First, we present a new definition of security that we call semi-static security and show a generic ``two-key" transformation from semi-statically secure systems to adaptively secure ones that have comparable-sized ciphertexts. Using bilinear maps, we then construct broadcast encryption systems that are semi-statically secure in the standard model and have constant size ciphertexts. Our semi-static constructions work when the number of indices or identifiers in the system is polynomial in the security parameter.
For identity-based broadcast encryption, where the number of potential indices or identifiers may be exponential, we present the first adaptively secure system with sublinear ciphertexts. We prove security in the standard model.
Category / Keywords: Date: received 11 Jun 2008, last revised 23 Jun 2008 Contact author: bwaters at csl sri com Available format(s): PDF | BibTeX Citation Version: 20080623:213441 (All versions of this report) Short URL: ia.cr/2008/268 Discussion forum: Show discussion | Start new discussion