Describe the BB84 protocol for quantum key exchange.

Suppose we attempt to implement the BB84 protocol but cannot send single photons. Instead we send $K$ photons at a time all with the same polarization. An enemy can separate one of these photons from the other $K-1$. Explain briefly how the enemy can intercept the key exchange without our knowledge.

Show that an enemy can find our common key if $K=3$. Can she do so when $K=2$ (with suitable equipment)?