Investigating Cube Attacks on the Authenticated Encryption Stream Cipher ACORN

The cube attack is an algebraic attack that allows an adversary to extract low degree polynomial equations from the targeted cryptographic primitive. This work applies the cube attack to a reduced round version of ACORN, a candidate cipher design in the CAESAR cryptographic competition. The cube attack on 477 initialization rounds of ACORN can recover the 128 bit key with a total attack complexity of about 2(35). We have also shown that linear equations relating the initial state of the full version of ACORN can be easily generated which can lead to state recovery attack with an attack complexity of about 2(72.8).