Cryptology ePrint Archive: Report 2015/123

Identity-based encryption with (almost) tight security in the multi-instance, multi-ciphertext setting

Dennis Hofheinz and Jessica Koch and Christoph Striecks

Abstract: We construct an identity-based encryption (IBE) scheme that is tightly secure in a very strong sense. Specifically, we consider a setting with many instances of the scheme and many encryptions per instance. In this setting, we reduce the security of our scheme to a variant of a simple assumption used for a similar purpose by Chen and Wee (Crypto 2013). The security loss of our reduction is O(k) (where k is the security parameter). Our scheme is the first IBE scheme to achieve this strong flavor of tightness under a simple assumption.

Technically, our scheme is a variation of the IBE scheme by Chen and Wee. However, in order to “lift” their results to the multi-instance, multi-ciphertext case, we need to develop new ideas. In particular, while we build on (and extend) their high-level proof strategy, we deviate significantly in the low-level proof steps.

Category / Keywords: public-key cryptography / identity-based encryption; tight security; bilinear maps

Original Publication (with minor differences): IACR-PKC-2015

Date: received 17 Feb 2015, last revised 24 Feb 2015

Contact author: Christoph Striecks at kit edu

Available format(s): PDF | BibTeX Citation

Version: 20150226:120302 (All versions of this report)

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