This paper gives the first formal exploration of plaintext awareness in the identity-based setting and, as initial work, proceeds in the random oracle model. The focus is laid mainly on identity-based key encapsulation mechanisms (IB-KEMs), for which the paper presents the first definitions of plaintext awareness, highlights the role of PA in proof strategies of INDCCA security, and explores relationships between PA and other security properties.
On the practical side, our work offers the first, highly efficient, general approach for building IB-KEMs that are simultaneously plaintext-aware and INDCCA-secure. Our construction is inspired by the Fujisaki-Okamoto (FO) transform, but demands weaker and more natural properties of its building blocks. This result comes from a new look at the notion of gamma-uniformity that was inherent in the original FO transform. We show that for IB-KEMs (and PK-KEMs) this assumption can be replaced with a weaker computational notion, which is in fact implied by one-wayness. Finally, we give the first concrete IB-KEM scheme that is PA and INDCCA-secure by applying our construction to a popular IB-KEM and optimizing it for better performance.Category / Keywords: public-key cryptography / plaintext awareness; identity-based encryption; key encapsulation mechanism Original Publication (in the same form): International Journal of Information Security