Delegatable Functional Signatures

We introduce delegatable functional signatures (DFS) which support the delegation of signing capabilities to another party, called the evaluator, with respect to a functionality F. In a DFS, the signer of a message can choose an evaluator, specify how the evaluator can modify the signature without voiding its validity, allow additional input and decide how the evaluator can further delegate its capabilities. The main contribution of this paper is twofold. First, we propose DFS, a novel cryptographic primitive that unifies several seemingly different signature primitives, including functional signatures as defined by Boyle, Goldwasser, and Ivan (eprint 2013/401), sanitizable signatures, identity based signatures, and blind signatures. To achieve this unification, we present several definitions of unforgeability and privacy. Finding appropriate and meaningful definitions in this context is challenging due to the natural mealleability of DFS and due to the multi-party setting that ...

• Type: Journal
• Year: 2016
• Where: PKC
• Authors: Michael Backes 0001, Sebastian Meiser 0001, Dominique Schröder
• Keywords: Cryptology, PKC 2016