Proxy Re-encryption with Delegatable Verifiability
Proxy re-encryption is a public key encryption technique that allows a proxy to perform re-encryption without exposing the corresponding plaintext. As a result, proxy re-encryption has increased utility, and can be used in a number of fields including clo
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Faculty of Business and Information Technology, University of Ontario Institute of Technology, Oshawa, ON L1H 7K4, Canada [email protected] 2 School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore [email protected]
Abstract. Proxy re-encryption is a public key encryption technique that allows a proxy to perform re-encryption without exposing the corresponding plaintext. As a result, proxy re-encryption has increased utility, and can be used in a number of fields including cloud computing. In previous proxy re-encryption schemes, a proxy is assumed to follow the protocol explicitly. However, this is far from the norm, and the assumption is not always true, especially in cloud computing where public cloud is considered untrusted. In this paper, we investigate the verifiability of the re-encryption process. Specifically, we first formalize the proxy re-encryption with delegatable verifiability and its corresponding security model. Then, we propose the first proxy re-encryption scheme with delegatable verifiability. Finally, security proofs of the proposal are also formally given in the proposed security models.
Keywords: Proxy re-encryption
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· Delegatable verifability · Trust level
Introduction
Proxy re-encryption [6] is a special type of public key encryption that allows proxies with re-encryption keys to perform transformations on ciphertexts, while proxies are unable to access the corresponding plaintexts. Due to this useful property, proxy re-encryption has been found very useful, and can be applied to various scenarios where dynamic ciphertext format is required, e.g., cloud and fog computing [19,20,22]. In previous proxy re-encryption schemes, a proxy is assumed to be semi-trusted, i.e., the proxy would follow the protocol exactly, and execute the specified re-encryption steps. However, this assumption is not always true in all proxy re-encryption based applications. For instance, in a cloud storage applying proxy re-encryption [19,20,22], the cloud plays the role of the proxy in proxy re-encryption. Cloud servers, in their efforts to perform computations quickly and inexpensively, may skip on re-encryption steps, for example, in order to save computing resources for other transactions. It is therefore quite likely that c Springer International Publishing Switzerland 2016 J.K. Liu and R. Steinfeld (Eds.): ACISP 2016, Part II, LNCS 9723, pp. 120–133, 2016. DOI: 10.1007/978-3-319-40367-0 8
Proxy Re-encryption with Delegatable Verifiability
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best practices are overlooked. Obviously, proxy re-encryption, while secure with a trusted proxy following the protocol explicitly, can fall apart when the proxy is dishonest and cannot be trusted. A natural question arises “how can the users trust that the cloud performs re-encryption correctly?” To the best of our knowledge, there are no proxy re-encryption schemes explicitly dealing with the verifiability problem. In this paper, we would like to take this for the first step. In particular, we define veri
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