Fault Attack on the Authenticated Cipher ACORN v2

Fault attack is an efficient cryptanalysis method against cipher implementations and has attracted a lot of attention in recent public cryptographic literatures. In this work we introduce a fault attack on the CAESAR candidate ACORN v2. Our attack is done under the assumption of random fault injection into an initial state of ACORN v2 and contains two main steps: fault locating and equation solving. At the first step, we first present a fundamental fault locating method, which uses 99-bit output keystream to determine the fault injected location with probability 97.08%. And then several improvements are provided, which can further increase the probability of fault locating to almost 1. As for the system of equations retrieved at the first step, we give two solving methods at the second step, that is, linearization and guess-and-determine. The time complexity of our attack is not larger than c·2179.19-1.76N at worst, where N is the number of fault injections such that 31≤N≤88 and c is the time complexity of solving linear equations. Our attack provides some insights into the diffusion ability of such compact stream ciphers

Finding state collisions in the authenticated encryption stream cipher ACORN

This paper analyzes the authenticated encryption algorithm ACORN, a candidate in the CAESAR cryptographic competition. We identify weaknesses in the state update function of ACORN which result in collisions in the internal state of ACORN. This paper shows that for a given set of key and initialization vector values we can construct two distinct input messages which result in a collision in the ACORN internal state. Using a standard PC the collision can be found almost instantly when the secret key is known. This flaw can be used by a message sender to create a forged message which will be accepted as legitimate