Detecting And Mitigating Selfish Secondary Users In Cognitive Radio

In this technology world due to the rapid growth of wireless techniques there leads to the shortage of spectrum. Dynamic spectrum access tends to be the suitable solution to overcome the spectrum scarcity issue and this is achieved through cognitive radio. Searching for the free spectrum or spectrum holes is the major job of any cognitive radio. This is known as spectrum sensing. Once the spectrum hole is available the cognitive radio can transmit the information to its intended receiver utilizing the free spectrum. In the cognitive radio environment, there are some malicious users also known as selfish users. This malicious user wishes to access the spectrum on its own and thus cause blockage to the cognitive users also called as secondary users from accessing the spectrum. This attack is known as Primary User Emulation Attack(PUEA) and it is considered as one of the important attacks in the physical layer of the cognitive radio. Primary user emulation attack leads to inefficient dynamic spectrum access by the cognitive radio. Hence this chapter focuses on mitigating primary user emulation attack (PUEA) effectively through authentication tag. Threat free environment paves way to utilize the spectrum holes in an efficient manner. The information about the spectrum holes is accepted by the cognitive radio only if it is appended with the authentication tag. The information about the usage of the spectrum and the authentication tag is sent to the cognitive radio by a third party who has a good relationship with cognitive radio. It is a trusty worthy node. The trust worthy node may get some benefit or may not get any benefit from the cognitive radio in future. It is assumed that still the trustworthy node is ready to help the cognitive radio. The authentication tag helps the cognitive radio in making a correction decision to occupy the spectrum. The strength of the authentication tag decides the robustness of the scheme. To enhance the robustness of the tag generated, a double layer authentication tag generation method has been proposed. Initially Sanskrit sutra named YRBS has been used to generate the seed value for Hash function. The output obtained using Hash algorithm is now fed as input to Rijndael algorithm. After several rounds of processing and permutations the double layered authentication tag is generated. By doing so the randomness of the tag has been improved when compared to the single stage. Higher the randomness of the tag generated greater is the time it can withstand Brute force attack. The tag so generated is combined with the spectrum free information and transmitted by the trust worthy node. Only the intended cognitive radio can decode the data. The other cognitive radio including the malicious node can receiver the information. But they cannot decode the data because the key to decode the data is known only to the trustworthy node and the intended cognitive radio. It is assumed that the key has been already exchanged between them in a secure manner. In this way the primary user emulation attack is mitigated. NIST statistical test suite is one of the important test suite to prove the randomness of the tag. Hence in this chapter to prove the randomness of the authentication tag it is validated through NIST test.