Page "Public-key cryptography" Paragraph 43

A public key will be known to a large and, in practice, unknown set of users.

All events requiring revocation or replacement of a public key can take a long time to take full effect with all who must be informed ( i. e. all those users who possess that key ).

For this reason, systems that must react to events in real time ( e. g., safety-critical systems or national security systems ) should not use public-key encryption without taking great care.

There are four issues of interest: