messages

In this paper, we study the problem of secure integrating public key encryption with keyword search (PEKS) with public key data encryption (PKE). We argue the previous security model is not complete regarding keyword privacy and the previous constructions are secure only in the random oracle model. We solve these problems by first defining a new security model, then give a generic construction which is secure in the new security model without random oracles. Our construction is based on secure PEKS and tag-KEM/DEM schemes and achieves modular design. We also give some applications and extensions for our construction. For example, instantiate our construction with proper components, we have a concrete scheme without random oracles, whose performance is even competitive to the previous schemes with random oracles.

A blind ring signature scheme is a combination of a ring signature and a blind signature, which allows not only any member of a group of signers to sign on a message on behalf of the group without revealing its identity but also the user who possesses the message to blind it before sending to the group to be signed. Blind ring signature schemes are essential components in e-commercial, e-voting etc. In this paper, we propose the first blind ring signature scheme based on lattices. More precisely, our proposed scheme is proven to be secure in random oracle model under the hardness of the short integer solution (SIS) problem.

A blind signature enables a user to obtain signatures on any message from an authority who cannot acquire any information on the message being signed. A blind ring signature scheme is designed as a ring signature scheme with the blindness property. The scheme allows any member of a group anonymously sign a message on behalf of the group. Also, the user with the message can blind it before transmitting to the group. At Asiacrypt 2010, Rückert constructed the first blind signature scheme using ideal lattices. Recently, Zhang, Jiang and Zheng, and Alkadri, Bansarkhani and Buchmann proposed two improved blind signature schemes based on the SIS problem and the Ring SIS problem in 2018 and 2020, respectively. At WISA 2019, motivated by these blind signature schemes, Le, Duong and Susilo constructed the first lattice-based blind ring signature scheme provably secure under the hardness assumption of the SIS problem in random oracle model. In this paper, we show that Rückert’s scheme, Alkadri-Bansarkhani-Buchmann scheme and Zhang-Jiang-Zheng scheme, and Le-Duong-Susilo scheme do not achieve blindness, i.e. the signer can link a valid message-signature pair after interacting with various users. We show that the cause of vulnerabilities of the blind schemes is that the blinding factors to hide real messages being signed are exposed by specific algebraic relations in the underlying rings. To hide the blinding factors, we use homomorphic encryption schemes. Finally, we propose a generic construction from a semantically secure homomorphic encryption scheme and a one-more unforgeable blind signature scheme that does not achieve blindness to a new blind signature scheme that achieves blindness as well as one-more unforgeability.

Recently, the notion of the key-insulated public- key system has been suggested to protect the security of users' private keys. A general idea of this system is changing the user's private key along with the time, but the user's public key remains unchanged. In this paper, we propose a new identity (ID)-based key-insulated signature scheme from bilinear pairings. As compared with the recently proposed ID-based key-insulated signature schemes, our proposed scheme has better performance in the batch verifying phase. For security analysis, our scheme is a provably secure key-insulated signature scheme in the random oracle model and under the computational Diffie-Hellman assumption. Meanwhile, to demonstrate the additional advantage of a key-insulated signature, we present a novel application based on the proposed scheme, called full delegation ID-based proxy signature scheme with time restriction. To our best knowledge, no such a proxy signature scheme is proposed until now.

Confidentiality and authenticity are two fundamental security requirement of Public key Cryptography. These are achieved by encryption scheme and digital signatures respectively. Wireless sensor networks are commonly used for critical security tasks such as intrusion or tamper detection, and therefore must be protected. The article proposes a provable secure signcryption scheme in Random oracle model for wireless security. It enables nodes to authenticate each other by keeping the information confidential. Also achieve data integrity in the communication. Security of the scheme is based on q-Diffie Hellman Problem. We modify the scheme proposed by Libert et al. and proposed a provably secure scheme with respect to security under assumptions of Strong Diffie-Hellman (SDH) and Diffie-Hellman Inversion (DHI) in the random oracles.

Kakvi and Kiltz (EUROCRYPT'12) proposed the first tight security reduction for RSA full domain hash signature scheme (RSA-FDH) with public exponent e < N1/4 in the random oracle (RO) model, and they left an open problem which called for a tightly secure RSA-FDH for N1/4 < e < N. In this paper, we consider the improved RSA (iRSA) trapdoor functions, introduced by Cao (Science in China'01), are functions that the security can be strictly proved to be equivalent to the factoring. We show that iRSA-FDH has a tight security reduction for e < N. Technically we construct iRSA lossy trapdoor functions, and then we apply the lossiness of the iRSA trapdoor functions to obtain tight security reductions for iRSA-FDH in the RO model. Finally, we propose a tightly secure blind signature scheme based on our iRSA lossy trapdoor functions in the RO model.

