Tracing Insider Attacks in the Context of Predicate Encryption Schemes

In a predicate encryption scheme an authority generates master public and secret keys, and uses the master secret key to derive personal secret keys for authorized use rs. Each user’s personal secret keySKf corresponds to apredicate f defining the access rights of that user, and each ciphertext i s associated (by the sender) with anattribute. The security provided is that a ciphertext associated with attributeI can be decrypted only using a personal secret keySKf for which f(I) = 1, i.e., for which the given access rightsf allow decryption of ciphertexts having attribute I . Predicate encryption generalizes identity-based encryption, broadcast encryption, attribute-based encryption, and more, and has been suggested as a mechanism for implementing secure information flow and distributed access control in scenarios involving multiple security domains. In this work, we introduce and study the notion of traceability for predicate encryption schemes, thus generalizing the an alogous notion that has been defined in the specific context of broadca st encryption. Traceability allows a group manager to apprehend malicious insiders who leak their personal secret keys to anadversary, or to determine which authorized users’ keys have b een compromised. In addition to defining the notion, we show how to add traceability to the most expressive predicate encryp tion scheme currently known.