Imprimitive permutations groups generated by the round functions of   key-alternating block ciphers and truncated differential cryptanalysis
  We answer a question of Paterson, showing that all block systems for the group generated by the round functions of a key-alternating block cipher are the translates of a linear subspace. Following up remarks of Paterson and Shamir, we exhibit a connection to truncated differential cryptanalysis.   We also give a condition that guarantees that the group generated by the round functions of a key-alternating block cipher is primitive. This applies in particular to AES. 
A. Caranti, F. Dalla Volta, M. Sala, F. Villani