Easy Simple Factoring-based Digital Signature Scheme

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.

ABSTRACTOptimal signatures (generating signatures as short as possible), which achieve the optimal bandwidth for communication, are extremely useful in bandwidth‐critical networks. Previous approaches use the random permutations with large block size as building blocks, which incurs less efficient implementations in the real world. Meanwhile, all the practical signature schemes are not optimal in bandwidth including PSS‐R (probabilistic signature scheme with message recovery ), FDH ( Full Domain Hash), and DSA (Digital Signature Algorithm). This paper presents three constructions for optimal signature schemes. All the proposals use both the random oracles and the ideal ciphers with smaller block sizes as building blocks to obtain optimal paddings for signature schemes. The ideal ciphers in our schemes can be implemented by real block ciphers (e.g., AES (Advanced Encryption Standard)‐256). Concrete implementations of these signature schemes can utilize the trapdoor permutations of Rabin and RSA, respectively. Surprisingly, RSA and Rabin (trapdoor permutations) lead to not only optimality in bandwidth but also a tight security. Therefore, besides yielding secure signatures with high efficiency, our proposals can also be flexibly applied to the bandwidth‐limited networks that reduces the communication cost as less as possible. Copyright © 2014 John Wiley & Sons, Ltd.

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.

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.

We study how to construct secure digital signature schemes in the presence of kleptographic attacks. Our work utilizes an offline watchdog to clip the power of subversions via only one-time black-box testing of the implementation. Previous results essentially rely on an online watchdog which requires the collection of all communicating transcripts (or active re-randomization of messages). We first give a simple but generic construction, without random oracles, in the partial-subversion model in which key generation and signing algorithms can be subverted. Then, we give the first digital signature scheme in the complete-subversion model in which all cryptographic algorithms can be subverted. This construction is based on the full-domain hash. Along the way, we enhance the recent result of Russell et al. (CRYPTO 2018) about correcting a subverted random oracle.

From the birth of the blockchain technology, multisignatures attract much attention as a tool for handling blockchain transactions. Concerning the application to the blockchain, multisignatures with public-key aggregation, which can compress public keys of signers to a single public key, is preferable to the standard multisignature because the public keys and the signature used in a transaction are stored to verify the transaction later. Several multisignature schemes with public key aggregation are proposed, however, there are no known schemes having a tight security reduction.We propose a first multisignature with public-key aggregation whose security is proven to be tightly secure under the DDH assumption in the random oracle model. Our multisignature is based on the DDH-based multisignature by Le, Yang, and Ghorbani, however, our security proof is different from theirs. The idea of our security proof originates from another DDH-based multisignature by Le, Bonnecaze, and Gabillon whose security proof is tightly one. By tailoring their security proof to a setting which admits the public-key aggregation, we can prove the tight security of our multisignature.

From the birth of the blockchain technology, multisignatures attract much attention as a tool for handling blockchain transactions. Concerning the application to the blockchain, multisignatures with public-key aggregation, which can compress public keys of signers to a single public key, is preferable to the standard multisignature because the public keys and the signature used in a transaction are stored to verify the transaction later. Several multisignature schemes with public key aggregation are proposed, however, there are no known schemes having a tight security reduction. We propose a first multisignature with public-key aggregation whose security is proven to be tightly secure under the DDH assumption in the random oracle model. Our multisignature is based on the DDH-based multisignature by Le, Yang, and Ghorbani, however, our security proof is different from theirs. The idea of our security proof originates from another DDH-based multisignature by Le, Bonnecaze, and Gabillon whose security proof is tightly one. By tailoring their security proof to a setting which admits the public-key aggregation, we can prove the tight security of our multisignature.

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.

