Quite surprisingly, we show that existing security definitions for IBE are not sufficient to realize DCC. In fact, it is impossible to do so in the standard model. We show, however, how to adjust any IBE scheme that satisfies the standard security definition IND-ID-CPA to achieve this goal in the random oracle model.
We also show that the impossibility result can be avoided in the standard model by considering a weaker ideal system that requires all users to be registered in an initial phase before any messages are sent. To achieve this, a weaker security notion, which we introduce and call IND-ID1-CPA, is actually sufficient. This justifies our new security definition and might open the door for more efficient schemes. We further investigate which ideal systems can be realized with schemes satisfying the standard notion and variants of selective security.
As a contribution of independent interest, we show how to model features of an ideal system that are potentially available to dishonest parties but not guaranteed, and which such features arise when using IBE.Category / Keywords: public-key cryptography / identity-based encryption, definitions, impossibility results, composability Original Publication (with major differences): IACR-ASIACRYPT-2015 Date: received 6 Sep 2015 Contact author: christian matt at inf ethz ch Available format(s): PDF | BibTeX Citation Version: 20150908:060224 (All versions of this report) Short URL: ia.cr/2015/862 Discussion forum: Show discussion | Start new discussion