摘要：Identity based encryption ( ΙΒε ) schemes have been flourishing since the very beginning of this century. In ΙΒε , proving the security of a scheme in the sense of IND-ID-CCA2is widely believed to be sufficient to claim that the scheme is also secure in the senses of both SS-ID-CCA2 and NM-ID-CCA2. The justification for this belief is the relations among indistinguishability (IND), semantic security (SS) and non-malleability (NM). However these relations have been proved only for conventional public key encryption ( ΡΚε ) schemes in previous works. The fact is that ΙΒε and ΡΚε have a difference of special importance, i.e., only in ΙΒε can the adversaries perform a particular attack, namely, the chosen identity attack . In this paper we have shown that security proved in the sense of IND-ID-CCA2 is validly sufficient for implying security in any other sense in ΙΒε . This is to say that the security notion, IND-ID-CCA2, captures the essence of security for all ΙΒε schemes. To show this, we first formally defined the notions of security for ΙΒε , and then determined the relations among IND, SS and NM in ΙΒε , along with rigorous proofs. All of these results take the chosen identity attack into consideration.
