Research On Attack Methods Of DSC Encryption Algorithm

The Digital Enhanced Cordless Telecommunications System?DECT?is the European Telecommunications Standards Institute?ETSI?standard for short-range cordless communications,which is widely used in residential and enterprise fields.DECT uses the cryptographic algorithms DSC for encryption to protect the confidentiality of communication.DSC cryptographic algorithm has the ability to guarantee the privacy of many enterprises and individuals in voice communication.At the CHES 2015 conference,Coisel and Sanchez proposed an improved cryptanalysis of DSC,which is the most effective attack against the DSC cryptographic algorithm up to now.Based on the CS attack,we present an improved attack.And after simplifying the posterior probability decision formula,a new attack is given.The main results obtained in this paper are as follows:1.Improved the CS attack against DSC cryptographic algorithm.By studying the nonlinear output in DSC,an information collection method with unknown memory is used to increases the utilization of information at the lowest round.Then,by using the information not considered of weight calculation in the CS attack,a new calculation formula of weight is proposed.At the same time,two technologies are used to improve the efficiency and reduce the time complexity of the attack.We present an improved pre-sieving technique to avoid the computation of evaluation indexes of a large number of incorrect secret keys,and use message classification technique to reduce the calculation time of evaluation indexes.When the time complexity of attack is the same as that of CS attack,the improved attack can achieve the same success probability of retrieving secret key by only 75%of keystreams used in the CS attack.Furthermore,by analyzing 2¹³ keystreams,the improved attack is able to increase the success probability of retrieving secret key from 55%to 90%.2.A new attack method for the DSC cryptographic algorithm is given.The candidate is a 3n bits state that are the linearly combinations of secret key.The posterior probability decision is used to give the decision formula of the correct state of the candidate,which is difficult to implement due to the large time complexity of the attack.For the feasibility of the attack,we make a compromise between correct rate and time complexity.The posteriori probability formula is simplified to reduce the time complexity.Based on this,two feasible evaluation indexes are constructed,which is used as basis of judgment.Thus,two new attack methods are put forward.Furthermore,we verify the feasibility of the two new methods through the experiments,and we compare the attack effects of the two new methods.The experimental results show that the attack effects of the two new methods are better than the existing methods.Although the attack effects of the two new methods are similar,one of them performs better than another on time complexity and memory complexity.When the time complexity of attack is the same as that of CS attack,the new method,which has less time complexity and memory complexity,can achieve the same success probability of retrieving secret key by only 61%of keystreams used in the CS attack.By analyzing 2¹³ keystreams,the new attack is able to recover the secret key with a success rate of 95%.The new method is the most effective one among the existing attacks to the DSC cipher.