  Currently used digital signatures based on asymmetric cryptography will be
vulnerable to quantum computers running Shor's algorithm. In this work, we
propose a new quantum-assisted digital signature protocol based on symmetric
keys generated by QKD, that allows signing and verifying messages in a simple
way implementing an integration of currently available classical and quantum
technologies. The protocol is described for a three-user scenario composed of
one sender and two receivers. In contrast to previous schemes, it is
independent of the message length. The security of the protocol has been
analyzed, as well as its integrity, authenticity and non-repudiation
properties.
