Organizer: Giorgia Azzurra Marson, Nina Bindel
At CRYPTO 2013, Boneh and Zhandry initiated the study of quantum-secure encryption. They proposed first indistinguishability definitions for the quantum world where the actual indistinguishability only holds for classical messages, and they provide arguments why it might be hard to achieve a stronger notion. In this work, we show that stronger notions are achievable, where the indistinguishability holds for quantum superpositions of messages. We investigate exhaustively the possibilities and subtle differences in defining such a quantum indistinguishability notion for symmetric-key encryption schemes.
We justify our stronger definition by showing its equivalence to novel quantum semantic-security notions that we introduce. Furthermore, we show that our new security definitions cannot be achieved by a large class of ciphers -- those which are quasi-preserving the message length. On the other hand, we provide a secure construction based on quantum-resistant pseudorandom permutations; this construction can be used as a generic transformation for turning a large class of encryption schemes into quantum indistinguishable and hence quantum semantically secure ones.
Tommaso Gagliardoni got his M.Sc. degree in Mathematics in 2011 at the Università degli Studi di Perugia, Italy. Since 2012 he is a member of the Cryptoplexity group led by Prof. Marc Fischlin at CASED (TU Darmstadt, Germany). His research interests focus on the connections between Cryptography and Quantum Information Processing. In particular, he studies how different models of adversarial interactions can affect the security of both classical and quantum cryptographical schemes and applications.