Messages encrypted with your private key can be decrypted only with your public key, and messages encrypted with your public key can be decrypted only with your private key. You can freely distribute a public key, and only you will be able to read messages encrypted using this key. To obtain a public key and a corresponding private key for your own use, you must request a certificate from a certificate authority. When you request a certificate, your copy of Communicator generates both a public key and the corresponding private key and sends the public key to the certificate authority. The certificate authority gives you a certificate, which is a digital document that binds a particular public key to an individual or entity.
Certificates help prevent the use of fake public keys for impersonation.
A certificate is like a driver's license, a passport, or any other personal ID that provides generally recognized proof of a person's identity. A certificate always includes a public key and the name of the entity it identifies. Most certificates also include an expiration date, the name of the certificate authority that issued the certificate, a serial number, and other information. Most importantly, a certificate includes the digital signature of the certificate authority. Every digital signature points to a certificate that validates the public key of the signer.