Identity-Based Proxy Cryptosystems with Revocability and Hierarchical Confidentialities

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  • WANG Lihua
    Network Security Research Institute, National Institute of Information and Communications Technology
  • WANG Licheng
    State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications
  • MAMBO Masahiro
    Faculty of Electrical and Computer Engineering, Institute of Science and Engineering, Kanazawa University
  • OKAMOTO Eiji
    Graduate School of Systems and Information Engineering, University of Tsukuba

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Abstract

Proxy cryptosystems are classified into proxy decryption systems and proxy re-encryption systems on the basis of a proxy's role. In this paper, we propose an ID-based proxy cryptosystem with revocability and hierarchical confidentialities. In our scheme, on receiving a ciphertext, the proxy has the rights to perform the following three tasks according to the message confidentiality levels of the sender's intention: (1) to decrypt the ciphertext on behalf of the original decryptor; (2) to re-encrypt the ciphertext such that another user who is designated by the original decryptor can learn the message; (3) to do nothing except for forwarding the ciphertext to the original decryptor. Our scheme supports revocability in the sense that it allows proxy's decryption and re-encryption rights to be revoked even during the valid period of the proxy key without changing the original decryptor's public information. We prove that our proposal is indistinguishable against chosen identity and plaintext attacks in the standard model. We also show how to convert it into a system against chosen identity and ciphertext attacks by using the Fujisaki-Okamoto transformation.

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