International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Two-Round AES Differentials

Joan Daemen
Vincent Rijmen
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Abstract: In this paper we study the probability of differentials and characteristics over 2 rounds of the AES with the objective to understand how the components of the AES round transformation interact. We extend and correct the analysis of the differential properties of the multiplicative inverse in GF($2^n$). We show that AES has characteristics with a fixed-key probability that is many times larger than the EDP. For instance, in the case of 2-round AES, we measured factors up to $2^{100}$. We study the number of characteristics with EDP $>0$ whose probability adds up to the probability of a differential and derive formulas that allow to produce a close estimate of this number for any differential. We show how the properties discovered in our study can be used to explain the values of the differentials with the largest EDP values and to construct new distinguishers using truncated differentials.
  title={Two-Round AES Differentials},
  booktitle={IACR Eprint archive},
  keywords={secret-key cryptography / AES, cryptanalysis},
  note={J. Daemen, V. Rijmen, ``Understanding two-round differentials in AES,'' in R. De Prisco, M. Yung (Eds.), SCN 2006, LNCS 4116, pp. 78-94, 2006; J. Daemen, V. Rijmen, ``Plateau characteristics and AES,'' IET Information Security, Volume 1, No. 1, March 2007},
  author={Joan Daemen and Vincent Rijmen},