Improved Impossible Differential Attack on Reduced-Round LBlock

LBlock is a 32-round lightweight block cipher with a 64-bit block size and an 80-bit key. This paper presents a new impossible differential attack on LBlock by improving the previous best result for 1 more round. Based on the nibble conditions, detailed differential properties of LBlock S-Boxes and thorough exploration of subkey relations, we set up well precomputation tables to collect the data needed and propose an optimal key-guessing arrangement to effectively reduce the time complexity of the attack. With these techniques, we launch an impossible differential attack on 24-round LBlock. To the best of our knowledge, this attack is currently the best in terms of the number of rounds attacked (except for biclique attacks).

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