Comment on “Practical quantum key distribution with geometrically uniform states”

In a recent paper, Kravtsov and Molotkov [Phys. Rev. A 100, 042329 (2019)] propose a quantum key distribution protocol and claim “the protocol security is analyzed by an explicit construction of the most optimal unitary attack” and “we provide an extensive security analysis of the proposed protocol by considering a general symmetric unitary attack, and give succinct relations for the asymptotic secret key rate in the case of $N=8$.” We show that these claims are erroneous and propose two attacks which are more effective than the attacks considered in the paper of Kravtsov and Molotkov.