An Improvement of the CS Attack to DSC Cipher

Abstract

Abstract The DECT standard cipher (DSC) is a 64-bit stream cipher, which was used in the digital enhanced cordless telecommunications (DECT) standard to protect the privacy of users. The Coisel–Sanchez (CS) attack proposed by Coisel and Sanchez in CHES 2015 is the most effective cryptanalysis against the DSC cipher up to now. Based on the CS attack, we present an improved attack in which an information collection method with unknown memory is used to improve the utilization of information and the message classification technique is adopted to reduce the computation time of evaluation indexes. Meanwhile, we present an improved pre-sieving technique to avoid the computation of evaluation indexes of a large number of incorrect candidates. Our known plaintext attack requires only 2 min of communication compared to 3 min for the CS attack. By analyzing 213 keystreams, our approach is able to increase the success probability of retrieving secret key from 55–89%. As far as we know, the attack we present in this paper is the most effective one among the existing attacks to the DSC cipher.