Paper 2016/926 Original: eprint.iacr.org/2016/926 ↗

LIZARD - A Lightweight Stream Cipher for Power-constrained Devices

Abstract

Time-memory-data (TMD) tradeoff attacks limit the security level of many classical stream ciphers (like $E_0$, A5/1, Trivium, Grain) to $\frac{1}{2}n$, 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 $\frac{2}{3}n$-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 $2^{18}$ keystream bits per key/IV pair, which would be sufficient for many existing communication scenarios like Bluetooth, WLAN or HTTPS.