Identity-based quantum signature scheme with strong security

In Identity-Based Encryption (IBE) system, the Private Key Generator (PKG) holds the master secret key and is responsible for generating private keys for the users. This incurs the key-escrow problem, i.e. the PKG can decrypt any user' any ciphertexts without any possible detection. Also, compromising the master secret key will enable an adversary to do anything to the whole system, and having the master secret key be unavailable implies that new users cannot obtain private keys from the PKG, and existing users cannot get their private keys back from the PKG when they lost them. To address the key-escrow problem and protect the master secret key as much as possible with strong security and availability, distributed PKG protocols supporting threshold policy have been adopted in some IBE schemes. In this paper, we propose a distributed PKG protocol that supports the policy to be any monotonic access structures. Also, we propose the first distributed PKG protocol that supports the dynamic changes of the PKGs and the policy, while remaining the master secret key unchanged. The two protocols do not need any third party acting as a trusted dealer to present, and the master secret key should never be generated or resided in any one single site. The protocols are applicable to a generic IBE template, which covers many existing important IBE schemes. When applied to this generic type of IBE schemes, the two distributed PKG protocols do not affect the encryption and decryption algorithms, and only each user knows his own private key.

Provably secure identity-based authenticated key agreement protocols with malicious private key generators

Blockchain systems built on classical cryptography face immediate risks from large-scale quantum computers, while purely quantum-based blockchains often rely on a single Private Key Generator (PKG) and incur heavy resource overheads. To overcome these issues, this paper proposes a hybrid quantum and post-quantum blockchain approach that removes single points of trust by using Distributed Key Generation and a dual-layer signature mechanism. This method integrates quantum digital signatures, rooted in the Fully Flipped Permutation problem, with classical post-quantum (lattice-based) cryptography, enabling users to switch between quantum and classical signatures according to security requirements and channel conditions. Delegated Proof-of-Stake with node behavior and Borda count has been incorporated to manage consensus, ensuring that witness nodes are regularly re-elected and malicious actors are penalized by distributing secret shares among multiple rotating witnesses. We eliminate the central vulnerability of a sole PKG while maintaining rigorous resistance to collusions. Our analytical model indicates that a fraction of transactions can use quantum signatures without system-wide bottlenecks, while the remaining transactions follow classical PQC paths with throughput approaching classical baselines under our modeling assumptions. Consequently, this hybrid method offers higher scalability, robust collusion resistance, and long-term security even under quantum-capable adversaries. This paper presents extensive theoretical analyses, probability models, and algorithmic complexities, demonstrating that our design provides resilient infrastructure that meets the key performance and security requirements of next-generation blockchain systems.

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.

Identity-based revocation system (IBRS) generates the ciphertext with a revoked identity list such that only the non-revoked identities can use their private keys to decrypt this ciphertext. IBRS can be efficiently applied in some practical applications, such as the pay-TV systems when the number of revoked identities are much less than the non-revoked ones. However, since IBRS is based on identity-based cryptography, it also suffers from the inherent key escrow problem where the private key generator (PKG) has full control of each user’s private key. As a consequence, it is hard to judge whether a pirated private key is generated by the PKG or the suspected user. There is no study on IBRS fulfilling accountability in literature to date. In this paper, we introduce the notion of accountable authority IBRS (A-IBRS), which provides accountability in IBRS schemes. In an A-IBRS, the aforementioned problem can be alleviated and resolved. Furthermore, a full black-box A-IBRS can distinguish the creator of a black box between the PKG and the associated user and the dishonest PKG is allowed to access the decryption results of the user private key. We formalize the definition and security models of the full black-box A-IBRS schemes. Then, we present a concrete full black-box A-IBRS scheme with constant-size master public key and private key. Finally, we prove the security of our scheme under the defined security models without random oracle.

In 1984, Shamir introduced the concept of an identity-based encryption. In this system, each user needs to visit a private key generation (PKG) and identify him- self before joining a communication network. Once a user is accepted, the PKG will provide him with a secret key. In this way, if a user wants to communicate with others, he only needs to know the ―identity‖ of his communication partner and the public key of the PKG. There is no public file required in this system. However, Shamir did not succeed in constructing an identity based encryption, but only in constructing an identity-based signature (IBS) scheme. In this paper, we propose an identity based encryption (IBE) based on the factorization problem (IFP) and double discrete logarithm problem (DDLP) and we consider the security against a conspiracy of some entities in the proposed system and show the possibility of establishing a more secure system.

The rapid development of network technology has brought new challenges to data security. As the first gateway of a certain mobile internet system, access authentication is an essential step that guarantees the internal security of the network. However, there are some problems in traditional cryptosystem-based authentication mechanisms, such as certificate management problem and centralized key escrow problem. Centralized storage of user information is restricted by the server, the security of the server is not within the user’s control, the stability of the server cannot be guaranteed, and personal privacy on the server may be leaked. In this paper, we focus on the private key escrow problem caused by the Private Key Generator (PKG) in Identity-Based Cryptosystems (IBC) mechanism and propose a Blockchain-assisted user public-private key generation scheme (BAKG) which introduces the blockchain to improve the robustness and reliability of key management. In BAKG, the user’s private key is determined by itself through combining the partial private keys from different PKGs, which prevents the risk of private key exposure caused by a single PKG. Meanwhile, based on the theory of the Combined Public Key (CPK) algorithm, we have designed a feasible blockchain-based key generation logic and developed a prototype authentication system based on the above concept. We further analyze the security of BAKG and the analytical results show that BAKG can meet various security requirements. In addition, according to the performance evaluation results, BAKG has good performance in both read/write consensus and different key length calculations, which means it has good potential for lightweight authentication applications.KeywordsBlockchainAuthenticationIdentity-Based CryptosystemsCombine public key

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.

