You need to make sure that the key does not belong to someone impersonating that person or organization. A certificate is a digital document that attests that a public key and its corresponding private key belong to a particular individual or organization. Certificates are issued by authorities who can vouch for the individual's or organization's identity and ownership of the public key. A standard for certificates is defined in the ITU-T Recommendation X.509. Cryptography Cryptography refers to a family of technologies that include encryption, decryption, authentication, and digital signatures.
Encryption transforms data into an unreadable form to ensure privacy.
Internet communication is like sending postcards in the mail. Anyone who is interested can read an Internet message. Encryption offers the digital equivalent of a sealed envelope. Authentication identifies an entity such as an individual, a machine on the network, or an organization. Digital signatures bind a document to the owner of a particular key and are the digital equivalent of paper signatures.