Cryptanalysis of Round-Reduced LED

In this paper we present known-plaintext single-key and chosenkey attacks on round-reduced LED-64 and LED-128. We show that with an application of the recently proposed slidex attacks [7], one immediately improves the complexity of the previous single-key 4-step attack on LED-128. Further, we explore the possibility of multicollisions and show single-key attacks on 6 steps of LED-128. A generalization of our multicollision attack leads to the statement that no 6-round cipher with two subkeys that alternate, or 2-round cipher with linearly dependent subkeys, is secure in the single-key model. Next, we exploit the possibility of finding pairs of inputs that follow a certain differential rather than a differential characteristic, and obtain chosen-key differential distinguishers for 5-step LED-64, as well as 8-step and 9-step LED-128. We provide examples of inputs that follow the 8-step differential, i.e. we are able to practically confirm our results on 2/3 of the steps of LED-128. We introduce a new type of chosen-key differential distinguisher, called random-difference distinguisher, and successfully penetrate 10 of the total 12 steps of LED-128. We show that this type of attack is generic in the chosen-key model, and can be applied to any 10-round cipher with two alternating subkeys.