A Cryptanalysis of HummingBird-2: The Differential Sequence Analysis
Hummingbird-2 is one recent design of lightweight block ciphers targeting constraint devices, which not only enables a compact hardware implementation and ultra-low power consumption but also meets the stringent response time as specified in ISO18000-6C. In this paper, the authors present the first cryptanalytic result on the full version of this cipher using two pairs of related keys, i.e., four keys. They discover that the differential sequences for the last invocation of the round function can be computed by running the full cipher, due to which the search space for the key can be reduced. Base upon this observation, they propose a probabilistic attack encompassing two phases, preparation phase and key recovery phase.