Highly Controlled, Fine-grained Delegation of Signing Capabilities
Michael Backes, Sebastian Meiser, Dominique Schröder · 2013
Delegation of signing rights is a central problem in security. Whereas delegating by giving power of attorney is well studied and digitally realized via delegatable anonymous credentials, directly delegating signing possibilities without the need for an external logic, can be done via malleable signature schemes. However, the existing schemes do not allow for privacy preserving, fine-grained malleability and they do not allow for a controlled way of further delegating the malleability. We bridge this gap by introducing delegatable functional signatures (DFS). We present the first construction of a DFS scheme. This construction is based on standard cryptographic primitives and shows that our strong unforgeability and privacy notions are achievable for arbitrary efficiently computable forms of malleability and delegatability. 1