Public Key Certificates
If all users subscribe to the same CA, then there is a common trust of that CA
User certificates can be placed in the directory for access by all users.
Or a user can transmit his or her certificate directly to other users.
- In either case, once B is in possession of A's certificate, B has confidence that messages it encrypts with A's public key will be secure from eavesdropping and that messages signed with A's private key are unforgeable