Paper 2015/1254

Identity-based Hierarchical Key-insulated Encryption without Random Oracles

Yohei Watanabe and Junji Shikata


Key-insulated encryption is one of the effective solutions to a key exposure problem. At Asiacrypt'05, Hanaoka et al. proposed an identity-based hierarchical key-insulated encryption (hierarchical IKE) scheme. Although their scheme is secure in the random oracle model, it has a ``hierarchical key-updating structure,'' which is attractive functionality that enhances key exposure resistance. In this paper, we first propose the hierarchical IKE scheme without random oracles. Our hierarchical IKE scheme is secure under the symmetric external Diffie-Hellman (SXDH) assumption, which is known as the simple and static one. Particularly, in the non-hierarchical case, our construction is the first IKE scheme that achieves constant-size parameters including public parameters, secret keys, and ciphertexts. Furthermore, we also propose the first public-key-based key-insulated encryption (PK-KIE) in the hierarchical setting by using our technique.

Note: Modified constructions and security proofs due to bugs in the proofs.

Available format(s)
Public-key cryptography
Publication info
A minor revision of an IACR publication in PKC 2016
Key-insulated encryptionHierarchical identity-based encryptionAsymmetric pairing
Contact author(s)
watanabe @ uec ac jp
2017-01-05: last of 4 revisions
2016-01-02: received
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      author = {Yohei Watanabe and Junji Shikata},
      title = {Identity-based Hierarchical Key-insulated Encryption without Random Oracles},
      howpublished = {Cryptology ePrint Archive, Paper 2015/1254},
      year = {2015},
      note = {\url{}},
      url = {}
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