We are trying to decide between a public$-$key and a secret$-$key cryptographic solution. Which of the following criteria would encourage us to choose the secret$-$key solution? Select all that apply best to secret$-$key cryptography.

A$.$

The system can apply a lot of computational power to cryptographic operations.

B$.$

Attackers should not be able to penetrate the whole system simply by attacking a critical crypto server.

C$.$

When someone loses the privilege to access the system, we must be able to revoke their access rights immediately.

D$.$

We are providing the service to an established user community whose members are already identified.

E$.$

The system will always be limited to a small user community.

F$.$

The process of adding new users must be easy to delegate.