  All the currently available unconditional security proofs on quantum key
distribution, in particular for the BB84 protocol and its variants including
continuous-variable ones, are invalid or incomplete at many points. In this
paper we discuss some of the main known problems, particularly those on
operational security guarantee and error correction. Most basic are the points
that there is no security parameter in such protocols and it is not the case
the generated key is perfect with probability $\geq 1-\epsilon$ under the trace
distance criterion $d\leq\epsilon$, which is widely claimed in the technical
and popular literature. The many serious security consequences of this error
about the QKD generated key would be explained, including practical
ramification on achievable security levels. It will be shown how the error
correction problem alone may already defy rigorous quantitative analysis.
Various other problems would be touched upon. It is pointed out that rigorous
security guarantee of much more efficient quantum cryptosystems may be obtained
by abandoning the disturbance-information tradeoff principle and utilizing
instead the known KCQ (keyed communication in quantum noise) principle in
conjunction with a new DBM (decoy bits method) principle that will be detailed
elsewhere.
