Slide Attack on Spectr-H64

We compare one round diffusion characteristics of the block cipher Spectr-H64 to those of AES-Rijndael and Safer K-64, in terms of the Avalanche Weight Distribution (AWD) criterion and observe a weakness in the round transformation of Spectr-H64. We exploit this weakness to break one round of Spectr-H64 extracting half of the key bits, and develop a chosen plaintext slide attack against the overall encryption algorithm, which works for 2 elements of the key space (out of 2). We also observe 2 weak keys, for which encryption becomes the same function as decryption, and 2 fixed points for each weak key.