Cryptology ePrint Archive: Report 2019/058

Tightly secure hierarchical identity-based encryption

Roman Langrehr and Jiaxin Pan

Abstract: We construct the first tightly secure hierarchical identity-based encryption (HIBE) scheme based on standard assumptions, which solves an open problem from Blazy, Kiltz, and Pan (CRYPTO 2014). At the core of our constructions is a novel randomization technique that enables us to randomize user secret keys for identities with flexible length.

The security reductions of previous HIBEs lose at least a factor of Q, which is the number of user secret key queries. Different to that, the security loss of our schemes is only dependent on the security parameter. Our schemes are adaptively secure based on the Matrix Diffie-Hellman assumption, which is a generalization of standard Diffie-Hellman assumptions such as k-Linear. We have two tightly secure constructions, one with constant ciphertext size, and the other with tighter security at the cost of linear ciphertext size. Among other things, our schemes imply the first tightly secure identity-based signature scheme by a variant of the Naor transformation.

Category / Keywords: public-key cryptography / hierarchical identity-based encryption, tight security, affine message authentication codes

Original Publication (with major differences): IACR-PKC-2019

Date: received 18 Jan 2019, last revised 27 Feb 2020

Contact author: roman langrehr at inf ethz ch, jiaxin pan at ntnu no

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Version: 20200227:210621 (All versions of this report)

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