Blind signature allows a user to obtain a signature from an authority on any document, in such a way that the authority learns nothing about the message that is being signed. The blindness is an important property which distinguishes the blind signature from other signature schemes. Partially blind signature is an extension of blind signature that allows a signer to sign a partially blinded message that include pre-agreed information in the resulting signatures. Recently, Liao et al. proposed a pairing-based provable blind signature scheme without random oracles, and Hu et al. proposed an efficient ID-based partially blind signature scheme with security proof. But in this paper, we show that the two schemes do not satisfy the blindness and partially blindness, respectively. Liao et al.'s scheme is linkability and in Hu et al.'s scheme, a malicious user can replace pre-agreed common information with a special information

Restrictive blind signatures allow a recipient to receive a blind signature on a message unknown to the signer but the choice of the message is restricted and must conform to certain rules. Partially blind signatures allow a signer to explicitly include necessary information (expiration date, collateral conditions, or whatever) in the resulting signatures under some agreement with the receiver. Restrictive partially blind signatures incorporate the advantages of these two blind signatures. In this paper we first propose a new restrictive partially blind signature scheme from bilinear pairings. Since the proposed scheme does not use Chaum-Pedersen's knowledge proof protocol, it is much more efficient than the original restrictive partially blind signature scheme. We then present a formal proof of security in the random oracle model. Moreover, we use the proposed signature scheme to build an untraceable off-line electronic cash system followed Brand's construction.

Certificateless multi-proxy signature

Electronic voting is an alternative mechanism of ballot based voting which empowers voters to cast their secret and secure vote electronically over a public channel. Many onward-thinking countries are adopting the electronic voting system to upgrade their election process. E-voting system is more complicated to construct. Thus it expects more security as compared to the postal voting system. The objective of the paper is twofold. Firstly, we proposed an efficient blind signature scheme using the identity-based cryptosystem in the random oracle model. The proposed scheme uses the combination of Boldyreva’s blind signature scheme and Choon-Cheon’s Identity-based signature. Additionally, we reduce its security to the Gap Diffie-Hellman Complexity (GDH). Under the adaptive chosen message and ID attacks it is secure against existential forgery attack. We show our proposed system performed better as compared to existing systems. Secondly, we construct an E-voting system based on our ID-based blind signature and Boneh’s short signature scheme (EVS-ID-BS) that fulfills the E-voting security requirements. To the best of our knowledge, EVS-ID-BS is the first practical implementation of E-voting system based on ID-BS Scheme which is constructed in the random oracle model. Proposed EVS-ID-BS scheme provides batch verifiability for a significantly large number of voters, needs less bandwidth cost and require less interaction with election authority.

Security proof is a key criterion to judge the satisfaction of the security requirements in a protocol. Recently, Chang et al. proposed a password-based three-party key exchange protocol without server's public key. The security goal of the proposed protocol is to eliminate various security threats. In this paper, we show that the proposed protocol is still suffered from the denial of service and the man-in-the-middle attacks. We also prove that the probability of an adversary breaking the AKE security of the protocol is non-negligible in the random oracle model.

Recently, the first ID-based restrictive partially blind signature scheme from bilinear pairing is proposed by Chen et al., which extends the concept of blind signature and possesses the excellent features of partially blind signature, restrictive blind signature and ID-based cryptosystem simultaneously. However, its computational cost is rather high. In order to improve its efficiency, Hu et al. presented another efficient scheme which requires less computing cost. Unfortunately, we find that an adversary can change the predetermined common information, which may include the expiry date and the face value of the e-cash in electronic cash system, without being discovered by the signer. So Hu et al.psilas scheme has security flaw when it is used in electronic cash system. In this paper, we present an improved ID-based restrictive partially blind signature scheme from bilinear pairing which overcomes the security weakness of Hu et al.psilas scheme. We analyze the security of our scheme in the random oracle model and compared the efficiency of our scheme with previous schemes.

In this paper, we propose a practical ID-based (partially)blind signature scheme. Our scheme combines the already existing notions of blind signatures and identity-based cryptography.The signatures are shown secure in the random oracle model. We show how to use our ID-based PBSs to construct an electronic cash (e-cash) system in which multiple banks can securely distribute untraceable e-cash.

Liao et al. proposed first blind signature schemes without random oracles from pairings and provided security proofs in CIS'05. However, we show that their blind scheme is neither blind, nor unforgeable, anyone not to query the signing oracle can forge signature of any message.

Blind signatures are at the core of e-cash systems and have numerous other applications. In this work we construct efficient blind and partially blind signature schemes over bilinear groups in the standard model. Our schemes yield short signatures consisting of only a couple of elements from the shorter source group and have very short communication overhead consisting of 1 group element on the user side and 3 group elements on the signer side. At 80-bit security, our schemes yield signatures consisting of only 40 bytes which is \(67\%\) shorter than the most efficient existing scheme with the same security in the standard model. Verification in our schemes requires only a couple of pairings. Our schemes compare favorably in every efficiency measure to all existing counterparts offering the same security in the standard model. In fact, the efficiency of our signing protocol as well as the signature size compare favorably even to many existing schemes in the random oracle model. For instance, our signatures are shorter than those of Brands’ scheme which is at the heart of the U-Prove anonymous credential system used in practice. The unforgeability of our schemes is based on new intractability assumptions of a “one-more” type which we show are intractable in the generic group model, whereas their blindness holds w.r.t. malicious signing keys in the information-theoretic sense. We also give variants of our schemes for a vector of messages.