  A quantum digital signature (QDS) protocol is investigated in respect of an
attacker who can impersonate other communicating principals in the style of
Lowe's attack on the Needham-Schroeder public-key authentication protocol. A
man-in-the-middle attack is identified in respect of a classical variant of the
protocol and it is suggested that a similar attack would be effective against
the QDS protocol. The attack has been confirmed through initial protocol
modelling using a automated theorem prover, ProVerif.
