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Impossible Differential Cryptanalysis of Lightweight Block Ciphers

Azimi, Arash | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46520 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Aref, Mohammad Reza; Mohajeri, Javad
  7. Abstract:
  8. Due to the ever-increasing growth of the ubiquitous computing systems such as RFID, IoT, etc. and their important security concerns specially in the domain of user’s privacy, a great attention from the cryptology community is attracted to the design and analysis of lightweight primitives. Lightweight primitives, including block ciphers, hash functions, stream ciphers, and authenticated encryption schemes, are those ones that are specifically tailored to the devices with extreme limitations in power, area and cost. It is natural that the conventional rules for designing a typical all-purpose primitive can not be used here identically, and designers have to relax the conditions of some conventional design
    rules, such as using smaller s-boxes, less complicated diffusion layers, simpler key scheduling or even eliminating it, etc. in lightweight block ciphers. Anyway, new design rules demand new external security analysis to make sure that the efficiency of this new structure is not achieved at a great expense in its security.
    One of the most popular technique to analyse the security of block ciphers is impossible differential attack which is based on the idea that some input and output differences are never compatible to each other. The attack is mainly devided into two steps. First, the attacker searches for a contradiction which occurs for a certain input and output differences, called impossible differential charachteristics. Then, he guesses some subkeys, collects some pairs of data and by partially encrypting or decrypting, sieve inappropriate pairs to have enough pairs whose differences conforms to the input and the output differences of impossible differential characteristics. Since the characteristics never happens, the guessed keys are wrong and by discarding wrong keys, the correct key can be recovered. This thesis focuses on analysing the security of lightweight block ciphers using impossible differential attack. In this thesis after a brief discussion about lightweight block ciphers, we present four impossible differential attacks which is applied to two lightweight blockciphers HIGHT and Piccolo. Using some ploys such as early abort technique, finding appropriate impossible differential characteristics and utilizing hash tables and key scheduling, we are able improve impossible differential attacks. For HIGHT, we present an impossible differential attack having least time complexity among all shortcut attacks. Moreover, we instantiate the first impossible differential attack on Piccolo lightweight block ciphers in single-key model
  9. Keywords:
  10. Impossible Differential Cryptanalysis ; Block Cipher ; Lightweight Encryption ; HIGHT Block Cipher ; Picolo Block Cipher

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