Anyone who wishes to sign messages or to receive encrypted messages must have a key pair. People may have more than one key pair. For example, someone might have a key pair affiliated with his or her work and a separate key pair for personal use. Other entities may also have key pairs, including electronic entities such as modems, workstations, and printers, as well as organizational entities such as a corporate department, a hotel registration desk, or a university registrar's office.
Corporations may require more than one key pair for communication. They may use one or more key pairs for encryption (with the keys stored under key escrow to safeguard the key in event of loss) and use a single key pair for authentication purposes. The lengths of the encryption and authentication key pairs may be varied according to the desired security.