Siamak Fayyaz Shahandashti
Attribute-Based Encryption with Key Cloning Protection
In this work, we consider the problem of key cloning in attribute-based encryption schemes. We introduce a new type of attribute-based encryption scheme, called token-based attribute-based encryption, that provides strong deterrence for key cloning, in the sense that delegation of keys reveals some personal information about the user. We formalize the security requirements for such a scheme in terms of indistinguishability of the ciphertexts and two new security requirements which we call uncloneability and privacy-preserving. We construct a privacy-preserving uncloneable token-based attribute-based encryption scheme based on Cheung and Newport's ciphertext-policy attribute-based encryption scheme and prove the scheme satisfies the above three security requirements. We discuss our results and show directions for future research.
Construction of Universal Designated-Verifier Signatures and Identity-Based Signatures from Standard Signatures
We give a generic construction of universal designated-verifier signature schemes from a large class C of signature schemes. Our constructions are comparable in terms of cost and size to their counterparts, while offering the following two main attractive features: Firstly, our constructions are provably non-delegatable beside being DV-unforgeable and non-transferable. Secondly, in our constructions, the signer and the designated verifier can choose different cryptographic settings of their own independently. We also propose a generic construction of identity-based signature schemes from any signature scheme in C and prove the construction secure against adaptive chosen message and identity attacks. We discuss possible extensions of our constructions to universal multi-designated-verifier signatures, hierarchical identity-based signatures, identity-based universal designated verifier signatures, and identity-based ring signatures from any signature in C.