Model design for a reduced variant of a trivium type stream cipher

We analyze the family of stream ciphers N-viums: Trivium and Bivium. We present the Trivium algorithm and its variants. In particular, we study the NLFSRs used in these generators, their feedback functions and their combination. Two reduced variants of these models are presented, labeled Toys. Finally, we delve into the open problems ingrained in these cryptosystems.WSI - II Workshop de seguridad informáticaRed de Universidades con Carreras en Informática (RedUNCI

Scalable method of searching for full-period Nonlinear Feedback Shift Registers with GPGPU. New List of Maximum Period NLFSRs.

This paper addresses the problem of efficient searching for Nonlinear Feedback Shift Registers (NLFSRs) with a guaranteed full period. The maximum possible period for an $n$-bit NLFSR is $2^n-1$ (all-zero state is omitted). %but omitting all-0 state makes the period $2^n-1$ in their longest cycle of states. A multi-stages hybrid algorithm which utilizes Graphics Processor Units (GPU) power was developed for processing data-parallel throughput computation.Usage of abovementioned algorithm allows to give an extended list of n-bit NLFSR with maximum period for 7 cryptographically applicable types of feedback functions

LIZARD – A Lightweight Stream Cipher for Power-constrained Devices

Time-memory-data (TMD) tradeoff attacks limit the security level of many classical stream ciphers (like E0, A5/1, Trivium, Grain) to 1/2n, where n denotes the inner state length of the underlying keystream generator. In this paper, we present Lizard, a lightweight stream cipher for power-constrained devices like passive RFID tags. Its hardware efficiency results from combining a Grain-like design with the FP(1)-mode, a recently suggested construction principle for the state initialization of stream ciphers, which offers provable 2/3n-security against TMD tradeoff attacks aiming at key recovery. Lizard uses 120-bit keys, 64-bit IVs and has an inner state length of 121 bit. It is supposed to provide 80-bit security against key recovery attacks. Lizard allows to generate up to 218 keystream bits per key/IV pair, which would be sufficient for many existing communication scenarios like Bluetooth, WLAN or HTTPS