  We discuss a continuous variables method of quantum key distribution
employing strongly polarized coherent states of light. The key encoding is
performed using the variables known as Stokes parameters, rather than the field
quadratures. Their quantum counterpart, the Stokes operators $\hat{S}_i$
(i=1,2,3), constitute a set of non-commuting operators, being the precision of
simultaneous measurements of a pair of them limited by an uncertainty-like
relation. Alice transmits a conveniently modulated two-mode coherent state, and
Bob randomly measures one of the Stokes parameters of the incoming beam. After
performing reconciliation and privacy amplification procedures, it is possible
to distill a secret common key. We also consider a non-ideal situation, in
which coherent states with thermal noise, instead of pure coherent states, are
used for encoding.
