Traitor-Tracing From Lwe Made Simple And Attribute-Based

A traitor tracing scheme is a public key encryption scheme for which there are many secret decryption keys. Any of these keys can decrypt a ciphertext; moreover, even if a coalition of users collude, put together their decryption keys and attempt to create a new decryption key, there is an efficient algorithm to trace the new key to at least one the colluders.Recently, Goyal, Koppula and Waters (GKW, STOC 18) provided the first traitor tracing scheme from LWE with ciphertext and secret key sizes that grow polynomially in log n, where n is the number of users. The main technical building block in their construction is a strengthening of (bounded collusion secure) secret-key functional encryption which they refer to as mixed functional encryption (FE).In this work, we improve upon and extend the GKW traitor tracing scheme:- We provide simpler constructions of mixed FE schemes based on the LWE assumption. Our constructions improve upon the GKW construction in terms of expressiveness, modularity, and security.- We provide a construction of attribute-based traitor tracing for all circuits based on the LWE assumption.