  Entanglement swapping between Einstein-Podolsky-Rosen (EPR) pairs can be used
to generate the same sequence of random bits in two remote places. A quantum
key distribution protocol based on this idea is described. The scheme exhibits
the following features. (a) It does not require that Alice and Bob choose
between alternative measurements, therefore improving the rate of generated
bits by transmitted qubit. (b) It allows Alice and Bob to generate a key of
arbitrary length using a single quantum system (three EPR pairs), instead of a
long sequence of them. (c) Detecting Eve requires the comparison of fewer bits.
(d) Entanglement is an essential ingredient. The scheme assumes reliable
measurements of the Bell operator.