The hash-and-sign RSA signature is one of the most elegant and well known signatures schemes, extensively used in a wide variety of cryptographic applications. Unfortunately, the only existing analysis of this popular signature scheme is in the random oracle model, where the resulting idealized signature is known as the RSA Full Domain Hash signature scheme (RSA-FDH). In fact, prior work has shown several “uninstantiability” results for various abstractions of RSA-FDH, where the RSA function was replaced by a family of trapdoor random permutations, or the hash function instantiating the random oracle could not be keyed. These abstractions, however, do not allow the reduction and the hash function instantiation to use the algebraic properties of RSA function, such as the multiplicative group structure of ℤ n * . n. In contrast, the multiplicative property of the RSA function is critically used in many standard model analyses of various RSA-based schemes. Motivated by closing this gap, we consider the setting where the RSA function representation is generic (i.e., black-box) but multiplicative, whereas the hash function itself is in the standard model, and can be keyed and exploit the multiplicative properties of the RSA function. This setting abstracts all known techniques for designing provably secure RSA-based signatures in the standard model, and aims to address the main limitations of prior uninstantiability results. Unfortunately, we show that it is still impossible to reduce the security of RSA-FDH to any natural assumption even in our model. Thus, our result suggests that in order to prove the security of a given instantiation of RSA-FDH, one should use a non-black box security proof, or use specific properties of the RSA group that are not captured by its multiplicative structure alone. We complement our negative result with a positive result, showing that the RSA-FDH signatures can be proven secure under the standard RSA assumption, provided that the number of signing queries is a-priori bounded.

Proxy signcryption is a novel cryptographic primitive that combines the functionality of a proxy signature with that of a signcryption. However, the security of all the known proxy signcryption schemes were proven in the random oracle, which has received a lot of criticism that the proofs in the random oracle model are not sound with respect to the standard model. Hence, it is an interesting research problem on how to construct a provably secure proxy signcryption scheme in the standard model. In this paper, motivated by Waters' signature scheme, we propose a new construction of proxy signcryption scheme based on bilinear pairing without using random oracles. Then, we use the techniques from provable security to show that the proposed scheme is indistinguishability under adaptive chosen ciphertext attacks secure under the decisional bilinear Diffie–Hellman assumption and existentially unforgeable under the computational Diffie–Hellman assumptions. Compared with the existing schemes with formal security proof, we show that no pairing computation is required in our proxy signcrypt phase with pre‐computations. To the best of our knowledge, our proposed scheme is the first provably secure proxy signcryption scheme in the standard model. Copyright © 2014 John Wiley &amp; Sons, Ltd.

In traditional public key signature, the public key of a signer is essentially a random string selected from a given set. It is infeasible to prove that a party is indeed the signer for a given signature. In general, the public key of a user needs a management authority to authenticate it. It results in that traditional public key cryptosystem (PKC) requires high maintenance cost for certificate management. Although, identity based cryptosystem (IBC) reduces the overhead of management, it suffers from the drawback of key escrow. Certificate-based cryptosystem combines the advantage of both PKC and IBC as it avoids the usage of certificates and does not suffer from key escrow. Recently, Liu et.al proposed an efficient Certificate-based signature and showed that the scheme was secure in the random oracles. Unfortunately, this paper shows that the scheme is insecure and discusses the flaws in their security proof. Then the corresponding attacks are given. To overcome the flaws, an improved scheme is proposed and the result shows that the scheme is provable secure against two game attacks of certificate-based signature in the random oracle model. The security is closely related to the computational Diffie-Hellman problem.KeywordsSecurity analysisattackimproved schemethe CDH problemcertificate-based signature

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.

Recently, Boneh and Boyen proposed a new provably secure short signature scheme under the q-strong Diffie-Hellman assumption without random oracles. This scheme is based on bilinear map which is different from Cramer-Shoup signature scheme (which is based on the strong RSA assumption). However, Tan TC[17] showed that Boneh- Boyen scheme is subjected to key substitution attacks in the multi-user setting. In this paper, we propose a new signature scheme. We prove that the proposed scheme is provably secured against existential forgery under adaptive chosen message attack in the standard model and also secure against key substitution attacks.

Confidentiality and authentication are two main security goals in secure electronic mail (e-mail). Pretty good privacy (PGP) and secure/multipurpose internet mail extensions (S/MIME) are two famous secure e-mail solutions. Both PGP and S/MIME use digital envelope to provide message confidentiality and digital signature to provide message authentication. However, these methods have the following two weaknesses: 1) digital signature provides non-repudiation evidence of sender that is not desired in some e-mail applications and 2) efficiency is low, since these methods use two kinds of public key cryptographic primitives: public key encryption and digital signature. To overcome the above two weaknesses, we introduce a new concept called deniably authenticated encryption that can achieve confidentiality, integrity, and deniable authentication in a logical single step. We first propose a deniably authenticated encryption scheme and prove its security in the random oracle model. Then, we design a secure e-mail protocol using the proposed deniably authenticated encryption scheme. The deniable authentication property protects senders’ privacy.