  Guaranteeing nonrepudiation, unforgeability as well as transferability of a
signature is one of the most vital safeguards in today's e-commerce era. Based
on fundamental laws of quantum physics, quantum digital signature (QDS) aims to
provide information-theoretic security for this cryptographic task. However, up
to date, the previously proposed QDS protocols are impractical due to various
challenging problems and most importantly, the requirement of authenticated
(secure) quantum channels between participants. Here, we present the first
quantum digital signature protocol that removes the assumption of authenticated
quantum channels while remaining secure against the collective attacks.
Besides, our QDS protocol can be practically implemented over more than 100 km
under current mature technology as used in quantum key distribution.
