2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/112988We 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.9 pages - corrected embarrassing typo in the titleGroup TheoryCryptography and Security20B15text