  A scheme of quantum authentication is presented. Two parties share
Einstein-Podolsky-Rosen (EPR) pairs previously as the authentication key which
servers as encoder and decoder. The authentication is accomplished with local
controlled-NOT operations and unitary rotations. It is shown that our scheme is
secure even in the presence of an eavesdropper who has complete control over
both classical and quantum channels. Another character of this protocol is that
the EPR sources are reusable. The robustness of this protocol is also
discussed.
