Generalized key delegation for hierarchical identity-based encryption
Michel Abdalla, Eike Kiltz and Gregory
Neven. IET Information Security 2(3), pages 67-78, 2008. Preliminary
version appeared in 12th European Symposium on Research in Computer
Security - ESORICS 2007, volume 4734 of Lecture Notes in Computer
Science, pages 139-154. Springer-Verlag, 2007.
Abstract: In this paper, we introduce a new primitive called identity-based encryption with wildcard key derivation (WKD-IBE, or “wicked IBE”) that enhances the concept of hierarchical identity-based encryption (HIBE) by allowing more general key delegation patterns. A secret key is derived for a vector of identity strings, where entries can be left blank using a wildcard. This key can then be used to derive keys for any pattern that replaces wildcards with concrete identity strings. For example, one may want to allow the university’s head system administrator to derive secret keys (and hence the ability to decrypt) for all departmental sysadmin email addresses sysadmin@*.univ.edu, where * is a wildcard that can be replaced with any string. We provide appropriate security notions and provably secure instantiations with different tradeoffs in terms of ciphertext size and efficiency. We also present a generic construction of identity-based broadcast encryption (IBBE) from any WKD-IBE scheme. One of our instantiation yields an IBBE scheme with constant ciphertext size.