  We present an approach to the unconditional security of quantum key
distribution protocols based on the uncertainty principle. The approach applies
to every case that has been treated via the argument by Shor and Preskill, and
relieve them from the constraints of finding quantum error correcting codes. It
can also treat the cases with uncharacterized apparatuses. We derive a secure
key rate for the Bennett-Brassard-1984 protocol with an arbitrary source
characterized only by a single parameter representing the basis dependence.
