SPEAKER: Mark Zhandry TITLE: Multiparty Key Exchange, Efficient Traitor Tracing, and More from Indistinguishability Obfuscation Abstract: In this work, we show how to use indistinguishability obfuscation (iO) to build multiparty key exchange, eﬃcient broadcast encryption, and eﬃcient traitor tracing. Our schemes enjoy several interesting properties that have not been achievable before: - Our multiparty non-interactive key exchange protocol does not require a trusted setup. Moreover, the size of the published value from each user is independent of the total number of users. - Our broadcast encryption schemes support distributed setup, where users choose their own secret keys rather than be given secret keys by a trusted entity. The broadcast ciphertext size is independent of the number of users. - Our traitor tracing system is fully collusion resistant with short ciphertexts, secret keys, and public key. Ciphertext size is logarithmic in the number of users and secret key size is independent of the number of users. Our public key size is polylogarithmic in the number of users. The recent functional encryption system of Garg, Gentry, Halevi, Raykova, Sahai, and Waters also leads to a traitor tracing scheme with similar ciphertext and secret key size, but the construction in this paper is simpler and more direct. These constructions resolve an open problem relating to diﬀerential privacy. - Generalizing our traitor tracing system gives a private broadcast encryption scheme (where broadcast ciphertexts reveal minimal information about the recipient set) with optimal size ciphertext. Our proof of security for private broadcast encryption and traitor tracing introduces a new tool for iO proofs: the construction makes use of a key-homomorphic symmetric cipher which plays a crucial role in the proof of security.