  This paper provides a security proof of the Bennett-Brassard (BB84) quantum
key distribution protocol in practical implementation. To prove the security,
it is not assumed that defects in the devices are absorbed into an adversary's
attack. In fact, the only assumption in the proof is that the source is
characterized. The proof is performed by lower-bounding adversary's Renyi
entropy about the key before privacy amplification. The bound reveals the
leading factors reducing the key generation rate.
