No abstract

No abstract

No abstract

Abstract.A group encryption scheme allows anyone to form a ciphertext for a given group member while keeping the receiver's identity private. At the same time, the encryptor is capable of proving that some (anonymous) group member is able to decrypt the ciphertext and, optionally, that the corresponding plaintext satisfies some a priori relation (to prevent sending bogus messages). Finally, in case of a dispute, the identity of the intended receiver can be recovered by a designated authority. In this paper, we abstract a generic approach to construct group encryption schemes. We also introduce several new implementation tricks. As a result, we obtain group encryption schemes that significantly improve the state of the art. Both interactive and non-interactive constructions are considered.

Digital content, protected by specific terms of use, is currently delivered to customers via a few selected content providers. Allowing arbitrary entities, not just trusted content providers, to resell legitimately purchased, protected digital content to another entity, adds additional challenges to a DRM environment. In this paper, we formally model the problem of reselling digital content, and we provide a secure construction based on one-time (proxy) signatures. Our construction allows an arbitrary seller to resell its digital content to any buyer. We ensure that the identity of the buyer is only known to the seller. The buyer can verify that the purchased content is genuine. After the transaction is completed only the legitimate current owner can use the digital content. Any illegal use can be identified by a trusted authority.