  We examine a situation that $n$ eavesdroppers attack the Bennett-Brassard
cryptographic protocol via their own optimal and symmetric strategies.
Information gain and mutual information with sender for each eavesdropper are
explicitly derived. The receiver's error rate for the case of arbitrary $n$
eavesdroppers can be derived using a recursive relation. Although first
eavesdropper can get mutual information without disturbance arising due to
other eavesdroppers, subsequent eavesdropping generally increases the
receiver's error rate. Other eavesdroppers cannot gain information on the input
signal sufficiently. As a result, the information each eavesdropper gains
becomes less than optimal one.
