



01828nas a2200121   4500008004100000245004800041210004700089490001000136520143200146100001901578700002201597856008701619       2017                        eng d00aQuantum Non-malleability and Authentication0 aQuantum Nonmalleability and Authentication0 v104023 a<p>In encryption, non-malleability is a highly desirable property: it ensures that adversaries cannot manipulate the plaintext by acting on the ciphertext. In [6], Ambainis et al. gave a definition of non-malleability for the encryption of quantum data. In this work, we show that this definition is too weak, as it allows adversaries to &ldquo;inject&rdquo; plaintexts of their choice into the ciphertext. We give a new definition of quantum non-malleability which resolves this problem. Our definition is expressed in terms of entropic quantities, considers stronger adversaries, and does not assume secrecy. Rather, we prove that quantum non-malleability implies secrecy; this is in stark contrast to the classical setting, where the two properties are completely independent. For unitary schemes, our notion of non-malleability is equivalent to encryption with a two-design (and hence also to the definition of [6]).</p><p>Our techniques also yield new results regarding the closely-related task of quantum authentication. We show that &ldquo;total authentication&rdquo; (a notion recently proposed by Garg et al. [18]) can be satisfied with two-designs, a significant improvement over the eight-design construction of [18]. We also show that, under a mild adaptation of the rejection procedure, both total authentication and our notion of non-malleability yield quantum authentication as defined by Dupuis et al. [16].</p>1 aAlagic, Gorjan1 aMajenz, Christian  uhttps://www.quics.umd.edu/publications/quantum-non-malleability-and-authentication