A series of encryption algorithms called A5 is used to secure mobile telephone communications, producing a pseudo-random sequence that will be exclusive OR (XORed) with the data flowing in the air interface in order to secure them. These algorithms are essentially composed of shift registers with linear feedback, controlled generally by a function or with another register in order to favor the randomness character of the keystream generated. Evolutionary algorithms are bioinspired calculation methods, whose principle is inspired by the theory of evolution, which consists in evolving a set of solutions to a problem given in order to find better results. This paper presents an improvement of the A5/1 algorithm by an evolutionary approach based on the use of particle swarm optimization algorithm (PSO) in order to limit some weaknesses and drawbacks found in the conventional A5/1 version, which have been cryptanalysed and several attacks have been published such as time memory trade off attacks and guess and determine attacks. Our technique does not alter the A5/1's architecture, but it does help to improve its shifting system by an evolutionary approach, which guarantees the quality of the keystream generated and makes it more complex and more secure.

Mobile phones are the most common communication devices in history. For this reason, the number of mobile subscribers will increase dramatically in the future. Therefore, the determining the location of a mobile station will become more and more difficult. The mobile station must be authenticated to inform the network of its current location even when the user switches it on or when its location is changed. The most basic weakness in the GSM authentication protocol is the unilateral authentication process where the customer is verified by the system, yet the system is not confirmed by the customer. This creates numerous security issues, including powerlessness against man-in-the-middle attacks, vast bandwidth consumption between VLR and HLR, storage space overhead in VLR, and computation costs in VLR and HLR. In this paper, we propose a secure authentication mechanism based new mobility management method to improve the location management in the GSM network, which suffers from a lot off drawbacks, such as transmission cost and database overload. Numerical analysis is done for both conventional and modified versions and compared together. The numerical results show that our protocol scheme is more secure and that it reduces mobility management costs the most in the GSM network.

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