An identity-based key infrastructure suitable for messaging applications

Abstract—Identity-based encryption (IBE) systems are relatively recently proposed; yet they are highly popular for messaging applications since they offer new features such as certificateless infrastructure and anonymous communication. In this paper, we intended to propose an IBE infrastructure for messaging applications. The proposed infrastructure requires one registration authority and at least one public key generator and they secret share the master secret key. In addition, the PKG also shares the same master secret with each user in the system in a different way. Therefore, the PKG will never be able to learn the private keys of users under non-collusion assumption. We discuss different aspects of the proposed infrastructure such as security, key revocation, uniqueness of the identities that constitute the main drawbacks of other IBE schemes. We demonstrate that our infrastructure solves many of these drawbacks under certain assumptions

Exclusion-intersection encryption

Identity-based encryption (IBE) has shown to be a useful cryptographic scheme enabling secure yet flexible role-based access control. We propose a new variant of IBE named as exclusion-intersection encryption: during encryption, the sender can specify the targeted groups that are legitimate and interested in reading the documents; there exists a trusted key generation centre generating the intersection private decryption keys on request. This special private key can only be used to decrypt the ciphertext which is of all the specified groups' interests, its holders are excluded from decrypting when the documents are not targeted to all these groups (e.g., the ciphertext of only a single group's interest). While recent advances in cryptographic techniques (e.g., attribute-based encryption or wicked IBE) can support a more general access control policy, the private key size may be as long as the number of attributes or identifiers that can be specified in a ciphertext, which is undesirable, especially when each user may receive a number of such keys for different decryption power. One of the applications of our notion is to support an ad-hoc joint project of two or more groups which needs extra helpers that are not from any particular group. © 2011 IEEE.published_or_final_versionThe 1st IEEE International Workshop on Security in Computers, Networking and Communications (SCNC 2011) in conjuntion with IEEE INFOCOM 2011, Shanghai, China, 10-15 April 2011. In Conference Proceedings of INFOCOM WKSHPS, 2011, p. 1048-1053The 1st IEEE International Workshop on Security in Computers, Networking and Communications (SCNC 2011) in conjuntion with IEEE INFOCOM 2011, Shanghai, China, 10-15 April 2011. In Conference Proceedings of INFOCOM WKSHPS, 2011, p. 1048-105

A modified identity-based encryption system for messaging applications

Identity-based encryption (IBE) systems are relatively recently proposed; yet they are highly popular for messaging applications since they offer new features such as certificateless infrastructure and anonymous communication. However, recent studies also reveal that the infrastructure needed for IBE systems may be as complicated as the conventional public key cryptosytems and not sufficient research has been conducted in relevant issues concerning the infrastructure. Firstly, there is the issue of the existence of the Private Key Generator (PKG) as a full-trusted third party. Since PKG generates and knows users’ private keys; the user privacy has not been fully achieved. This issue leads to non-repudiation problem where PKG can not only decrypt messages but also can fabricate a valid signature on behalf of any registered user. Secondly, the key-revocation leads tremendous calculations for PKG. In the case of a key-lost, finding a descriptive identity for a user may be difficult. Thus, a new master secret key is generated resulting in changing private keys of every user registered in the system. With this thesis, a new modified IBE infrastructure is proposed to overcome the stated problems. The master key is secretly shared by two parties, Registration Authority (RA) and Private Key Generator (PKG). In addition, PKG shares the master key with every registered user. With this approach, PKG will not be able to acquire the master key provided that there will be no collusion between the parties, RA-PKG and PKG-users

Towards Secure Identity-Based Cryptosystems for Cloud Computing

The convenience provided by cloud computing has led to an increasing trend of many business organizations, government agencies and individual customers to migrate their services and data into cloud environments. However, once clients’ data is migrated to the cloud, the overall security control will be immediately shifted from data owners to the hands of service providers. When data owners decide to use the cloud environment, they rely entirely on third parties to make decisions about their data and, therefore, the main challenge is how to guarantee that the data is accessible by data owners and authorized users only. Remote user authentication to cloud services is traditionally achieved using a combination of ID cards and passwords/PINs while public key infrastructure and symmetric key encryptions are still the most common techniques for enforcing data security despite the missing link between the identity of data owners and the cryptographic keys. Furthermore, the key management in terms of the generation, distribution, and storage are still open challenges to traditional public-key systems. Identity-Based Cryptosystems (IBCs) are new generations of public key encryptions that can potentially solve the problems associated with key distribution in public key infrastructure in addition to providing a clear link between encryption keys and the identities of data owners. In IBCs, the need for pre-distributed keys before any encryption/decryption will be illuminated, which gives a great deal of flexibility required in an environment such as the cloud. Fuzzy identity-based cryptosystems are promising extensions of IBCs that rely on biometric modalities in generating the encryption and decryption keys instead of traditional identities such as email addresses. This thesis argues that the adoption of fuzzy identity-based cryptosystems seems an ideal option to secure cloud computing after addressing a number of vulnerabilities related to user verification, key generation, and key validation stages. The thesis is mainly concerned with enhancing the security and the privacy of fuzzy identity-based cryptosystems by proposing a framework with multiple security layers. The main contributions of the thesis can be summarised as follows. 1. Improving user verification based on using a Challenge-Response Multifactor Biometric Authentication (CR-MFBA) in fuzzy identity-based cryptosystems that reduce the impacts of impersonators attacks. 2. Reducing the dominance of the “trusted authority” in traditional fuzzy identity-based cryptosystems by making the process of generating the decryption keys a cooperative process between the trusted authority server and data owners. This leads to shifting control over the stored encrypted data from the trusted authority to the data owners. 3. Proposing a key-validity method that relies on employing the Shamir Secret Sharing, which also contributes to giving data owners more control over their data. 4. Further improving the control of data owners in fuzzy identity-based cryptosystems by linking the decryption keys parameters with their biometric modalities. 5. Proposing a new asymmetric key exchange protocol based on utilizing the scheme of fuzzy identity-based cryptosystems to shared encrypted data stored on cloud computing