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(32) elements of the key space (out of 2(256)). We also observe 2(128) weak keys, for which encryption becomes the same function as decryption, and 2(32) fixed points for each weak key.