You're not talking to other sites directly. Alice can tell you, "Here's a message from Bob. His public key is 0x1234," when Bob's public key is actually 0x5678

You're not talking to other sites directly. Alice can tell you, "Here's a message from Bob. His public key is 0x1234," when Bob's public key is actually 0x5678. This opens a new avenue for trolling: publish a fake key for someone else and watch all their messages get dropped.