A trusted third-party organization or company that issues digital certificates used to create digital signatures and public-private key pairs. The role of the CA in this process is to guarantee that the individual granted the unique certificate is, in fact, who he or she claims to be. Usually, this means that the CA has an arrangement with a financial institution, such as a credit card company, which provides it with information to confirm an individual’s claimed identity. CAs are a critical component in data security and electronic commerce because they guarantee that the two parties exchanging information are really who they claim to be.
A CA can be within the organization itself or outside organization depending on the purpose of the certificates. A company may issue certificates to its employees for reason that only its employees can access to the company database but an internet user might request for a certificate from a well-known and trusted CA in order for him to do on-line transaction securely.

Digital certificates are the digital equivalent (i.e. electronic format) of physical or paper certificates. Examples of physical certificates are driver’s licenses, passports or membership cards. Certificates serve as identity of an individual for a certain purpose, e.g. a driver’s license identifies someone who can legally drive in a particular country. Likewise, a digital certificate can be presented electronically to prove your identity or your right to access information or services on the Internet.