With the $-------------$ scheme, if an adversary succeeds in obtaining or computing the private$$

$$key of the directory authority, the adversary could authoritatively pass out counterfeit public$$

$$keys and subsequently impersonate any participant and eavesdrop on messages sent to any

$$participant$.$

$$A$.$ public key authority

$$B$.$ publicly available directory$$

$$C$.$ public key certificates$$

$$D$.$ public announcement$$