The advent and development of RFID tags and Wireless Sensor Networks which have less accessibility to the required sources for carrying out the computations have iired many researches to optimize these devices so that by considering the limitations, the desired efficiency can be obtained and the mounting costs of this type can be minimized. To present appropriate solutions for the security of these applications, Lightweight Cryptography, in both fields of cipher designing and cryptanalysis, has received increasing attention. In this regard, many block ciphers have been introduced, such as PRESENT, CLEFIA, and KASUMI, each of which has been considered by international organizations and researchers. Meanwhile, some block ciphers, like MIBS, have been created by compiling or lightening some parts of other ciphers. In the analysis of lightweight block ciphers, some conventional methods like Differential cryptanalysis, Impossible Differential cryptanalysis, and Biclique cryptanalysis have been used. This thesis, while further investigating the metrics of lightweight block ciphers, introduces some new and well-known lightweight block ciphers. Then some new cryptanalyses have been conducted on two lightweight block ciphers which use 80-bit key, namely, MIBS and PRESENT, using Biclique cryptanalysis. These cryptanalyses were carried out on the full round versions of these ciphers and the results obtained were found to be better than other cryptanalyses conducted so far on these two lightweight block ciphers. The attack on MIBS which uses matching without matrix method has computational complexity of 2 78.98 , data complexity of 2 52 chosen plaintexts and memory complexity of 2 17.17 bytes. The attack on PRESENT has computational complexity of 2 79.41 , data complexity of 2 22 chosen plaintexts and memory complexity of 2 17.17 bytes. Keywords 1- Lihgtweigh Block Cipher 2- Cryptanalysi 3- Biclique Cryptanalysi 4- Metrics of Lightweight Block Cipher 5- MIBS block Cipher 6- PRESENT block Ciphe 7- Security of Lightweight Block Ciphers
