  An important class of cryptographic applications of relativistic quantum
information work as follows. B generates a random qudit and supplies it to A at
point P. A is supposed to transmit it at near light speed c to to one of a
number of possible pairwise spacelike separated points Q1; : : : ;Qn. A's
transmission is supposed to be secure, in the sense that B cannot tell in
advance which Qj will be chosen. This poses significant practical challenges,
since secure reliable long-range transmission of quantum data at speeds near to
c is presently not easy. Here we propose different techniques to overcome these
difficulties. We introduce protocols that allow secure long-range
implementations even when both parties control only widely separated
laboratories of small size. In particular we introduce a protocol in which A
needs send the qudit only over a short distance, and securely transmits
classical information (for instance using a one time pad) over the remaining
distance. We further show that by using parallel implementations of the
protocols security can be maintained in the presence of moderate amounts of
losses and errors.
