  We study and solve the problem of distilling secret key from quantum states
representing correlation between two parties (Alice and Bob) and an
eavesdropper (Eve) via one-way public discussion: we prove a coding theorem to
achieve the "wire-tapper" bound, the difference of the mutual information
Alice-Bob and that of Alice-Eve, for so-called cqq-correlations, via one-way
public communication.
  This result yields information--theoretic formulas for the distillable secret
key, giving ``ultimate'' key rate bounds if Eve is assumed to possess a
purification of Alice and Bob's joint state.
  Specialising our protocol somewhat and making it coherent leads us to a
protocol of entanglement distillation via one-way LOCC (local operations and
classical communication) which is asymptotically optimal: in fact we prove the
so-called "hashing inequality" which says that the coherent information (i.e.,
the negative conditional von Neumann entropy) is an achievable EPR rate.
  This result is well--known to imply a whole set of distillation and capacity
formulas which we briefly review.
