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Open AccessArticle

Revocable Identity-Based Encryption and Server-Aided Revocable IBE from the Computational Diffie-Hellman Assumption

1
Department of Computer Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
2
Department of Mathematics, Hangzhou Normal University, Hangzhou 310036, China
3
Westone Cryptologic Research Center, Beijing 100070, China
4
Faculty of Information Technology, Monash University, Clayton VIC 3800, Australia
*
Author to whom correspondence should be addressed.
Part of this work was published in ACISP 2018. This is the full version.
Cryptography 2018, 2(4), 33; https://doi.org/10.3390/cryptography2040033
Received: 30 August 2018 / Revised: 11 October 2018 / Accepted: 18 October 2018 / Published: 23 October 2018
(This article belongs to the Special Issue Public Key Cryptography)
An Identity-based encryption (IBE) simplifies key management by taking users’ identities as public keys. However, how to dynamically revoke users in an IBE scheme is not a trivial problem. To solve this problem, IBE scheme with revocation (namely revocable IBE scheme) has been proposed. Apart from those lattice-based IBE, most of the existing schemes are based on decisional assumptions over pairing-groups. In this paper, we propose a revocable IBE scheme based on a weaker assumption, namely Computational Diffie-Hellman (CDH) assumption over non-pairing groups. Our revocable IBE scheme is inspired by the IBE scheme proposed by Döttling and Garg in Crypto2017. Like Döttling and Garg’s IBE scheme, the key authority maintains a complete binary tree where every user is assigned to a leaf node. To adapt such an IBE scheme to a revocable IBE, we update the nodes along the paths of the revoked users in each time slot. Upon this updating, all revoked users are forced to be equipped with new encryption keys but without decryption keys, thus they are unable to perform decryption any more. We prove that our revocable IBE is adaptive IND-ID-CPA secure in the standard model. Our scheme serves as the first revocable IBE scheme from the CDH assumption. Moreover, we extend our scheme to support Decryption Key Exposure Resistance (DKER) and also propose a server-aided revocable IBE to decrease the decryption workload of the receiver. In our schemes, the size of updating key in each time slot is only related to the number of newly revoked users in the past time slot. View Full-Text
Keywords: revocable identity-based encryption; server-aided revocable identity-based encryption; CDH assumption revocable identity-based encryption; server-aided revocable identity-based encryption; CDH assumption
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Hu, Z.; Liu, S.; Chen, K.; Liu, J.K. Revocable Identity-Based Encryption and Server-Aided Revocable IBE from the Computational Diffie-Hellman Assumption. Cryptography 2018, 2, 33.

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