A Web certificate is an electronic document used to identify an individual, a company, or any other entity. Like a passport, a certificate provides generally recognized proof of an entity's identity. In the Internet world, most certificates follow the X.509 standard. An X.509 certificate binds a public key to a subject identity. Figures 3 and 4 show what a certificate looks like using Windows graphical interfaces.
Certificates help prevent the use of fake public keys for impersonation.
Only the public key associated and certified by the certificate works with the corresponding private key possessed by the entity identified by the certificate. So, now we know what PKI and Web certificates are. First, we have to find a CA that issues certificates. In the Internet model, we have to find a public CA, instead of one that only works in a private network. Once registered with VeriSign, developers can use the VeriSign APIs to obtain a certificate through a program.