Meet-in-the-middle through an Sbox:
We present, with this on going work, a new improvement for meet-in-the-middle attacks. Its main novelty is to discard wrong keys by looking for possible transitions through an Sbox between some forward computed input bits and some backward computed ones, in contrast to looking for a collision of values as it is normally done. This will allow us to increase the number of attacked rounds. We have applied this improvement to PRESENT, DES, PRINCE and the biclique analysis of the AES, being in able to improve the previously known attacks. We are investigating the combination of this work and other ideas that might improve the results. With this work, some theoretical questions have arised and we are able to provide some answers that will be crucial for providing information about how to design an sbox for resisting to this kind of attacks, and also allow to know what to look for when performing the forward and backward computations.