Răzvan Roşie

Răzvan Roşie

RC4 is a stream cipher included in the TLS protocol, and widely used for encrypting network traffic during the last decades. Spritz is a possible candidate for replacing RC4. Spritz is based on a sponge construction and preserves the byte-oriented behaviour existing in RC4, but introduces an interface that provides encryption, hashing or MAC-generation functionalities. We present here the results obtained after applying several statistical tests on the keystreams generated by Spritz when used in the cipher mode. Our methodology makes use of 1024 keystreams of 2^25 bits. The algorithm was tested against the DieHarder test suite. None of the tests failed. Few tests produced weak results that were corrected when the number of samples increased.

Răzvan Roşie

We propose a preimage attack against cryptographic hash functions based on the speedup enabled by quantum computing. Preimage resistance is a fundamental property cryptographic hash functions must possess. The motivation behind this work relies in the lack of conventional attacks against newly introduced hash schemes such as the recently elected SHA-3 standard. The proposed algorithm consists of two parts: a classical one running in O(log |S|), where S represents the searched space, and a quantum part that contains the bulk of the Deutsch-Jozsa circuit. The mixed approach we follow makes use of the quantum parallelism concept to check the existence of an argument (preimage) for a given hash value (image) in the preestablished search space. For this purpose, we explain how a non-unitary measurement gate can be used to determine if S contains the target value. Our method is entirely theoretical and is based on the assumptions that a hash function can be implemented by a quantum computer and the key measurement gate we describe is physically realizable. Finally, we present how the algorithm finds a solution on S.