  In the direct communication quantum channels the authorized recipient (Bob)
and the non-authorized recipient (Eve) have different abilities for
verification of received information. Bob can apply the feedback to commit the
sender (Alice) to perform verification. Eve has to use for verification an
indirect method based on the measurement of a set of incompatible observables
enough for determination of the coding basis used by Alice.
  In the protocol of direct communication regular modification of coding basis
and masking it with an equilibrium in average information carrier density
matrix prevents reconstruction of coding basis by the results of Eve's
measurements of an arbitrary set of observables. This provides unconditional
security of the channel.
