A new security relation between information rate and state size of a keystream generator

Abstract

Bogazi˘ci University, Electrical-Electronics Engineering Dept., 34342 Bebek, Istanbul, Turkeyanarim@boun.edu.trAbstract. Wireless communication in near eld applications has been becoming widespread.Most of the devices such as sensor networks or RFID applications are operated in constraintenvironments and some of these prevalent technologies require security applications. As oneconclusion, design and analysis of lightweight cryptographic algorithms has been one of thefavorite research subjects for last decade. We have seen that mostly lightweight block ciphershave been designed as symmetric encryption algorithms. The main reason is that stream ci-phers are supposed to have large internal states due to the strict requirement related to theirresistance against Tradeo attacks (Time-Memory-Data tradeo : TMDT). In this work, weintroduce a new stream cipher encryption mode by making use of error correcting codes,constituting a new tradeo between information rate of the employed code and the internalstate size of the keystream generator. This tradeo enables us of decreasing the state sizewithout sacri cing the security against TMDT attacks.The classical stream cipher encryption relies on deterministic keystream generation both attransmission and at receiver sides. On the other hand, we propose a noisy and nondeter-ministic keystream production, which we call the Noisy Keystream Encryption (NKE). Thereceiver does not need the noise sequence to decrypt the ciphertext. However, it is a di-cult problem for an attacker to recover the keystream sequence under the known plaintext