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Improved Distinguisher-Based Cryptanalysis of Block Ciphers

Mirzaie, Atiyeh | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56415 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Aref, Mohammad Reza; Ahmadi, Siavash
  7. Abstract:
  8. With the continuous development of networks and communication technologies, security evaluation of cryptographic primitives, including block ciphers, which serve as the foundation for securing numerous communication protocols in these networks and technologies, has become more crucial than ever before. Inadequate security at block ciphers endures a risk to the overall security architecture of a system. Therefore, significant attention has been devoted to the development of methods for breaking and evaluating the security of block ciphers, known as cryptanalysis. In this thesis, we investigate division property-based integral cryptanalysis, which is one of the latest distinguisher-based cryptanalysis. We present ideas to improve these attacks. To do so, we first explain the concept of the division property and then introduce an automated method for searching integral distinguishers. This method starts by modeling division property propagation by a system of linear inequalities. Then by choosing an appropriate objective function, the problem of searching distinguisher transforms into a Mixed Integer Linear Programming problem. As an application of this technique, we focused on two newly proposed ciphers, SAND-64 and Shadow-32. These ciphers have been specifically designed to overcome the difficulty regarding security evaluation and data confidentiality in the Internet of Things (IoT) nodes, respectively. For SAND-64, we obtained a 12-round integral distinguisher with 23 balanced bits and a data complexity of 263 chosen plaintexts. Using this distinguisher, we presented 15 and 16-round integral attacks with time complexities of 2105 and 2109.91, and memory complexities of 252 and 285 bytes, respectively. Additionally, for Shadow-32, we found a 10-round integral distinguisher in the decryption direction with 16 balanced bits and a data complexity of 231 chosen ciphertexts. Subsequently, we extended it to 11 rounds with a novel idea, without increasing the data complexity or reducing the number of balanced bits. Finally, we proposed a 14-round attack in the decryption direction with a time complexity of 256.429 and a memory complexity of 224 bytes. Our proposed cryptanalyses demonstrate significant superiority due to attack complexity and the number of rounds compared to previous attacks
  9. Keywords:
  10. Block Cipher ; Mixed Integer Linear Programming ; Division Property ; Integral Distinguisher ; Cryptographic Protocols ; Cryptographic Algorithms Analysis

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