An Efficient Hierarchical Identity-Based Encryption Scheme for the Key Escrow

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

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.

Identity-based Cryptography (IBC) is an exciting alternative to public-key Cryptography (PKC), as it eliminates the need for certificate that is a major issue in PKC. However, IBC suffers from an additional limitation viz. the key escrow problem — that is — a user's private key is generated by the central trusted Key Generation Centre (KGC) — that being a single entity, lends itself to the security vulnerabilities in the cryptosystem. One of the prominent solutions proposed as Secure Key Issuing Protocol by Lee. et al. which uses a distributed protocol to generate the private key for user. However, this approach entails significant communications overhead. Hence, in this paper we have proposed an improved Identity based Secure Key Generation Protocol that gives the complete solution of key escrow problem, using clustering based approach. The proposed scheme involves less number of authorities in the computation of the public/private key pair and hence is more efficient. As we further analyze in the paper, our protocol also provides protection against the possible collusion attack in Lee's protocol. To the best of our knowledge, this is a simple, yet efficient and unique attempt to overcome the key escrow problem in IBCs.

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.

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

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.

Attribute-Based Encryption (ABE) is a promising cryptographic primitive for fine-grained sharing of encrypted data. However, ABE has a major shortcoming which is called the key escrow problem. Key generation center (KGC) can generate the secret key of a user with arbitrary set of attributes. Even worse, KGC can decrypt ciphertext directly using its master key. This could be a potential intimidation to data security and privacy. In this paper, we propose a novel ciphertext-policy ABE scheme without key escrow. In our construction, we use two authorities, KGC and OAA (outsourced attribute authority). Unless KGC colludes with OAA, neither KGC nor OAA can decrypt the ciphertext independently. Our scheme is proved to be selectively secure in the standard model. We give universal methods for transforming both KP-ABE and CP-ABE with a single authority to solve the problem of key escrow. Our scheme naturally supports outsourcing the decryption of ciphertexts.

Hierarchical Identity-Based Encryption HIBE provides an efficient solution to the security problems existed in cloud storage. However, the key escrow problem, which is an inherent problem in HIBE, primarily hinders the widespread adoption of the cryptographic scheme in practice. To address the key escrow problem, this paper introduces a provably-secure escrow-free model, which employs multiple Key Privacy Authorities KPAs to restrict the power of Public Key Generators PKGs in HIBE scheme. We instantiate the model into an escrow-free HIBE scheme that is referred to as the EF-LW-HIBE scheme, based on the HIBE scheme introduced by Lewko and Waters. Utilizing the Dual System Encryption methodology, we prove that our EF-LW-HIBE scheme is IND-ID-CCA secure.

Hierarchical identity-based encryption (HIBE) introduces the concept of hierarchical identity in identity-based encryption (IBE) which eases the burden of key generation centre. Anonymous identity-based encryption is another extension of IBE in which the ciphertext leaks no information about the target identity. In this paper, we propose a new anonymous hierarchical identity-based encryption system. Unlike previous anonymous HIBE system, our system needs no key delegation in decryption, i.e., the user can decrypt the ciphertext directly if his identity vector is the prefix of the target identity vector. So it is not necessary for the user to know the target identity vector, which enhances the practicality of anonymous HIBE systems. Our system is constructed in composite order groups and proven adaptive security and anonymity from four static assumptions by using the dual system encryption technique.

Most of the proposed E-cash systems require that the shop and customer belong to the same bank, which becomes the bottle-neck of E-cashpsilas wide application. Fangguo Zhang et al. proposed a model of electronic cash using multi-banks, but a trusted third party is needed in their system. To solve this problem, we propose a new electronic cash scheme based on group signature from bilinear pairings. In the new scheme, the shop and customer need not belong to the same bank, and a trusted third party is not needed. The identity based public key cryptosystem is used, the KGC (key generator center, or central bank) can only control partial private key of the customer, the customer known all private key of himself, so the private key escrow problem in the identity based public key cryptosystem is solved in the system. As the scheme is certificateless, the management and maintenance of the public key is much simplified.

Dependable and secure computing in medical information systems

Mobile agents are autonomous software entities that are able to migrate across different execution environments through network. Proxy signcryption is very suitable for protecting mobile agents. However, previous proposed proxy signcryption schemes mainly make use of certificate-based public key system and identity-based public key system. In this paper, we present a secure mobile agent protocol using self-certified proxy signcryption. The use of self-certified public key system has the following advantages: (i) the storage space and the communication overheads can be reduced in that the certificate is unnecessary; (ii) the computational costs can be decreased since the authenticity of public keys and the validity of proxy signcryption are carried out simultaneously in a single step; (iii) there is no key escrow problem since the system authority does not know the users' private keys. Therefore, our protocol is suitable for mobile electronic commerce (m-commerce) application in which mobile devices have limited storage capacities and computational resources.

Identity-based cryptosystems were introduced to overcome one of the main problems in public key encryption, the generation of public and private keys. In the identity-based cryptosystem, an identifier such as an e-mail address of a user can be used to generate public and private keys by a trusted third party. The trusted third party uses a system-wide master secret to provide private keys to a user. Identity-based cryptosystems can be constructed using the idea of pairings. This article discusses four different identity-based cryptosystems: the Boneh-Franklin scheme, the Cock's scheme, the Authenticated IBE scheme and the Hierarchical IBE scheme. This article also discusses the security notions considered for the identity-based cryptosystem. The security notions considered are: one-wayness, indistinguishability, semantic security and non-malleability. An architecture consisting of a public parameter server and private key generator for the implementation of the identity-based cryptosystems is also discussed.

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.

At Eurocrypt 2005, Waters presented an identity based encryption (IBE) protocol which is secure in the full model without random oracle. In this paper, we extend Waters' IBE protocol to a hierarchical IBE (HIBE) protocol which is secure in the full model without random oracle. The only previous construction in the same setting is due to Waters. Our construction improves upon Waters' HIBE by significantly reducing the number of public parameters.