Most anonymous Conference Key Distribution (CKD) systems cannot provide forward security, which is a very important property. Even though some CKD systems provide that property, they can only provide partial forward security, not perfect forward security. An identity-based CKD scheme with user anonymity is proposed in this paper. Under the one-way hash (OWH) [1] and bilinear Diffie-Hellman (BDH) [2] cryptographic assumptions, the proposed scheme is secure against passive attacks, impersonation attacks and conspiracy attacks. Moreover, by distributing a random number to the participants through the Private Key Generator (PKG), this scheme provides perfect forward security, that is, even if the private keys of all the participants (including the chairman) are compromised, the conference key contributed by the chairman in the past will not be compromised.

Since computer systems and communication become each time more pervasive, information security takes attention, requiring guarantees for data authentication, integrity and confidentiality. Pervasive communication and computer systems intend to provide access to information and services anytime and anywhere, demanding cryptographic systems more practical and that consider the characteristics of emerging network paradigms, such as wireless communication, device constraints and mobility. Identity-Based Cryptography (IBC) is an asymmetric key cryptographic technology that employs as user’s public key any unique information related to the identity of the user. IBC efficiently manages keying material and provides an easy way to issue a pair of keys applying user information. However, it assumes the existence of a Trusted Third Party (TTP), called Private Key Generator (PKG), which is responsible for generating the corresponding user private key. Relying on a TTP and using an identity as the base of the scheme result in different weaknesses on the system, as the inherent key escrow problem. This chapter investigates those weaknesses, and it points out the stat-of-the-art of proposed solutions to avoid them. This chapter also provides an overview of Identity-Based Encryption (IBE), Identity-Based Signature (IBS) and Identity-Based Key Agreement (IBKA), emphasizing IBE due to being an open problem for many years. This chapter concludes highlighting IBC applications and future trends.

Post-quantum secure identity-based signature achieving forward secrecy

Recently, Tseng et al. proposed a new notion for identity-based signature (IBS) scheme to resist ephemeral secret leakage (ESL) attacks, called leakage-free identity-based signature (leakage-free IBS), and devised the first secure leakage-free IBS scheme. However, they only considered the situation of the leakage of ephemeral secrets used for generating the signatures. Notice that the private key extraction procedure is probabilistic as well in their scheme, that is, there are ephemeral secrets used by the key generation center to generate the signers’ private keys. It is practical to consider that if the adversary comprises these ephemeral secrets, then he can reveal the master key of the system. Therefore, it is desired to introduce a new security notion for the leakage-free IBS schemes to consider the ESL attacks on both private key extraction and signing procedures. In this paper, we present such security notion. Moreover, we propose two IBS schemes that are proved to be secure under the new security notion.

Hierarchical Identity-Based Encryption (HIBE) is a generalization of Identity-Based Encryption (IBE) that mirrors an organizational hierarchy, however, the residual key escrow problem has still remained. This paper introduces a new scheme, based on the security notion of anonymous ciphertext indistinguishability against key generation center (ACI-KGC) security proposed by Chow, to remove the inherent key escrow problem. The scheme employs multiple Identity Certification Authorities (ICAs) which can ensure that the Private Key Generators (PKGs) distribute private key without knowing the list of user’s identity information, so as to prevent malicious PKGs from decrypting message on behalf of user or maliciously make user’s private key public. Security analysis shows that the scheme can solve the key escrow with keeping the high-efficiency and security of HIBE system. In contrast to Chen’s T-HIBE and Chow’s scheme, to generating the user’s private key, our scheme does not require the multiple KPAs or the complex interactive protocol which take too much extra computation costs. And comparing with GS-HIBE, our scheme focuses on solving the key escrow problem with outstanding performance and security of HIBE system.

The objective of the PKA encryption scheme is to complement, or replace, existing Public Key Infrastructures (PKI) [1]. In this scheme, the initialization step is based on the secure exchange of addressable cryptographic tables between the communicating parties. These tables are generated either with random numbers, or with arrays of addressable Physical Unclonable Function (PUFs). The subsequent communications between the parties can therefore occurs over untrusted channels, by exchanging dynamically generated public keys. Private keys are, generated independently with all communicating parties using their cryptographic tables, and the shared public keys. The private keys are combined with methods such as the Advanced Encryption Standard (AES) to encrypt and decrypt the communication between users. The generation of private keys is done without mathematical computations that are potentially vulnerable to quantum computers using algorithms such as the one developed by Shor [2]. PKA is fast and requires approximately 800 CPU clock cycles. We implemented, and tested the PKA dynamic key exchange scheme in legacy systems to secure PC-to-PC communication, and PC to smart card communication with AES.

Due to the limited energy of underwater wireless sensor network (UwWSN) and the need to protect node location privacy, aggregate signature (AGGS) scheme which can batch verification signature is proposed to meet these requirements. Due to moving at high speed and the limited bandwidth of communication in vehicular ad hoc network (VaNET), certificateless aggregate signature (CTLAS) with the private key being generated by the signer itself and PKG (Private Key Generator) is proposed to solve the above problems. Recently, Yang et al. proposes a CTLAS scheme which can be applied into VaNET and Hua proposes an AGGS scheme which can be applied into UwWSN. This paper shows that Yang et al.'s CTLAS scheme and Hua's AGGS scheme both are not secure. In Yang et al.'s CTLAS scheme, an attacker can forge a signature assume that the attacker cannot know the masker key of PKG but the attacker can replace the public key of the signer. In Hua's AGGS scheme, a malicious node can forge a signature for any nodes after the malicious node obtains a temporary key. As an improvement, this paper also proposes an improved method for Yang et al.'s scheme and Hua's scheme respectively.