Flexible Redactable Signature Schemes for Trees - Extended Security Model and Construction

At ISPEC ’12, Samelin et al. show that the redactable signature scheme introduced at VLDB ’08 by Kundu and Bertino does not always preserve the structural integrity of the tree signed. In particular, they show how redaction of non-leaves promotes descendants and allows a third party to add new edges to the signed tree. This alters the semantic meaning of the tree and is not acceptable in certain scenarios. We generalize the model, such that it offers the signer the flexibility to sign trees where every node is transparently redactable. This includes intermediates nodes, i.e, to allow redacting a hierarchy, but also the tree’s root. We present a provably secure construction, where this possibility is given, while remaining under explicit control of the signer. Our security model is as strong as Brzuska et al.’s introduced at ACNS ’10. We have implemented our secure construction and present a detailed performance analysis.