  Identification schemes are interactive protocols typically involving two
parties, a prover, who wants to provide evidence of his or her identity and a
verifier, who checks the provided evidence and decide whether it comes or not
from the intended prover. In this paper, we comment on a recent proposal for
quantum identity authentication from Zawadzki, and give a concrete attack
upholding theoretical impossibility results from Lo and Buhrman et al. More
precisely, we show that using a simple strategyan adversary may indeed obtain
non-negligible information on the shared identification secret. While the
security of a quantum identity authentication scheme is not formally defined in
[1], it is clear that such a definition should somehow imply that an external
entity may gain no information on the shared identification scheme (even if he
actively participates injecting messages in a protocol execution, which is not
assumed in our attack strategy).
