I am attempting to break 3-round SPECK48/96 using a known-plaintext attack, provided with 10 PT-CT pairs. Here is a diagram:
I have seemed to almost figure this out, but I cannot figure out how the right side affects the state of the text, due to the left rotation.
Say I am trying to attack the first set of 8 bits on the left side (24...31). That means I will perform the
rotr 8 and addition, then make my $sk_0$ guess on the 16...23 bits. I then XOR with the right side.
$sk_1$ will then be guessing bits 8...15 as those are the bits that were affect by $sk_0$ (due to
rotr 8). However, this
rotl 3 will cause the bits that were affected by the subkey to move in the other direction, so now each round's subkey guess will be affecting different parts of the plaintext (as opposed to on the left side, where I can trace the movement of these bits).
I may have not been clear but I was trying to explain my thought process...I just cannot seem to figure out how to approach this.