Hierarchical Identity-Based Chameleon Hash and Its Applications

At ACNS 2008, Canard et al. introduced the notion of trapdoor sanitizable signature (TSS) based on identity-based chameleon hash (IBCH). Trapdoor sanitizable signatures allow the signer of a message to delegate, at any time, the power of sanitization to possibly several entities who can modify predetermined parts of the message and generate a new signature on the sanitized message without interacting with the original signer. In this paper, we introduce the notion of hierarchical identity-based chameleon hash (HIBCH), which is a hierarchical extension of IBCH. We show that HIBCH can be used to construct other cryptographic primitives, including hierarchical trapdoor sanitizable signature (HTSS) and key-exposure free IBCH. HTSS allows an entity who has the sanitization power for a given signed message, to further delegate its power to its descendants in a controlled manner. Finally, we propose a concrete construction of HIBCH and show that it is t-threshold collusionresistant.