Certificateless Proxy Re-Encryption Without Pairing: Revisited

Proxy Re-Encryption was introduced by Blaze, Bleumer and Strauss to efficiently solve the problem of delegation of decryption rights. In proxy re-encryption, a semi-honest proxy transforms a ciphertext intended for Alice to a ciphertext of the same message for Bob without learning anything about the underlying message. From its introduction, several proxy re-encryption schemes in the Public Key Infrastructure (PKI) and Identity (ID) based setting have been proposed. In practice, systems in the public key infrastructure suffer from the \textit{certificate management problem} and those in identity based setting suffer from the \textit{key escrow problem}. Certificateless Proxy Re-encryption schemes enjoy the advantages provided by ID-based constructions without suffering from the key escrow problem. In this work, we construct the \textit{first} unidirectional, single-hop CCA-secure certificateless proxy re-encryption scheme \textit{without} \textit{pairing} by extending the PKI based construction of Chow et al. proposed in 2010. We prove its security in the random oracle model under the Computational Diffie-Hellman (CDH) assumption. Prior to this work, the only secure certificateless proxy re-encryption scheme is due to Guo et al. proposed in 2013 using bilinear pairing. They proved their construction is RCCA-secure under $q$-weak Decisional Bilinear Diffie-Hellman assumption. The construction proposed in this work is more efficient than that system and its security relies on more standard assumptions. We also show that the recently proposed construction of Yang et al. is insecure with respect to the security model considered in this work

A Type-and-Identity-based Proxy Re-Encryption Scheme and its Application in Healthcare

Proxy re-encryption is a cryptographic primitive developed to delegate the decryption right from one party (the delegator) to another (the delegatee). In a proxy re-encryption scheme, the delegator assigns a key to a proxy to re-encrypt all messages encrypted with his public key such that the re-encrypted ciphertexts can be decrypted with the delegatee’s private key. We propose a type-and-identity-based proxy re-encryption scheme based on the Boneh-Franklin Identity Based Encryption (IBE) scheme. In our scheme, the delegator can categorize messages into different types and delegate the decryption right of each type to the delegatee through a proxy. Our scheme enables the delegator to provide the proxy fine-grained re-encryption capability. As an application, we propose a fine-grained Personal Health Record (PHR) disclosure scheme for healthcare service by applying the proposed scheme

Shared and searchable encrypted data for untrusted servers

Current security mechanisms are not suitable for organisations that outsource their data management to untrusted servers. Encrypting and decrypting sensitive data at the client side is the normal approach in this situation but has high communication and computation overheads if only a subset of the data is required, for example, selecting records in a database table based on a keyword search. New cryptographic schemes have been proposed that support encrypted queries over encrypted data. But they all depend on a single set of secret keys, which implies single user access or sharing keys among multiple users, with key revocation requiring costly data re-encryption. In this paper, we propose an encryption scheme where each authorised user in the system has his own keys to encrypt and decrypt data. The scheme supports keyword search which enables the server to return only the encrypted data that satisfies an encrypted query without decrypting it. We provide a concrete construction of the scheme and give formal proofs of its security. We also report on the results of our implementation

Shared and Searchable Encrypted Data for Untrusted Servers

Current security mechanisms pose a risk for organisations that outsource their data management to untrusted servers. Encrypting and decrypting sensitive data at the client side is the normal approach in this situation but has high communication and computation overheads if only a subset of the data is required, for example, selecting records in a database table based on a keyword search. New cryptographic schemes have been proposed that support encrypted queries over encrypted data but all depend on a single set of secret keys, which implies single user access or sharing keys among multiple users, with key revocation requiring costly data re-encryption. In this paper, we propose an encryption scheme where each authorised user in the system has his own keys to encrypt and decrypt data. The scheme supports keyword search which enables the server to return only the encrypted data that satisfies an encrypted query without decrypting it. We provide two constructions of the scheme giving formal proofs of their security. We also report on the results of a prototype implementation. This research was supported by the UK’s EPSRC research grant EP/C537181/1. The authors would like to thank the members of the Policy Research Group at Imperial College for their support

Cost-effective secure e-health cloud system using identity based cryptographic techniques

Nowadays E-health cloud systems are more and more widely employed. However the security of these systems needs more consideration for the sensitive health information of patients. Some protocols on how to secure the e-health cloud system have been proposed, but many of them use the traditional PKI infrastructure to implement cryptographic mechanisms, which is cumbersome for they require every user having and remembering its own public/private keys. Identity based encryption (View the MathML sourceIBE) is a cryptographic primitive which uses the identity information of the user (e.g., email address) as the public key. Hence the public key is implicitly authenticated and the certificate management is simplified. Proxy re-encryption is another cryptographic primitive which aims at transforming a ciphertext under the delegator AA into another ciphertext which can be decrypted by the delegatee BB. In this paper, we describe several identity related cryptographic techniques for securing E-health system, which include new View the MathML sourceIBE schemes, new identity based proxy re-encryption (View the MathML sourceIBPRE) schemes. We also prove these schemes’ security and give the performance analysis, the results show our View the MathML sourceIBPRE scheme is especially highly efficient for re-encryption, which can be used to achieve cost-effective cloud usage.Peer ReviewedPostprint (author's final draft

ID-based Ring Signature and Proxy Ring Signature Schemes from Bilinear Pairings

In 2001, Rivest et al. firstly introduced the concept of ring signatures. A ring signature is a simplified group signature without any manager. It protects the anonymity of a signer. The first scheme proposed by Rivest et al. was based on RSA cryptosystem and certificate based public key setting. The first ring signature scheme based on DLP was proposed by Abe, Ohkubo, and Suzuki. Their scheme is also based on the general certificate-based public key setting too. In 2002, Zhang and Kim proposed a new ID-based ring signature scheme using pairings. Later Lin and Wu proposed a more efficient ID-based ring signature scheme. Both these schemes have some inconsistency in computational aspect. In this paper we propose a new ID-based ring signature scheme and a proxy ring signature scheme. Both the schemes are more efficient than existing one. These schemes also take care of the inconsistencies in above two schemes.Comment: Published with ePrint Archiv

Controlled secure social cloud data sharing based on a novel identity based proxy re-encryption plus scheme

Currently we are witnessing a rapid integration of social networks and cloud computing, especially on storing social media contents on cloud storage due to its cheap management and easy accessing at any time and from any place. However, how to securely store and share social media contents such as pictures/videos among social groups is still a very challenging problem. In this paper, we try to tackle this problem by using a new cryptographic primitive: identity based proxy re-encryption plus (IBPRE ), which is a variant of proxy re-encryption (PRE). In PRE, by using re-encryption keys, a ciphertext computed for Alice can be transferred to a new one for Bob. Recently, the concept of PRE plus (PRE) was introduced by Wang et al. In PRE, all the algorithms are almost the same as traditional PRE, except the re-encryption keys are generated by the encrypter instead of the delegator. The message-level based fine-grained delegation property and the weak non-transferable property can be easily achieved by PRE , while traditional PRE cannot achieve them. Based on the 3-linear map, we first propose a new IBE scheme and a new IBPRE scheme, we prove the security of these schemes and give the properties and performance analysis of the new IBPRE scheme. Finally, we propose a new framework based on this new primitive for secure cloud social data sharingPeer ReviewedPostprint (author's final draft