On Design of Robust Lightweight Stream Cipher with Short Internal State

The stream cipher Sprout with a short internal state was proposed in FSE 2015. Although the construction guaranteed resistance to generic Time Memory Data Tradeoff attacks, there were some weaknesses in the design and the cipherwas completely broken. In this paperwe propose a family of stream ciphers LILLE in which the size of the internal state is half the size of the secret key. Our main goal is to develop robust lightweight stream cipher. To achieve it, our cipher based on the two-key EvenMansour construction and thus its security against key/state recovery attacks reduces to a well analyzed problem. We also prove that like Sprout, the construction is resistant to generic Time Memory Data Tradeoff attacks. Unlike Sprout, the construction of the cipher guarantees that there are no weak key-IV pairs which produce a keystream sequence with short period or which make the algebraic structure of the cipher weaker and easy to cryptanalyze. The reference implementations of all members of the LILLE family with standard cell libraries based on the STM 90nm and 65 nm processes were also found to be smaller thanGrain v1while security of LILLE family depend on reliable problem in the symmetric cryptography. key words: Even-Mansour, lightweight, stream cipher, short internal state, TMD tradeoff.