Unlike previous CCA2-secure cryptosystems that use IBE as a black box, our approach is endogenous, very simple, and compact. It makes direct use of the underlying IBE structure, and requires no cryptographic primitive other than the IBE scheme itself. This conveys several advantages. We achieve shorter ciphertext size than the best known instantiations of the other methods, and our technique is as efficient as the Boneh and Katz method (and more so than that of Canetti, Halevi, and Katz). Further, our method operates nicely on hierarchical IBE, and since it allows the validity of ciphertexts to be checked publicly, it can be used to construct systems with non-interactive threshold decryption.
In this paper we describe two main constructions: a full encryption system based on the Waters adaptive-ID secure IBE, and a KEM based on the Boneh-Boyen selective-ID secure IBE. Both systems are shown CCA2-secure in the standard model, the latter with a tight reduction. We discuss several uses and extensions of our approach, and draw comparisons with other schemes that are provably secure in the standard model.
Category / Keywords: public-key cryptography / chosen ciphertext security Publication Info: An extended abstract is to appear in ACM CCS 2005. Date: received 26 Aug 2005, last revised 7 Jun 2006 Contact author: eprint at boyen org Available formats: Postscript (PS) | Compressed Postscript (PS.GZ) | PDF | BibTeX Citation Note: Minor corrections in Table 1. Version: 20060607:202930 (All versions of this report) Discussion forum: Show discussion | Start new discussion