Cryptology ePrint Archive: Report 2007/221

Generalized Key Delegation for Hierarchical Identity-Based Encryption

Michel Abdalla and Eike Kiltz and Gregory Neven

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@*, 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.

Category / Keywords: public-key cryptography / Hierarchical identity-based encryption, key delegation, broadcast encryption.

Publication Info: A preliminary version of this paper appears in the proceedings of ESORICS 2007. This is the full version.

Date: received 7 Jun 2007, last revised 9 Jun 2007

Contact author: kiltz at cwi nl

Available format(s): Postscript (PS) | Compressed Postscript (PS.GZ) | PDF | BibTeX Citation

Version: 20070609:095056 (All versions of this report)

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