›› 2011, Vol. 26 ›› Issue (4): 722-731.doi: 10.1007/s11390-011-1171-2

• Information Security • Previous Articles     Next Articles

Differential Attack on Five Rounds of the SC2000 Block Cipher

Ji-Qiang Lv (吕继强)   

  1. Department of Computer Science, Ecole Normale Superieure, 45 Rue d'Ulm, Paris 75005, France
  • Received:2010-11-25 Revised:2011-05-03 Online:2011-07-05 Published:2011-07-05
  • Supported by:

    This work as well as the author was supported by the French ANR Project SAPHIR II.

The SC2000 block cipher has a 128-bit block size and a user key of 128, 192 or 256 bits, which employs a total of 6.5 rounds if a 128-bit user key is used. It is a CRYPTREC recommended e-government cipher in Japan. In this paper we address how to recover the user key from a few subkey bits of SC2000, and describe two 4.75-round differential characteristics with probability 2-126 of SC2000 and seventy-six 4.75-round differential characteristics with probability 2-127. Finally, we present a differential cryptanalysis attack on a 5-round reduced version of SC2000 when used with a 128-bit key; the attack requires 2125.68 chosen plaintexts and has a time complexity of 2125.75 5-round SC2000 encryptions. The attack does not threat the security of the full SC2000 cipher, but it suggests for the first time that the safety margin of SC2000 with a 128-bit key decreases below one and a half rounds.

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